A Numerical Study of the Ej[fect "of the Mountainous Terrain of Japan on 1lropical C:::yclones

A triply-nested, movable mesh model ..~as used to study the effects of mountainous terrain on the landfall of tropical cyclones onto the islands of Japan. The integration domain spanned 43" latitude and 47" longitude with finest resolution of 1/6". Numerical experiments were separately performed for three cas4~s. In each experiment a storm was embedded onto a stationary Haurwitz type wave at the initial time:, and moved in a north-northeast direction at about 10 to 12 m S-I. In the first experim4~nt, the tropical cyclone struck the southwest Izu Peninsula in eastern Japan~ The second and third respectively made landfall on the Kii Peninsula in the central part of Japan and on the island of Kyushu in western Japan. In order to isolate some of the effects on the storm system resulting from its interaction with the mountainous terrain, these simulations \were compared with supplemental experiments performed with a flat land condition. In all three cases It was found that the presence of the mountainous terrain greatl~' enhanced the storm decay after landfall. As the storm approached Tokyo Bay rapid wt~akening occurred as dry air from the mountain region to the west of Tokyo was advected into the eye and eyewall region of the storm. Upon leaving eastern Japan and again moving over open water, the storm never underwent reintensification. In the case of the storm leaving western Japan, reintensification over the Sea of Japan occurred very slowly as compared with the experiment run with a flat land distribution. Apparently, the above behavior was related to the structural change which occurred to the storm system during the passage Oller the mountainous islands. The precipitation pattern was also greatly affected by the presence of the mountainous terrain. As the storm made landfall over central Japan, the area of hc~aviest rainfall shifted to the right of the storm track, where strong upslope winds de\lelope:d. This storm eventually travelled over the high mountains of east-central Japan and rapidly decayed by the end of the experiment. Although performed for an idealized experimental design, these experiments reveal some of the important effects the mountainous terrain may have on the behavior of tropical cyclones making landfall on Japan. Understanding these effects should prove useful in forecasting more accurately the behavior of the storms.~ of