Analyses of the convection character and forecast difficulty of autumn typhoon inverted trough heavy downpour

Abstract

The cause of heavy downpour in three autumn typhoons with inverted trough after landfall has been analyzed using NCEP 0.5°× 0.5° reanalysis data, FY-2G satellite data, Doppler radar data, the intensive observation data and so on. Continuous influences of mesoscale convective systems gave rise to the heavy downpour. There was a continuity or reinforcement of water vapor convergence, θse and forced lifting near the inverted trough. So was near the weakened typhoon center. The analyses show that more instable atmospheric stratification over the typhoon inverted trough than at the weakened typhoon center was the main cause of heavy downpour occurred at the inverted trough. Different instable energy, atmospheric stratification and way of cold air influence resulted in different convection character and intensity during the weakening of"Fitow"(1323) and"Megi"(1617). For"Dujuan"(1521), there was almost no cold air influence. The mesoscale convection formed and developed when continuous growing instable energy in warm and moist air was triggered by low level shear, ground mesoscale convergence and coast forcing. It leads to operational precipitation forecast deviation that forecasters did not know well about the convection character, intensity and persistent period, in addition to the fact that the rainfall provided by numerical models was less than the observed.

Keywords

• typhoon
• heavy downpour
• forecast difficulty
• atmospheric stratification
• convection character