梅雨前線に伴うメソスケールの降水に対する対流のパラメタリゼーションのインパクト

Abstract

Four cumulus parameterizations, including the moist convective adjustment (MA), Kuo-Anthes (KA), Kain-Fritsch (KF) and Arakawa-Schubert (AS) schemes, were coupled into the Japan Spectral Model (JSM) and tested in the case of successively developed cloud clusters along the Baiu front during the period from 16 to 17 July 1993 in western Japan. All four experiments with these four parameterizations simulated synoptic features well: locations of lows and the front. The mesoscale precipitation associated with the Baiu front was, in contrast, sensitive to the convective parameterization. Intense precipitation in the Kyushu district was caused by the successive development of cloud clusters. This characteristic feature was simulated by the experiment with the AS scheme. The other three schemes were, however, not so effective in describing the mesoscale precipitation system in the Baiu front. Three sensitivity tests in which the number of types of clouds was reduced to two from six in the AS scheme were also performed to examine the importance of cloud interaction. None of the three simulated the characteristics of the Baiu frontal precipitation. The results suggest that a sophisticated parameterization of convection is necessary to simulate mesoscale precipitation associated with the Baiu front, which is characterized by weakly baroclinic forcing and significant convective instability. An additional experiment for the latent heating in the AS scheme was also performed. The result showed that precipitation in the Baiu frontal zone was greatly affected by the diabatic heating.