[A-CG49] Kuroshio Large Meander

[ACG49-05] Reduction of Rainfall during Typhoon Passage by Warm Ocean Core Associated with Kuroshio Large Meander: A Case Study of Typhoon Talas (2011)

*Naoki Morita¹, Yoshihiro Tachibana¹, Yuta Ando², Kasuga Satoru¹, Takashi Mochizuki² (1.Mie University Graduate School of Bioresources, 2.Department of Earth and Planetary Sciences, Kyushu University)

Keywords:Kuroshio large meander, SST, Typhoon Talas, Heavy rainfall

Typhoon intensity and rainfall depend on sea surface temperature (SST). SSTs in southern Japan, which is often hit by typhoons, are likely influenced by the path of the Kuroshio, a warm ocean current. When the Kuroshio makes a large meander, it creates a local warm water core near the Japanese coast. Here, we show that the warm core may reduce rainfall through numerical experiments using Typhoon Talas, which caused unprecedented damage in 2011. The warm core, with SSTs about 2 {degree sign}C higher than the surrounding water, reduces rainfall by 4% (28 mm). The mechanism is as follows. As the north side of the center of a typhoon has an easterly wind direction, the east coast is subjected to onshore winds, which intensify the horizontal water vapor flux toward land, resulting in heavy rainfall. If there is a warm core to the north of the typhoon, the pressure adjustment mechanism above the warm core, which lowers the sea level pressure, causes a cyclonic wind anomaly, which strengthens the offshore wind in the southern part of the warm core, leading to a local weakening of the onshore wind. The effect of the weakened onshore wind is stronger than that of the increase in water vapor evaporating from the warm core, resulting in reduced horizontal water vapor flux inflow and reduced precipitation. Local-scale SST anomalies must thus be considered in the prediction of local precipitation. Such reverse SST effects are likely general to another meteorological phenomenon not limited to the investigated typhoon.