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猫儿山风场演变特征及对桂林前汛期暴雨强度与落区的指示作用

Implications of wind field evolution characteristics at Maoershan Mountain on the intensity and location of pre-flood season rainstorms in Guilin

  • 摘要: 利用2015—2024年4—6月桂林市兴安县猫儿山高海拔气象观测站逐小时风场资料、桂林市国家和区域级气象观测站逐小时降雨量、猫儿山高海拔气象观测站风场、桂林站探空及ERA5再分析资料,研究猫儿山地区降水及风场特征,并分析猫儿山高海拔气象观测站风场资料对对流层低层风场的代表性及风场演变特征对桂林前汛期暴雨的指示作用,结果表明:(1) 猫儿山地区迎风坡的日降雨量及强降水频次高于背风坡。背风坡高海拔站点风向分布均匀,风速较小;迎风坡站点主要盛行风向为SSW-SW,风速更大。(2) 猫儿山高海拔站点风向、风速与桂林探空各层次风向、风速均呈显著正相关,其中猫儿山东南侧1250 m气象观测站逐小时风资料可以较好地体现低空急流的演变,可将其作为指标站。(3) 猫儿山高海拔站南风转北风和西南风突然增强这两项特征对桂林暴雨落区与强度具有指示意义。分析2022年“6·5”和“6·21”2个暴雨过程及对应的2类相似个例发现,当指标站南风转北风后5~8 h,桂林中部降雨增强;当指标站西南风分量陡增后0~3 h,漓江上游降雨增强,而3~6 h后桂林中部降雨减弱。该结果可为漓江上游地区和桂林城区的预报预警业务提供有价值的参考。

     

    Abstract: Based on hourly wind data from high-altitude meteorological station on Maoershan Mountain in Xing'an County of Guilin, hourly rainfall data from regional meteorological station across Guilin, Guilin station radiosonde records and ERA5 reanalysis data from April to June 2015-2024, this study explores precipitation and wind field features of Maoershan region. It analyzes the represent ativeness of high-altitude station wind observations for lower tropospheric wind and the indicative role of wind evolution on pre-flood rainstorms of Guilin. Main conclusions are as follows. (1) Windward slopes of Maoershan Mountain record higher daily rainfall and severe precipitation frequency than leeward slopes. Wind directions distribute evenly with low wind speeds at high-altitude station on leeward slopes. Stations on windward slopes are dominated by SSW-SW winds with larger wind speeds. (2) Wind direction and speed at high-altitude station on Maoershan Mountain show significant positive correlations with wind parameters at all vertical layers of Guilin radiosonde profiles. Hourly wind data from the 1250 m meteorological station on the southeast side of Maoershan Mountain can capture low-level jet evolution, so this station is set as the indicator station. (3) Hourly wind evolution at high-altitude station on Maoershan Mountain can indicate severe precipitation distribution and intensity. This paper analyzes two rainstorm events on 5 June and 21 June 2022 plus two groups of similar cases. Rainfall over central Guilin strengthens 5~8 hours after wind shifts from south to north at the indicator station. The rainfall over the upper reaches of the Lijiang River intensifies within 0~3 hours after the sharp rise of southerly wind component at the indicator station and the rainfall over central Guilin weakens 3~6 hours after this sharp rise. The results provide practical references for forecast and early warning work of the upper reaches of the Lijiang River and urban areas of Guilin.

     

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