南海夏季风爆发的年际变化及其机制

【作者】 温之平；

【导师】 黄荣辉； 贺海晏；

【作者基本信息】 中国科学院研究生院（大气物理研究所） ， 气象学， 2006， 博士

【摘要】 由于南海夏季风爆发的迟早对于中国东部和东亚地区夏季季风降水的年际变化有很大影响,故本文利用NCEP/NCAR-2再分析资料和NOAA的OLR资料,通过资料分析和数值诊断模式的模拟,研究南海夏季风爆发的年际变化及其机理。本文不仅揭示南海夏季风爆发前大气环流和大气热源及水汽汇的变化特征;而且还从前期北半球中高纬地区大气环流异常,低纬地区大气热源异常,局地经向环流的变异和30~60低频振荡等来揭示影响南海夏季风爆发迟早的大气的动力和热力条件,并从经向垂直环流异常的角度探讨了南海夏季风爆发迟早的物理机制。主要结论有:1.就气候平均而言,南海夏季风爆发前,中南半岛地区和南海地区的大气热源及水汽汇有明显的变化。中南半岛地区的大气热源和水汽汇快速增强,这是与苏门达腊大气热源和水汽汇的加强北移密切相关;分析结果还表明,在南海季风爆发前,南海地区大气热源和水汽汇受到加里曼丹附近大气热源和水汽汇的加强北移以及我国东南部大气热源和水汽汇的发展南移的影响,故南海地区的大气热源和水汽汇则增强较缓。并且,从分析的结果可以看到,亚洲地区对流层中上层经向温度梯度逆转的东西向差异与这些地区的大气热源和水汽汇变动密切相关。2.在南海夏季风爆发迟年和早年的前期,对流层高中低层的位势高度和水平环流的异常分布存在明显的差异:在爆发早年,存在乌拉尔山及其以西地区为高度场负距平(距平气旋),中纬度大陆地区为位势高度正异常(距平反气旋),东亚沿岸为位势高度显著负异常(距平气旋),鄂霍次克海上空为高度场正距平区(距平反气旋)的距平波列;而在爆发迟年的情况正好相反。进一步分析还发现,从4月初开始,对流层高、中、低层50~60oN平均的位势高度距平的东西向差异就十分明显,这种差异对预测南海夏季风爆发的迟早有较好的参考意义。3.引起南海夏季风爆发迟早的大气热源和水汽汇的分布特征有明显的不同。分析表明,前期中南半岛和西太平洋上空的大气热源和积云对流的强度及位置变动、我国江南东部的大气热源和积云对流的向南扩展以及苏门答腊和“大陆桥”一带的大气热源和积云对流的强弱及其向北的移动都与南海夏季风爆发迟早有密切的联系。当5月1~15日期间中南半岛周围和菲律宾周围上空对流异常偏强时,会导致孟加拉湾、南海中北部和副热带西太平洋一带的850hPa位势高度更多还原

【Abstract】 The NCEP/NCAR-2 reanalysis data and NOAA OLR data are employed to composite and numerical diagnostic studies on the interannual variations and related physical mechanisms of the onset of South China Sea Summer Monsoon (SCSSM). The study reveals that the onset of the SCSSM has a close connection with the preceding anomalous circulation over mid and high latitude areas in northern hemisphere, the variation of local meridional vertical circulation over eastern Asia and the activities of 30-60d low-frequency oscillation. The main conclusions are as follows:1. Before the onset of SCSSM, as for climatological normals, there exist distinct differences in the variation of atmospheric heat sources and moisture sinks between over Indo-China Peninsula (ICP) and over South China Sea (SCS). The atmospheric heat sources and moisture sinks enhanced rapidly over the ICP, and increased slowly over SCS. The rapid development of the atmospheric heat sources and moisture sinks over ICP is closely related to the northward movement of heat sources and moisture sinks in Sumatran. While the slow increase of heat sources and moisture sinks over SCS is also associated with northward (southward) movement of atmospheric heat sources and moisture sinks in Kalimantan (in southeastern part of China). Further analysis also reveals that the zonal differences of meridional temperature gradient reversion in mid-upper troposphere over ICP and SCS are closely related to the variations of atmospheric heat sources and moisture sinks over the corresponding places.2. During the first half month of May, anomalies of goepotential height and horizontal circulation in troposphere are quite different in early and late monsoon years. In early monsoon years, there exists a anomalous wave train with negative anomalies of geopotential height field (anomalous cyclone) over Ural-mountain and its western region and along the seacoast of eastern Asia, the positive anomaly (anomalous anticyclone) over middle latitude continent and Okhotsk Sea. However, the phases of anomalous wave train is opposite in late monsoon year. What’s more, the zonal differences of meridional averaged (over 50-60oN) geopotential height anomalies are very obvious from the beginning of April. This signal may play an important role in prediction of the onset of SCSSM.3. The early onset and late onset of SCSSM are affected by the strength and position alteration of heat source and cumulus convection over ICP and west Pacific, the southward movement of those in southeastern part of South China and the northward propagation and intensity of those in Sumatra and“land bridge”region. In the first half month of May, if the convection activities over ICP and Philippine sea strengthen, which will result in a negative anomaly of geopotential height and a anomalous cyclone at 850hPa over Bay of Bengal, central and northern part of SCS and subtropical western Pacific, then the onset of SCSSM will happen earlier. Whereas reverse. 4. The local meridional circulation anomaly located in eastern Asia is very important for the establishment of SCSSM. The physical mechanism of meridional circulation variation is更多还原