土壤湿度对中国西北地区夏季气候年际变率模拟效果的影响

利用耦合陆面过程模式CLM3的全球大气环流模式NCAR CAM3进行2组1979～2000年5～8月的集合试验,研究了表层土壤湿度对中国西北地区夏季气候年际变率模拟的影响。结果表明:在相同海温强迫条件下,采用年际变化的表层土壤湿度(ISSM)时,CAM3模式对于夏季西北地区气温和降水年际变率的模拟能力明显好于采用气候态的表层土壤湿度(CSSM)。计算表明,1979～2000年CSSM试验和ISSM试验模拟的西北地区夏季气温距平与ERA40资料的相关系数分别为0.60和0.65; CSSM试验模拟的西北地区夏季降水距平与CMAP资料的相关系数仅为0.29,而ISSM试验模拟结果与CMAP资料的相关系数为0.48。在相同海温强迫条件下,ISSM试验比CSSM试验能更好地模拟出中国西北地区夏季降水年际变率。

Impact of soil moisture on simulation of interannual variability of summer climate in northwestern China

The potential role of surface soil moisture(SSM)in improving the simulation of interannual summer climate in the northwestern China was investigated with a coupled land-atmosphere climate model. Two ensemble simulations for 22 boreal-summer seasons(1979～2000)were conducted by the Community Atmosphere Model version 3(CAM3)with specified observed sea surface temperature(SST). The impact of SSM on the simulation of summer climate in the northwestern China was investigated by the model with interannually varying SSM(ISSM)and climatological SSM(CSSM)respectively. Results show that under the specified observed SST, the interannual variability of summer temperature and precipitation simulated by the CAM3 with ISSM is better than that with CSSM over the northwestern China. The correlation coefficient of temperature between the simulations with CSSM(ISSM)and the ERA40 is 0.60(0.65)over the northwestern China. The correlation coefficients resulting from the comparison of the observed and the simulated summer precipitation over the northwestern China increase from 0.29 in the CSSM to 0.48 in the ISSM. The possible effect mechanisms of SSM on simulating the precipitation anomaly in the northwestern China were explored. Firstly, the interannual variability of the ground evaporation anomaly can be simulated by CAM3 with ISSM better than with CSSM in the western China, resulting in the anomalous precipitation simulated by CAM3 with ISSM more closely to the CMAP in the northwestern China, where there is an obvious positive correlation between the observed precipitation and the observed local ground evaporation anomaly. Secondly, the interannual variability of summer precipitation anomaly in the northwestern China is significantly influenced by the upstream atmospheric circulation over the mid- and high- latitudes of Eurasia, which can be simulated by the CAM3 with ISSM better than with CSSM, leading to the interannual variability of summer precipitation anomaly in the northwestern China better reproduced by the model with ISSM.