This thesis conducts an observational study of a large cyclonic gyre that developed in the Western North Pacific (WNP) in late July 1989. For a period of six days, azimuthally-averaged winds at 850 hPa remained cyclonic out from the center of circulation to the 2000 km radius, with azimuthally-averaged tangential wind speeds at or greater than 10 m s−1. The gyre exhibited an asymmetric convection pattern, with the center, north and west flanks devoid of large convective areas, but the southern and eastern flanks maintained large-scale convective regions, extending as much as 4000 km in longitude.
Prior to gyre formation, an active MJO existed over the Indian subcontinent. The active MJO helped create an anomalously strong upper-tropospheric jet over central Asia and a jet exit region over northeastern Asia and the WNP. This created a favorable equatorward wave-breaking environment that allowed an upper-tropospheric trough to penetrate from the midlatitudes into the subtropics, and deposit a cutoff low in the WNP. Cyclonic vorticity maxima coming from the west engaged the upper-level low, with several orbiting the upper-level cyclone, and establishing a large-scale cyclonic circulation. A second wave-breaking event expanded the size of the subtropical gyre and helped create the eastern flank of convection.
This case is compared in detail to a 1988 case examined by Molinari and Vollaro (2012), which also developed during an active MJO in the Indian Ocean. Gyre-related disturbances and the possibility of Rossby wave dispersion are also examined.
|School:||State University of New York at Albany|
|Department:||Earth and Atmospheric Sciences-Athmospheric Science|
|School Location:||United States -- New York|
|Source:||MAI 51/01M(E), Masters Abstracts International|
|Subjects:||Meteorology, Atmospheric sciences|
|Keywords:||Gyre, MJO, Monsoon, Subtropical, Tropical cyclones, Wave-breaking|
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