基于加权损失函数的我国近海海面风速预报

Prediction of Sea Surface Wind Speed in China’s Offshore Areas Based on Weighted Loss Function

关键词:  海面风速  预报订正  加权损失函数

Key words:  sea surface wind speed  forecast correction  weighted loss function

摘要:

数值模式的海面风速预报存在偏差，基于数值模式的统计模型虽然能在一定程度上减小偏差，但由于大风样本严重不足，其对大风的预报效果仍然差强人意。在系统检验 ECMWF 的 24 h 海面风速预报的基础上，利用 XGBoost 模型构建了适用于中国近海的海面风速预报订正模型。该模型不仅从整体上具有不错的预报准确度，还通过采用加权损失函数的训练方式，明显改善了大风的预报效果。利用 2022年 1月—2023年 1月我国近海14个浮标观测数据对模型进行独立检验，模型的平均误差和均方根误差分别为0.11 m·s-1和1.75 m·s-1，其中，对于 7～9 级风，模型的预报准确度较 ECMWF 显著提高，均方根误差分别降低了 15%、25%、24%。此外，当模型应用在未参与训练的网格点上时，模型仍然能获得较 ECMWF 更准确的预报。该模型操作方便容易使用，可为中国近海海面风速预报尤其是大风预报提供参考。

Abstract:

Sea surface wind speed forecasts based on numerical models often exhibit deviations. Although statistical models based on numerical models can reduce the deviation to a certain extent, their performance in predicting strong winds remains suboptimal due to the scarcity of strong wind samples. This study systematically evaluated the 24-hour sea surface wind speed forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF) and employed the XGBoost model to develop a correction model tailored for China’s offshore areas. This model not only demonstrated good overall forecasting accuracy, but also significantly enhanced the prediction of strong winds through the use of a weighted loss function during training. The model was independently tested using observational data from 14 buoys in China’s offshore waters from January 2022 to January 2023. The average error and root mean squared error of the model were 0.11 m s-1 and 1.75 m s-1, respectively. The forecast accuracy of the model for wind speeds classified as levels 7 to 9 was significantly improved compared to that of the ECMWF, with root mean squared errors reduced by 15%, 25%, and 24%, respectively. Furthermore, when applied to grid points not included in the training, the model continued to provide more accurate forecasts than the ECMWF. This model is easy to operate and use and can provide reference information for sea surface wind speed forecasting, especially strong wind forecasting, in China’s coastal waters.