动力降尺度CMIP5的2006—2035新疆夏季降水变化

评估了CMIP5 9个模式对新疆夏季降水的模拟效果,从中选取5个较好的模式结果,利用RegCM4动力降尺度再集合平均。通过对CMIP5 9个模式的评估,发现CanCM4、CMCC-CM、CNRM-CM5、HadCM3、MIROC4h对新疆夏季降水的模拟较好。进一步分析动力降尺度和集合平均结果,发现动力降尺度能更好地描述新疆复杂地形造成的降水,同时发现2006—2035年比1976—2005年新疆夏季的总体降水有所减少,存在明显的减少趋势。在空间分布上主要表现为天山山脉和其南侧降水显著减少,昆仑山山脉北缘降水显著增加,这与2006—2035年新疆东北侧500 hPa出现的位势高度正异常和与之相对应的反气旋式环流异常有关。这一环流异常造成了天山山脉上空水汽的显著辐散和昆仑山山脉北缘上空水汽的显著辐合。

On the precipitation changes over Xinjiang in summers from 2006 to 2035 through the dynamical downscaling of CMIP5 model results

The simulation of summer precipitation over Xinjiang in nine CMIP5 models had been evaluated. Five of the nine models, which can well present the summer precipitation over Xinjiang, were chosen for dynamical downscaling by RegCM4. Those five models are CanCM4, CMCC-CM, CNRM-CM5, HadCM3 and MIROC4h. Through analyzing the ensemble mean of dynamical downscaling results, it is shown that dynamical downscaling can well simulate the precipitation caused by topography over Xinjiang, and the total precipitation over Xinjiang in summers from 2006 to 2035 decreases than that from 1976 to 2006. In terms of the differences in spatial distribution of the precipitation, precipitation significantly decreases over the Tianshan Mountains and its south, but significantly increases over the north slope of Kunlun Mountains. This is caused by the positive anomaly of geopotential height and anticyclonic circulation anomaly at 500 hPa. This circulation anomaly induces the significant moisture flux divergence over Tianshan Mountains and convergence over the north slope of Kunlun Mountains.