Influence of subtropical circulation systems on the changing El Niño-Indian summer monsoon relationship

Abstract Remote factors have a significant influence on the variability of Indian summer monsoon rainfall. The study investigates atmospheric conditions influenced by the El Nino episodes on the variable summer monsoon over India. Four composites of years were selected based on the occurrence / non-occurrence of El Nino and extreme monsoons over India. This study examines the upper tropospheric and lower tropospheric wind patterns, tropospheric temperature, and velocity potential for 1958 to 2019 using Japanese Reanalysis 55 (JRA 55) data. The regional meridional circulation established by the north-south pressure gradient is more susceptible to the monsoon condition over the Indian Subcontinent than the external factors. The spatial variability and intensity of Australian High in the southern hemisphere play a prominent role in the Indian summer monsoon characteristics. Subtropical circulations in both hemispheres influence monsoon conditions over India irrespective of El Nino condition. The tropical zonal circulation has appeared to be modulated by the El Nino Southern Oscillation (ENSO) condition over the tropical Pacific Ocean, thereby modify the monsoon circulation.