用惩罚项提升神经网络天气预报的精确度,不牺牲准确性。
Improving the sharpness in neural network-based parametric post-processing of ensemble forecasts

- 在损失函数中加入惩罚项,抑制预测区间过宽问题。
- 2米气温预报的预测区间宽度减少8.2%至12.5%。
- 适合关注预报精度与不确定性平衡的研究者。
统计后处理已被证实能有效提升多种气象变量的集合预报质量。案例研究显示,后处理可修正集合预报通常存在的低估离散性和潜在偏差,同时优化体现预报能力的评分准则。但其代价通常是精确度下降:中心预测区间的宽度和预测不确定性增加,尤其在短时效时更为明显。本文针对基于神经网络的参数化后处理方法,通过在损失函数中引入惩罚项,旨在缓解这一现象。实验基于欧洲中期天气预报中心(ECMWF)提供的EUPPBench基准数据集中的2米气温集合预报,采用高斯分布作为预测分布,并以连续排序概率分数(CRPS)为损失函数进行验证。结果表明,引入惩罚项后,名义中心预测区间宽度相比无惩罚项情况显著降低8.2%至12.5%,同时概率预报的平均CRPS和预测均值的均方根误差(RMSE)未出现恶化。
原文摘要 · Abstract (English)
Statistical post-processing has proven to be an effective tool in improving ensemble forecast of different weather variables. Case studies show that post-processing can remedy the typically underdispersive and potentially biased behaviour of the ensemble while optimizing a proper scoring rule expressing the forecast skill. The price of these positive effects is generally a deterioration in sharpness; the width of the central prediction intervals and the uncertainty of the predictions are increasing, especially for shorter lead times. This work aims to reduce the extent of the latter phenomenon for neural network-based parametric post-processing methods by extending the network's loss function with a penalty term. We demonstrate the effect of the proposed technique for 2m temperature ensemble forecasts of the European Centre for Medium-Range Weather Forecasts downloaded from the EUPPBench benchmark dataset and verified against synoptic observations. Here, the predictive distribution is Gaussian, and we use the continuous ranked probability score (CRPS) as loss function. The case studies confirm a substantial relative decrease ($8.2\%-12.5\%$) in the width of the nominal central prediction interval compared to the width of the predictive distribution computed without the penalty term, while there is no deterioration in the mean CRPS of probabilistic forecasts and in the RMSE of the predictive mean.
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