基于GRU深度学习的短时临近降水预报订正方法

Short-term Precipitation Correction Based on GRU Deep Learning

  • 摘要: 为提高短时临近降水预报准确率, 提出一种订正广西对流尺度数值预报模式(GRAPES-GX)降水预报产品的深度学习方法。该方法通过神经网络对实况进行时空特征提取, 以门控循环网络(GRU)为基础框架, 针对降水产品进行改进, 并用于GRAPES-GX降水预报产品订正。在此基础上, 设计了大气物理规律适配模块, 通过物理条件匹配机制订正模式预报降水强度与落区的系统性误差, 增强训练样本中预报产品和实况的特征相关性, 并协同优化模型参数, 获得更优的订正效果。广西区域试验结果表明: 订正模型在各预报时效、各降水强度等级的TS(threat score)评分均得到正技巧, 总体TS技巧评分为2.21%。对于不低于0.1 mm·h-1、不低于2 mm·h-1、不低于7 mm·h-1、不低于15 mm·h-1、不低于25 mm·h-1和不低于40 mm·h-1降水强度预报TS技巧评分分别为5.67%、3.59%、2.18%、1.46%、1.01%和0.46%。0~2 h、2~4 h和4~6 h时效预报TS技巧评分分别为4.77%、1.28%和0.91%。

     

    Abstract: To improve the accuracy of short-term precipitation forecasts, a deep learning method is proposed to correct numerical model precipitation forecast products. This method extracts spatiotemporal features from numerical model forecasts and observations using a neural network and performs corrections based on a gated recurrent unit (GRU) framework. Additionally, an atmospheric physics adaptor module is meticulously designed to address systematic errors in the intensity and displacement of numerical model forecast by leveraging physical condition mechanisms. The module plays a crucial role within the overarching model framework, which consists of three integrated components: Feature network, recurrent-revising network, and physical adaptor. The feature network extracts precipitation intensity, distribution, motion characteristics and other related atmospheric physical features from precipitation in situ and numerical model forecast data, serving as input to the recurrent-revising network. Recurrent-revising network utilizes a recurrent neural network structure to adjust grid point forecast results on a time-step basis. Deep neural networks are used to extract spatiotemporal variation features from numerical model forecast data and historical observations, learning systematic errors in the evolution processes to correct the precipitation magnitude and distribution. The physical adaptor is an atmospheric physics adaptation module, which preprocesses numerical model forecast data using frequency distribution fitting and distribution deviation correction methods. In Guangxi convective-scale model precipitation forecast data, when there are significant differences between numerous samples and the precipitation in situ, the feature correlation is low, making it a challenge to capture systematic error characteristics during neural network training. By preprocessing the samples with the physical adaptor, differences between forecasts and observations are reduced, enhancing feature correlation between training input datasets and observations, thus facilitating better neural network training and achieving superior correction skills. This method not only adheres to but also integrates fundamental atmospheric physical laws governing precipitation evolution, thereby offering a robust and innovative approach for post-processing numerical model short-term precipitation forecasts. By incorporating these physical principles into the model framework, corrected forecasts not only reflect statistical patterns but also adhere closely to the underlying physical processes driving precipitation dynamics. Experimental results in Guangxi indicate that the model demonstrates positive threat score skills across various forecast times and precipitation intensities. Specifically, for different precipitation intensities (average of all times), threat score skills for 0.1 mm·h-1, 2 mm·h-1, 7 mm·h-1, 15 mm·h-1, 25 mm·h-1, and 40 mm·h-1 are 5.67%, 3.59%, 2.18%, 1.46%, 1.01%, and 0.46%, respectively; for different lead times, threat score skills for 0-2 h, 2-4 h, and 4-6 h are 4.77%, 1.28%, and 0.91%, respectively; and the overall average threat score skill across all precipitation intensities and times is 2.21%.

     

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