Weakening of South Asian monsoon circulation and its interaction with western north Pacific tropical convective activities in a changing climate

The study addresses the role of climate change on the interaction between the Indian Summer monsoon rainfall (ISMR) and western north Pacific (WNP) convective activities. We have examined two high-resolution climate model simulations, with and without anthropogenic forcing (i.e., HIST and HISTNAT), using a variable resolution model. The study is supplemented by detailed diagnostics and innovative techniques like causal network analysis which bring out the interaction of convective activities between the two regions which is altered by the influence of anthropogenically forced climate change. Our results shows that the weakening of ISMR re-orient the cross-equatorial winds along with large-scale moisture transport towards the western tropical Pacific which significantly increase the genesis potential index (GPI) over the region by 9.6%. Further we noted the probability of the occurrence of extremely low sea-level pressure (SLP) i.e., SLP < 995.5 hPa around areas near Taiwan and part of Chinese mainland is significantly higher by 10.3 % in the HIST simulation as compared to that of HISTNAT. The use of causal effect network analysis showed a significant causative link between the Indian monsoon circulation index (IMI), WNP tropical cyclone activity (GPI) and winds over the tropical Indo-Pacific (IPWND). The results show a weakening of the IMI can lead to possible enhancement of GPI and IPWND, with a certain time-lag. It is noteworthy to mention that the time lag of interaction between the IMI, GPI and IPWND are different in the two simulations with a significantly shorter time scales in HIST (~ 5 days) compared to that of HISTNAT where it is significantly larger (>20 days).