An Analysis of Tropical Wind Fields in Relation to Typhoon Formation over the Western Pacific

Abstract

The characteristics of the upper (200 mb) and the lower (850 mb) tropospheric wind fields for the period between July and October 1980 over the tropical western Pacific are analyzed, focusing on typhoon formation. GMS satellite wind data and rawinsonde data are used to produce the grid point wind fields. The MASCON model (Dickerson, 1978) was used to adjust the interpolated lower wind fields.Most of the typhoons and tropical storms that occurred during 1980 originated from easterly wave disturbances in the ITCZ. The easterly wave disturbances move in a westward direction before recurving and propagating north and northeastward along the region of large high cloud amounts in which they develop into storm intensity. The origin of the wave disturbances is traced back to as far as near or east of the international date line. The intensity of a given wave disturbance in its early stage is not related to the intensity at its most developed stage. Whether the disturbance develops to tropical storm intensity or not is related to the large scale wind fields surrounding the disturbance. Development of easterly wave disturbances into tropical depressions and storms occurs around the area where the easterlies from the east are confluent with both the westerlies from the west and the southerly winds form the southern hemisphere. This confluence area moves eastward and westward over a period of 10 to 30 days and most of the typhoons and tropical storms appear when the westerly wind region expands eastward.

The Origin of Tropical Disturbances in the Equatorial Pacific

“…In the large-scale wind fields, as discussed in Heta (1990) for the western Pacific, the strength of initial wave disturbances was not related with their later development into typhoons. The development of tropical storms was generally recognized around the triple confluent point of the easterlies from the east, the westerlies from the west and southerlies from the southern hemisphere at the 850 mb level.…”

“…The data and the method of analysis are similar to those in Heta (1990), except for enlarging the area of analysis toward the east by adding the GOES satellite wind data. The upper (200 mb) and lower (850 mb) tropospheric wind fields at 00 GMT were mainly prepared based on GMS and GOES cloud wind vectors and the station rawinsonde data at the 200 mb and the 850 mb levels, respectively.…”

“…In the previous analysis (Heta, 1990), it was shown that the development of the tropical storms into typhoon intensity occured near the area of as- cending motion of a large-scale tonal wind cell. These points are analyzed using the Geostationary Observational Environment Satellite (GOES) at 135W and GMS at 140E wind data for the whole equatorial Pacific area (110E*90W, 30S*30N) and others in July and September, 1980 as shown in the next section.…”

“…In the previous paper, Heta (1990) analyzed tropical cyclones, which appeared during the summer of 1980 over the western Pacific, based mainly on the Geostationary Meteorological Satellite (GMS) wind data. The disturbances were detected from the mean position of the positive vorticity and convergence regions at the 850 mb level and negative vorticity and divergence regions at the 200 mb level.…”

Atmospheric Boundary Layer Wind Field in the HEIFE Area

“…In recent years it has been widely adopted to simulate the wind field for wind engineering as well as for analysis of the synoptic-scale field (e.g. Barnard, et al, 1987, Mitsuta et al, 1989, Chen et al, 1990, Heta, 1990.…”