The combined influence of west pacific subtropical high and tropical cyclones over the northwest Pacific on Indian summer monsoon rainfall

The present study examined the interrelationship between the Indian summer monsoon (ISM) rainfall, west Pacific subtropical high (WPSH) and Tropical cyclone (TC) activity over the western north Pacific (WNP) Ocean during the peak monsoon season in 1951-2019. When WNP TCs are inactive (active), there is a noticeable 10° westward (eastward) shift is observed along with intensification (weakening) of WPSH. The WPSH and WNP TC activities are divided into four categories: Eastward shift of WPSH with active TCs (EA) and inactive TC (EI), westward shift of WPSH with active TCs (WA) and inactive TCs (WI) in order to investigate the combined influence of WPSH and WNP TCs on ISMR during NonENSO, El Niño, and La Niña. In EA NonENSO cases, a surplus (deficit) rainfall was noticed over central (southern peninsular) India as a result of moisture convergence (low CAPE, abnormal moisture divergence and downdraft); however, the rainfall is above normal over the Indian subcontinent. During EI NonENSO case, an excess (deficit) regional rainfall activity was observed over eastcentral India and parts of north India (southern peninsular India) through regional changes in atmospheric circulations and mid-tropospheric vertical velocity. In contrast, WI (WA) NonENSO cases, the majority of India (southern peninsular and northeast India) experiences excessive precipitation while east-central India (east and west central India) undergoes deficit rainfall. This pattern is consistent with the spatial distribution of moisture flux convergence, CAPE and mid-tropospheric vertical velocity. In the case of NonENSO, the westward shift of WPSH associated with inactive TCs is one of the favourable conditions for ISMR. In general, the effect of eastward (westward) shift of WPSH along with more (less) TC during NonENSO case is favourable to ISMR. On the other hand, rainfall patterns during ENSO are significantly associated with the circulation changes teleconnected to the El Niño and La Niña conditions.