MJO对中国春季降水影响的数值模拟研究

Numerical simulation study of the Madden-Julian Oscillation influences on spring precipitation in China

利用IAP-AGCM4.0模式,通过多初值集合数值模拟研究了赤道附近的大气季节内振荡(MJO)传播的两个关键位相期对中国东部春季降水的影响。当在赤道中东印度洋及赤道西太平洋引进异常非绝热加热(强MJO活动)强迫时,模式很好地模拟出了中国东部地区春季降水的异常形势,模式模拟与先期所作的诊断分析结果极为相似,即在MJO的第2—3(6—7)位相,中国长江中下游地区多雨(中国东部大部分地区降水偏少)。对模式输出的高度场、风场、散度和涡度场以及水汽输送场的分析表明,中国春季降水异常的发生分别与异常非绝热加热在东亚/西北太平洋地区所造成的异常大气环流形势密切相关。对逐日响应场的分析表明,就MJO活动影响中国春季降水的可能物理过程及机制进行的讨论表明,赤道附近的异常对流加热不仅可以在赤道附近激发产生大气的罗斯贝波和开尔文波型响应,而且,还会在大气中激发产生从热带到中高纬度的罗斯贝波列遥响应。但是,由于异常对流加热发生的地区不同,大气遥响应场的形势也会十分不同,它所导致的影响也就很不一样。当异常对流加热发生在赤道中东印度洋(对应MJO的第2—3位相)时,大气的罗斯贝波列遥响应将在东亚/西太平洋地区形成有利于中国东部(尤其是长江中下游地区)春季降水偏多的形势;当异常对流加热发生在赤道西太平洋(对应MJO的第6—7位相)时,大气的罗斯贝波列遥响应将在东亚/西太平洋地区形成不利于中国东部春季降水的形势。

The influences of the two propagating phases of the ern China are studied through ensemble numerical simulations Madden-Julian Oscillation （MJO） on spring precipitation in east- with the multi-initial fields by using the IAP-AGCM （Institute of Atmospheric Physics-Atmospheric General Circulation Model）. When anomalous diabatic heating （strong MJO convection） is respectively introduced in an area over the equatorial eastern Indian Ocean and equatorial western Pacific, the anomalous pat- terns of spring precipitation in eastern China are reproduced very well as shown in the model＇s results. And the numerical sim- ulation results are similar to our previous data diagnoses, that is, corresponding to the 2 - 3 （6- 7） phases, there is more pre- cipitation in the middle and lower reaches of the Yangtze River （less precipitation in the most parts of eastern China）. The ana- lyses of the simulated geopotential height, wind, divergence, vorticity and water vapors transport showed that the genesis of a- nomalous spring rainfalls in eastern China is closely related to anomalous pattern of the atmospheric circulation over the western North Pacific/East-Asia caused by anomalous diabatic heating （strong MJO convection activity）. Through analyzing daily re- sponse fields, the physical process and mechanism for spring precipitation anomalies in eastern China due to the MJO activity are discussed. It is shown that atmosphere responses excited by anomalous diabatic heating over the equator are not only the Rosshy and Kelvin wave patterns in the equatorial atmosphere, but also the Rossby wave-train pattern in the atmosphere from the tropics to middle-high latitudes. If the location of anomalous diabatic heating is different, the response pattern in the atmos- phere will be different and its influence on weather and climate is also different. When there is anomalous convection heating o- ver the equatorial eastern Indian Ocean （corresponding to the 2 - 3 phases of the MJO）, the atmospheric Rosshy wave-train re- sponse will lead to an anomalous large-scale circulation over the western North Pacific / East-Asia, which is favourable to cau- sing more precipitation in the middle and lower reaches of the Yangtze River. When there is anomalous convection heating over the equatorial western Pacific （corresponding to the 6 - 7 phases of the MJO）, the atmospheric Rossby wave-train response will lead to an anomalous large-scale circulation over the western North Pacific/East-Asia, which is unfavourable to causing spring precipitation in the most parts of eastern China.