赤道东太平洋海温异常对6月中国南方降水影响的数值模拟

Numerical simulations of the effects of the preceding equatorial Eastern Pacific sea surface temperature anomaly on the Southern China rainfall in June.

利用NCARCAM3.0大气环流模式,研究6月长江流域及以南地区降水对前期赤道东太平洋海温异常的响应。首先,在赤道东太平洋1997年9月至1998年6月实际海温异常基础上构造的理想化海温异常,依据持续时间不同叠加相应的海温异常值在气候平均外强迫场上,设计第1组敏感性试验;其次,在上组试验中的前期9月至次年6月持续有海温异常的敏感性试验基础上,改变加入模式中的海温异常强度,设计不同强度海温异常对大气环流和降水影响的第2组试验;最后将上述海温异常值取反加入相应的赤道东太平洋区域,设计一组拉尼娜事件的试验。以(25°—30°N,110°—120°E)区域平均的降水距平值代表整个长江流域及其以南地区降水,模拟结果表明:(1)不同的持续时间强迫得到的降水距平峰值在11月,次年6月其值为最小,整体上降水距平有随持续时间的缩短而减小的趋势。表明前期秋季赤道东太平洋较强的厄尔尼诺事件发生时对6月降水有重要影响,证实了前期诊断分析的结论;(2)模式中加入不同强度的厄尔尼诺事件,在长江流域及其以南地区均有明显的降水正距平(最小降水距平为0.287mm/d,最大为1.98mm/d),降水正距平范围与实际情况接近,表明模式在模拟该地区异常降水时有较好的稳定性,模拟结果值得信任。另外模拟的降水距平有随着海温异常强度的增强而增大的趋势;(3)当模式中加入不同强度拉尼娜事件的海温异常时,模拟结果不稳定,与厄尔尼诺的影响结果不完全相反,与前期诊断分析结果不符。而只有在拉尼娜相当强时模式才能在长江流域及以南地区模拟出一定范围的降水负距平。

Using the NCAR CAM3 model, we designed several sensitive experiments to simulate the response of the atmospheric circulation and precipitation in June to SST anomalies （SSTA） over the equatorial Eastern Pacific. Firstly, we constructed idealized SS- TA based on the observational SSTA over the equatorial Eastern Pacific during September 1997 to June 1998. We performed the first series of sensitive experiments by incorporating the idealized SSTA in different durations, that was, from the preceding September to June, the preceding October to June, the preceding November to June, the preceding December to June, January to June , May to June, June. Secondly, on the basis of the SSTA in the first series of experiments, we changed the SSTA by adding or substracting 0.5 ℃ The second series of sensitivity experiments were conducted to simulate the precipitation response to the intensity of SSTA persistent from the preceding September to June. Finally, the SSTA in the second series of experiments were changed from positive to negative, and the third series of sensitive experiments were done. The precipitation anomaly averaged over the area （25° - 30°N, 110° - 120°E） was used to represent the rainfall anomaly in the Yangtze River basin and its southern area （YRBS）. We found that, （1） the precipitation response to El Nifio with different durations varies with the maximum rainfall anomaly appearing in November and the minimum in June. The anomalies of the precipitation attenuated when the duration is shorter, meaning that the strong SSTA in the preceding autumn affects most significanty rainfall in the YRBS. This confirms previous diagnostic analysis results. （2） The pre- cipitation anomalies over the YRBS are not sensitive to the intensity of the equatorial Eastern Pacific SSTA. There is always obvious positive precipitation anomaly over the YRBS under strong or weak SSTA. The area coverage of the positive precipitation anomaly agrees with the observation, suggesting reasonable model results. The intensity of the precipitation anomaly increases with that of the SSTA. （3） When opposite SSTA are put in the model, the simulated results are different from the results of the diagnostic analysis for a La Nina event. Negative precipitation anomaly could be reproduced only when the negative SSTA are intensive enough.