The intensity and size of a TC determine the degree/severity of destruction during the landfall process. In the recent years, intense TCs with different intensity changes/rates have been frequent over the north Indian Ocean (NIO). Most of the studies over the NIO basin have been focused on track, intensity, or rainfall predictions. Size-intensity relations are not well studied over this basin. Over the global oceans, it is demonstrated that the microphysical processes are vital for size and intensity change predictions. Therefore, the present thesis is aimed at exploring the evolution of size-intensity relationships and the MP processes that control them using reanalysis products and high-resolution mesoscale models.

The thesis reveals that the intensity is strongly correlated with TC Fullness (CC-0.7) and Rmax (0.6), than the R34 (0.5). Analysis shows that size changes are weakly related to intensity changes (0.37-0.39). It indicates that size does not monochromatically change with intensity. TC size and intensity relationship depends on convective distribution in the TC region, the environmental relative humidity, and surface energy fluxes. A strong and wider (lower) heating in the inner core with Kessler (WSM3) causes larger (smaller) TC sizes. Sensitive experiments reveal that for any particular resolution, the simulated size differs by 30&ndash50 km among the MP schemes, while the size changes 5&ndash15 km (2&ndash4 km) between 6-km and 2-km (3-km and 2-km) grid-resolutions for any MP scheme. The study concludes that TC-size is more sensitive to MP-schemes than the higher/cloud-resolving grid-resolution. The MP-heating is highly correlated with precipitated particles as compared to Non-precipitated particles. During rapid intensification (RI), heatgenerated processes such as condensation, freezing, deposition, etc. dominate due to the moist environment. Whereas in the rapid weakening TCs MP heating is distributed asymmetrically around the TC center due to the combined effect of heating processes (condensation) and cooling processes (sublimation, evaporation, etc.). Assimilation of the thermodynamic profiles that are obtained from INSAT-3DR provides better TC characteristics such as size, intensity, intensity changes, and size. It can be concluded that the assimilation improved the RH and it leads to better MP-heating (and warm-core) through well-defined precipitable and non-precipitable hydrometeors. The inner-core MP heating adjusts the radial and tangential winds, promoting vertical velocities, hence improving the TC characteristics.  The present thesis provides insights into cloud microphysical processes controlling changes in TC characteristics, particularly TC size and intensity changes over Indian Seas

Keywords: Tropical cyclones, Size, and intensity changes, North Indian Ocean, Microphysical processes, INSAT thermodynamic profiles, High Resolution Mesoscale model