A high resolution simulation on Asian climate by Community Atmosphere Model 4
Background, aim, and scope Asian climate is characterized by the Indian monsoon, the East Asian monsoon and inland aridity, which is complex and sensitive to global change. The formation and variation of the climate system are correlated with lots of external forcings, such as solar radiation, land-sea distribution and ice sheet. The Tibetan Plateau is also demonstrated to have a vital effect on the Asian monsoons and inland aridity. Besides the large scale plateau, the meso- and small-scale mountains also show great inlfuence. These mountains not only affect the regional precipitation and circulation, but also inlfuence large scale weather systems such as monsoons and westerly jet lfow. The climate model CAM4 is with much higher resolution, it can relfect a more realistic topography and resolute those meso- and small-scale mountains to evaluate the climate effect of them.Materials and methods The precipitation data is a daily database from Asian Precipitation-Highly Resolved Observational Data Integration Towards Evaluation of Water Resources of Japan. Its spatial resolution is 0.25°×0.25° from 1951 to 2007. Other meteorological variables such as sea level pressure, horizontal wind and temperature is from ERA-Interim reanalysis data of European Center for Medium-Range Weather Forecasts(ECMWF). The reanalysis data is from 1979 to present with a resolution of 0.75°×0.75°. Besides the meteorological data, the climate model we used to simulate is the CAM4. The CAM4 is the sixth generation of the NCAR atmospheric general climate model. The horizontal resolution is 0.47°×0.63° (latitude×longitude) in the simulation.Results With the apparently increased resolution of global climate model, the modeling result conducted by CAM4 with high resolution is compared with APHRO precipitation and ERA-Interim reanalysis data to evaluate whether and in what extent the simulating capability is improved. (1) The CAM4 with high resolution can well simulates the large scale Asian monsoon — aridity climate pattern. (2) More importantly, the Asian monsoon precipitation are well presented, including the Indian monsoon rain centers over the west coast of the Indian subcontinent, the southern Himalaya mountains, Bangladesh and the west coast of Indochina peninsula, and the East Asian monsoon rain gradient decreases from southeast to northwest. The CAM4 also shows more precipitation in winter and less precipitation in summer over arid inland of the Central Asia, which is different compared to inland China, where the most raining season is summer. (3) The atmosphere circulation simulated in high-resoluted CAM4 is more realistic, such as the 850 hPa wind difference over the Indian ocean, the Indian subcontinent, the Bay of Bengal and the Indochina peninsula of the Indian monsoon region, the wind direction turning from southwesterly to southeasterly over east China of the East Asian monsoon region, and the summer bypassing lfows over the south Tianshan mountain in Xinjiang. (4) Besides, the surface temperature and sea level pressure patterns of the Asian monsoon and interior aridity are also well simulated, including the large scale climate systems such as the Siberian high, the Aleutian low and the western Paciifc high, and the seasonal variations of the meso-scale pressure and temperature centers and gradients. (5) The spatial correlations show that the correlation between CAM4 and meteorological observation are signiifcant on global, North Hemisphere and continent scale. The surface temperature has a very high correlation between high-resoluted CAM4 model and meteorological data. The correlation coefifcient of surface temperature is above 0.9. The correlation coefifcient of sea level pressure, 850 hPa zonal wind and meridional wind is above 0.9, 0.9 and 0.8 on global scale, respectively. The correlation coefifcient of precipitation over Asia is no less than 0.7.Discussion The results suggest that the precipitation center is always located over upwind regions no matter over monsoon or inland arid areas while the downwind regions always get minimum rainfall. The character is accordance with the relationship between the convective activity and mountains. Besides, the wind field also changes near mountainous regions and obviously different from other regions. The related temperature distribution can be directly inlfuenced by temperature advection change caused by wind variation. As a result, the atmosphere circulation and vertical structure are changed, which can also inlfuence large scale climate systems. Lots of studies show that more realistic precipitation and wind ifeld can be simulated with higher topography resolution in climate models. Therefore, high-resoluted climate models need to be used to study the detailed monsoon and arid climate and inner difference over Asia and study the relationship between precipitation, atmosphere circulation and mountains.Conclusions The results show that the high-resoluted CAM4 model can improve the simulation skill over Asian, where the climate system is characterized by complex monsoons and aridity. With the improved resolution, the differences between the Indian monsoon and the East Asian monsoon, and between the arid Central Asia and inland China are obviously presented. Besides, it suggests a great inlfuence of meso- and small-scale mountains on convection centers and precipitation distribution.Recommendations and perspectives The high-resoluted CAM4 model is very helpful for detailed study of the complex Asian climate and to deep our understanding of the inlfuence of the mountain topogaraphy. The sensitivity experiments related to meso-scale mountain need to be designed to further ifnger out its climate effect.
NETL
NSTL
万方数据
维普
