亚洲季风区纬圈剖面内准40天周期振荡的环流结构及其演变

THE STRUCTURE AND EVOLUTION OF THE CIRCULATION WITH QUASI-40 DAY PERIODIC OSCILLATION IN ZONAL CROSS-SECTIONS OVER ASIAN MONSOON REGION

摘要:

本文利用1979年FGGE LevelⅢb资料研究了30°E—150°W范围内赤道和15°N纬带两个剖面内的准40天周期振荡的环流和温度场结构,讨论了它们的变化及其与亚洲地区季风活跃和中断的关系。发现有以下结果:(1)亚洲季风槽内的上升气流不仅构成了强大的经向季风环流圈,同时在其两侧也形成了东、西向(纬偏异常)环流圈,并受到准40天周期扰动的显著影响。季风槽两侧的热力学结构显著不同。(2)15°N纬带上60°E以西的北非和沙特阿拉伯上空的下沉(上升)区域向东扩展至南海—菲律宾地区导致其东面(西面)的高(低)层东(西)风动量下(上)传,使得季风中断(活跃),引起130°E以西地区低层西风和其东面太平洋上空的高层东风发生相互作用。向东传播的正(负)温度扰动与强的上升(下沉)运动相结合使得这一地区成为准40天周期振动的能量源地。(3)在赤道剖面上,扰动风场的位相向东向上传播,准40天周期的扰动动能向扰动位能转换,西风动量向下传播,其动力学特性与开尔文波有明显的不同。

Abstract:

Based on FGGE Ⅲb data of 1979, a study was done of the structure of the circulation and temperature field with quasi-40 day periodic oscillation (QDPO) in the cross-sections along 15° N and Equator over 30°-150° W, and a discussion of their changes and relation to the active and the break monsoon over Asia is also presented. The results are as follows:1)The updrafts within monsoon trough over Asia not only form the strong meridional circulation cell, but also East-West(an anomaly from zonal mean) circulation cells with different thermodynamic structure over both sides of the trough, which may be significantly affected by QDPO.2) At 15 °N the downdrafts(updrafts) covering north Africa and Saudi Arabia west of about 60 °E intensify as they extend eastward to the South China Sea-the Philippines around 130 °E, then cause downward (upward) transport of easterly (westerly) momentum in the upper(lower) air east(west)of it, which leads to break (active)monsoon with interaction beteen the lower(upper)-level westerly(easterly) west(east)of 130 °E. The eastward propagating positive (negative) temperature perturbations are associated with strong upward(downward)-motions, implying that this region is a kinetic energy source for QDPO.3)On the equatorial cross-section, the wind perturbations propagate eastward and upward with westerly momentum transporting downward, while the kinetic energy for quasi-40 day periodic perturbations were converted into potential energy, which means that the perturbations are significantly different from Kelvin wave in dynamic properties.