Offline Performance of a Nonlocal Deep Learning Parameterization for Climate Model Representation of Atmospheric Gravity Waves

Aman Gupta, Aditi Sheshadri, Sujit Roy, Valentine Anantharaj

Abstract: Gravity waves (GWs) make crucial contributions to the middle atmospheric circulation. Yet, their climate model representation remains inaccurate, leading to key circulation biases. This study introduces a set of three neural networks (NNs) that learn to predict GW fluxes (GWFs) from multiple years of high-resolution ERA5 reanalysis. The three NNs: a 1x1 ANN, a 3x3 ANN-CNN, and an Attention UNet embed different levels of horizontal nonlocality in their architecture and are capable of representing nonlocal GW effects that are missing from current operational GW parameterizations. The NNs are evaluated offline on both time-averaged statistics and time-evolving flux variability. All NNs, especially the Attention UNet, accurately recreate the global GWF distribution in both the troposphere and the stratosphere. Moreover, the Attention UNet most skillfully predicts the transient evolution of GWFs over prominent orographic and nonorographic hotspots, with the 1x1 model being a close second. Since even ERA5 does not resolve a substantial portion of GWFs, this deficiency is compensated for by subsequently applying transfer learning on the ERA5-trained ML models for GWFs from a 1.4 km global climate model. It is found that the re-trained models both (a) preserve their learning from ERA5, and (b) learn to appropriately scale the predicted fluxes to account for ERA5's limited resolution. Our results highlight the importance of embedding nonlocal information for a more accurate GWF prediction and establish strategies to complement abundant reanalysis data with limited high-resolution data to develop machine learning-driven parameterizations for missing mesoscale processes in climate models.