Machine Learning Gravity Wave Parameterization Generalizes to Capture the QBO and Response to Increased CO2
Published in Geophysical Research Letters, 2022
Key Points
Neural networks trained on one annual cycle accurately emulate a physics-based gravity wave parameterization when coupled to a climate model
Although trained on only one phase of the Quasi-Biennial Oscillation, the emulator generates the entire cycle of the oscillation
The emulator captures key qualitative features of the response of the original gravity wave parameterization to enhanced CO2
Abstract
We present single-column gravity wave parameterizations (GWP) that use machine learning to emulate non-orographic gravity wave drag and demonstrate their ability to generalize out-of-sample. A series of artificial neural networks (ANN) are trained to emulate the momentum forcing from a conventional GWP in an idealized climate model, given only one view of the annual cycle and one phase of the Quasi-Biennial Oscillation (QBO). We investigate the sensitivity of offline and online performance to the choice of input variables and complexity of the ANN. When coupled with the model, moderately complex ANNs accurately generate full cycles of the QBO. When the model is forced with enhanced CO2, its climate response with the ANN matches that generated with the physics-based GWP. That ANNs can accurately emulate an existing scheme and generalize to new regimes given limited data suggests the potential for developing GWPs from observational estimates of gravity wave momentum transport