Analysis Of Tropical Cloud Clusters In Typhoon Inactive Periods During 1998-2009

Tropical cloud cluster is the precursor of tropical cyclone, though many studies showed a high relationship between TC and their large-scale environment in recent 20 years, the change characteristics of tropical cloud cluster in TC inactive periods have been studied. By using the only data of global tropical cloud clusters by far, the features tropical cloud clusters over the Western North Pacific Ocean in recent 20 years are analyzed. The downward trend of typhoon genesis mainly occurs in July-October after late 90s and there are two significant decrease regions:one is over South China Sea(13°N-23°N,110°N-120°N) and the other is the eastern part of WNP (13°N-23°N,145°N-170°N) where the typhoon occurs. The tropical cloud clusters shows an increasing trend for each individual month except January. The source of cloud clusters associated with typhoon significant decrease regions has a remarkable increasing trend. NECP/NACR reanalysis dataset is used and the result shows the stronger vertical wind shear correlated significant with tropical cloud cluster ascending trend after 1998 while it is disadvantageous to the generation of typhoon.