[A-OS18] Kuroshio Large Meander

[AOS18-P05] Impact of a Marine Heatwave Attributable to a Kuroshio Large Meander on Extreme Heavy Rainfall Caused by an Extratropical Cyclone

*Eigo Tochimoto¹, Satoshi Iizuka¹ (1.National Research Institute for Earth Science and Disaster Resilience)

Keywords:Kuroshio Large Meander, Extratropical Cyclone, Extreme rainfall

Extratropical / Tropical cyclones often cause extreme rainfall events over eastern coastal region characterized by a western boundary current and an extended coastal mountain range. On 12–13 April, 2020, extreme heavy rainfall event was occurred over the east of the Kii Peninsula, Japan. Concurrently, the Kuroshio large-meander started from 2017 caused the notable positive sea surface temperature (SST) anomalies along the coast south of Japan. The present study examines the impact of the positive SST anomaly on the heavy rainfall event associated with an extratropical cyclone using numerical experiments. The control simulation (CNTL) showed that strong low-level easterly winds associated with a cold conveyor belt in the northeast of the cyclone brought humid airmass toward east of the Kii Peninsula, resulting in strong updraft and local intense precipitation. A sensitivity experiment in which the SST anomalies attributable to the LM was removed showed at least 25 % reduction of the maximum precipitation for 3 hours because of the smaller latent and sensible heat fluxes from the sea surface compared to those in CNTL. Thus, the SST anomalies attributable to the LM contributed to the heavy rainfall. Furthermore, additional numerical experiment without the evaporation of rainwater and ice pieces indicated that cold air temperature from the near surface to middle troposphere over land were maintained by the evaporation and contributed to the persistent of horizontal temperature gradient along the coastal region. Our results suggest that air-sea interaction on synoptic- and meso-scale can drive extreme precipitation. We have confirmed that there was another heavy rainfall event affected by warm SST anomalies attributable to the meander of the Kuroshio south of Japan on 2 May 2012. A sensitivity experiment in which SST values are replaced by those for climate values showed the reduction of total precipitation for CLM from CNTL.