南太平洋辐合带季节循环及与地形和非绝热加热变化的联系

Features of seasonal cycle of South Pacific Convergence Zone in association with forcings of topography and diabatic heating

中文关键词:  南太平洋辐合带  季节变化  地形作用  非绝热加热

英文关键词:SPCZ  Seasonal changes  Topography  Diabatic heating

中文摘要:

      利用1981—2015年NCEP/NCAR月平均资料、NOAA的逐月CMAP（CPC（Climate Prediction Center）Merged Analysis of Precipitation）降水资料以及GODAS的月平均洋流资料和SODA的月平均风应力资料，定义了南太平洋辐合带（SPCZ）的关键区域，对南太平洋辐合带的季节变化特征及南太平洋辐合带的形成和维持原因进行了分析。结果表明，在南太平洋辐合带，4月存在由东西风切变型辐合带向东风辐合型辐合带转变的现象，而12月则存在相反的转换。在对流层低层，南太平洋辐合带区域的向上伸展高度和辐合在北半球冬季较其他季节明显高和强。引起南太平洋辐合带形成与维持的原因有2个方面：一是地形作用。由于地形的阻挡，造成等位涡线发生沿澳大利亚地形的绕行，利于澳大利亚地区反气旋性环流和南太平洋辐合带区域气旋性环流的形成与维持；同时，在地形和科里奥利力共同作用下，还易使暖海水在南太平洋辐合带区域汇聚，形成高海表温度区，从而加热大气，利于南太平洋辐合带的形成与维持。二是非绝热加热作用。南太平洋辐合带区域范围内的热源作用可以使其上方的大气受到加热，并产生加热强迫纬向梯度，驱动低层大气产生辐合。这些结果对深刻认识全球环流特别是南半球热带环流变化有重要意义。

英文摘要:

      Based on monthly mean data including NCEP/NCAR reanalysis, CMAP precipitation, GODAS oceanic current, and SODA wind stress from 1981 to 2015, we have investigated the characteristics of seasonal changes in the South Pacific Convergence Zone (SPCZ) and possible mechanisms for the SPCZ formation and maintenance. A key region of the SPCZ is identified. The results show that in the SPCZ region, there is a transition from convergence zone caused by wind shears between easterly and westerly winds to that caused by easterly winds in April, and an opposite trend of transition occurs in December. In the middle and lower troposphere, the upward extension of the SPCZ and convergence are significantly higher and stronger in winter than in other seasons. Two mechanisms explain the formation and maintenance of the SPCZ. First, topography plays a certain role. When blocked by topography, the equatorial vortex travels along the Australian terrain. Such condition is conducive to the formation and maintenance of the anticyclonic circulation in the Australian region and the cyclonic circulation in the SPCZ region. Meanwhile, with the effect of the Coriolis force, warm sea water tends to converge in the SPCZ and forms an area with high SST, which heats the atmosphere above and contributes to the formation and maintenance of SPCZ. Second, diabatic heating imposes essential impact on the SPCZ. Heat source in the SPCZ warms the atmosphere above and produces the zonal gradient forcing, which drives convergence in the lower atmosphere. All results are meaningful for scientists to better understand the global circulation, especially that in the southern hemisphere.