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青藏高原东南部色季拉山夏季小时降水特征分析

Characteristics of summertime hourly precipitation over the Sygera Mountains on the southeastern Tibetan Plateau

  • 摘要: 位于高原东南缘的色季拉山是雅鲁藏布大峡谷水汽通道西北侧的重要地形,该地区夏季降水频率远高于周边山脉。本文利用2016—2021年6—8月青藏高原(以下简称高原)东南部色季拉山9个自动站的小时降水资料和ERA5逐小时再分析资料,分析了色季拉山夏季小时降水和小时强降水事件的时间分布特征,对比了在海拔高度和山谷走向的影响下,降水的空间分布特征。结果表明:(1) 色季拉山夏季以持续时间为1~3 h的短历时降水事件最为频发;夏季,小时强降水时次对总降水量的贡献率达52.6%,且这些强降水时次主要出现在持续时间超过6 h的长历时降水过程中。。夏季小时降水事件和小时强降水事件均在午后和夜晚发生频率较高,降水量也在午后和夜晚达到峰值。(2) 受海拔高度和山谷走向等多种因素的影响,夏季小时降水事件和小时强降水事件的特征在色季拉山不同区域存在差异。山顶站小时降水事件的降水量、降水频率和降水强度均高于山谷站;准南北走向山谷站小时降水事件和小时强降水事件的降水频率均高于准东西走向山谷站。合成分析结果表明:色季拉山地区夏季降水空间分布受地形热力与动力作用的协同影响。地形降水率表明地面饱和比湿和经向风的日变化主导了两种走向山谷站降水的日变化特征,二者在准南北走向山谷造成的降水率均高于准东西走向山谷。

     

    Abstract: Located on the southeastern margin of the Tibetan Plateau, Sygera Mountains constitutes a critical topographic feature on the northwestern flank of the water vapor channel of the Yarlung Zangbo Grand Canyon. The summer precipitation frequency in this region is substantially higher than that in surrounding mountain areas. Based on hourly precipitation data from 9 automatic meteorological stations on Sygera Mountains in the southeastern Tibetan Plateau (hereafter referred to as the TP) and hourly reanalysis data of ERA5 provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) from June to August 2016-2021, this study examines the temporal distribution characteristics of summertime hourly precipitation events and hourly heavy precipitation events over the Sygera Mountains.. Furthermore, the spatial distribution characteristics of precipitation under the influences of altitude and valley orientation are compared. The results are as follows. (1) During summer, short-duration precipitation events (lasting 1-3 hours) are the most frequent type. Summertime hourly heavy precipitation events contribute 52.6% of the total summer precipitation, primarily consisting of persistent rainfall with durations lasting more than 6 hours. Both precipitation events exhibit higher frequencies in the afternoon and evening, with precipitation amount also peaking during these periods. (2) Due to influence of elevation and the orientation of valleys, the characteristics of precipitation events vary across different regions. Precipitation amount, frequency and intensity of hourly precipitation events at mountaintop stations are higher than valley stations. The frequency of both precipitation events is higher at stations in quasi-north-south oriented valley than quasi-east-west oriented valley. The result of Composite analysis indicates that the spatial pattern of summer precipitation across Sygera Mountains is a product of synergistic thermodynamic and dynamic topographic influences. Orographic precipitation rate shows that the diurnal variations of surface saturated specific humidity and meridional wind dominate the precipitation diurnal cycle in both valleys, these factors exert a stronger effect, resulting in greater precipitation rates in quasi-north-south oriented valley compared to quasi-east-west oriented valley.

     

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