南半球环状模事件的准地转调整过程分析

本文利用NCEP/NCAR逐日再分析资料,分析了南半球环状模（SAM）事件生命过程中的准地转调整过程.由于SAM沿纬圈的水平尺度远远大于临界尺度罗斯贝变形半径,因此要求纬向风场在地转调整过程向气压场适应以达到地转平衡.研究结果表明,在纬向平均环流中,异常Ferrel环流强度的变化超前于SAM强度变化约2/16位相,异常Ferrel环流能够通过超前的整层大气质量的经向输运,改变中高纬度的质量分布装状况,导致中、高纬度地区间的位势高度梯度异常变化,而中、高纬度地区间的位势高度梯度异常发生变化就意味着SAM强度和位相发生变化；而当SAM强度和位相发生改变后,即中、高纬度地区南北方向上的位势高度梯度发生变化后,可破坏中纬度地区纬向风场与位势高度场之间的地转平衡,产生地转偏差；地转偏差产生后,又可驱动经向散度风场,造成Ferrel环流异常的变化,由此形成一个自我内部循环调整过程.

Analysis of the Quasi-geostrophic Adjustment Process of the Southern Hemisphere Annular Mode

The quasi-geostrophic adjustment process of the circulations associated with the Southern Hemisphere Annular Mode (SAM) is studied by employing the NCEP/NCAR reanalysis daily data. To SAM, which is a planetary scale system with the space scale along the latitude larger than the Rossby deformation radius, the wind field inclines to change itself so as to fit the pressure field in the process of geostrophic adjustment. The results show that the evolution of SAM lags behind the variation of the Ferrel cell anomaly about 2/16 phases, indicating the Ferrel cell changes the geopotential height anomalies in middle and high latitudes through its meridional transporting of the atmosphere mass. As the changing of the geopotential height anomalies in middle and high latitudes means the temporal evolution of SAM, SAM’s transition from positive to negative phases is demonstrated to be driven by the leading mass transportation of Ferrel cell. When the SAM changes or the meridional geopotential height gradient in middle latitudes changes, it then destroys the geostrophic equilibrium between the zonal wind field and the geopotential height anomaly in middle latitudes, causing the geostrophic deviation; then the geostrophic deviation drives the meridional wind filed, changing the anomalous Ferrel cell, and forming a self-adjustment internal process cycle.