Generative Modelling of Stochastic Rotating Shallow Water Noise
This work addresses uncertainty estimation in weather and climate predictions by improving stochastic parameterization of subgrid-scale processes, though it is incremental as it builds on prior methodology.
The authors tackled the problem of calibrating non-Gaussian noise in stochastic fluid dynamics models by replacing a PCA-based method with a generative model, which avoided imposing Gaussian constraints and yielded good results in RMSE, CRPS, and forecast rank histogram metrics on a stochastic rotating shallow water model.
In recent work, the authors have developed a generic methodology for calibrating the noise in fluid dynamics stochastic partial differential equations where the stochasticity was introduced to parametrize subgrid-scale processes. The stochastic parameterization of sub-grid scale processes is required in the estimation of uncertainty in weather and climate predictions, to represent systematic model errors arising from subgrid-scale fluctuations. The previous methodology used a principal component analysis (PCA) technique based on the ansatz that the increments of the stochastic parametrization are normally distributed. In this paper, the PCA technique is replaced by a generative model technique. This enables us to avoid imposing additional constraints on the increments. The methodology is tested on a stochastic rotating shallow water model with the elevation variable of the model used as input data. The numerical simulations show that the noise is indeed non-Gaussian. The generative modelling technology gives good RMSE, CRPS score and forecast rank histogram results.