1998年夏季亚洲地区低频大气环流的特征及其与长江中下游降水的关系

A study of the characteristics of the low-frequency circulation on Tibetan plateau and itsassociation with precipitation over the Yangtze valley in 1998

中文关键词:  低频振荡，青藏高原，长江中下游，夏季强降水

英文关键词:Low-frequency oscillation, Tibetan Plateau, Mid lower reaches of Yangtze River, Summer heavy rain

中文摘要:

      利用日本GAME资料、TRMM卫星资料及中国730站降水资料研究了1998年夏季亚洲地区对流层至平流层低频振荡（LFO）的传播特征及该年长江中下游夏季降水变化的LFO型，结果表明：1998年5—8月，在青藏高原经纬度上，对流层LFO的东西向传播特征与季节变化有关。在东西方向上，高原和东亚大陆雨季开始前，LFO以向东传播为主；在雨季开始后，LFO以向西传播为主。南北方向上，LFO的传播在雨季前后基本一致，高原南北两侧均向高原传播。在南北方向上，青藏高原是LFO的汇；而在东西方向上，高原西部只在雨季开始后是LFO加强区，使西传进入高原的LFO继续西传。整个大气层以对流层顶（100 hPa）LFO最强，进入平流层LFO迅速减弱。1998年夏季长江中下游降水存在两次明显的LFO循环，我们根据两次降水LFO各位相合成分析了降水、500和100 hPa LFO环流以及沿30°N LFO垂直环流。结果表明：来自西伯利亚向南传播和来自孟加拉湾及南海向北传播的LFO气旋（降水谷值期）和反气旋（降水峰值期）形成了高原东部上空LFO气旋（降水谷值期）和反气旋（降水峰值期）以及来自中纬度西太平洋南下西移经日本、黄海到达中国大陆东部海洋上空的LFO反气旋（降水谷值期）和气旋（降水峰值期）的共同作用造成了长江中下游地区强烈的下沉（降水谷值期）和上升（降水峰值期），形成长江中下游降水LFO谷值期和峰值期。

英文摘要:

      The propagation characteristics of the atmospheric low frequency(LF, 30-60 days) oscillations(LFO) around the Tibetan Plateau from troposphere to stratosphere, and its relationship with the floods over the mid lower reaches of the Yangtze River in the summer of 1998 are studied, based on the GAME dataset from Meteorological Research Institute (MRI)/Japan Meteorological Agency, the TRMM satellite rainfall and the 730 station precipitation over China. The results show that the zonal propagation direction of LFOs of horizontal winds varied with seasons in troposphere during May to August in 1998. The eastward propagation of LFOs was remarkable before the rainy season of the Tibetan Plateau and the eastern Asian continent, while the westward propagation was significant after the start of the rainy season. The northward LFOs from the south side of the plateau and the southward LFOs from the north side were both significant whatever before or after the start of the rainy season. The plateau was a LFO sink in the meridional direction, and in the zonal direction, the west part of the plateau was an intensifying area for the continual westward LFOs over the plateau only after the start of the rainy season. Besides, the strongest LFOs occurred at the tropopause (100 hPa), and rapidly decayed after entering the stratosphere. The rainfall presented two LFO cycles over the mid-low reaches of Yangtze River in the summer of 1998. According to the phases of the two rainfall LFO cycles, the composite analyses of precipitation distribution, LF circulations at 500 hPa and 100 hPa, and LF vertical circulation along 30°N are performed. It is the joint effect of the mid upper tropospheric strong 30-60 days filtered cyclone (anticyclone) over the eastern plateau and the LF anticyclone (cyclone) over the western subtropical Pacific that induced the whole layer LF subsidence (ascending) motion over the mid lower reaches of Yangtze River, which provided the favorable condition for the break (maintenance) of precipitation.