How do sea surface temperature forcings drive the westward extensions of the Western North Pacific subtropical high?
The subtropical highs - large regions of subsidence centered between 30°-40°N - in boreal summer months are strong drivers of tropical cyclone (TC) activity. In particular, the strength of the Western North Pacific subtropical high (WPSH) shows strong ties to TC landfalling probabilities over the western North Pacific (WNP) basin. An enhanced subtropical high extends further west, resulting in a shift of TC tracks to the west and an increased chance of landfalls. A weakened subtropical high tends to retreat further east, resulting in eastward shifts in tracks and thus a decreased likelihood of TC landfalls. Many studies have pointed to large-scale zonal gradients in sea surface temperatures (SSTs) as the main driver for the WPSH’s zonal variations. Through atmosphere-only simulations in the Community Earth System Model version 2 (CESM2), I explore in more detail how SSTs contribute to the westward extension of the WPSH and how these SST forcings impact TC steering flow.
