Frontogenetic Regions in the Far East Citation Huang, Hsia-Chien (1938) Frontogenetic Regions in the Far East. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/e6jy-3360. https://resolver.caltech.edu/CaltechTHESIS:01312025-213644065 Abstract No abstract. Item Type: Thesis (Dissertation (Ph.D.)) Subject Keywords: (Meteorology) Degree Grantor: California Institute of Technology Division: Engineering and Applied Science Major Option: Meteorology Thesis Availability: Public (worldwide access) Research Advisor(s): Krick, Irving Parkhurst Thesis Committee: Unknown, Unknown Defense Date: 1 January 1937 Record Number: CaltechTHESIS:01312025-213644065 Persistent URL: https://resolver.caltech.edu/CaltechTHESIS:01312025-213644065 DOI: 10.7907/e6jy-3360 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 16980 Collection: CaltechTHESIS Deposited By: Benjamin Perez Deposited On: 04 Feb 2025 22:21 Last Modified: 04 Feb 2025 22:26 Thesis Files PDF - Final Version See Usage Policy. 34MB Repository Staff Only: item control page

FRONTOGENETIC RIDIONS IN THE FAR F.AST ,< . Thes1~ by Ha1a-Ch1en Huang. In Partial Fulr1llment o'f' the Requirements for the Degree or Doctor of Ph~ losophy, Oal11"ornia. Institute 01· 'l echnology, 1 Pasadena, Cal1forn1a, 1937. C:JN'l'b NTS Summary 1 I. Introduction l II. Mathe matical and Physical Aspects of the Field 3 of Motion III. F'ronto genesie in a F ield of Motion 9 IV. Sources and Treatment of Material l.6 V. Air Masses and Field of Motion 1n the Far Ea.st 20 VI. FI'ontogenet1c Re g1one 1n the Spring Se a.son 26 VII. Frontogenetic Regions 1n the Su1mrer f;;eason 32 VIII. Frontogenet1c Regions 1n the Autumn S6 a son 42 I X. Frontogenet1c Re g ions in the Winter Se a eon 49 X. Acknowledgement 57 References 58 Chart.a 61-88. LIST OF CHARTS l.,ront.1spteee CHART I Deforma.t1on Fields and Isotherms-April P.27 II Wind D1reetions over China-April II III \vo<I Field 1n the Far East-April 29 IV D1Str1 but1on or F in the F•·a r East-April V Frontogenetic Lines and cyclonic ·rracks ll 1n the Far East-April 30 VI Def'ormat1on .W ields and Isotherms.July 34 VII l•ott Ir ield in t,he Far Jw,st-July VIII D1atribut1on of F 1n the .tt'ar Ea.st-July IX Frontogenetic L1-n es and Cyclonic Tracks ti 1n the Far East-July :; X ~ynoptic Chart of August 19, 1932 40 XI n ll ti It 20, t,I ti XII ti It u tl 21, H It XIII !-t It ,, !I 22, II u XIV Deformation Fields and Isotherms-September 43 xv 1~,.q Field in the Far E;ast -September 45 XVI U1str1but1on or F 1n the .trar Ea.st-September XVII B'ront.ogenet1c Lines and Cyclon1e 'l'racks in the Far East- September XVIII Deformation Fields and Isotherms-January n 46 49 CHAH'r XIX xx Field in tbe .B'ar East-January \vo<I Distribution of 1'' in the Far East- January XXI XXII Frontogenetic Ltne and cyclonic Aet1v1ty- January 5l Synoptic Chart of January 15, 1933 54 tt XXIII 0 XXIV x.xv 50 II ti tt 16, 17, n Deformation 1neld and Isotherms .... January 16, 1933 XXVI 55 Deformation li'ield and Isotherma-Janu.ary 17, 1933 XXVII II synoptic Chart or January 18, 1933 tt MAP O_E., THE FAR EAST .F ■ :t: I t • -Ji;•• a 'It Nalilal T. . Baa UliYenilf Ofllawalw; •~x• ■ WeadierdllrtefuatnAIII .... .........,...... " ... "zc,a;,, Summary The general field of motion of the atmosphere in too I.i,a.r East 1a a deformation type with the deforma.tion axis in a NE-SW direction which orients the frontogenetic lines of the Far East to run in that saroo direction along tte Asiatic coast at varying distances from it. The actual position of the lines is different in different sea.sons and is de pendent up on the seasonal activity of the two anticyclones, the Pacific High and the Siberian High, which actually control the field of motion of the region. Due to the preponderant activity of the Pacific High and the Siberian High in the summer and winter respective - ly thar-e is only one frontogenetic line found for each of these two seasons. In the other seasons there are two lines, one offshore and one inland. All the frontogenetic lines deter- r mined by the frontogenetic theory are essentially in agreement with the actual frontal activit y in the region shown by the observed cyclone tracks. The region from the Formosa Strait northeastward to the Japanese Islands is specifically frontogenetic for most se as ons of the year while the land area of the northe rn pa.rt of China ls only · effectively frontogenetic in the summer season. The difference in orientation of the isotherms betwee n the t wo mentioned regions is the main reason for this fact. Winter cyclones in the Ii'ar East take place at a cold front betwe e n t wo types of air masses of Ps origin, not between Pe and true Tp. They ar-e developed from wave perturbations. Typhoons are forroe d dynamically at the line of convergence betwe en the Equatorial Pacific and the Tropical Pacific air masses a t the southws st corner of the North Pacific Ocean. The loc a tion of for ming and treje ctorie s conform w1 th the position of this line. - 1 FRONTOGE NET IC RE GION S IN THE l"AR EAST I. Introduction First, we know that in the atmosphere various types of air me.sees ( M) exist .. . Usually the difference of potential temperature(G) between dissi.\tnilar types must exceed 10°c ' before tbey can be classified as distinct masses. mass moves closer- to /~ When one another mass. as their p otential temperatures are different, a.n increase in ths value of . and~~ ~f Will occur and f1ne.lly a rapid transition zone Will arise between them. The masses in this case are, according to T. Bergeron, ( 1) called the •1Frontalmaese 11 or the Frontal Masses and the zone the ttli, rontalzonent• or the Frontal Zones .. These two naims can be further grouped into a simple abreviation of FM. Once a Frontal Zone has been formed any further development w111 quickly intensify the zone into a re al Front { F'} • is the fundamental 1dea. of front formation. M~FM- - F . Thie Thus the proce es is: Any other process of front formation, suc h as by heating the air on one side and cooling on the other side, would be a minor one . The reverse process of front destruction would of course be the reverse, 1.e. F-FM-M. The idea of air masses and air mass boundaries or fronts be- tween the d1sslm1lar types has be e n brought down first from w. Koppen's work in 1879-1882 (2). Dove, Blasius, and Helmholtz from purely tr.ieoretlcal consideration arrived at their believe that discontinuity surface must exist between the cold northern - 2 - currents and the warm southern currents. Later on Ficker, Fe sslers and E xners studied the occunence of the migrating cold waves Which actually are the material proof of the existence of cold fronts at the earth's surface. However, the immediate attack on the problem of front formation has only been made in very recent years. T. Bergeron first introduced the use of the term ''Frontogenesefl or Frontogenesis for front formation and "Frontolyse 11 or Frontolysis for front destruction . By frontogenesis is rooant the formation of a new front or the 1ntensifice,tion of preexistent front. In both these cases the solenoids, the cells bounded by adjacent isobaric and isosteric surfaces, in the frontal zone are increased With the saroo change oe 1n the values of oe '?Ix..- and~ Therefore we can sirnply define Frontogenesis as a pro~_e se wh1ch increases the number of solenoids or too values o fiJ')(., ~ """nd 00 o';}- • The reverse i.e true for Frontolys1e. li'rontogenesis can be dealt with by a two dimensional or preferably by a three dimensional n:ethod. is rather complicated for practical use. method Tbe later method In the present study no attempt has been made to discuss tbs theoretical side in detail, but a practical determination of the frontogenetic regions in the Far E ast is desired. The method of the study Will be limit- ed to a two dimensional application. T. Bergeron' s and Sverre Pe tterseen• s ideas on frontogene sis will be the theoretical basis for the study, use being made generally of Petterssents latest paper (3) and also his lectures at the California Institute of Technology, Pasadena, California; U.S.A., 1935. - 3 I I. Mathematica l and Physic a l Aspe cts of the Field of Motion Supposing that the motions in the atmosphere are adiabatic, frontogene sis can be re gar-ded as a p urely kinematic al proce es and fr-om a field of motion we can e a sily discover the change in the distribution of a conservative property belonging to the air particles after a change of time t.. In order to find a place where l!'G ie likely to occur, 1t is necessary to introduce some concepts regarding two dimensional fields of motion. If u and v are ttl:3 components of the velocity in the .x and y direction respectively and they are each functions of x and y we Will have : Expanding the se by Taylor•e Series and ne glecting the terms of highe r orders we obta in: ( 2-) uu o +0ZJX. -u..x+ otA.1/),.+-• • • • • •• o";}- (} V =Vo+~ X, + t; 1j- -+ - - - -- --· We may rewrite trese e q uations as follows: LA-= Uo+ a..x:.,+ bX. -C..4;J- ( 3) V = V- o "1, +- b ~ + C X.. 0 - the coe ff1eients Will ha.Ve the following values: -4 W1th these coefficients, equation (3) indicates four components of motion in a two dimensional field, namely, th3 first term 1s the translation (u 0 , v 0 ),, second, the dilatation (+ a) or contraction ( -e), third, the divergence (+ b) or convergence ( -b) and fourth, tbe clockwise { or anti-cyclonic) rotation ( -c) or counter-clockwise (or cyclonic) rotation ( + c). Th3 streamline picture a of translation a.re shown below: .. ...... ......,.. .... ► ' + " ► . ... Pig . 3 Fig . 2 F1g .1 Field of V= Vo Combine d field A gl nee on the above stream line pictures sho e tha t th3re is no tendency to bring one particle nearer to anot her particle. Thie kind of motion , therefore, has no influence on FG, but will mrely distort the original configuration of an cx-line field to a new con iguration when the motion 1s superimposed . For the second term, when (a) ls positive , the stream line picture of u = a.x 1s: ----.. .. .. ... .,... ... F1g.4 Field of u.=e.x Apparently, the motion 1s ·tending to destroy a front long the - 5 When ( a) 1a ne gat1ve the stream picture of v = Y-axis. -ay will show the following result: I , t Fig.5 Field O•f V = -ay The Y component is then tbs effective one 1n FG a.long the Xaxis . Combining the above fields, we obtain a stream 11ne picture : '( F1g. 6 Combined f1e ld of' U= ax and V= -ay Tha above picture shows a. pure deformation field, and the X- axis 1n the combined field in th1e case is the a.xis of dilatation, also the deformation ax.ls . {Note that 1f U = -ax and V= ay, Y be cons s the deformation axis). <}rl The third term, When (b) 1e positive I the stream line pictures of U = bX and V= bY ehow tte motion of particles along the X and Y-axis With a separating tendency . F1g . 7 Fig . 8 Field of V= by - 6 Combining the fields, ,vs obta1n a dive r·gent flow and, ot" course, ;I Fig.9 Combined field of U = bX and V = bY Contrarily, when (b) 1s negative, the motion in the field will br1:ng part1cle s concentrating along tl::18 X and Y-axis and a convergent fl .ow w111 be found by combining the fields. y I - - ... ·> - 1-<- ... .. .. -- ~ I ~ X . --~ ... I I ~ f i ' I ' ' l I • '' µ t - .. . ...- - .,_ ; '': .,, ,..! ' j 'I ,I ~ Fig. 11 Fig.lo F ield of U = Combined field. F ield of V = -by -bX This 1s, theoretically, a very eff ective frontogenet1c field. The fo'W"th t erm, since u is 1nd6pendent of x and v of y, gives e. etream- l:tne: p icture of circul.a r rota tion w1tb eitoor cloekw1se ( e being negative) or counter-..;clockw1se ( c being pos1t1w) dir e et ion-. ... ( }(_ (i V F1g.l4 Fig.13 F ield of V = CX Field o f U=-CY - 7 The notion w111 have no inrluence either on FG or FL as '1:-S -iA there 11 no tendency to bring the particles closer or f nrthetjapart. From the above four components of the field o.f motion many stream line patterns can be developed by euper1mposing them 1n various degrees of intensity. However, only a few patterns of central stream 11nes of hyperbolic type, that is -<.. -<.. ~ to say b < a - c >0, Will be of interest 1n this research problem because they are most often found in tbil Far East. The p tterne are shown below: . ig.15 Hyperbolic stream llnee ( After Sverre Petterssen) - 8 An actual fie ln. of curved str-e am lines V is to say b-a u:~- ~ 1 tnout center, that. C = b+a , has also been found in the Far East.,. and w111 be discussed later -. Fig . 16 c < - 0b-a = b +a Vo ):. Curved stream 11.ne .e when ti: (After Sverre petterasen) - 9 II I. Itrontogenesis in a Field of Motion If a ce rt a in kin d of velocity field be superi mp osed upon a g iven distribution o f mete orolog ic al ele me nt s af t er a t ime t t he ne w confiGuration of the distribution of me t eorologica l ele ments mu s t be 'the result of the motion o f tra field . oz Let be any conserva t i ve property suc h a s p ot.ent :i.al te mperatur e or s pe cifi c humidity . Along a line of F'G the al-l ines must app ro a c h e a ch other more r apidl y t han in any p ortions o f the :fie lfl. - 'v'o< a s t he gr adient of tbs of t he grad i ent . We shall def ine oz-lines and - \'v o</ t he magnitude In order to se e wha t happe ns between t wo iso-cx line s a long a. line norma l to t he l ine of FG , we may apply t he we 11 known tr ansformat ion equ a ti on of hydrodyna.m i cs: c hoosing a n axis norma l to tr..e l i ne of FG. (4} P utting \"7o< j in the symbolic e q ue.tion, we have: (5 ) where ~ is the r a te of t r..e change of \'Clo<\ referre d to a moving s y ste m of coord i nat es f ixed to tl"]3 line of FG , <')~'-7t1 t he r a te of chs.nge of \vcx l a t a fixed sta tion, line of FG. Whe n t he iso-o< of \vo<I is inc reased . V too vel ocity of the line s move tosre t he r t he v a lue Let F=~ which is a.n expression showing how q uickly the lso-cx' 11.ne s move t ogether . Therefore - 10 - we might call F the Frontogenet1cal Function. To have FG, F must be a maximum along a line normal to t03 line of I<,G or - F . and 2>:z ot-J'- < o, %~ o N being the distance on the line norma l to the line 02.F If ~ > O, a condition of FL would arise. of FG.. Taking the right hand side of equation ( 5), to solve for , do( T-t we know that d ==o<'(X,1 ,-t). Differentiating totally with respect tot we obtain: = ,}o( :➔-r- = + 3X ;)o( u.. +- ~d- 1l o';}c,t.+v =v,t he wind ~ + V • vo<.. velocity. Since c)._ is a conservative property, we can write: ( '7) C8) The change of (9) Since Vo(. -#= ~t ~+V•Vo( =O =-v·"vol.._ tt: is: 'Q ~=~'t = -"vv·vo<-v -vvo<.. is a vector we ma.y write: (Io) ovo( _ o\vo{I n a-t whe re n denotes the dire ctlon of a vector and can be wr1 tten (l I) ~ 'Vt.= ~~ . Equation ( 9) be corms: ( I 2-) 'YI. 4b-otl = -"vV·Vcl.-V ·V Vo(. Multiplying (12) by (11), we have: ( \ 3) cl 4) n·n=f olvt\ 3 = -Vr/..·VV•Vo<-Vo<.•V·vvoc. \ Vo( l Which glve s tbs first term of equation (5). - 11 - The second term of the right hand side of equation (5) is V•v\'!;7o<I Which can be solved first by putting ( tS) vex -n\vo<j. Mul t1plying this equation by ( 11) , we obtain: uo<· Vo<: ( \ 6) 11.. •Yl [vo</ = lv<><l ( \ 7) '7ol.·'i7 ol.. The variation of \vo</ is: Expanding the le ft he..nd aide of this equation, it be co mes: \~I.Z Vo<'. ·vvo<.- v'o< ·Vo<· 'i7 lvo<I = v' \vo<I (I 9) I v « 1.z ( 20) 2'17o(·V 17cx - 'Q'o<· (vo<I vo< v'jv'o<.j lv"'l:i. = v r \ v o < \ is equal to ;:1 • ~;1 or, by equation ( 11), equal where 1 Therefore, equation {20) becomes: to 11-n.. , i.e., 1. ~VO(-vvo1. I Vol I (2. I) -vjvoc::( =1;1\vcxj (2.2..) Substituting equation (14) and (23) into the right hand side of equation (5), we obtain: (Z4 J Finally, ~\'QO(I = ~ ( 2. 5 ) F= -vo<·vV•vo(-Vo<·V•vv+ TT vv°'· Vo< \ vo<. I W I Vo< I F - -vo<·VV•"vo<'.-vot-vvcx(-v--VJ - Since ex is conservative IJo that We may write: c2 6 > F = _ \'v'c>( \ -v is ne ce sse.rily equal to v . 5Zo(.-vV ·Vo<. \'vo< I In the foregoing e:q__uation -v°" is the gradient of the iso-cx lines, whlle •f~ 1 is the unit vector of Q'cx . The vector ~ 1·vv gives the variation in v, trJS wind velocity along the vector llne e of <vex • Equation (2.6) shows that the frontogenetica.l function is the product of th3 gradient of tte iso-cx lines multiplied by this last :.ttae...tor. Since the gradient of iso-0{ lines 1s a V6'ctor so we may use r for the unit in the direction Re writing equation (26) then - 12 - be corro s: (27) F- Put.ting Y=m i. + Yl j , we obta in: where : - ~~ =a+b ou =-C ~13- M =c ~x.,, ~ = b-a ., i}"J- =-{nf@+b)-l-n_\b-o.)} \v1o<j (3I) = -{ b+a(m'.<_Y{)} \v1o<l. Tl:¥3 following diagram shows the distribution of the iso-o< line s in a field of motion where tr£ X-axis has been chosen as t be axis of deformation and <P taken a:-s the angle between the line tangent to the iso-ol lines and the X-axis. distance h is the perpendicular to tl:l:l iso-c:,<'. Tre lines a.nd \vo<.I Fig. 17. is equal to 1/h. e.nd 'YL=C,c-il ~ In this way we can substitute for · m=- S.;,..,_ <P in the lest equation and get: ( 32 ) F = ( d 0r.1 2. <p - b) lvo< I . This equation becomes useful in calculating the va lue of F, -the frontogenetical function, from an iso-cx line field superimposed on a field of motion. Obviously if b in the e quat1on is ne gl1gible, the angle(\) cannot be larger than 45° otherwise F V/111 be negative and frontolysis will arise. - 13 This is exactly true 1n the case of pure deformation fields when b=O. For other fields the sign of lf is d.ependent up on whetr.i.er the 11ne of iso- cl::.. sector. is in ths f'rontogenetic or frontol ytic This term, fr ontoge rttical sector is use d t o design- a.te the r-egion bounded by two lines of l'll = O, on either side of a. dilatation axis ( which may not coincide with the X-axis). = O, we c an solve cos 2 ¢= g_ Sl.nce when F to : get the angle between theee t wo lines, 2 q:>1 , or t r.e angle of the f'r ontoge netical sector, Pe tte r-ssen uses 2 ¢ 1 for this angle and calls it the frontogenetical angle, as determined by-¾to avoid con f usion wit h the treasured angle angle between the iso- ex lines and tte deforma tion a.xis . This latter angle if smaller tha n ct ¢ Which re mains the ¢' ind icates that the iso- lines fall in the frontogenetlc sector and F is natur ally positive. The s maller the anf!le ~ the closer the iso-cx. in comparison to the ¢' 11nee move to the center and the more effe ctive the frontogenetic function. Substituting then the 1 term (cos 2 Cl) - cos 2<P ) in the last e quation we get~ ( 33) F.::::: a(.~2.q> - C,h.7 :z.¢') lvo<l . a mo s t use f u l eQ uat ion as it e,llov1 s the sepc1.rat 0 consideration o f the: a;:, ove mntloned angles .. Summarizing the pr inciples of frontogenee.ls, it r:::tay t hen be state..d that there i s a t:rontogane tic region where the iso-ct l ines ;:n~ t;:e an angle ¢ with 'the deformat ton a xis in a de forr1ation fie ld smaller than the :frontogenetica} angle ¢' , and s imilarly that there -1'-~ - 1s a. frontolytic region where the angle 4) cp' . is larger than the Thla is shown for a simple case in Fig. 18. Tbs value of F is tbs product of cos 2 <p - cos 2~'multi- plied by the scalar value of \v '-l 0 Naturally the distri,b u- • tion of Fis 1n coincide nce with the distribution of provided that the iso-d other. \v~l 11nee are ne a rly parallel to each A study of the streamlines shows tha. t the line of frontogenesis moves with th3 current of tbs field but that it remains a substantial line which will in t1me be i n tensified into a real front or Will change a wee.le front into a strong one Fig. 18 E'ig .. 19 Under the f'rontogenetic conditions the process of frontogene sis can be 111.u strated by the above diagram., :B'ig. 19. Since too 1so- o<. lines are in a field of motion the particle e will be carried along the stream lines. cp 1n this case has been chosen less than 45° with the x-axis and b has been neglected, 1n Wh1ch case too iso-cx closer together after a t.ime t. lines as shown are brought The solid iso-o< lines re pre sent the original configuration and the dotted lines the changed configuration of tbs iso- o( line field after a t1m t. - 15 Exam1ning the diagram we can find tha t the re a.re t wo kinds of mot,10.n which have affected the cha.nge s in the iso-o<. line f1€ ld, namely, the rot a tion of the lines towards the X-a xls and tba moving of t re iso-o< lines towards each other. corre ep ond to t rie two terms in the equation of' F' . ing mot1on will not stop until the iso-0< TtEse Ti::ie rotat- line s are p ar allel w1th the x-a xis b ut 1 t can be sta ted the,t the f ronto genet1c - ' function will only be positive when t 1s less than 45° With the X-axis ( in the a b ove general oa.se) .. F'or wrie n <p is greater than 45 ° orig ina lly,, the stream lines o f the field of motion have to rot ate the iso- ex lines .for just so much longer a pe r iod before f' r ontogenesis can become 8ff ectlve. The time needed for this pre - FG work together with t hat necessary for l<' G may often be of' such dura tion that the pse udo-coneervat1sm of the air mas s properties is overcome so that in regions lines originally oriented at angle e of mo!'€ than 45 ° w1 th t i10 X-a xis, condi tlone are unfavorable for F'G and t r..te gre a ter the angle t be less f a.vorable, as may be e hOW'n in co mputa tion of too magnitude of tbs frontogenetica.l !'unction unde r v arying conditions. - 16 ... IV. SOURCES AN D THEATMENT OF MATERIALS The coneepts presented above forr;'.i the basis for the tre a t- ment of the F'rontogenetic regions of the F'ar East. Presented herewith, data at the pre sent time is insufficient for an exact study of all phases of the subject in these regions. There is available only surface wind data, a few ieo-thermal charts and the daily we at her maps from various sources. The principal material for the study of the fields of motion 1n the Far S ast were found in the papers written by W. Werenskiold (5.. ) and c.c. Chu(6). W. V'.'e renskiold inte gra-ted the mea.n air tr ans- port over the North Pacific Ocean 1nto resultant streamline pictures for the various months, While c.c. Chu has listed the me an monthly wind force and the preva illng Wind dire ct ions in Js,n._uary, l\pril, July, and S-.epte mber for eighty st2,tione 1n China. Combining the t wo sets of data a rathe r complete cha.rt of atmospheric circulations covering the North Pacific Ocean, the Japanese I elands and the coastal re glens of Ch ina\ can be obt a ined for each season of the year .. These seasonal wind cha rts form the p rincipal aid 1n finding the deformation fields in the F'ar East. It is rather regrstable that the data are restricted to water regions and sea. coe.sts but in the same light because of the s moothness of the surfaces over Which the air moves, the flow should be representative. The only air mass property ava11a.b le was surface temperature, obtained from scattered sources: nai.ooly (7;) a paper by c.c. Chu, nThe Toormornetric Char ts of the Zi-Ka-Wei ObsGrvs,tory (8), the E' ilot ' Charts of the North Pacific prepRred by the U. S.N. - 17 Hydrographic Office (9;) and the daily weather maps of the Zi-Ka-We1 Observatory and the Imperial Marine Observatory, Kobe, Japan. The temperatures given in c _.c. Chu• s paper have been reduced to sea level while the data over the ocean on the Pilot Charts are naturally at sea. leva 1. It is an advantage that these 1~:;.tter data should be intrinsically representative. The daily temperature reports given on the we a.ther charts should also be of similar character since most of the stations are in sea level regions. Change of pressure Will only vary too temperature a.bout 2 to 3°c. so the isotherms may be considered as approximate potential tempera.ture s. Dally inland temperatures would not, be representative but by using the me an of long term re cords this error is negligible. Tbe procedure in the treatment of these data is as follows: First from a glven Wind chart a deformation field is located a.nd . the values of the coefficients a,b,c, determined. superimposed isotherm map too distribution o.f l~o<I Next from a is found. Fr-om these calculations and measurements the value of F at vs,rious points can be found and from the fle ld of F the line of Frontogene els ca,n be located. A deformation field can be easily found when a str-eamline picture of the atmospheric circulation 1s obtained from a careful study of Wind charts and a precise construction of the streamlines~ The values of a., b, and c, are obtained by using the equations previously introduced, 1e.: 'LA-= Uo + (bto.)X-C"3- --V :::. --U- o t C:;L+Cb-d.) ef' • Since a center 1s defined as a point where u and v vanish s1multaneously, for a center at X0 ,Y 0 , we have: and Xo= ,u_ ='vlo+( b+a)Xo-C-;J-o- O V == Vo+C:Co+(b-~)"a-o=O u.,-c o+b, - 1/4-o V C, 0 1 b-a b+~ I - c,, C, 6-C -Vo d+b , -c C, b-O - 18 :l 1. z._.,,. rr b-a+c~o t he field •will have a center. By parallel trans- lat ion of the system of coordinates to the center we obtain -u..- :::::(b+a)X,-C"J( dropping indices): -1[ ::::: CL+( b-o..) "J- Substituting the above in the equation of a strai g ht stream line thru the center we get: In this last e qua ti on the actual value of the slope of a straight streamline through the center relative to the X-axis can be readily obtained from a given deformation field graphically and the re fore the values of a in terms of c found for that line. For a curved streamline the equation is: cl".} d.,x,, = _:1[_ =C.t,4-fb-3.)1J ul ( b+ d)X- -G:J- = C t(b-o.) 1- 6 + 3 - C --2a::X, For determining b in terms of c, the e,bove equation is used. Taking a syste m of coordinates thru the center of the deformati-on field shown above the slope { is constant along any strai g ht .line thru the center and can be found for points in any de formation field. The values of ~ for these sarae p oints are similarly obtained fro m the curved streamlines through the points. order to make the value of In --V: more representative, in actual oL~ • pra.ctice measure ments were made at many p oints 1 a strai g ht line I drawn thru the center and the mean value taken. With this value of b obte.ined from the curved streamlines and the value of a previously found from the straight streamlines the ratio of b/a for a given point is calculated. From this the Width -19of the frontogenetic rJector may be readily computed from eq {32),. This together w1 th the ve.lue s of a, b and c, found for the deformation field chosen are shown on the &.ecompanying ch&rts, along With the small sketch in 1;,he corner Which shows the direction of the de formation axis. For the second part of the f'ormula, the relative value of Ive,{! is me a.sured from th3 isothermal chart where the isotherms are taken as the lso-o< lines, according to the formula \voe'.\= 71 , h being the normal distance between two adjacent lines. All the contour lines of (~o<'.I are the result of measurement of \vo(/ through the· field. After the \v1°q chart is prepar-ed the F for a. given point is obtained by multiplying the value of term. 1v-o<( with the Ceo 2¢-~2</)' Thia latter term includes the measurement of' ~ through the whole field. taken Repeating these extensive calculations contour 11ne s of F can be drawn. Finally through the points of of maximu.11 curvature of these F contours e. lins can be drawn which represents where the frontogenetcic function is most effective. If any new front is to be formed or an e xisiting front is to be intensified it can be expected in this region. - 20 - v. AI R _MASS"u'_ e,S AND FIELD S OF MOTION I N THE FAR Eft.,ST. {10) ---In a previous paper the a.uthor has made e,n investigation of the air masses of North China. Trie Air Masses classified the re in are the :Polar Biberian (Pg..), the Tropical Pacific ('Ip) and the Polar Pacific ( Pp types. They are found to be the principal types in the Far Ea st and play the important roles in Frontogene sis in that region. However, one additional type of Air Maes, tte .E que,torial Pa.ciflc (Ep), which may be distinguished from the general type of warm Tp :nentioned above 1e considered here. There are several definite reasons for considering this distinction. First, the stream lines over the tropical region of the North Pacific ocean . clearly show a discontinuity between the air coming from the sernlpermanent Pacific High and tha.t from more southerly regions. _ • This discontinuity line is called by W. Werenskiold the ttequatorial ( 11) line of convergence., in his worlt a,n d is probably coincident with ( 12) the "Intertropikfront 0 mentioned in 'Physikalische Hydrodynamik' by V. Bjerknes. This line can even be verified by a wind shift on the da.ily weather charts of the Far East, in the summer season. secondly, the different identity of the air masses is shown by a comparison of the soundings in Tp air made at Honolulu, Hawa11, Which is in the TP belt and those made in Tp air on the China coast which comes from a more southern region of the Pacific Ocean. This fact has B.lready been pointed out and discussed by the author in his paper '' Air Masses of North China 11 • Therefore it is logical to subdivide the general type of Tp mass into two sub-types of warm, moist air. The one which is - 21 on the north side of this dis continuity line will still bear the original symbol Tp denoting the air mass as originating in the sub-tropical zone of t he North J?aciftc Ocean. The other which comes from the more southerly reg ions of the Pacific Oeean will be identified by the new symbol Ep • The line of discontinu1 ty or "equatorial line of convergence» will thus mark the boundary of the two air masses. 'I'his Equatori al Paciflc a ir mass comes to the region of the Far F.as t only in the summer season. Beginning in the late Spring season a low pressure area gradually forms in the northern part of Indo-China.. As the thermal equator which 1s the hottest belt on the globe continues to move northward after the sun, the low pressure area 1s enlarged and oecomes a l~most a per manent system on the da ily weather charts of the Ii'ar East during t he months J une, Jul y, and .August. 'l' h1s low pressure system undouhtedly induces the Ep air to come from the south across the geographical e quator , appear ing as a steady south to s outhwest wind due to the influence of the ea rth's rotation. E . Gl:lerz1(l3)eal led this current the Philippine Stream coincident wi th the path it fre quently takes. It is not clearly known to what 11mi t s the current extends into As i a , { a rough i dea can be round in the author• s previously mentioned paper undar the sec ti en devoted to ·rp air masses and also in C. C. Chu' s paper uc1rculation of atmosphere over Chine: 1 under the section on wind direction in July), but its activity around the Ph ilippine Islands, the southern China c cas t and the adjacent seas during the summer 1s well knovm. The Polar Siberian and the ·rro pical .l:'acif ic however remain the - 22 - t.wo principal .Air Masses 1n the Far East . They appear almost all the year and continuously converge over tbs re g1on to form a marked frontal zone. However, this zone 1s a.n oscillating one dl.J3 to the normal monsoon tendencie e of the region. the colder half of the year the In frontal zone w111 lie a.t soma distance offshors and in the warmer part of the year near the In the spring and autumn tbs Ps mass e as1ly coast or inland. • develop& into a certe.in type of modified air found to exist in the zone between the two principal ty~ s. This modified type of Ps war-rants consideration as it still has frontal importance 1n the Far East as will later be shown. D~ to the essential difference of their source regions, the Ps and the Tp air ar-e quite different in their properties. From the sounding data obtained in China the average value of SE, the equivalent potential temperature, for Pa air ls around 270-280°A. in too winter season, 290-300°A. 1n the Spring and Autumn and 310-320°A .. in the summer. The properties of TP a1r are not clearly known in Asia due to a lack of' sounding data, however they can be Judged by data obtained in other locations. Too ~ value of TG and TP. 1n the u.s., which have a simila,r circula.tlon to the Tp air in Asia, is about 320°A ( 14) during the winter season. .At Honolulu, at a lower· latitude the Tp air has a winter value of about 34o 0 A. Using the me an value of the above two sets of date. to give a rough idea of the val us of Tp air in Asia and comparing it with the winter value of Ps air, we can conclude that thsre is a temperatur-e difference of 30...l~Oo be tween the two principal types, Pa and TP. This - - 23 throws some light on the resultant frontal and cyclonic activity to be expected between the two masses. Tba fourth air mass l? p 1s the least known on the China coast and is likewise of least importance in considering Frontogeneeis in the Far F~ aet. However there must be a f a irly large tempera- t.ure difference between the Tp and Pp air because of their different origin and becomes most effective 1n produc·i ng f ronts where they meet over the Northern part of tre North pacific Ocean throughout most of the year. The resultei.nt interaction 'between them might we 11 be the ca.use of the 1ntens1f1eation of an existing front or of a cyclone ae it moved up from the south. Fields of Motion T~ field of motion of the atmosphere 1n the Far East 1e distinctly controlled by two well known se mi permanent ant1cycones the Pacific High 1n the southeast over the ocean and the Siberian High in the northwest over the land, together with the well known cyclonic system tthe Aleutian Low' in the nortrea.st as tte focal center of their outflow. The Pe.elf ic High has a permanent ee at 1n the 'Horse Latitude• zone between longitude 140 to 150° w. It shrinks and enlarges its dominating area 1n the course of tbs year. but it exists at all times. The most e,cti ve period is the summer wbsn the ocean te mpe re.ture is lower t han the te mpe rature at the same latitude in adjoining land are as. With a. more intensive center than the Pacific High,. t~ Siberian High on the continent is most active in the winter season. - 24 During the summer it almost disappears as it r-etre a ts pole wa.rd. However the low center for Asia land ar-eas in summer is still far to the southwest of India and Per sia ( b a sed up on the map o f ( 15) p ressure distribution in 11 P hysikalische Hydrodynamiktt Which indica t e s tha t the air flow s till comss from Sibe r ia a t this time. ( 16) c.c. Chu has mentioned t,he northerly winds in Sinki a ng, ¥fest China, during the su111r00 r sea son, which would ve r ify the e xiste nee of a northern current 1n the inland of . Asia during that se as on. Occa- sionally a High in Biberia or northwest China ce.n be found on t~ weather charts o f the Far East during the mid-summer period also. Therefore the continuance of this frontal zone ca n be expected during the summer even though the Ps source is not a..s easily seen as in the winter. The Aleutie.n Low in the northeast is lH~ewise semi-permanent in its nature. Of course,. it is mor-e pronounced in the winter than at any otoor time tiecause the region is comparatively warmer than tre continents on the two sides of the low at this season. From these semi -permanent pressure syste ms we ca n expect a field of motion of the deformative type for the Far E a.st as a whole, as s hown be low ( F1g. 20) • Tbs dilatation axis o f the deformation field runs in a southwest-northeast direction roughly paralleling the coast. Since this particular distribution of pressure in the Fa.r Ea st is not entirely up-set in any season of the year, the field of motion 1s nearly a st~mdard one for the region. It should be best developed in the Win•ter season, how- ever, be cause both the cyclone and anticylone s controlling it are Yr '- I-/ FIG. 20 . "t. .. " ,, I '"" "' THE GENERAL FIELD OF MOTION IN THE FAR EA$!' ... cr .f:=· I\) - 25 well defined 1n the1r loca.t1on at this season. For other seasons though mod11'1cat1on has occurred to a c,onsiderable extent the essential shape of the field of motion is still about the same and the orientation of' the def'ormat1on axis remains about fixed . ·r. Bergeron, based his statement upon this cona1derat1on in pointing out that the :itar Ea.st is a (17) region of £i'rontogenes1s. However the field of property (isotherms) must also be studied 1ri 1 t .s relation to 'the field or flow because JJ', the rrontogenetlc function as shown above is a funct1-,n of ¢, the angle between the isotherms and the def'orrnat1on axis and the magn1t.ude of ·t he temperature a.acendent. If the isotherms 1n the Far East should make a very large angle, say larger than ¢', (the angle of the frontogenet1c sector) w1 th the· deformation axis then there wouJ.d be frontolys1s instead of frontogenesis. 'rhis 1s the point which has to be determined in practice and which ,,111 be treated 1n the examples to follow. 26 - VI. FRONTOGENET IC RE GIO NS I N THE SPRI NG SEASON Theoretica lly it is not p osslb le to eppl y t he principles of frontogene sis in a linear field of motion, as d1s cusood e.bove, to a study of frontogenesis in a le.r ge field of motion between two air masse s from different source re g ions be ca use in such a large field the motion will no longer be line a r. Thus in this study we shall re s trict the e,r e a of investi ga.tion to a, vicinity where frontogenesis is expected .. In this wa y the field under co n sidera tion will be small and too genera l theory of fr'ontogenesis in a. linear field of motion can still be use d . The effect of the various se e" sons of the year on t rie setup of the v a rious fields will f irst be considere d . Spring is the season when the Siberian Hi g h on the land begins to weaken thoug h still active while the Pa cif ic High on tbs ocean becomes more pronounce d . As the Siberian High becomes we aker and more elongiited, it has a tende ncy to spllt up and a secondary High form over the Japa.ne s6 Islands. Ps air mass over the ocean. This High f orms a modified Thus tl~ r-esult ant field of motion in the Far East is a little more co mplicated by this addition than a.t. any otb!9r season. The fields will exist between these Highs and the Aleutian Low to the nortbsast. From the wind chart over the North Pacific, we find three well defined deformation fields as a result of the above distribution of pressure. One, labelled Deformation li' ield 2, is over Japan - 27 · - proper, and a third, Deformation Field 4, is far to the northeast •in the vicinity of the Aleutian Islands, ( Chart 1). Continued study of a combined wind chart showing ocean and continent data indicate the presence of another field. On the land wind direc- tions along the China Coast clearly show a line of convergence between the on-shore and the off-shore currents. It is evident that there is a line dividing the different Wind dire ctlone in the on shore current at a point soroowhere near the outlet of the Yantze River. Winds south of this line a.re generally north- east, while north of it they a.re southwest, (Chart 2). This line is apparently the axis of contraction of a deformation field. Other branches of the circula t ion substantiate the existance of this, Deformation Field 3, along the coastal provinces of China. Of the above four deformation fields, number 1 is formed by a'northwestern current on one side and a southeastern current on the other side. The former current should be modified P 8 air at.. this season with a rather long life history over the sea, while the southeastern current is naturally Tp• The resultant field is almost pur-ely deformative in character with the deforma- . ) tlon axis running in a southwest-northeast direction. constants in equation ( 32..) motion is equal to zero. coefficient tbt Of the for this field of Therefore /J' ls 45°. Deformation Field 2 is interposed between the modified returning P 8 air on the east side and an op posite current of modified Pa on the w~ st side which has a shorter life history over water~- The field has been rotated a little, but • b' is - 28 still nearly equal to zero. Of these two fields, the latter is relatively unimportant since it exists between two modified types of the same air mass, p8 , On the other hand the properties of the Tp and the modified p 8 air differ widely and tbe resultant action in field number 1 will be of major 1mporte.nce. Deformation l!'ield //3 is, generally spe eking, also in one air mass, with fresh p 8 air on the nortl:!vvest side and modified P 8 air on the southeast side. Since cold and dry Pe air very easily loses its characteristic properties 1n moving southward and acquires others by passing over a warm water surface, the properties of these two masses are quite different. .Accordingly from a frontogenetical standpoint this field will be more important than field 2. Unfortunately the streamlines over the northwestern sector of the field can not be completely drawn because of insuf'ficient Wind data over the region. However the de formation axls indicated by the re mainder of the data. still seems to be in the nort 11.e ast-southwe st dlre ct ion. A slight positive rotation is also observed 1n this field in the northeast. Deformation field 4 le composed of a current from the southwe st and another from the north through the Bering Strait. The two currents involved, due to the high latitude of the place would be Polar Pacific and Polar Arctic air respectively. Because of 1 ts location outside the region of the Far East it has not been investigated in th1e paper. Although three well defined deformation fields are found in - 29 the Far East, it 1s discovered upon studying ths isothermal field superimposed on 1t-he field of' motion that only two fields Will have \ D. Ii',. 2 is not only ir1,si gnif icant for frontogene tica l importance. f:rontogene sis from the stend-ooint of the air masses involved as . ... _ . ....- t; has alre a,dy tfeen -:r:>-0i-nt.e.d -.eut:, • hut also when the orientation of the isotherms in the field of motion is considered, since they ( make an angle larger t h&.n /,', in this part1cula1~ case larger than 45°, with the deformation axis. The v.nue of F' cannot therefore be positive, until an appreciable rotation of too isotherms in the field of motion has been a.ccomplished. In D.F. 1 however tbs an5le 4> is e verywhere smaller than/,'. The Fronto3enet1ca.1 function F' is positive throug hout the field and a line of frontogene sis is obt a ined alone the east coast of Japan parallel to t he deformation axis of the field. (Chart 3&4) The parallel direction of these two line s results from t he orientation of the isotherms nearly parallel to the deforme.tion axis of the f' ie 1.d. 3 has a.n ~mgla ¢ smaller than r' in some parts of the field, partlculr.,rly in the northwestern he.l f , but larger than ¢' in the remainder of the field. of [vo(I This together with the large value in this region yields a large positive value of 13' in the northwestern portion of the field, Which locates the frontogenetic line far inland .. It should be noted. ae;ain that the streamlines in the northwest section of the field are not completely drawn a.nd similarly the isotherms are posslbly doubtful due to the insufficiency or the information pertaining thereto. The line of' fronto- - 30 ge ne sis dete r mined for this f ield may t hen v ary somewhat from its ind ica ted p ositi on , particularly as the de f o nnat ion field c han ges . TQ.e abo ve two lines of f'ront o ge ne si s de t ermi ned for the region of' the -Tar L ast dur ing t he t:;p ring SE:Rson denote p lace s whe r e front c l syst ms are likely to be develo ped or i ntens i f ie d . The one de t er mined f rom D. V. 1 ls the ma i n fronto geneti c line in the Far Ea.st . r.rhe air maB ses involved are eEscntially d lf- f erent and in this sea,son prod uce t he most inte n se sys t ems i n t he re g ion. The ot her line is a seconda ry line o f :front.ogenesis be c ause i t 1 s still wit hi n one general t ype o f s.ir mas s, name ly Ps . Toorefo:re With an even chance f or frontal action t he d6 vel- opement o f t he l atter fr ont wi ll n o t be a,s i ntense as t he firs t. An examina tion o f t he da ily weat her c harts f or t he Far Eas t ind ic a tes a co rrespon den ce betwe en t he f'ronto genetl c lines n.:"6 ntioned above and the cy c loni c tr a c ks . Si nce the latter c an be regarded a s t he t ra ces of disturb a nces moving along a front the verification i s excellent . P ublishe d he re wit h i s a c ha.rt ( Chert 5) of' cyc lonic t r nc ks i n the Ifer Ea st f or t r.i.e month o f Ap ril reprodu ced f ro m t he a ai l y weat her c harts of t he I mp6r i 2 l MBr i ne Observ a t ory , It i s rather i nt e rest i ng to no te the two general group s of c y c lonic t rac ks that see m to co rrespon d very we ll to ( 18} t he t wo l ines of fronto ge ne sis . .A not her pape r , S hi o- Wang Sune./ s Chart of t he Normal 1':r& c ks of Extra Trop ica l Cyc l one s of Eas t e rn Asia als o shows this agree rr..- ent . The tr 8.c ks i n the southern group a.re so i dentical With the - 31 main f ronto genetic line that their locat ion and direction are appare ntly the s ame .. 1-{ort h noting i s the fact that the cyclones following these tra cks in t i:'.i.e southern group ar-e usually s trong, wh ic h is to be e xpe cte d from t he strong intera ction be t we en the Tp a i r and t he mod ified P s a ir along the raa ln fr onto genetlc line. Wha.t i s of greatest ·1nte re s t fro m the st B.ndpo,int o f this investigat ion, howe ve r , is tha t in April there is no cyclonic tra ck p as sing tr1rough Nort h China according to the J apanese Marine Observatory ts Chart. A refe r ence to the re p roduci;ion made here of Shio-Wang Sung 's ssr ie s of Normal Tra cks, shows his Number 3 tra ck suddenly chang ing in direction fr om the east do wn to the south at a p oint near latitude L~ 70 and long itude 115°, leaving a wi de are a of North China free fro m cyclonic a ctivity . Actually during this period Nort h Chlna always suffers from dry weather and in serious cases e ven drough may r-esult f rom this cyclonic and frontal inactivit y . The reason for t his ina ctivit y is not due to t he air mas s itself be c ause t here exists a prevalent onshor-e curre n t of mod i( 19) fl e d Ps during April. The fundamental re ason is shown by a glance at t he cha.r t of ' F' ' for Apr il . The negative va lue of F in the region of Nor-th China results from the large angle f/; , betwe en too isot l1Brmal lines a nd the deformation axis there. Tbe secondary line of frontogenesis i n the b'ar E ast appears a mong too northern group of cyclonic t ra cks, a s de termine d fr om t he sources mentioned above. The .dir-e ction of the line closely parallels the cyclonic t ra ck s reproduced fr om the Japanese weather charts . This close rel at i on indica tes t hat the line is app arently responsible for t he observed development of these f ront a l cyclone s . - 32 - VII. l:i'RONTOG ENETIC RE:G IO NS I N THE Sill,li'iER SEASON The summer wind eondi tion in the Far East is entirely con- trolled by the Paci~ic High. The High in this season has mov ed f'rom its wi-r1ter post tion of around 34·ON. and 140 0 -{ . Long itude to a center at about 42°N. a nd 150° w. At the same time the ( 20) pressure incTea.ses from the winter average of 1020mb. to a seasonal value of 1025mb. while ite area increases significant- ly with 1ts 1015mb . i s obar extending northwestward about 20° 1nto a position near the J"apane se Archipelago. On the other hand over the land, the Siberi a n High at this time appears to exist only in the western part of Siueria.. The result of thi s pres s ure t'ield read just,ment g ivers a steady pres- sure gradient from ocean onto the l and. A southe-aut to :;; outh- west wa rm marine current covers the entire region of the Far East being popularly called the ' s ummer Honseon' of' Asia . From t he available wind data in the Far East one main o.eformation field can be found f'or this season .. ·rhe field i s formed by the above mentioned tsummer monsoon' fro m the south and. the north- ern polar current from Siberla. ·rhere are several indications to ver1t'y the existance of this northern polar current in northwest China during the summer season, although as mentioned above., the Siberian High is not prominent on the map . 0 or Urumchi {Lat.43 • 45' N. , Long . 87 Long .83 0 0 At t wo s tat ions, Tiwha 0 t 40' E .) and Kuchar {Lat.41 40 N. , 00 *El .) in Sinkiang .P:rovince or Ghinese Turkus tan ' a nd one station, Chunching {Lat ,. 29°33' N.,Long.l06°33' E . ), 1n the Szechuan - 33 Provincet western China r e ported prevalent nor- th and northwes t winds in J uly, while prevalent wind di rections at all the eigh ty stations scattei-'ed along the China Coast a.nd t.:cast Pr-ovinees a re southeast to s outhwest. C.C . Chu noting this says that the sum- mer monsoon useems to have rea ch ed i ts nor thern limit» in southern ( 21). Mongolia . Probably a logica l pos ition for the boundary or the summer monso on and tb.e northern polar cuFrent in the summer will be, Ju st through Hutjertugol to Chun - chtng in a nor theast-s outhwest directio n . { 22) V . Bj erknes and others in their book show the center of the s ummer deforma tion fi e ld in As i a. to b-e i n a. place somewher e near North l~ia.nchuria '" during the month of August . From the author 's determ.ina tion, t he center in J uly seems to be in t,he northwes ter-n corner of' Inner Mongolia. '!'hi s can be verified by drawing a line a.ividing the wind s in the su..T1J.ID.er mons oon, :from the northwest winds to the North whicb. lino s eems to be the axis of' dil a tation of the deformation ri eld . 'J.lhe line runs 1n a SW- NE direction across North China and r.1anchur1a .. If we a llow t,hi s line to be the dilatation axis of the det·orma.tion field the center of the field will be a long the line a t its int ers ec t ion with the contrac t- ion a.x1s which 1s readily l ocated in the d ivergent fie l d ot"· the monsoon wind s . Thi s center appears to occu.r i n the southwe st corner or Inner Mongolia . Generally speaking, this d eforma tion field is in good agreement wi t h that drawn by V. B jerknes and hi s co-a uthors for the peri od one month l ater . 'l'he dotted str eam lines in the northern current indicate tha t, they are a little doubtful due to a lac k of data. - 34 A gl a nce at t he July Def"ormation Fi e ld Chart ( Chart 6 ) shows tha t t he ma in f ield on the Asi a continent is a pu re c1eformat1ve t ype with the d e forma.tion a xis t h ich in this c a se i s the dilat ation ax1s running in a S'W - NE direction . Since t he isotherms in the field ar-e quite irre gul ar the distribution o f' F' l s not coincide nt with the contour llnes of \vo< \ a s is usually expecte d . Ove r the J apan sea t he isot herms show a tro ugh a.s the effe ct of the well known Okhotsk sea Curr·ent, co mi ng down fro m t he Okhotsk Sea in the north, and cooling the a ir at t he surfa ce over t hi s re g i on. Along the southeas t border of Inner Mongol ia t he isot herms show anothe r trough. 'l'he wedge s hape d isothe r m field be t wee n the se t v-10 t r o ughs apparentl y indicates the domination of this t erritory by the warm maratime a ir of too summer monsoon f rom th6 south . Thi s aga in shows that the line of conve rgence betwee n the summe r monsoon and the northern p ola r curr ent must exi s t the re as indic a ted by the dll a. t a t ion axls of the field. The fronto gene tic line o f t he field, due to this part icul a r feat ure of the isothe r m field, sh ould only extend f rom Whang Ho or the Yellow Rive r val ley to Manchuria running in the SVi -NE direction along the deformation a xis of the field . { Cha rt 7&8). This line is tb:3 ma in fr onto genetic line for the summe r se ason i n the F'ar E ast because as se e n from this a nalysis it 1s derived f rom the main defor mation field formed by the t wo principal t ypes of tropi cal mara.t1me a nd p olar continent a l a ir masses . A co mparison between this frontogenetic line and Sung's normal cycloni c tr e ck s in the Far East ( Cha rt 9) s how the line in g ood - 35 agreement with t r ac k :P o. l a nd t r ack No. 2.. which are the tr e. c k s of about 70% ot: the cyclones i n t he summe r sea son . On the Japan- e ee we at he r Charts the a c t ual cyclonic t r a c k s i n J·u1y, 1933 do n ot f ollow the r ronto genetic line ve ry well, but generally spe a king ths 1:r ori gin is c oncent ra te d around t h is line . One si gni fi ca nt point concerning t his f ield and its l oc a tion is that bot h t he J ap anese Che,rts and Sung ' s cycl on ic t r a ck Chart for the summe r season sho w no cyclone t r a c k s p assing t hrough the r e gion betwe en the Whan5 Ho and the Yantze Valle y whe re a re g i on of frontolysis exists . This is i n dica t ed on the Che.r t of Distri- bution of F in the Fa r East for the month o f July . ( Chart 8) Be side s t he ma in de f ormation field for the. sea son a field of s pe ci a l interest is found i n the sout hwes t corne r o f the Nor th Pa ci fic Ocean . This field is ide ntif ie d accord i n g to stre a m line patte rns as a curve d stre amline field Wit hout center. (see stream line p attern chart, Fig. 16). The Ai r Viasses involve d i n this field are t he Eq ua torial Pacific on the southwest side and the Trop ica l P.acif ic on the northeas t side . The conve rgence of the air tb9 o f f l ow which i s c a lled by "% . i Je convergen ce H a nd in Bj erknes' r e n s k i o l d b o o k the 0 a curved line running in a SE -N Y direction . ve r gence ie ap preci able . Since tt10 11 0 (!Ua toria~ line Inte r t rop ikfronttt, is Along t rie line con- p rope r ties of t he Ep and Tp air masses are not e s sentially d iffe rent a s ob se rve d at t he surfa ce an a ctive fr ont a l syste m could not be e xpected but nevertheless the fo r ma tion of the Ty phoon in t he Fa r East c e,n be explained by the existence o f this special field . The Typhoon is a tropic a l c y clone - 36 of unusual violence f ormed on the edge o f trie doldrum be lt. The vi gorous n a ture of t hese t r op ica l cyclone s is undoubte dly d ue to the large a mount of energy availab le i n the t wo ad j a,ce nt war m mari t ime a i r masses Ep a nd Tp, each With high te mperature and humid ity . What t1e ne vd here to explain tbe formation of the Typho on is the introduction of ro t ation to start the vortex motion, since their ori gi n seems to be in t his zone betwee n the se t wo t ype s of air. P0t ter ssen, from a hydrodynamic equation where S is the Spe ci fic Volume, 1J = -S -q-p-,A.X v P the a. t mo s pher ic p ressure,. A a vertic2.l ve ctor Who se magnitude is 2 wsin <p, W being t he velocity of earths rot a tion , <t> the latitude ( 23) a vector representing velocit y ~ has po inted out t hat c on- and v ver gence produces pos itive curl or cyclon ic rota tion as shown by the following equa tion: - it( ~ v ) = - c:Lr.V(>d ~-v) +1v SX: (-v-P) where the l a.st t arm 'vSx. (-v-P) is the number of so l enoid s in the horizontal plane a.nd is usually quite small, e spe cla lly in t he •ryphoon region where the te mpBrature distribution is p ractica lly uni form . Having neglected the l ast term, too equation is -½ ( eu.,J_ V) :=: - clv-. V (A t ew,L v ) _ex:p r-essing the rate of change of curl v With time as p rop ortional to the convergence of v (-div . v ) times the bra cketed term. From t h i s e quation we can f urtbBr solve curl v to obtain a mer€ detailed expression for the relation between curl v and -div.v. Let the t wo vectors be exp ressed - 37 -d1v.v =-b , then:- and take the ave r age ~t =-b(A+ X ) ( 1) -4¥-=-b(B+ Y) ( 2) --1:t-=-b (C+ Z ) ( 3) Re writing e qua.tion ( 1) dX_+bX=-bA a=t a nd t aking the integra l we have ~ X. = e (fbA e dt tK) ( 5) = e -b\_-A e bt+ K) ( 6} = -A+ Ke At t ~o, and Equation ( 4) bt -bt, x = o. ; 0 =-A - K , -bl ( 7) or K = A. -bt ( 7 ) the n be co me s X=A ( ~ -1 ) Simili ar-ly Y =B le -1 ) -bl -bi ( 9) Z =C (..e - 1) ( 10) -bt v == )\ le -1 ) ( 11) Lwt,l theref or e ( 8) Equation (11) indi ca tes that curl vis a function of A and increases exponentially with tr..e increase of convergence, le . - div .v, ~n d time t. In the field of motion referred to above convergence is quite pronounced _so tha t a posi tive curl v is very easily produced and intensified. whe re the l a titude angle has a small value. However, ne ar the equator, f is small and)\ is s mall, curl v still Wit h t he increased value of A wit h the in- • crease of latitude curl v must becor.ne act.ive even with the magnitude of the converge nce {-div . v) remaining the same . This ex- pl a ins why Typhoons are usually formed along the line of convergence between Ep a nd Tp at lat itudes not lower than 10° and are quickly intensifie d as they move to higher latitudes- . - 38 From the above discussion of t he for mation of Typhoons the movement of these storms can f urt:-her be an a l yse d . In the trop ic a l zone the Typhoon should follow a pat h whe r e t he converge nt flo w is most a ctive i n orde r to mainta in a nd i nt e nsi f y i t s vorte x motion. 'l'he re fore t he "e qua toria l line of co nverge n ee " is nat urally the normal tra c k o f t he Ty phoon as will be bo rne out b y l at6r i nve sti-1gat ions.· Upon the arriva l in t ~ t emperat e zone, howe ver , t he 11 e q uato- ri a l line of convergence H is no longer d istin ct , but the t empera ture v a ri a tion be gins to pla y an i mp or t ant part. In ot he r wor d s as the storm be gins to a s s uroo t he p o s ition of a n Ext ra -trop ical Cy clone it Hill be i nf lue nce d by f rontoge ne s i s a t t h i s l a t i tude. During the summe r season the r e l s a reg ion o f fr ont oly si s a long the China co as t and over t he coas t a l provin ces , wh i le a s li g htly f rontogenetic region e x i sts to t he e ast over t he ocean. Thls distribution o f the f ro n to ge ne tic a l fun ctions Will g i ve a de ge ner a ting effect to t he t yphoon as i t move s i n l a nd but wl ll r10 l p to r e ge ner at e it as it move s ove r t he o cean . The pr i mar y fa ctor governi ng t he movement of the typhoon is the general wind sy s t em Whic h has a de ep sout hv1estern current ove r this re g ion . Therefore it appe ar s n a tur al t he.t the typ hoon re a c h ing the se l a titude s r e curve n or t heas t whereupon the f r onto genetic effect of t he oce an ma i n t a ins the storm' s i n t ens ity . If t he fiel d of motion d e f l e c t s t he s torm on l and , as is rarely ob se rved in t hese l a titudes , the f'rontol ytic effect 'there on helps to destr oy it. - 39 The line with the frontoge ne tic symbol in the south-we st c orner of Chart VIII, is sketched in a ccordance wit h these ideas of typhoon move ment. Actually mos t t ypho ons in July and Au gust do .fo llow t his trac l-~ into t he mi ddle l a t i tud es a s obse rved on Chart I X. Bef'ore t he mo nth of June and af t -er Se p t ember- the tte q ua tori al li ne of conve rgence 11 based on c ha rts of a verage s .,. is no longer observe d in the Far East and since tbe occurence of a typhoon is gene rally r a re du rin g tha t pe r i od , this s e e ms to g ive mat e ri a l proof t hat t he forma tion of t he typ hoon ls definite ly re l e,te d to the conve rgent flow a long t he "e qua tori al li..vie o f convergen ce be t ween t hese two a. ir masse s, Ep and Tp • The study of a ctual Typ hoon forma tion in th1s ;, articul a r f ield of curved streamlines wit hout cente r has enab le d the a uthor to find a clo se relation between tr:ie pos ition of the ce n t e r of the Pa cific Hi gh and the formation o f' Typhoo n s i n t he Far Ee.st . Brie f - ly s t a t e d t he relations are as fol lows: - \\ he n t he P a ci fi c Hi g h is d ispla ce d t o tbs e ast from its normal po s i t . ~ ~ low p r,ec•s ure re g ion ove r the ocean nort hee.st e r e a ee d . of the Philipp i ne I slands is in- At this stage s outhwes t Winds are a ctive over the South China f:ea whi le li g ht a n d irre gul a r winds are observed i n the flat pressu re f ield no rtheas t of t he Philipp ines . When the Pac i f ic H1gh sta rts a return to its more a verage po sition as shown by a wes t ward ext e nsion of t he i sobars and of t he nort he a s t. t r ades ., t he Winds in t he f lat p ressure re g ion mel'.ltl one c1 northeast o f t he P hilippine s beg in to s how a cyclonic cir cul at ion. •rhis develop me nt continues with t he southwestward movement of tte Pa ci f ic Ri c h or an intensif1c a ti on of t he Hi gh Center- itself. As the cyclon i c cent e r moves i nto hi gher l a tj_tude s an a ct ive Typ hoon i s f orID3 d . Actue.l examples - 40 c an be easily ob t a ined fr om t he summer weather charts. is g iven here in Charts ( 10) to (12_). One example I t is seen that during the four days of formation o f too resultant Typhoon the Paci f ic High has moved a long dist a nce f r om nortteast to sout hwes t . At the s a me tlro the we stwe.rd move me nt of the ' Equatori a l line of conve r gen ce ' a s s hown by a zi g- z a g line on the map c an a ls o L"El tra ced. Conversel y it is i mp ort ant to note tha.t Ty-p hoons a.re rare ly o·bserved in t he J!'ar East when eithe r, the Pacific Hi g l'l i s moving towards the e a st, or it re mains in the east, or it a lready occupies an extn:1 me we s t e rn posi t i on at the same time that the center is wel l developed . The correlation o f t he facts above no t ed in the formE' tion of Typhoons ca n be eXplalned by t he theory of Typ hoon formation based on the conver gent flow occurring in tbs curve d stre nnline f' ie ld f i e l d existing in the southwest corns r o f the North P aci f ic Oce an. The fir s t e sse nti a l appe a.rs to be the rnoV6 ment of t he Pa cific Hi gh which de cr ea se s t he pres s ure gr ad ient over t tis reg ion normal ly occupied by this llne . This allovrn a flow of Ep air rrom t he southwest into the re g ion to te es t a bli she d . Next when the Pacif ic Hi gh moves b a c k from the east it natur a lly incre ases t he pressure grad i e nt towards too southwe s t and extends the northeast current to meet the Ep current mentioned . This c onvergence p ro - duce s cyclonic curl and e xplains the cyclo n ic ci.rcula tion which f' orms a t thl.s t ime . A continue.nee or the se condi t lons e.llows the Typhoon to be developed . As e. c heck on t his 1 t appears that whe n t he Pa ci f ic High move s into a n extremely we ste rn p osit i on an d re na ins a ctive the - 41 ''E quator ie.1 l ine of convergence• Will be pushed down to a p osition in the very low latitudes where the t erm )\_ , ie . 2 WSin p small to create an appre ciable value of curl. is too 'l'he re fore the favor- able cond ition for the formation of Typ hoons in the l?ar East natural ly follows the wes t we,rd extension of the Pacific High a f t e r its eastward d i s p lace ment has a llowed an i nfl ux of Ep air Wit h whic h a converg,'6nt f low i s es t ablis hed . It is believed t hat a, more det> a iled study of actua l cases occurring i n t hi s c urved s t ream line field will est abli s h r eliable rules f or the forecasti n g of this phenomena. - 42 VIII. :F'RON'i'OGENETI C :Tu: GIONS I N THB.: AUTU:s:'. N ~1.b.:ASON Generally s peak in g , the f e a.ture s o f t he atmosp her ic circulation in the Far Eas t during the Autumn sea.son c an be expe cted to be quite lll{e those found 1n the Spr i ng s0 a.son , be ca use the climat ic cond l t ions in the t wo seasons are esse ntially si:nila r. Howeve r some re mar ks a bout the transi tlonB,l c hange of t he p ressure f le l ds can be ma de he re . The ma in anticy cl one over the Pacific Oce an , t he Pacif ic Hi g h, is not as acti ve during t he fall as it is in the spring . Not only its domin&,ting a.r·ea has shrunk but a le.o t he center of the Hi g h ha e moved to t he north a.bout 6 degrees to a cente r at a.bout 38°N, 11~2°w. On the other hand the mai n ant i cyclone on the .As i a Continent, t he Sibe r i an Hi gh, shows a.n inc r easing prom ine n ce co rn pared to its s p rine; pos ition . The reason for this reversal of activity o f the two rnaln antic y cl ones du.ring the t wo d ifferent se aE,ons c a n be attribute d t o the dif fe rence t he oce an a nd the l ancl . it y of a VU3.t er i n te mp;:- r 2.tures ove r Due to the hi gh spe ci f ic heat a.nd mobil- s urf a ce the oce a n te mpe r e.tures are raore reluct ant t han t hose over the continent to follow the c hange of sol&r intensity d urin g the course of tra year . Conse q uently t he contine nt a l surface i s re l a tively v1ar m comp ared to the ad j a cent ocean surfa ce in the s pring sea son , b ut colder in the aut u mn . f, glance at t he spring and autumn isother ms superi mp osed. on Charts ( 2 ) and ( 14) indica tes this d i ffere nce. These t emp€ n ,. tur e rel a tionships be t ween the ocean and continenta l e.reo.s in Sp ring and Autumn in a - 43 lar ge measure a ccount for the r e lative i n t ensities o f the principal a nticy clones mentioned ab ove. Under t he a ction o f the p ressure fields d iscus sed above the de forma ti on f:i.eld s fou.nd f'or t, his season in the F&. r .t.: ast e.re bas ical ly t hG same as t ho se f ound i n the f?pr ing , b ut d l ss i ri:i lar in s ome p oints. They tota l s ix in n u mber , one i n t he t rop ics and five in t he t e ro po r a t e zone . { Chart 14) Of the f ive f :l.e lds in the t e mpe ra.t e zone only one is ne w Wh i le the re ma.in ing fou r c a.n be i de ntified fr o m tro Sp ring def or mation field c hart . The f i e ld not i denti f ie d fr om the spring chart se ems to be th.€ sys te m loc a ted ne a r t he Kantchatka Peninsula . Th i s system , howe ver, has no i mp ort a nt p lEce i n thi s invest i gation be cause of it s po si t lon out side of the re gion under considerat ion . F urt hermo re the l arge a n g le the isotherms in t his area ma l-cf.3 Wit h the deforr.natlon ax is would. onl y produce frontolysis . Labe l l i n g t he ot her four de f or- mation f i elds in the te mperate z one Wit h tr1e S <C:lillB numbers i:; iven si r;i ilar f i e l ds o n t he s p r ing c ha.rt t he t rf.!.nsition o f the se f ields c an be exa mi ned . It Will be noted t hat F' ie ld E, No . 2 e.nd 3 show a s h i f t northwa rd a nd li' ie l ds No . 1 and. 21- & shi f t n or t he a stws.rd . Shifting of' a ll of t he ee syste ms c a n be di re ctly o r ind ir-e ctly e.cco unted for b y t he s hrinking and northward re3r e ss i on of the :- a ln P ac i fi c Hi gh . The a i r m.Rs s symbols u se d for t he c orns s pondi ng deformat ion fie l dq i n the s pring se ason c ctn s till be used v: lt h the one excep ti on ot tr.ie air me ss on the nort h side of d e ''o rma tlon i' i eld No. 1 Whi c h now rn& y be calle d :?p ins te ad of 1,:od i f i e d P 8 • r..rhi e . i s due - 44 to t he no rt hwa rd s hi f t of t he mi n or d i ve r gence cent er ( now a t 45°N a n d 155°E) whi c h Will fe e d a i r sout hwa.rd fr om t he n ort he rn reg ion s of t bs Pa c i f i c Ocean . The s ymbols a r-e t he n Tp a.nd Pp f or F' i e l d No . 1, ?ti.edifie d Ps ancl e i t he r RP s or RPp for F ield No . 2 , P s and (24 ) RP s for Fie l d No . 3 and RPp and .AC( J\rctic cont 1ns nt a l f o r No. 4 . 'T'he def o r ma tion f ields t he mse l ves are loc Et e d as before b y a c a r eful study of wi nd d a t a av a i lab l e . E' i e l d No . 3 , whic h i s l oc a te d a l on e; t he co ast a l re g ion of' t he Pe i - Ch1-Li Gul f i s r a t he r diff icult t o find d ue t o t he weak c hara.c- teris tic s of t he cur re nts in the sys te m. Howe ver , on W~ We rens k iold'· s msan a ir t r a n sp ort c har t, t here i s appare ntl y a d i vergence ce nter in t he Pei-Chi-Li Gul f . Si mila rl y on c.c. Chut e c har t of wind data al on g t he Nor t h Ch lna co a s t , a li ne may be d r awn d ivid ing the gene r a l on- shore curre nt o f a ir al on g t he co a s t int o t wo group s , wi t h s ou thwes t Wi nds on t he nort h s i de o f t he l i ne a nd n orU1e as t wi nds on t he s out h s i d e. Just ab o ut 100 mile s i n l a nd fro m t he Pe 1 - Chi-Li co as t t o t he n ort hwes t, a p re v ale n t nort hwes t curre nt i s ob se r ved . Comb i n i ng these t wo cu rre nts a de fo r.·0 a ti on f i e ld e xi st ing over t he co e.s t a l re gi on be co me s appar e nt . Fr om anothe r s t a ndp oi n t, t he sudde n bend i ng of' t he iso t he r ms a l on g the co as t 3 ive s a noths r i nd i c at ion of t. he p resence o f t hi s f i eld be t we en t wo d i ffe re n t a i r mas se s . Comp ar i n g thi s f i e ld No. 3, wi t h its s p r ing co unte rpart, t he a ctiv i t y i s de cr ea s e d be c a u se o f t he d i mi ni shi ng s tre n gt h of t h-s on- shor e c urrent. Howe ve r , i t s houl d be a well d e f ine d s ys t e m r€ t a i ning f ro n t ogene t i c i mp ort a n ce be c a.use of t he marked d iffe r e n ee be t ween t he p rope rties o f i t s Ps f r esh fro m t he nort h and i ts mod i- - 45 fied re t urn ing Ps fr o m over t he ocean. The p o s it ion of the isot r.B r ms in t he field, aga.in limit the fronto genetic act ion to a s mall area j b ut t he crowd ing of these isotherms along t he de for mat io n axis is to be no te d . field prepa re d !'or Cha.rt (15) of tbe f.1e p t. shows t he laree st v &lue over the Pe i-Chi- Li Gul f a.nd 3 ive s t he fun ction 1" a l rirf_;e VE< lue :i. n that reglon due to the favor-able or1ent €,tion o f the iso t herms. De format i on F ield No. 1, re ma.ins almos t the snme as in the Sp ring sea son . Its char:::, cter i st ics are not c hange d by the desig- n a tion of the a ir on t he north side as Pp since t he ~ro per-ties of Pp air in that loca tion are about t he s ame as t hose in the modl f led Ps a.ir wit h 2 . long life h istory ove r the sec: . ThereforB the syste m l s just as a ctive and should be trie ma in s yEtem of the sea~1 on in t he Far Er:. st. par t to t he NE F ore over, tbB actlon of' t h is field and its counter- ( F'ie l d No . 4 ) w1 11 r-e sul t i n the i' or·n!at ion of . intense systems pass ing a long their combined di lat ation axis . Thie e ct i on i s fur the r d ie.cus sed i n a l a t (.:; r para3rap h . From t he frontogenetlc p oint of view Fie l d r, o . 2 , doe s. not have a R i mpor·tF-.nt ;:.;. role a.s in the s p ri ng no1H:on , beca use the isothe r ms in tha t f:LeJ. d make 1.:m even l a :eger angle ¢ With the deforrnf: t l on axis _ur- lng the a utumn than i n tbs f\ Jrin g d ue to the e.dded p os:1. t ive ro t ation of t t..e def ormat ion axis o f the s ystem . 'l'l."£ frontogene tic line s c a lcula t e cl fr o Ei t hese four pr incipal dGforma tion f'ield c in the te mperr-. te zone a nd the t he:cr::iaJ. chart f or U10 s ame season are shown on Char-t ( 16 ) . The e out he :rn line i s t he m2.i n front oge ne ti.c line e. nd is colncident ·•r i t h t he ma in - 46 rrontoge ne tic l i ne o f t he s pri ng season , whereas the n o rthern one over t he continental area ma tc hes t he co rres pondin g se c ondary line on Chart (4). Betwe e n t he t wo lines a re e; l on of f rontolys i s i s observed over the Yel l ow Se a , Kore a and t he J apan S.e ~ . 'l'hi s fronto l ytice.l r eg ion i s no t a.s lare:..e as tha,t noted i n t he spr i ng sea son but i ts l0 ca tion and shape i s simi l ar . From t hi s co mpar i - son one c an read ily understand the s i mi lDr i ty be t ween the ge ne ral weat~r c ondi t ions in t he Fa.r Eas t in the r;pring e.nd in the Aut umn . The re l a tion between t he fronto e;enetic lines and t he cy cl one movement s c an be ni cel y obs erved on chart ( 17) , where these l i ne s end a ctual c y c lone t ra c ks for the mont h have bee n p lotte d for c omparison . I t i s a:onar ent th.., t the c vc lonlc t ra cks have t wo o re J. ~ V ~- dominant paths corre spo ncling t o the t,wo lines of f ro ntogene sis . On t he Japa.ne se Cy cl oni c Track Chart f or Se p t e mbe r , 19 32 , the re is on ly one c ycl on i c tr,'.3-Ck i n t he northe rn gronp v:h:tle in Sung ' s norma l c y cloni c t r n c ke f or autumn th:H'G are t no t rclcks g iven wl th ra t her de f i nite directions e.nd one With B. rat her i r r e cular tra ck . The sou t hern e;roup of cy clonic tra c k s which corns e.pond to t he rn2,i n f ron t oge:netic l ine b ot h on the J a panese Cha.rt and on :.ung ' s Chart c omprise ab o u. t 70% of the t racks for t he sea son . Thi s 9reponde r - a n ce o f d i s t ribut ion of cy cl ones along t he so uthern track ~.s c ompared wit h the ne e.rly equal dis t ribut i on of t he t wo grolJ.ps in the s.pr ing seas on must be due to the greater act i v i ty of' the fie l d No .l ( Wit h it s co ,binea ac tion wit h F i e l d No . 4 ) over L•:l.e l d No . 3 a t th 1 s tirr.e . 1 e t we e n the t wo g,roups of cycloni c t rn cks a large Brt"i &, i nc l ud - - 47 1ng North China and Japan ls free from cyclonic tr a cks as shown on the Japane ne Chart and sung.- s Chart. Th1e fact ie e~la1ned by tte re g1on of frontolysis on Chart 16 coincident w1 th this area . An 1mportant obee rvation cnn be ma.de he re regarding Chart (J:1) . The cyclone trac!rn in the southern group show {!enera.lly parallel dire ct1<ms w1 th the me.in frontogenetic line for the season, but do not fall a.long the re g1on of this line. This apparent discrepancy between them can be sho1.,n to be due to the fact that tre frontoge net1c line represents more closely the po itlon of the actual fronts While tre cyclonic trnclcs tr ce the centers of the cyclone movement only. When a frontal cyclone beeooes occlude d the center of the system is necessarily removed froo the mean position of the front, as shcJwn ln the accompanying skoteh. CYCLONE TRACK FF.O~!'l'AL LINE(average pos1tior:j 1''ig .21 Observing tl:e day to de.y roovezmnt of' the oonter- and the naln front of t : syste::i, tvio llree c n be plotted an shown . It ls ap- parEnt then that ,hil~ the center and the front are together at the left of the picture the distance between the two lines will be lo.rg ?' ~nd lsrcer as the svstom becomes more occluded_. ' ~ 'l'hl s 18 in ac;rceu:.ent w:tth th6 facts shown on Chart (ll) where the cyclonic ' tracks and the main fronto netic line arc ve ry close to eoch other - 48 a t the southern part o f the J a panese Ar c h ipelago , but ·,ide ly separated near t,he Aleutian Isle.rids . It is noted t ,.iat front a l systems alon g t he n;.a i n front oge - netic line at this season ar-e mo r e active than in tt:e Spring d ue to t i.1e (!O tab ined action of De ormat io n i:' ielcls J. and 14- me ntioned above. r'urt he rm.ore the outbr6 aks of cold a ir in t hi }3 seas on are mor-e intense t han in Spring since the Giberian I·Iit; h, Vlhich is responsible for t he cold alrJ) is more active. b i ne to rnak 'I' he '--~e two com- the occlusion process more p1~ominent i n t l1i s season and tl1e separa tion between the frontogene tic line and the c y clonic tra. c ks should be more noticeable . Tbis i.s V6ri f ied by a compa ri son of Chart (5) f'or i\pri l and Chart (l7) f or f.';ep t ember . The Deformat i on :F' i e ld No . 5,. in the sout hv1est c orner of Chart (VJ. ) in t he trop ica l zone is a remnant or' Ue 1 e quatorial line of convergence' in the Far Eas t, prevl.ously expla ined i n the Gumr.-ier d iscussion . the Typhoon . It is importB.nt only i n the format ion of The deformation axi s of the syBtem i s re a lly the • ' e q u' torial llne of convergence' and during this season run s i n an e,lmort East - vie s t dire .c tlon. The intere st .i.ng t hing to note on Chart {.U) i n connection with t h is line i s thc. t the tracks of t wo Typhoons oc cur ve r y c ose to it . Theoe tr a c'rn t,a1::en from the Jap a.no se Charts are the only t wo Typ hoons for the month of 8Bp t. 1932 . The thUi:!,) rule ind ic a ting that a 'ryphoon recurves north- e o.ster ly ae it moves n orth is not verif i ed i n thl s ca se , oince these two con t:i.rnmd we stv,rard along the l ine of converge nce . This s eems to furthGr verify the theory that the 'equatorial line of convorr5e n cet :l e the t ra ck of Typhoons . - 49 I X. F RONTQGE NE TIC RE GIONS I N '11 F£ WI NT.ER S'~;AS'ON . Dur i ng t he wint er season the dominat i on o f t he Siberia n Hi gh over t be s 1at 1c Continent is absolute . This High is so re ll def i ned a nd so extr emely active that i t s uniform off-shore fl ow directl y r e aches the trop ical re g ion of t,he No rth pa cif i c o cean . The P opul a r name 11 vt int er monsoon of Asia•' is norma lly ueed t o de s- i e;nc,te t his flow. The Pacific Hi gh i n t his se a. son , although not o,s active a s i t was in the summer see,son still i s we ll d ef ined but i n a 1:101"6 eas tern p os i tion and sencls a uniform southeasterly flo w tow2.rds the F'ar Eas t re lon . 0 The r-e sul t ls t o br i ng t his flow of Tp into dire ct co nta ct wi t h t he f l ow fro m .As ia of P 8 a i r i n the winte r seas on. Inspe c t i ng t he wind c hart s of t he Fa.r ~a st i t is found t ha,t one l arge s c a l e def ormation field exi s t s a t this tLr.G, being we ll l=' o'(' l"\'1.. ed def ined in it s eha1)e as it i s d i re ctly ,I by t he t wo uniform flows co ming from t he S1ber 1an Hi gh and t he pa. ci f lc Hi gh . The f'ie l d i s n ot a pure l y de formation t ype , as the deformat ion axi s of too field i s not exa c tly co-inc i dent Wit h the dil atati on axi s . A s li g ht c on vergence i s ob se rve d i n t he f iel d, whic h i n.creases /J' , the fron t o gene t i c al angle to ab out 50° . Anot her deforma tion f ie ld of mu c h s rn.e,lle r size should exi s t in South !1a nc hur l a be c ause da ta show a converge nt Wind fl ow in t his are a. . Thi s conve r ge n t f low con si s t s of a NE to sv- curre nt on t he eas t s i de and a W t o NW curr-ent on t he we st s i de . The Swall def or - mati on f ield shown i n t he nort hwes t cor ne r of Chart ( 18 ) re pre sent s t he plot fr o m t .he act ual vrind data av ai l able . I t i s obv i ous that - 50 in the p osl tio n shown 1 fronto ge ne s i s ca nnot be a ctive on the rig ht side of t he field be c a use of t he l a r ge a ngle , a l mos t 90G-1 t ha t t he isothe r ms make with t he de f or matio n axis, b ut on the l e f t side f ronto gene tic p ossib ilities are evident f rom tbe decreases va lue of cp . Furthermore if t h is field is move d of f s hore by t he s tron g currents of Fr es h P s, a nd the counte r current o.f a i r to the ea st be maint a ine d , the frontogenetic p os s i b ilitie s be c ome e xt e nded through bot h s ide s of the fiel d Wit h t he ne w orient at i on of isot he r ms of f s hore. The shape o f t h i s par t i c u l ar field s hows a p rono.unced p ositive rot a tion, p rob ab ly due to t he influence of t,he coas t line on t he orient a tion o f the isotherms. The i mpor t a nce of the se f a ctors will be p ointed out s hortly . The frontogene tic line for this Winte r sea s on, a s dete r mined f r om the one l arge deformation fiel d mentio ne d above i s s hown on Cha rt ( 20) . Ttlr ~ t he f ield i s rat her l a.rge f or con sidering a line a r field of motion in dealing With fro n togenes1 s but ne vert he less sin ce t he f lows 1n the field a r e uni f orm due to ea c h of t he Hi gris being a ctive a nd the surfa ce traverse d b y the t wo f lows b eing s moot h, the app lic abilit y o f the ge ne r a l pr i ncip le s o f frontogene s is to this particular ca se- should be muc h l a r ger t han us,ual. By u s ing the s ame fronto genetic eq ua tion to c alcul a te t he value of F , the line of f r-ontogenes ls ob t a i ned f or wi nt e r runs in a nearly p ara llel direction wit h t he As iatic co Rs t a nd not f a r from it. An examina tion of thi s line indic a tes tha t i ts existence in this p osition results from the large value of \v0<l words the crowde d isotherms along the coa st a l , or in other re g ion s of Asia. ( Char t) 19 - 51 '1'he line howe v e r o ccurs wi t h in Ps a i r . Thi s chara cter - istic make s i t dif fe r e n t fr om ot her front ogeneti c lines be c a use it appar entl y doe s not re p r ese nt a re g i on of frontogene s is be tween t wo ori gina l l y di f fere n t air ma s ses but r at he r wi t h in one a ir ma ss . Tl16 effect o f t he s ma l l d.e f'o:rma ti on f i e l d re f e r r ed to above n ow be c omes si gni f ic ant, i n contributing t o t he for mation o f ne w cold f ron t wi thi n the Ps o ut b re aks. The co unte r-curre n t refer rnd t o a.bove i s e v ide ntly ma int a i ned b y antic yclogenesi s behind a c y cl one to t bs ea.s t. The format ion of suc h cold front s between p o s itive is a l lo bar i c cent ers has been po i n ted out, to t he write r , i n nume rous ca ses on l and by Pr of. Krick , and al t hough s uch deta iled da t a are n o t av a ilable ln the observ a tions in t h i s re g ion the a c t ion ind ic a te s tbs s a me result. In a dd ition the po s itive rot a.tl on evident i n t hi s f ield should have a n i nfluence i n f a cili t a. ting t he f orma tion o f wave cyclones on such a fr on t. The i mp or t a nt f a ct tha t t his forma tion of t he ne w P olar fr on t of f t he co a s t of As i a occu r s be t ween fre s h P 8 a ir a nd modi f i ed or r et ur n i ng p 6 a i r has not bee n previousl y reco gn ized. An e xamina tion o f t he cyclone tra ck s and t he d i s tr ibution of c yclones in t his re g ion shows t he a ctua l i mp ort a nce of t hi s fr ontogene t ic a l line. Cha.r t ( 21) is prepare d f or t hi s p urpo se . It c an be see n that mo s t o f the c yc lones dur ing t h i s season occur a long t h i s fron to ge ne tic line. N. V. Stre mous s ov ha s s tud i e d t he sy nop tic proces se s in t he ( 25 ) Eas t ern Part o f t he As i a tic Con tinent and tr.tG Ad j a. ce n t !?Bas . The a ut hor ha s not had t he o pp ortuni ty t o r ead h i s Whole pape r - 52 b ut has only ha d av a il able t he En gli sh Su mmar i es quoted in the ( 26) Bulletin o f the Ame ric a n Eete or ologica l Socie ty. He p oints out tha t' in winter cyclogene s i s shift s f ro m t he l a n d to t he sea , t a.k ing p l a ce at t he P olar Fr on t betwee n Conti ne nt a l P olar a nd i- ari tiroo Trop ica l a i r rnasse st. The idea tha t Mr . St remouss ov sug gest s tha t Wi n t er c yclones in t he F ar Eas t are f ormed a t the Polar Front is quite t r ue b ut evide ntl y t1e f'e lt t ha t once of fs hore t he front occup ied a p osition be t ween Cont i ne nta l-Pol ar ( P 8 ) a nd maritime-Tro p ic a l a ir ma sses , {Tp ). The c hart s ( 22-24 ) he r e p ub lis he d tend to show tha t t he winte r- cyclone s a re f orme d on the P ol a r F'ront befo r e it re a ches a p os it i on in its southwa r d t ravel t ha t would lndlca te t he inte r a ct ion be t ween t he p 8 a nd the Tp. This can bs p rove d. by t he f a ct t hat most o f t he Wi n t e r cyclones in the Far East a r e st a rted a long the s out he as t e rn Chi na coa st to the J a pan I s l a n d s where eithe r abst r a ctly co ns i de ring t he position of the Pacific Hi gh in the Winter se a son or pr a ctic a ll y t ra cing the air· flow fro m the daily we ather c harts of the Fa r Ea. st, there s hould be no re a l maritime - Tr op ical a ir. The a uthor has examined many winter c ha.r t.s for t he F'ar E a st a nd found. tha t t he cyclones are forme d at t he cold f r ont by wave perturba tions during the course of t he sout h e a stward move me nt o f the Pola r front to its so uthe r nmost p osition betwe en the real mar itime Paci f ic or Tp air. Th is c a n be theore tic a lly exp l a ined by di a - gram and p r a ctically illustra ted by examp l e s. From the t heoretic a l p oint of view a cold f ront develop ing a t t he fronto genetlca l line s h ould a t f irst move r ap i dly sout hward beca use of t he l a r ge offs hor e p re s s ure gr ad l ent a l ways - 53 p resent along too coas t al re g ions of As i a a t t hi s se a eon, a s evidenced by the outflow of air from tr...e divergent cent er of t he Siberian High, Under this condition of r pid movement 0 t he cold f r ont s hould be rela tively free fro m VJ ave perturbations and should appear as a s mooth curve. As this r ap id move ment southward begins to diminish the air masses on each side of t he front continue to be modified by the journey over t he warm oce an surface, and instability developes . ly e_ Conse que nt- flat vvave is very easily produced alon g the fr ont and t he first s te p in cycl ogene sis is comp lete d . If the main High on the As iatic Continent s till sends a strone; current southward the cyclogene sis may r-emain in this st age , ie . in the form o f a flat wave structure, or tr1a se waves may even be de stroyed . On t he other r1and the col d front gen- erally be comes less a c t ive and the develo ped wave becomes stronger. ere st . Finally an o c cluding cyclone is f orroo d at the wave An ide a lized pro ce ss of this kind is illustra te d by t he diagrams below: - Fig . 22 As occlusion continues and brings t he cold front to its most southerly p osition Where V. Bjerknes and othe rs have shown ( 2 7) its ave ra ge s ea sonal p osition to be, it meets the real mar itime Tropi ca l air, Tp , f rom the Pacifi c Hi g h, and ne w waves may tend to develope along lt. - 53b F1g .. 22 Ideal case of Cyclogenes1s at cold front by a wave per t urbation . I f C. ( 1) Initial cold front H / / C. . f. (2) First indi cation of Cy clogene sis , the flat wave etage . ( 3) Cy clone s t age . '11. (4) Occlusion s t age. ,. F. t - 54 E xamp le s of comp lete and incomp lete cyclogenesis from a. cold front in the winte r se a son in a gre ement with the above discussion i dea c a n be e a sily found on t he d a ily weather c harts of the Far E ast. 1~n examp le o f complete cycloge nesis is g iven be low; ( Chart 22-•24) . The cyclone chosen for thi s e xa mp le only took three days f or its fu ll deve l opment. The f ir El t day , Jan. 15, 1933, of the map ser ies even the front itself' which develops t he cyclone is ha rd to reco gnize. One day l a t er the existence of a fr ont a l system is evident on t he map with an apparent v1ave f ormat ion alre a dy on the front . E vide ntly one of t he wave ere sts of the syste m, p ro bably the fore most one , fine.lly develops into a cyclone near Kyushu Isle.nd of Japan as s ee n on the map for J a n. 17,1933. It is cle ar that there should be no real Tp air in the warm sector of the cyclone at its ince p tion be c a use the circul a tion field dur in g these days shows the air with a continuous ly northerly t ra. j e ct ory be hind a previously exist ing .fr ont Wh ic h has move d south ;ard. 'l'herefore t he cyclone is not the result of t he intera ction betwe e n cold P ol a r Siberian a nd warm Tropi c a l Pa ci fi c air masses but r a ther between t he t wo types o f Polar Siberian a i r ma.sse s pr-eviously discussed . The above examp le also serves as a good illust ra tion of a ctual frontogenesis in the field of motion . On Jan. 16, a second.e.ry de f ormation field is f:) r me d in t re general frontogenet i c re g ion a t a pos iti on betwee n the China coa.st and the Japan<:!Se Is1andl:!; With the ra~ult a nt s p litting of the High :1.n the - 55 north. 'f he deformat ion axis of this f ield which is shown on the auxilary c hart for J an. 16th ( Chart 25), makes an angle with t he isothe rms smaller than t he front o genet ic angle ,¢ t, in the reg ion on the we st s ide of thi s ax is. Thus we would expect the development of' the frontal sy s te @ to be accelerated in this territory. b€ ob serve d , Two indica tions o f thi s development c an f ir st , the incre ased crowd ing of the i s ot herms along the southe as t e rn China co ast as shown on the auxiliary chart for J a n. 17th, Chart ( 26), and by t he quicl{ly developed low center on the map for tha.t date . J?rom the de f ormation field and isotherm chart for J an. 17th., we c an see t hat the deforma tion axis of the field has been negatively rot a ted. The r-e sul t of this rotation brings tlia axis and the isotherms more ne arly parall e l, a condition Whic h would lead to further inte nsifi c a tion of the syste m on the next day . This anti ci- pa te d dee pe ning is shown on the map for Jan . 18th,(Cha.rt 27) the press ure e.t t he center of the cyclone having dropped from 759mm ( 29 . 9in.) to 737mm ( 29 .O) during the 24 hours . It should be noted t he.t i n such cases t he cyclone Will not develope until some time after the cold front r ee. c hes the water, be c ause before tha t time the front is moving too rap idly a.nd the air is still relatively st able . The fact that most of the c yclones in the Fa.r East during the winte r season a ctually start in the area fr om the southeastern China co ast t o t he southern part of the Japan Islands alre ady offers proof of t _h i s. - 56 (28) Mr. Ri chardson , from a stati s tic a l study on the d istri- b ution of c yc lones over the Nort h Pa cific o ce an in t he winter s ea s on, ( see Chart 21.) , shows that t he re g ion o f maximum cy- clonic fre q uency i s quite far re move d fr om the Paci.fie Polar Front ( Pc. zi f ischs Polar f ront of Paz . PF) as determined by V. Bj erkne s and others in their bo ok Physikalische Hydrodynami k . Actually Richards on 1 s di agram p l a ce s the s torm tracks a long the computed frontogenetlc line g iven above, rat her than along the deformation a xis as i nd ic a ted 1n the above re fe re n ee. These t wo lines r e present different thin gs 1:,.nd do not ne cessarily have to follow e a ch ot her- clo se ly. The deformation ax is, is formed b y t he f ield of motion onl y, While t he frontogenet ic line is determined f rom the distribution of the frontogeneti c function F , the prod uct of \vo< I and ¢, which ha s the re a l im- p o:!'.'ta nce in determining t he zone o f fr ont a l a ctivity . When the t wo a.re not coincident with e a c h othe r , as is t he case when t i10 maxi mum \vro<\ zone does not f a ll along the deformation ax is, or when the angle ¢ i s s uc h that it d oe s not g ive a l arge p ositive v a lue o f F a long the axis, t he a ctual fr ontal activity or the r esult a nt cy cl one t ra cks c a nnot coincide with the de for mation axis of tbs f ield of motion. This is just what happens over the Pa cl f'lc Ocean in the winter se a.s on when t he cyclonic t ra c k s and t he de forma tion axis denoted in the Phy s ika.li sche Hydrodynamik are quite wide ly sepa - r a te d . The c hari:-i cte ristics and the re a. l i mport a n ce of a fr ontogeneti c line a re t hus fur the r established by t his interestin g example . - 57 - x. ACKNO WLEDGE i\~ NT S The aut hor wishes to express his thanks to P rof. Irving P. Kr ick, the Di re ctor o f the ![eteorolog i c a l Department, Cal i f. Institute of Te chnolo gy, Pas adena f or his guidance in this re searc h proble m and sugge s t ions in the preparation o f the manuscrip t, a.nd to Ur . Pa tr-lclr Harney, graduate student of tha t Institute f or his interest in proof r e adine; the manuscri pt and discussin g t he material. He also wi shes to thank Dr . H. U. Sve rdrup,. t he Director o f the Scripps Insti tute of Oce a no graphy , University of Ca lifornia, La Jolla, f or his k indnes s :i.n f urnishing t he Japanese We a.ther char ts for e xte nde d use, and t he Lib:ra.ry of the U. s . We a t he r Bure a u for loaning t he aut hor v ar ious articles pertinent to this study. Final a cknowledgement ls due the China Founda tion f or the fin ancial supp ort Which made t he p roject p ossib le . - 58 REFERENCES { 1) T. Bergeron, Uber die dreid1mens1onal Verkn.upfande Wett.eranalyse, Geofysiske Publikasjoner Vol.V, No.6, Oslo, 1928. { 2) Literatures of the authors mentioned here listed in 11. Ber- geron• s paper cl ted above. 'l'he author has read Ficl{er 's paper-s of "Die Ausbrei tung ka.l ter Luft in H.ussland und Nord- . a:sien •i, Wien, 1910 and "Das Fortschre1 ten der Er-waJMllungen (der Vlarmewellen) in Rm.1sland und Norda sien 11 , Wien, 1911. ( 3) Sverre Pett,erssen, Contribution to the 'theory -o f Fronto- genesie, Geof'ysiske Pu.blikasjioner Vol. XI, No.6, Oslo, 1936. ( 4) Sverre Petterssen, Kinematical and Dynamical Properties of the Field of Pressure with Application to Weather Forecasting, Geof . Publ. Vol.X, No.2, Oslo, 1933. (5) W. Werenskiold, Mee.n monthly Air Transport over the North Pacif'ic Ocean, Geof'ysiske Publikas joner Vol .II, No. 9, 1922. (6) c.c. Chu, Circulation of' Atmosphere over China, Memoir of the National Research Institute of Meteorology, Nank1ng, China, 1934. ( 7) C .c. Chu,. A Brief' Survey on the Climate of China , Jfomoir of the National Research Institute of Meteorology, Nanking, China, 1936. ( 8) E. Gherzi, Atlas ·rhe:rr1ometrique de la Chine, Observatorie de Zi-Ka-Wei, Shanghai, China, 1934. ( 9) :Pilot, Cha rt of the tl orth Pacific Ocean, Hydrogr a ph1c Of'f'ice or· the Navy Department and the We-at her Bureau, 0 . s . A. (10) Hsia- Chien Huang, Atr I,Iasses of North China, ( n<'>t yet. published) . - 59 (11) w. Werenskiold, loc. cit .. p.- 16 .. (12) V. Bjerknes and others, Physlka lieche Hydrodynamik, 1933. (13) E . Gherz1, Air Uasses acting over China and the adj a cent fjeas, Beitrage zur Phys ik der fre1en At mosphare, 24 Band, heft. I, Leipzig, 1936. { 14) H. C. Will ot, America n Air I.la s s Properties, M..I ~T . Meteoro- g ical Papers, lliI .I.T ., Cambridge~ ~Sas s ., u .s . A., 1933. (15) V. Bjerltnes and Others 9 10c. cit. p .• 20 .. (16) c.c. Chu, loc. cit. p. 1 6 . ( Circulation of At mo.sphere over China) (17) Sverre Pett.erssen, loc. cit. p. 2 . (18) Shio•~lang Sung, 'I'he .Ex tra-trop ical Cyclon"t9s of' the Eastern China and their characteristics , l\.Ieraoir of the National Research Institute of Meteorology r Na nklng, China, 1931. (19) c.c. Chu, loc . cit. p. 16 . ( Circul a tion of At mosphere over China) ( 20) V. Bjerknes and others, loc. cit. p. 20. (21) c.c. Chu, loc. cit. p . 16 . ( Circula tion of At mosphere over China~ (22) V. Bjerknes and other s , loc. cit. p. 20. (23} Sverre Petterssen, loc. cit .. p . 2. (24) Gerhart Schirw; Die pra ctische Wett e r a.nalys e, Ha mburg , 1932. (25) N.V. Stremouss ov, About t he Synoptic process in the Zas tern Part of the Asiatic Contine nt and the Adj a cent Se as , J n. of Geophys'ic s, Vlad l '\7ll3 tok , Dec. 1934. ( 26) Bulletin of ·the American Mete orolog ica l Society, Vol .l.7, No .10, October, 1936. - 60 (27) V . Bj e rkne s and others, loc. cit. p. 20. ( 28} Robert W. Richa rd s on, Winter Air :ca ss Uonverg ence ov e r 'the Nor th Pacific, Monthly Wea ther Review, J une 1936 . - 61 - EX:PL.4.NATIOii OF SYMBOLS USED ON SYNOP'.i'IC CHA:KTS Unless otnerwlse indicated? the charts are f'or the observations of 12 noon, 120°E Standard Time. o Clear () Partly Cloudy Overcast Raining Snowing Intermittent r a in a rea Shower Rain area Cold front .__._._ Warm front Occ,luded front Air mass symbols are as given in the t,ext. Number of barbs on wind arl'. ows g ives velocity in Beaufort Scale. 1 One half barb represents one Beaufort unit, and ea ch full barb two ~eaufort units. Pressures in mm .. are given to the upper right of the station, and temperatures in degrees Centigrade to the lower right of the stat ion.