Anomalous Moisture Transport and Oceanic Evaporation during a Torrential Rainfall Event over Western Japan in Early July 2018

Abstract

17 During a torrential rainfall event in early July 2018, profound enhancement of 18 moisture influx from the south and its convergence occurred over western Japan, which 19 is investigated in this study on the basis of objective analysis and forecast data from the 20 Japan Meteorological Agency Meso-Scale Model. The heavy rainfall over western 21 Japan is found to accompany enhanced oceanic evaporation extensively around Japan, 22 Sekizawa et al., Anomalous Oceanic Evaporation during a Torrential Rainfall Event in 2018 2 especially around the Kuroshio and entirely over the Sea of Japan. Linear 1 decompositions of the anomalous moisture flux and surface latent heat flux anomalies 2 applied to the high-resolution data reveals that the intensified speed of the low-level 3 southerlies was the primary factor for the pronounced enhancement of both the moisture 4 transport into the heavy rainfall region, especially in its western portion, and 5 evaporation around the Kuroshio into the southerlies. An additional contribution is 6 found from positive sea-surface temperature anomalies to the enhanced southerly 7 moisture inflow into the eastern portion of the rainfall region. These findings have been 8 confirmed through a backward trajectory analysis, which suggests that anomalous 9 moisture supply to air parcels into the rainfall region primarily through the enhanced 10 wind-forced evaporation roughly corresponds to about 10% of the precipitable water 11 anomaly over western Japan. 12 (Citation: Sekizawa, S., T. Miyasaka, H. Nakamura, A. Shimpo, K. Takemura and S. 13 Maeda, 2019: Anomalous moisture transport and oceanic evaporation during a torrential 14 rainfall event over western Japan in early July 2018. SOLA, 15A, 22-25, 15 doi:10.2151/sola.15A-005.) 16 17