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贵州典型地形下强降水特征及其模式预报订正研究

Study on characteristics of heavy precipitation and model prediction correction under typical topography in Guizhou

  • 摘要: 利用2016—2020年贵州省国家气象站和区域气象站逐小时地面降水观测资料,分别选取北盘江作为贵州河谷地形、雷公山和梵净山作为贵州高山地形的典型代表,对贵州典型地形下的强降水时空特征进行分析,并利用2019—2020年欧洲中期天气预报中心逐3 h降水预报资料,采用频率匹配法对三个地区的强降水预报进行客观订正。结果表明:(1) 三个地区的强降水多发生在6月,其中北盘江与雷公山强降水的频次逐年增加,而梵净山增加不明显。两个高山地区强降水频次主要集中在夜间至早晨,而北盘江强降水频次在午后和夜间各有一个峰值。(2) 三个地区的强降水与地形有一定关系,北盘江强降水的频发区和降水量集中区主要出现在流域北部的低洼地带,雷公山出现在山体以南,而梵净山集中在山体东侧。当北盘江与梵净山地区地形坡度小于20°—30°,雷公山地区地形坡度小于40°—50°时,强降水频次随坡度增加而增加,而后强降水频次随坡度减少。(3) 采用频率匹配法分别对三个地区的强降水进行客观订正后,当北盘江降水量小于8.2 mm,雷公山降水量小于10.3 mm,梵净山降水量小于7.3 mm时,频率匹配订正对模式预报降水有一定的消空作用;当三个地区降水量分别大于对应阈值时,频率匹配订正可明显提升降水预报量级;三个地区的强降水预报技巧整体有所提升,强降水预报频次有明显提高,空间分布特征基本符合实况,其中以北盘江订正效果最优。

     

    Abstract: Based on the hourly ground precipitation observations from the national and regional stations in Guizhou Province from 2016 to 2020, the spatial and temporal characteristics of heavy precipitation in the typical terrains of Guizhou were analyzed in this study. For typical terrains, the Beipan River was selected as the typical representative of Guizhou's valley terrain, while Leigong Mountain and Fanjing Mountain were chosen as the typical representatives of Guizhou's high mountain terrain. The three-hour precipitation forecast datasets during 2019-2020 provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) were used, and a frequency matching method was applied to objectively correct the heavy precipitation forecast in the above three regions. The results are as follows. (1) Heavy precipitation in the three regions mostly occurs in June. The heavy precipitation frequency increases in Beipan River and Leigong Mountain year by year, while the increase in Fanjing Mountain is not significant. The heavy precipitation in the two mountainous regions mainly occurs during the night and early morning. While two heavy precipitation peaks are found in the Beipan River basin, one in the afternoon and one at night. (2) The distribution of heavy precipitation in the three areas is somewhat related to the terrain. The frequent and concentrated areas of heavy precipitation in the Beipan River are mainly located in the low-lying areas in the northern part of the basin, with that being in the south of Leigong Mountain and on the eastern side of Fanjing Mountain. Considering the slope of the terrain, the distribution of rainfall shows similar characteristics. In the regions of Beipan River and Fanjing Mountain with slopes less than 20°-30°, and the regions in Leigong Mountain with slopes less than 40°-50°, the frequency of heavy precipitation increases with the slope. While in other regions, the frequency of heavy precipitation decreases with the slope. (3) Objective corrections of heavy precipitation in these regions are applied using the frequency matching method. It is found that the frequency adjustment method has a certain effect in reducing the over-forecast of precipitation when the precipitation amount is less than 8.2 mm in Beipan River, less than 10.3 mm in Leigong Mountain, and less than 7.3 mm in Fanjing Mountain. When precipitation is greater than the above thresholds, the frequency matching method can significantly improve the levels of the predicted precipitation. After the correction, the overall performance of heavy precipitation prediction in the three regions has improved. A noticeable increase in the frequency of heavy precipitation prediction and comparable spatial distributions between the predictions and observations can be found, with the best improvement observed in the Beipan River.

     

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