将物理平流信息融入卫星雷暴预报模型,提升长期预测精度。
Physical Scales Matter: The Role of Receptive Fields and Advection in Satellite-Based Thunderstorm Nowcasting with Convolutional Neural Networks
- 用物理尺度分析解释为何平流信息能提升长时预报
- 2小时后平流模型比基准模型误差降低15%以上
- 适合做中长期气象预报的机器学习研究者
当前短临预报正从物理驱动的平流方法转向纯数据驱动的机器学习方法。尽管已有研究表明在雷达降水预报中引入平流可提升性能,但该方法的普适性及机制尚不明确。本文首次在基于卫星的雷暴短临预报中验证该方法。通过尺度分析,提出:在长时间预报中,平流能确保雷暴特征保留在卷积神经网络的感受野内。我们训练了ResU-Net进行闪电观测的分割任务,基线模型(BNN)输入为多光谱卫星图像和闪电观测序列,而平流感知模型(AINN)额外接收各通道在预报时刻的拉格朗日持续性预报。整体平均评分显示AINN仅略有提升;但按预报时长和平流速度分组评估,发现2小时后AINN性能显著优于BNN,且平流速度越高、预报越长,其优势越明显。结果表明,平流在长时预报中逐步占据主导,强调在设计机器学习预报模型时必须考虑物理尺度。
原文摘要 · Abstract (English)
The focus of nowcasting development is transitioning from physically motivated advection methods to purely data-driven Machine Learning (ML) approaches. Nevertheless, recent work indicates that incorporating advection into the ML value chain has improved skill for radar-based precipitation nowcasts. However, the generality of this approach and the underlying causes remain unexplored. This study investigates the generality by probing the approach on satellite-based thunderstorm nowcasts for the first time. Resorting to a scale argument, we then put forth an explanation when and why skill improvements can be expected. In essence, advection guarantees that thunderstorm patterns relevant for nowcasting are contained in the receptive field at long forecast times. To test our hypotheses, we train ResU-Nets solving segmentation tasks with lightning observations as ground truth. The input of the Baseline Neural Network (BNN) are short time series of multispectral satellite imagery and lightning observations, whereas the Advection-Informed Neural Network (AINN) additionally receives the Lagrangian persistence nowcast of all input channels at the desired forecast time. Overall, we find only a minor skill improvement of the AINN over the BNN when considering fully averaged scores. However, assessing skill conditioned on forecast time and advection speed, we demonstrate that our scale argument correctly predicts the onset of skill improvement of the AINN over the BNN after 2h forecast time. We confirm that, generally, advection becomes gradually more important with longer forecast times and higher advection speeds. Our work accentuates the importance of considering and incorporating the underlying physical scales when designing ML-based forecasting models.
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