Winter Air Mass Convergence in the North Pacific Ocean

Abstract

Winter Air Mass Convergence in the North Pacific Ocean ROBERT W. RICHARDSON University of California, Berkeley During the past half century several studios of cyclono tracks havo been made in the United Statos, but so' far ns can be determined nono have yet been published for -tho north Pacific area that aro based on consistent and complote data. Tho Imperial Marino Obsorvatory at Kobo has made possible such a study through tho publication of daily weather charts, and it is upon data furnished by these charts that this papor is in largo part based. Cyclone frequency maps were made by L. B. Corwin and the writer by tabulating tho frequency of cyclono paths for each five degree square of latitude and longitude in the north Pacific for the decade, 1923 to 1932, inclusive. The twelve months of the year wore grouped in pairs so that the resultant maps show January-February , March-April, May-June, etc., frequencies of storm paths. To facilitate the interpretation of these maps isarithms were drawn at decimal frequency intervals . A study of tho three maps of winter months (November to April, inclusive) shows two well marked zones of frontogonesis , one extending from the vicinity of tho East China Soa through tho Japj nnose archipelago, across the north Pacific botween latitudes 40° and 50°, and terminating in Boring Soa (region of Bristol Bay), tho other describing an irregular curve in tho Gulf of Alaska. In sharp contrast to this the group of maps representative of snmmoT conditions show nothing comparable in tho way of high cyclone frequoncy zones. It is concluded from this that no woll defined fronts of the atmosphere persist south of Bering Sea from May to Octobor. The most significant conclusion dorivod fiom this study portains to tho location of tho Pacific polar front. Reference to Physikalische Hydrodynamik, 1933, of which V. Bjerknes is the senior author, explains the Norwegian use of the concept of deformation. Through the application of this concept the position of the Pacific polar front is established for the month of February. Upon investigation it is found that tho neutral point of the deformation field thus derived lios in an area registering no cyclone tracks in ten years, while the front passes through a zone having fewer than ten eyclono tracks during the decade of observation. Otherwise stated, tho Bjerynesian front lios approximately twenty degrees south of the axis of maximum cyclone frequency . That this axis is a valid criterion of the location of the front in question is partially borne out by air temperature data, regrettably, howevor, available only for stations in the Japanese group of islands. Further corroborative evidence is furnished by Horace Byers' paper on the Air Masses of the North Pacific in which he statos that 70% of the frontal systems of the north Pacific area have their origin in the general region of the East China Sea, from whence they travel in a northoasterly direction towaTd the OuIf of Alaska. As for the principal air niasses involvod, the Norwegians hove concluded that marítimo polar air convorges with maritime tropical air to form tho Pacific polar front. This is a logical designation of air masses considering their location of the front. If, however, the front is found to lie twenty degrees to the north, as it is tho writer's contention that it does, the maritime polar air will no longer be in a transitional state, but simply polar continental air converging with air of tropical Pacific origin. (W) Ot.bíi findings in this study concern tho Pacific arctic front located in the Gulf of Alaska. Hero, again, the axis of maximum cyclono froquoncy does not coincido with tho front dolinoatsd by tho Norwegians , although the discrepancies are much less marked than in tho caso of the Pacific polar front. The front, as located through the use of tho cyclone frequency map.«, was compared with Worenskiold'.s linos of air convergent^ and strong agreement was found to exist betweon the two. The principal air masses involved havo boon derived front tho synoptic charts of the California Institute of Technology, from Byers' papor, and Werenskiold's nir transport maps with tho decision that along...