用粗粒化时间步长训练神经网络,实现大气平流模拟92倍加速且不降分辨率。
Acceleration of horizontal numerical advection for atmospheric modeling through surrogate modeling with temporal coarse-graining

- 通过时间粗粒化让模型跳过柯朗条件限制,用大时间步训练神经网络预测通量。
- 最大提速92倍,仍保持0.60的决定系数,速度越快精度越低但可控。
- 在不同季节、垂直层次泛化良好,适合需快速迭代的预报或数据同化场景。
机器学习代理模型可加速地球科学模拟,但现有方法或提速有限,或牺牲空间分辨率。本文提出一种基于时间粗粒化的机器学习求解器,通过允许模型采用远大于柯朗-弗里德里希斯-勒维(CFL)条件规定的时间步长进行训练,实现不损失空间分辨率的加速。该框架采用卷积神经网络,输入浓度与CFL数,输出质量通量。在10天地表水平平流模拟中,对应4至32倍于基线时间步的粗粒化因子下,决定系数r²为0.60–0.98。速度提升与精度下降呈线性关系:每提速10倍,精度损失r²=0.24,最高达92倍加速,同时保持r²=0.60。模型仅用1月地表风场数据训练,以检验跨季节和垂直高度的泛化能力。4倍粗粒化模型成功再现72层垂直结构;8至16倍模型覆盖多数垂直层,32倍则失败。模型对季节变化泛化良好,唯六月与十月出现不稳定。经微调后,此类模型适用于需要速度换精度的场景,如筛选工具、集合模拟或数据同化。
原文摘要 · Abstract (English)
Machine-learned surrogate modeling of advection may accelerate geoscientific models, but existing approaches have either achieved limited speedup or have sacrificed spatial resolution compared to the model they are trained to emulate. We developed a machine-learned solver that speeds up advection simulations without sacrificing spatial resolution through the use of temporal coarse-graining, where the model is trained to take larger integration steps than dictated by the Courant-Friedrich-Lewy (CFL) condition. Our solver framework includes a convolutional neural network that takes concentrations and CFL numbers as inputs and outputs mass flux. Our solvers emulate 10-day ground-level horizontal advection simulations with r$^2$ values against the baseline ranging from 0.60--0.98 with temporal coarsening factors of 4 to 32 times the baseline integration time step. Speed increases and accuracy decreases with increased coarsening, with $r^2 = 0.24$ in accuracy lost for every factor of 10 gained in speed, reaching a maximum 92$\times$ speedup while maintaining $r^2 = 0.60$. We deliberately trained our solvers only on January ground-level wind data to examine their ability to generalize across seasons and vertical heights. The 4$\times$-coarsened learned solver successfully reproduces simulations over 72 vertical levels. The 8$\times$--16$\times$ solvers (but not 32$\times$) emulate most vertical levels. The learned solvers also generalize well across seasons, except for instabilities in June and October. With additional fine-tuning, these learned solvers could be appropriate for operational use where trading accuracy for speed could be advantageous, such as in screening tools, in ensemble simulations, or with data assimilation.
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