The structure of pressure anomalies generating 1979 meteotsunami in Nagasaki Japan
Weather Research and Forecasting (WRF) model was used to compute the pressure jumps over the East China Sea. The JRA-55 reanalysis dataset was used for giving initial condition and for four dimensional data assimilation (4DDA) in synoptic scale motion. Three levels of domain were given: whole East Asia region, west Japan and southeast China, and the East China Sea including coastal area with the horizontal resolution of 50 km, 10 km, 2.5 km respectively.
As the results of WRF run, the cold dry air along southeast edge of the polar front subjet and the warm air along north edge of the subtropical subjet genarated the strong horizontal wind shear and large horizontal gradient of equivalent potential temperature nearby Shanghai, China. The sinking current of cold dry air has generated the anomalous pressure jumps propagating the East China Sea with the traveling distance longer than 800 km. Behind 100-150 km (west) of the pressure front, a train of the pressure wave had occurred with the amplitude of 1-3 hPa. The train of the pressure wave had almost faded before reaching to the coastal area of west Kyushu, with the travelling distance of about 400-500 km and with propagating speed was slower (~100km/h) than pressure front (~140 km/h). The time lag between two different pressure anomalies was about 70~80 minutes, nearly twice of the oscillation period (i.e. the interval between first and ternary wave) in the Nagasaki Bay. The resonant ocean long wave generated by the pressure wave would propagate toward the west Kyushu however the pressure wave was faded on the way.