Preliminary Study On Maximum Potential Intensity Change Of Tropical Cyclone

The intensity change of tropical cyclone(TC),especially rapid change and maximum potential change,is one of the difficulties and cutting-edge scientific issues in current typhoon business and forecasting.It is so closely related to the mechanism of intensity change which has not been fully understood,the simulation to sea-air interaction which has not been completed under storm conditions.Early studies mainly focused on TC maximu0 m potential intensity(MPI),which has made great progress in the rapid change of typhoon intensity(including enhancement and weakening).But maximum potential intensity change of tropical cyclone is still less concerned.The temporal and spatial distribution characteristics of typhoon intensity change in the northwest Pacific were statistically analyzed using the data of Typhoon Yearbook from 1949 to 2015 in this article.The analysis on possible influence of correlated marine and meteorological factors on rapid change and maximum change of TC intensity was discussed in this paper.The results show that nearly 47% TCs in the Northwest Pacific Ocean are accompanied by rapid intensifying process during the past 67 years.Almost 40% TCs include rapid weakening process.The frequency of maximum change(including enhancement and weakening)which has reached the level of rapid change,the proportion of the rapid intensification in TC life both decrease.In addition,the statistics show that there are significant climatic drift trends in TC rapid changes in the northwest Pacific: the northernmost latitude of rapid intensity drifts southward significantly;the southernmost latitude drifts northward slightly;the easternmost longitude moves significantly westward;the westernmost longitude slightly moves eastward.That is,the region of rapid intensification has the trend of southwestward contraction.The analysis of the environmental factors such as vertical wind shear,water vapor(flux and flux divergence)in the middle layer,ocean factors(sea surface temperature and the depth of mixing layer),and the overflow layer on high level found that the north boundary of TC rapid-intensifying region moves northward may associated with southward and westward expansion of the weak shear zone.That the south boundary of TC rapid-intensifying region drifts southward results in the northward expansion of high-SST area.The analysis also shows that TC rapid weakening process occurs mainly in the sea area where vertical wind shear is higher and SST is relatively lower.Based on the above,the possible impact factors(including the vertical wind shear,sea surface temperature,ocean heat capacity,water vapor transport,etc.)of the maximum change of typhoon intensity were analyzed,which indicated that the 6-hour-ago vertical wind shear and sea surface temperature have good correlations with TC maximum potential intensity change.The regression fit from 2010 to 2014 shows that this correlation has some significance for the forecast of TC maximum potential intensity change(MPIC).