Differences between the Intense Precipitation Associated with Subsynoptic-Scale Baiu Frontal Depression Simulated by an AGCM and Described in Observational Studies

Abstract

We compared features of the precipitation associated with subsynoptic-scale Baiu frontal depression simulated by an atmospheric general circulation model (AGCM; T106L56: a spectral primitive-equation model with 56 σ levels and triangular spectral truncation at zonal wavenumber 106) with the features had been described in observational studies. The 21-year model integration from 1979 to 1999 was constrained by observed sea-surface temperature and sea-ice distribution. As typical examples, this paper examines simulation cases for June 1991.Comparisons with past observational results showed that the AGCM properly simulated the Baiu front and the Baiu frontal precipitation in the averaged elds for a 15-day period in June 1991. However, the area of the largest 1-hour precipitation is simulated at about 500 km northeastward from the area of the largest averaged precipitation. We also found signicant differences between the simulations and the ob servations when we examined the daily precipitation and the maximum 1-hour precipitation for each day simulated by the model. While precipitation associated with subsynoptic-scale Baiu frontal depressions was relatively well simulated, intense precipitation in the trailing portion of these depressions was signi cantly underestimated.The result of the present study indicates that the ability of the AGCM to reproduce such extreme pre cipitation events must be examined in detail by comparing simulated daily and hourly precipitation with observational studies as well as by statistical analyses.