Heat and Moisture Budgets during the Period of HUBEX/GAME in the Summer of 1998

By using the high-resolution GAME reanalysis data, the heat and moisture budgets during the period of HUBEX/GAME in the summer of 1998 are calculated for exploring the thermodynamic features of Meiyu over the Changjiang-Huaihe (CH) valley. During the CH Meiyu period, an intensive vertically-integrated heat source and moisture sink are predominant over the heavy rainfall area of the CH valley, accompanied by strong upward motion at 500 hPa. The heat and moisture budgets show that the main diabatic heating component is condensation latent heat released by rainfall. As residual terms, the evaporation and sensible heating are relatively small. Based on the vertical distribution of the heat source and moisture sink, the nature of the rainfall is mixed, in which the convective rainfall is dominant with a considerable percentage of continuous stratiform rainfall. There are similar time evolutions of the main physical parameters (〈Q 1〉, 〈Q 2〉, and vertical motion ω at 500 hPa). The time variations of 〈Q 1〉 and 〈Q 2〉 are in phase with those of −ω 500, and have their main peaks within the CH Meiyu period. This shows the influence of the heat source on the dynamic structure of the atmosphere. The wavelet analyses of those time series display similar multiple timescale characteristics. During the CH Meiyu period, both the synoptic scale(∼6 days) and mesoscale (∼2 days and ∼12 hours) increase obviously and cause heavy rainfall as well as the appearances of the maxima of the main physical parameters. Among them, the mesoscale systems are the main factors.

Development and Rapid Intensification of Tropical Cyclone OCKHI(2017)over the North Indian Ocean

Tropical Cyclone OCKHI over the North Indian Ocean during 2017 underwent dramatic development and rapid intensification very close to the land-Sri Lanka,extreme South Indian coast and Lakshadweep area during its initial developmental stage and caused extensive damages over these areas.On examining the physical and structural mechanism involved in such development,it is observed that the initial development was associated with axi-symmetrisation of the vortex that could be associated with Vortex Rossby waves near the eyewall.Associated with the expulsion of high vorticity from the centre during asymmetry mixing,there was outward propagation of eddy angular momentum flux in the lower levels that strengthened a low level anticyclone to the northeast of the TC centre which in turn enhanced the cyclonic inflow near the TC centre.The rapid intensification phase was associated with vertical non-uniform heating with upper and lower tropospheric warming associated with latent heat release in convection.During the mature phase,the system sustained‘very severe’intensity even under increasing vertical shear and lower ocean heat flux under the influence of a break in the sub tropical ridge to the north of the system centre that enhanced the poleward outflow in the upper troposphere.