【摘要】 通过分析NCAR CCM3气候模式的15年积分结果,从形成降水的垂直运动和水汽供应条件的角度,试图揭示该模式在东亚季风区产生不合理虚假强降水的可能原因.与观测的降水分布相比,CCM3模拟的东亚季风区降水中心位置偏西,雨量偏强,其中对流降水占虚假降水中心总降水量的82%左右.进一步分析发现,对流层上层200 hPa副热带急流南侧的散度季节变化与110°E以西的虚假降水季节变化具有较好的对应关系,急流入口区附近的直接垂直环流上升支位于青藏高原东北部,同时由于急流南侧对流层上层辐散引起的抽吸作用,加强低层的垂直运动,从而为虚假的强对流降水形成提供上升运动条件.分析对流层低层的水汽(比湿)分布和水汽输送表明,模拟的青藏高原地区大气的水汽含量比NCEP/NCAR再分析的水汽含量高,经过高原从孟加拉湾输送到虚假降水中心地区的水汽偏强,从而为虚假的强对流降水形成提供了充足的水汽条件.因此,在改进气候模式对东亚季风区虚假降水的模拟性能时,除了对模式物理过程做改进外,在青藏高原附近地区的水汽分布和水汽输送以及对流层上层西风急流位置和强度模拟的合理性方面也需要引起足够的重视.更多还原

【Abstract】 A possible reason for the unreasonable simulation of maximum rainfall center over East Asian monsoon region has been investigated by analyzing the 15 years’ integration results of National Center for Atmospheric Research(NCAR) Community Climate Model(CCM3).The focuses of the analyses are on the vertical motion and water vapor supply which affect the formation of precipitation.Compared with the observed precipitation distributions,an unrealistic heavy precipitation center simulated by CCM3 occurs in the inland area of China in summer.The location of the heavy rainfall center extends westward and the rainfall intensity is very strong,in which convective precipitation accounts for about 82% in the total amount of unrealistic rainfall center.Further analysis indicates that the seasonal evolution of the divergence at 200 hPa along the southern side of the East Asian subtropical westerly jet is consistent with the seasonal evolution of precipitation center to the west of 110°E.The ascending motion of the direct meridional circulation near the jet entrance area at 200 hPa is located on the northeastern Tibetan Plateau.Due to the pumping effect resulting from the upper divergence,the intensified vertical motion at the low level is provided for the unrealistic convective precipitation formation in western China.Analyses of the tropospheric water vapor distributions and water vapor transportation demonstrate that the simulated specific humidity in CCM3 is higher than the National Centers for Environmental Prediction / National Center for Atmospheric Research(NCEP/NCAR) reanalysis over the Tibetan Plateau and the water vapor transport from the Bay of Bengal through the Tibetan Plateau to the area of unrealistic rainfall center is stronger,supplying enough water vapor for the formation of the heavy precipitation directly.Therefore,much more attention should be paid to the accurate simulation of the water vapor distribution and water vapor supply near the Tibetan Plateau and the related location and intensity of the East Asian subtropical westerly jet at upper level for the improvement of precipitation simulation over East Asia,besides the improvement of model physics processes.更多还原