Eastward-Propagating Property of Large-Scale Precipitation Systems Simulated in the Coarse-Resolution NICAM and an Explanation of its Appearance

抄録

Using the Non-hydrostatic ICosahedral Atmospheric Model (NICAM) on an aqua-planet with a uniform longitudinal sea surface temperature, precipitation systems (PSs) with coarse horizontal resolutions are studied. An eastward-propagating (EP) property of the PSs is seen even though the horizontal resolution becomes coarser to 112 km, as long as the vertical stratification is kept conditionally unstable. The appearance or disappearance of the EP property is explained in comparison with mesoscale (100 km) and large-scale (1,000 km) PSs, a non-precipitation system (NPS), and a system simulated by a dry model with positive-only wave CISK heating (DP). By assuming that the height and the updraft intensity of convection are common in these systems, the turnover times of representative convections are estimated. Compared with the time scale of the equatorial beta (T_β), where its effect essentially works and the distinct EP property appears, the turnover times of the large-scale PS and DP are longer than T_β, producing the EP property, whereas those of the NPS and mesoscale PSs are shorter, inducing no EP property. These results are consistent with observations and model outputs (Nakazawa 1988; Nasuno et al. 2007, 2008).