[A-CG34] Climate Variability and Predictability on Subseasonal to Multidecadal Timescales

[ACG34-04] Impacts of midlatitude western North Pacific sea surface temperature anomaly on the subseasonal to seasonal tropical cyclone activity: case study of the 2018 boreal summer

*Tomoe Nasuno¹, Masuo Nakano¹, Hiroyuki Murakami², Kazuyoshi Kikuchi, Yohei Yamada¹ (1.Japan Agency for Marine-Earth Science and Technology, 2.Geophysical Fluid Dynamics Laboratory)

Keywords:Tropical Cyclones, western North Pacific, midlatitude sea surface temperature anomaly

The sea surface temperature anomaly (SSTA) is a key factor controlling the tropical cyclone (TC) activity over the western North Pacific (WNP). The primary impacts of the tropical and subtropical SSTA associated with the El Nino Southern Oscillation and Pacific Meridional Mode on the WNP TC activity are well established. On the other hand, impacts of midlatitude SSTA on tropical disturbances are not well understood. In this study, we explored the local and remote impacts of the midlatitude WNP SSTA on the large-scale atmosphere and TC activity at intraseasonal to seasonal time scale by a case study of boreal summer 2018, using a suite of sensitivity simulation dataset with a global cloud-system resolving model (NICAM). The 2018 summer are characterized by positive SSTA in the tropical and central subtropical Pacific, as well as midlatitude WNP, with strong Asian summer monsoon and enhanced TC activity. We executed experiments forced by (1) global SSTA (CTL) and (2) the SSTA regionally restored to the climatology over the midlatitude WNP (MWNPCLM). Comparing the large-scale atmospheric response and TC track density between the two simulations, we found that the midlatitude warm SSTA partly elucidate the active TCs in 2018 and their zonal distributions. As a response to the SSTA, cyclonic circulation was enhanced over the WNP subtropics and anomalous upward (downward) motion was formed in the eastern (western) part of the WNP. These led to anomalous zonal contrast of TC activity over the WNP, which appeared clearer for intense TCs and during the active period of the Intraseasonal Oscillation. The results suggest that the midlatitude SSTA can systematically affect the lower latitude atmosphere and TC activity in some cases.