We present the measurements of cloud-base height variations over Aryabhatta Research Institute of Observational Science, Nainital (79.45E, 29.37N, 1958 m amsl) obtained from Vaisala Ceilometer, during the nearly year-long Ganges Valley Aerosol Experiment (GVAX). The cloud-base measurements are analysed in conjunction with collocated measurements of rainfall, to study the possible contributions from different cloud types to the observed monsoonal rainfall during June to September 2011.

A cyclogenesis index (CSGP) is introduced and its variations have been evaluated for the period 1979 to 2008. It is found that CSGP is able to distinguish different categories of storms over North Indian Ocean. The relative roles of contributing parameters are analyzed to study the influence of CGSP with respect different background states. It is found that vorticity, convergence, relative humidity and convective instability should be high enough to offset the negative impact of shear parameter.

The Indo-Pacific warm pool (IPWP) has warmed and grown substantially during the past century. The IPWP is Earth’s largest region of warm sea surface temperatures (SSTs), has the highest rainfall, and is fundamental to global atmospheric circulation and hydrological cycle. The region has also experienced the world’s highest rates of sea-level rise in recent decades, indicating large increases in ocean heat content and leading to substantial impacts on small island states in the region.