ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Archive > Volume 42 Issue 11 > 2016,42(11):1325-1334. DOI:10.7519/j.issn.1000-0526.2016.11.004 Prev Next
Cause Analysis on the Lack of Tropical Cyclone’s Generation in the Northwest Pacific and South China Sea in August 2014
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Abstract:
Based on the conventional meteorological observation data, NCEP/NCAR 1°×1° monthly mean reanalysis data, the outgoing longwave radiation (OLR) data observed by the NOAA satellite and the data from the Typhoon Yearbook of China Meteorological Administration, this paper analyzed the causes for the no generation of tropical cyclones (TCs) in the northwestern Pacific and South China Sea (SCS) in August 2014. The results show that the invading of the polar cold air led to the further eastward and southward movement of the subtropical high in northwestern Pacific during the first twenty days in August. In the last ten days the cold air became weaker, then the subtropical high moved westward and southward, driving the convergence zone between the easterly trade wind in the south side of the subtropical high and the equatorial westerly to be located abnormally further southward than normal. The weaker Miscarene high caused the Somali jet and the crossequatorial flow over the eastern Indian Ocean to get weakened, and the low and midlevel monsoon depression or monsoon trough over the Indian Peninsula to be extremely inactive. Additionally, along with the weaker Australian high and its position deviation, the crossequatorial flow over the southern SCS became weaker too. The SST of the tropical cyclone genesis was much lower than normal during the first dekad of August, so the warm and moist air in the area with lower SST could not form. In addition, the weak convection in the northwestern Pacific and SCS, the stable atmosphere and large vertical wind shear were unfavorable for the generation and development of tropical cyclone. In the lower level over the ocean between SCS and the east of Philippines, there was positive vorticity and negative divergence, but the convergence was not strong enough for the formation or development of TC. The weak updraft at the highlevel troposphere caused by the South Asia high and the easterly disturbance south to the subtropical high could not accomplish the upperlevel divergence process, being difficult to support the maintenance and intensification of the upward flow. Hence, the four tropical disturbances in the abnormally southward ITCZ did not develop into tropical cyclones.
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