Possible Roles of the Sea Surface Temperature Warming of the Pacific Meridional Mode and the Indian Ocean Warming on Tropical Cyclone Genesis over the North Pacific for the Super El Niño in 2015

This study reveals the potential roles of the sea surface temperature (SST) warming associated with the Pacific Meridional Mode (PMM) and the Indian Ocean (IO) warming on tropical cyclone genesis (TCG) in the North Pacific (NP) by focusing on the super El Nino event that occurred in 2015. We used the global non-hydrostatic model to conduct perpetual experiments by integrating for 30 months to obtain a climatological condition for July 2015 and examine sensitivities to SST in the warming region of PMM and IO on TCG over NP. We showed that if SST associated with PMM is warmer, the monsoon trough in the western North Pacific (WNP) and vertical wind shear over the eastern North Pacific (ENP) become weaker, reducing TCG in the WNP and increasing TCG in the ENP. We also show that if SST over IO is warmer, the monsoon trough in the WNP becomes weaker, although the vertical wind shear over the ENP does not change appreciably. We found that with SST warming associated with PMM or over IO, the anticyclonic anomalies over WNP intensify. We confirmed that if SST is warmer for PMM in the absence of the El Nino forcing, the cyclonic anomalies over WNP intensify as in previous studies. The present results imply a non-linear response for the forcing of the warm SST associated with PMM and El Nino.