Characteristics Of Inner-Core Microwave Brightness Temperature In Western North Pacific Tropical Cyclones And Its Application In Cyclone Intensity Prediction

The inner-core convection in Tropical Cyclone(TC)can both provide latent heat release and transport mass and momentum,which is one of the key components in TC maintenance and intensification.In this paper,the brightness temperature characteristics of TC inner-core over the Western North Pacific have been analyzed in different intensity change categories and the periods before and after Rapid Intensification(RI),and their applications in RI prediction by using the85-GHz and 37-GHz microwave data from the Special Sensor Microwave Imager(SSM/I)on the United States Defense Meteorological Satellite(DMSP)and the Microwave Imager on Tropical Rainfall Measurement Mission Satellite(TRMM).Then,a TC intensity prediction scheme for the Western North Pacific has been developed based on the Statistical Typhoon Intensity Prediction Scheme(STIPS),and the application of inner-core 85-GHz and 37-GHz microwave signals in TC intensity prediction has been analyzed.The main conclusions are presented as follows:(1)In low wind shear,the inner-core microwave brightness temperatures which describe convection and precipitation are mainly located at the shear left in the RI TCs comparing with the TCs during other intensity change categories,and the average brightness temperature area in shear left is larger than that in shear right.The areas of 85-GHz Polarization Corrected Temperature(PCT)of 190-225 K and 225-250 K,37-GHz PCT of 260-270 K account for less than 30 %,50 %and 60 % of total inner-core region during 12 hours before RI onset,respectively.After RI onset,microwave brightness temperatures moves toward TC center from shear left,and finally appears a symmetrical ring pattern.Meanwhile,the frequency of minimum 85-GHz PCT below 190 K was higher during RI than that during other intensity categories and the frequency of minimum37-GHz PCT below 250 K was higher than that during other intensity categories except for the TCs during rapid weakening,and both of them appear increase tendencies before RI onset.(2)In strong wind shear,the inner-core microwave brightness temperatures which describe convection and precipitation are mainly located at the up shear region during RI,and thedifferences of average area of the strong scattering signals between up shear and down shear regions are larger during RI than those during other intensity change categories.The area of85-GHz PCT of 225-250 K accounts for less than 40 % of total inner-core region during 12 hours before RI onset.After RI onset,only the areas of 85-GHz of 225-250 K and 37-GHz of 260-270 K appear symmetrical ring patterns.Meanwhile,the frequencies of minimum 85-GHz PCT below190 K and minimum 37-GHz PCT below 250 K are significantly higher during RI than that during other intensity categories,but the former changes a little before and after RI onset,while the latter decreases before RI onset and increases after RI onset.(3)The results of predicting RI using the brightness temperature features show that the probability of RI is nearly twice as large as the climatological mean when the areas of 85-GHz PCT below 190 K and 190-225 K,37-GHz PCT of 260-270 K in the shear left account for more than 0.5 %,2 %,and 5 % of total region than those in shear right in low wind shear,respectively.However,the probability of RI is nearly triple as large as the climatological mean when the area of85-GHz PCT below 190 K and 190-225 K,37-GHz PCT below 260 K in the up shear account for more than 0.6 % of total region than down shear in strong wind shear,respectively.When considering a single brightness temperature feature,the area of 85-GHz below 190 K has a better prediction of RI under both low shear and strong shear conditions.(4)The results of TC intensity prediction model show that in both weak and strong wind shear conditions,the model would work better after adding inner-core microwave predictors.Compared with low wind shear,the model produced a smaller improvement in strong wind shear.In the experiment of independent samples,the model with microwave predictors produced improvements above 4 % at each forecast time in low shear,especially at 12 h and 72 h.However,the model with microwave predictors produced improvements less than 4 % at each forecast time in strong shear and the improvements were better from 36 h to 60 h.In the experiments for TC cases,the improvements were also seen after adding inner-core microwave predictors in different wind shear conditions,among which there were larger improvements in the cases without RI,while smaller improvements in the cases with RI.