Reparameterizing 4DVAR with neural fields
This work addresses a computational bottleneck in numerical weather prediction, offering a novel method that is incremental in improving efficiency and stability.
The authors tackled the computational difficulty and optimization challenges of 4DVAR in numerical weather prediction by reparameterizing it with neural fields, resulting in more stable initial condition estimates without spurious oscillations compared to a baseline.
Four-dimensional variational data assimilation (4DVAR) is a cornerstone of numerical weather prediction, but its cost function is difficult to optimize and computationally intensive. We propose a neural field-based reformulation in which the full spatiotemporal state is represented as a continuous function parameterized by a neural network. This reparameterization removes the time-sequential dependency of classical 4DVAR, enabling parallel-in-time optimization in parameter space. Physical constraints are incorporated directly through a physics-informed loss, simplifying implementation and reducing computational cost. We evaluate the method on the two-dimensional incompressible Navier--Stokes equations with Kolmogorov forcing. Compared to a baseline 4DVAR implementation, the neural reparameterized variants produce more stable initial condition estimates without spurious oscillations. Notably, unlike most machine learning-based approaches, our framework does not require access to ground-truth states or reanalysis data, broadening its applicability to settings with limited reference information.