Role of south-west Indian orography in modulating large-scale monsoon circulation.

During the summer monsoon season, the Indian region experiences prominent south-westerly winds that extend up to the Philippines. These south-westerly winds encounter the Western Ghats (WG) and Deccan Plateau (DP). Many studies have discussed the role of WG in modulating the monsoon flow, convection and rainfall over the Indian region. However, the orographic influence of south-west orography (DP and WG both) on large-scale monsoon circulation remains unexplored. An experimental global model simulation was conducted with removed DP and WG orography to investigate this. The results showed that modifying the orography can alter the wind flow across the Philippines, Western North Pacific, and Bay of Bengal, leading to mid-tropospheric heating changes due to the monsoon trough position over these regions. This change in the monsoon trough position results in the stationary Rossby wave. The stationary Rossby wave generated strengthened winds over the south Bay of Bengal (BoB), which merges with the Philippine anticyclone over the Western North Pacific. The dynamical and thermodynamical changes are observed near Western North Pacific. Consequently, there is an increase in rainfall over the Western North Pacific and a decrease in rainfall over India. This study also found that the change in the monsoon flow affects the low-pressure systems and tropical cyclones. This work highlights how the South-West Indian orography affects the monsoon flow and synoptic variability across India, the West North Pacific, and the Philippines anticyclone. Thus, understanding the monsoon flow over the orography will help understand the dynamics. [ABSTRACT FROM AUTHOR]