Effects of sea surface temperature anomalies on heavy rainfall in Tsushima Strait in late July 2020

Short-period responses of moisture and precipitation to sea surface temperature (SST) are investigated in model simulations for the case of heavy precipitation in the Tsushima Strait on 26 July 2020, where both atmospheric and oceanic fronts were established and SST was much lower than the climatological normal (30-year average in late July) in the vicinity of the strait. Compared with the experiments using the climatological normal SST, the surface latent heat flux and water vapor are lower (higher) in the cooler Tsushima Strait (warmer southern East China Sea) in the control experiment. The area-mean precipitation is lowered by the reduced moisture supply over the cooler adjacent sea in the Tsushima Strait. The heavy rainfall is enhanced in the strait via the transport and convergence of remote moisture from the East China Sea. The ensemble-mean maximum rainfall in the strait is higher than that using the climatological normal SST, whereas the maxima are lower over land because of the northward shift of the precipitation area caused by the cool SST anomaly. Although the strong surface baroclinicity over the SST front in the Tsushima Strait and the remote sea surface conditions over the southern East China Sea do not directly influence heavy rainfall, the SST anomaly in the vicinity of the strait influences it. The intensity and area of heavy rainfalls potentially leading to natural disasters are sensitive to large SST anomalies in the marginal seas adjacent to highly populated cities near the coast. In this case, when there is a local negative SST anomaly, the area of heavy precipitation shifts away from land, reducing the rainfall over populated areas.