Relative role of individual variables on a revised Convective System Genesis Parameter over north Indian Ocean with respect to distinct background state

Abstract. Abstract. Tropical storms are intense low pressure systems that form over warm tropical ocean basins. Depending upon the intensity, they are classified as depressions, cyclones and severe cyclones. Northern Indian Ocean (NIO) is highly prone to intense tropical storms and roughly 5–7 tropical storms are forming over this basin every year. Various Cyclogenesis indices are used to forecast these tropical storms over various basins including NIO. In this aspect we propose a revised Convective System Genesis Parameter (CSGP) to identify regions favourable for storm genesis. The revised CSGP is constructed by using different combinations and thresholds of five variables namely, the Low Level Relative Vorticity, the Low Level Convergence, the Shear co-efficient, the Convective Instability parameter and the Humidity parameter. The relative role of each individual variable on CSGP is analysed separately for different categories of the storms over both Arabian sea and Bay of Bengal. The composite structure of the CSGP for different categories of the storms is further evaluated separately for distinct large scale background state. The results show that the revised CSGP is capable of distinguishing different categories of the storms. The CSGP exhibits large variability during distinct large scale background state. It is also found that the individual variables contribute in a different way during monsoon and non-monsoon seasons. The revised CSGP can be used to forecast all categories of convective systems such as depressions, cyclones and severe cyclones over NIO during the monsoon as well as non-monsoon seasons.