Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Efficient high-dimensional variational data assimilation with
  machine-learned reduced-order models   Data assimilation (DA) in the geophysical sciences remains the cornerstone of
robust forecasts from numerical models. Indeed, DA plays a crucial role in the
quality of numerical weather prediction, and is a crucial building block that
has allowed dramatic improvements in weather forecasting over the past few
decades. DA is commonly framed in a variational setting, where one solves an
optimization problem within a Bayesian formulation using raw model forecasts as
a prior, and observations as likelihood. This leads to a DA objective function
that needs to be minimized, where the decision variables are the initial
conditions specified to the model. In traditional DA, the forward model is
numerically and computationally expensive. Here we replace the forward model
with a low-dimensional, data-driven, and differentiable emulator. Consequently,
gradients of our DA objective function with respect to the decision variables
are obtained rapidly via automatic differentiation. We demonstrate our approach
by performing an emulator-assisted DA forecast of geopotential height. Our
results indicate that emulator-assisted DA is faster than traditional
equation-based DA forecasts by four orders of magnitude, allowing computations
to be performed on a workstation rather than a dedicated high-performance
computer. In addition, we describe accuracy benefits of emulator-assisted DA
when compared to simply using the emulator for forecasting (i.e., without DA).

26
The categories of this paper are: bayes-an
5
The categories of this paper are: gr-qc
22
The categories of this paper are: chao-dyn
30
The categories of this paper are: q-alg
11
The categories of this paper are: hep-lat
31
The categories of this paper are: ao-sci
10
The categories of this paper are: q-bio
28
The categories of this paper are: alg-geom
21
The categories of this paper are: adap-org
6
The categories of this paper are: astro-ph
7
The categories of this paper are: hep-th
20
The categories of this paper are: acc-phys
37
The categories of this paper are: supr-con
3
The categories of this paper are: physics
35
The categories of this paper are: mtrl-th
25
The categories of this paper are: patt-sol