Pre-monsoon Convective Events and their Variability over the State of Odisha

Abstract:

The state of Odisha on the eastern coast of India is prone to numerous convective events throughout the pre-monsoon (March-May) season. This study is aimed to identify the variability in the pre-monsoon convective activity and, subsequently, the pre-monsoon rainfall over the state of Odisha for the recent decade. The pre-monsoon convective events are segregated into two different categories, viz., severe convective events (SCE) and moderate convective events (MCE), and they are identified using two different sets of threshold values of three convective indices, viz., Convective Available Potential Energy (CAPE), K Index (KI) and Total Totals Index (TT) from the ECMWF (European Centre for Medium-Range Weather Forecast) 5^th Generation Reanalysis (ERA5) dataset. Preliminary results suggest an increasing trend of number of events for both the categories (SCE and MCE). Interestingly, the spatial distribution of the number of events shows a rising pattern in the northern and eastern districts of Odisha for both SCE and MCE. Analyses of the two rainfall products given by ERA5, i.e., Total Precipitation (TP) and Convective Precipitation (CP), suggest that the CP in the highest degree occurs in the northern districts mostly. These results are validated using the surface observations, and it shows a similar signature as the ERA5 rainfall data. Further, the differences of Specific Humidity (SH), Relative Humidity (RH) and Temperature (T) between the lower level (LL, 900-600 hPa) and the Upper Level (UL, 500-200 hPa) are investigated. The T difference is more in the western districts and less in the eastern districts, but the difference is decreasing over the years. Both the SH and RH differences show that the difference is higher in the eastern districts, signifying higher moisture content in the LL in the eastern districts than the western districts. Also, results related to variability in multiple cloud hydrometeors, viz., cloud liquid water, rain water, cloud ice, and snow and their impact on these convective events will be presented. Furthermore, the large scale features, such as moisture transport and land-ocean contrast, will be critically investigated to understand their roles in instigating these events.