Abstract. A multiseasonal simulation over eastern Asia and its sensitivity to cloud radiation and surface processes is analyzed. The model used is the NCAR Regional Climate Model (RegCM), the period of simulation is 13 months in length, and the emphasis of the analysis is on surface climatology, monsoon circulations, cloudiness, surface solar radiation, and top of the atmosphere outgoing longwave radiation. The model reproduces the basic features of the seasonal evolution of east Asia climate, but it overpredicts the intensity of the mature phase of the eastern Asia monsoon. Surface solar radiation is comparable with observations, while outgoing longwave radiation is mostly underestimated. Different formulations of large-scale cloud-producing mechanisms are shown to significantly affect cloud profiles, the surface and top of the atmosphere radiation budgets, and as a consequence, the simulated surface climatology. 'Variations in surface characteristics affect precipitation simulation in different ways during the cold/dry and warm/wet seasons. This paper emphasizes the importance of examining cloud radiation processes in regional climate models in greater detail than has been done in past studies.

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Abstract. The performance of the NCAR regional climate model (RegCM) for east Asia, where topography and shoreline are rather complex, is examined through experiments to simulate the climate during 1 month using ECMWF data as lateral boundary conditions, before its application in the nested GCM/RegCM method to predict future climate changes caused by global warming. In this study, June and January climates, in which typical precipitation phenomena in Japan such as "bai-u" and winter snow are observed, are simulated using the model with lateral resolutions of 50 km (Base case) and 25 km (High case). The resolution effects of the model are also examined using a series of sensitivity studies. The main results are as follows: (1) In June and January, while cyclones passing over the inner region tend to be more intensified in the model (sometimes unrealistically) than those observed, weak cyclones in the outer region are usually not well simulated in the model. This seems to be due to the stronger control by the lateral boundary conditions. Anticyclones are stronger in the simulation than those observed, especially in the inner region, which leads to overestimation of the sea level pressure there. (2) The model yielded a lower surface air temperature than that observed, especially in January, which may depend on the performance of BATS or the radiative transfer scheme. (3) The model tends to overestimate the regional mean precipitation in the inner region and underestimate it in the outer region in June, while it was slightly underestimated in the inner and outer regions in January. Overestimations are caused by overdeveloped simulated cyclones or by the large amount of precipitation on the unrealistic topography such as a steep slope facing a moist tongue. Underestimation is due to stronger control by the lateral boundary conditions that prevent the development of cyclones or fronts. (4) In the high-resolution models, weak cyclones in the outer region and anticyclones in the inner region are more realistically simulated, although they do not greatly improve the model results in the Base case. Precipitation is increased by ---10-15% of that in the Base case in the inner region in June and January due to enhancement of cyclones or fronts, where the high-resolution effect of topography is only ---1/5 of the total high-resolution effect of the model in June. In January, for northwestern Japan, high model resolution contributes to the correction (increase) of precipitation there. Generally, the high-resolution effect of the model on the surface air temperature does not systematically improve the results but does vary locally by the improvement of model topography. To improve the model results, the lateral boundary should be moved outward (the domain of the model should be extended to the west and south) and/or the precipitation scheme should be improved, including the adjustment of parameters. BATS or the radiative transfer scheme should be improved. More recommendations for the improvement of the model are proposed.

A long‐term numerical experiment has been conducted using the Whole Atmosphere Community Climate Model (WACCM) to investigate the response of the middle atmosphere to time‐varying spectral solar irradiance over multiple 11‐year cycles, modeled on the basis of observed 10.7‐cm radio flux (F10.7). The model domain covers from the Earth's surface to the lower thermosphere with approximately two‐degree horizontal resolution and 66 vertical layers. Sea surface temperatures are prescribed by a climatological annual cycle, and boundary data for chemical compositions are held constant. The experiment does not include spontaneous nor imposed quasi‐biennial oscillation. Temperature and ozone differences near the stratopause between solar max and min, typically 0.8 K and 1.6% corresponding to approximately 100 units of F10.7 variation, have general agreement with the current scientific understanding. The model's dynamical responses as an indirect solar effect are substantially weak during winter against evidences from past empirical studies. The indirect solar signal tends to appear when the polar vortex becomes weak. The most striking signal is more frequent stratospheric sudden warmings during solar max in the Northern Hemisphere late winter through early spring, supporting observed tendencies. This modulation has an aspect of the annular mode and results in a major impact on the troposphere in early spring. Such a signal, however, does not appear in the Southern Hemisphere where the model has a westerly bias. There is no marked response in the equatorial lower stratosphere.

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