On the Epochal Variability in the Frequency of Cyclones during the Pre-Onset and Onset Phases of the Monsoon over the North Indian Ocean  

作　　者：P.P.BABURAJ S.ABHILASH K.MOHANKUMAR A.K.SAHAI 

机构地区：[1]Department of Atmospheric Sciences,Cochin University of Science and Technology,Cochin 682016,India [2]Regional Meteorological Center,India Meteorological Department,Chennai 600006,India [3]Advanced Center for Atmospheric Radar Research,Cochin University of Science and Technology,Cochin 682022,India [4]Indian Institute of Tropical Meteorology,Dr.Homi Bhabha Road,Pashan,Pune 411008,India

出　　处：《Advances in Atmospheric Sciences》2020年第6期634-651,共18页大气科学进展（英文版）

基　　金：UGC BSR for providing facilities and support

摘　　要：In this paper we examine the epochal changes in the frequency of cyclones over the North Indian Ocean during the pre-onset and onset phases of the monsoon.We consider three epochs;namely,the early(1955-74),middle(1975-94)and recent(1995-2014)epochs.It is found that the number of cyclones in the Bay of Bengal(BOB)decreases throughout the three epochs.Over the Arabian Sea(ARB),however,there is a decrease in the early epoch,before then reaching a minimum in the middle epoch followed by an increase in the recent epoch,thus exhibiting epochal variability.Dynamic and thermodynamic parameters along with Genesis Potential Index(GPI)are examined to understand the frequency variation in cyclogenesis over the ARB and BOB.Over the ARB,thermodynamic factors such as mid-level moisture,surface latent heat flux and sensible heat flux,and dynamic parameters such as lower-level convergence and upper-level divergence,are favorable during the early and recent epochs but unfavorable during the middle epoch,and these results are found to be consistent with the observed epochal variability in the frequency of cyclogenesis.However,all these influential parameters are found to have decreased over the BOB during the entire 60-year period.

关 键 词：EPOCH INDIAN moisture 

分 类 号：P444[天文地球—大气科学及气象学]