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CN 11-1768/O4

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长江中下游地区夏季强降水前期的三维环流结构特征分析
作者:
作者单位:

1.中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室;2.中国科学院大学

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基金项目:

国家重点研发计划2018YFC1507603,国家自然科学基金41875112, 91637211


Three-Dimensional Circulation Structure of Summer Heavy Rainfall in the middle-lower reaches of the Yangtze River Valley
Author:
Affiliation:

1.University of Chinese Academy of Sciences;2.State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics,Institute of Atmospheric Physics,Chinese Academy of Sciences

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    摘要:

    利用1959-2013年台站逐日降水观测资料和JRA-55逐6小时再分析资料,分析了长江中下游地区夏季强降水对应的前期三维环流结构。通过对长江中下游地区373个强降水样本的大气环流场合成分析发现,在长江中下游地区对流层中上层存在暖异常,暖中心位于300 hPa。在静力平衡和准地转平衡的作用下,高层暖异常上层存在反气旋式环流,下层存在气旋式环流。一方面,暖异常通过高层的反气旋式环流异常,使得其北侧的200 hPa西风增强,并促使高层急流东伸、南移到长江中下游地区北侧附近,增强了长江中下游地区高空辐散;另一方面,暖异常通过低层的气旋式环流异常,加强了吹向长江中下游地区的西南风,使低层水汽输送及辐合增强。暖异常所引起的高低空环流异常的有利配置,对长江中下游地区夏季强降水形成有重要作用。300hPa 暖异常在降水前48小时已经存在于青藏高原东部的400-300hPa 高空,700hPa 气旋式环流提前24小时出现在四川盆地中低层。高低层的环流要素相互配合并随时间东移,暖异常率先到达长江中下游地区,并配合低层气旋式环流和水汽辐合区,导致了长江中下游地区的强降水。

    Abstract:

    By using the daily station data and Japanese 55-year Reanalysis Project (JRA-55) data in the course of 1959-2013, a three-dimensional background circulation structure of summer heavy rainfall in the middle-lower reaches of the Yangtze River Valley (MLYRV) is analyzed. Composite analyses of circulation in advance of 373 heavy rainfall days reveal that a prominent warm anomaly with a center at 300hPa emerges in the upper troposphere over MLYRV. Because of hydrostatic and quasi-geostrophic equilibriums, an anticyclonic (cyclonic) anomaly forms above (below) the warm center. On one hand, the warm anomaly makes the westerly winds to the north of the warm center strengthened by high-level anticyclonic circulation anomaly, which results in the jet stream in the upper-level over East Asia shifting southward and eastward to the north side of MLYRV. So the upper-level divergent anomaly field over MLYRV is enhanced. On the other hand, the cyclonic anomaly below the warm anomaly reinforces the low-level southwesterly winds to MLYRV, which makes more water vapor transporting to MLYRV and convergence stronger. The favorable configuration of high and low altitude circulation anomalies caused by warm anomalies plays an important role in the formation of strong precipitation in MLYRV. The 300 hPa warm anomaly exists at 400-300 hPa in the eastern part of the Qinghai-Tibet Plateau 48 hours before the precipitation in MLYRV, and the 700-hPa cyclonic circulation appears in the middle and lower layers over the Sichuan Basin 24 hours ahead of schedule. The high and low circulation elements cooperate with each other and move eastward with time. The warm anomaly first reaches MLYRV, and cooperates with the low-level cyclonic circulation and water vapor convergence area, resulting in strong precipitation in MLYRV.

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  • 收稿日期:2019-02-01
  • 最后修改日期:2019-04-23
  • 录用日期:2019-05-16
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