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基于优选物理因子的两湖地区冬季降水相态判识方法研究

Research on Winter Precipitation Phase Discrimination Methods in Hunan and Hubei Based on Optimal Physical Factors

  • 摘要: 本文基于2000-2019年ERA5再分析资料以及中国地面基本气象观测资料,统计分析了两湖地区复杂地形下各类降水相态时空分布特征,并优选物理因子,分别构建基于数据重采样技术的轻量级梯度提升树模型(ADASYN-LGBM和Hybrid-LGBM),以及引入FocalLoss损失函数的全连接神经网络模型(FocalLoss-MLP),最终采取软投票策略集成单一模型(Ensemble),结果表明:两湖地区冬季降水相态频次空间分布特征与地形、环流与气候背景相关,其中受南岭地形阻挡和冷暖空气交汇影响,湖南冻雨频次显著高于湖北;昼夜时段对不同降水相态的分布也具有一定影响。特征重要性分析指出2m温度、0℃层高度以及厚度因子在模型判识过程中起到了主导作用,昼夜二分类因子、纬度作为辅助变量仍有一定贡献。四种模型均指示对主导类别雨的判识效果最优,雪、冻雨和雨夹雪次之,尤其对于雨夹雪(样本占比2.2%)这一类别测试集TS评分仅为8-18%,这与雨雪相态过渡阶段,气象特征重叠、边界模糊有关。其中Ensemble模型能弥补单一模型对某类别降水相态判识较弱的缺点,进一步提升整体识别精度,但模型性能高度依赖样本数量。

     

    Abstract: Based on ERA5 reanalysis data and Chinese surface basic meteorological observation data from 2000-2019, this study statistically analyzes the spatiotemporal distribution characteristics of various precipitation phases under complex terrain conditions in the Two Lakes region, optimizes physical factors, and constructs lightweight gradient boosting tree models based on data resampling techniques (ADASYN-LGBM and Hybrid-LGBM), as well as a fully connected neural network model incorporating FocalLoss function (FocalLoss-MLP). Finally, a soft voting strategy is employed to ensemble individual models (Ensemble). The results show that: The spatial distribution characteristics of winter precipitation phase frequency in the Two Lakes region are related to topography, circulation, and climate background. Influenced by the blocking effect of the Nanling Mountains and the convergence of cold and warm air masses, the frequency of freezing rain in Hunan Province is significantly higher than that in Hubei Province. Diurnal periods also have certain impacts on the distribution of different precipitation phases. Feature importance analysis indicates that 2m temperature, 0℃ level height, and thickness factors play dominant roles in the model discrimination process, while diurnal binary classification factors and latitude serve as auxiliary variables with certain contributions. All four models demonstrate optimal discrimination performance for the dominant category of rain, followed by snow, freezing rain, and sleet. Particularly for sleet (accounting for 2.2% of samples), the test set TS scores are only 8-18%, which is related to the overlapping meteorological characteristics and blurred boundaries during the rain-snow phase transition stage. The Ensemble model can compensate for the weakness of individual models in discriminating certain precipitation phase categories and further improve overall recognition accuracy, although model performance is highly dependent on sample size.

     

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