Regional variabilities of rainfall and convective parameters during the summer monsoon period: their linkage with El Niño Southern Oscillation

The present study explored the influence of different convective parameters such as lower tropospheric stability (LTS), low and medium cloud covers (LCC and MCC), and convective available potential energy (CAPE) on the regional variability of Indian summer monsoon rainfall (ISMR). The variabilities and trends of summer monsoon rainfall over the west coast (WC), central India (CI), northeast (NE) and northwest (NW) regions of India were analyzed during the period 1979–2015. The linkage of convective parameters and ISMR with ENSO were also examined based on spatial and 21-year sliding correlations. The ISMR shows considerable regional variability with maximum (moderate) rainfall in the WC and NE regions (CI) and minimum in the NW regions. The ISMR shows an increasing trend in all four regions, except in the NE region, where the trend is negative. All the convective parameters exhibit significant trends; however, the trend values highly vary from one region to another. A positive correlation is observed between LTS and ISMR in the WC and CI regions. The increase in specific humidity or LTS may cause more moisture to be trapped within the lower levels which increases the low-level clouds and thus rainfall. The rainfall and CAPE are exhibiting an in-phase (out-of-phase) relationship over the WC and NW (WC and CI) regions. The out-of-phase relationship may be due to the high and low orographic influence over the WC and CI regions, respectively. Both the LCC and MCC are positively correlated with ISMR over all regions; however, a robust relationship is observed in the case of LCC. An out-of-phase relationship between Niño 3.4 index with rainfall and LCC is observed over most of the Indian regions during the summer monsoon season. However, an out-of-phase relationship is observed between Niño 3.4 index and LTS over the eastern and southeastern parts of the country. On the other hand, in the case of CAPE, a significant out-of-phase relationship is dominated only over the CI region.