The Benefits and Challenges of Downscaling a Global Reanalysis with
Doubly-Periodic Large-Eddy Simulations
Abstract
Global reanalyses like ERA5 accurately capture atmospheric processes at
spatial scales of O(10) km or larger. By downscaling ERA5 with
large-eddy simulation (LES), LES can provide details about processes at
spatio-temporal scales down to meters and seconds. Here, we present an
open-source Python package named the “Large-eddy simulation and
Single-column model - Large-Scale Dynamics”, or (LS)2D in short,
designed to simplify the downscaling of ERA5 with doubly-periodic LES. A
validation with observations, for several sensitivity experiments
consisting of month-long LESs over Cabauw (the Netherlands),
demonstrates both its usefulness and limitations. The day-to-day
variability in the weather is well captured by (LS)2D and LES, but the
setup under-performs in conditions with broken or near overcast clouds.
As a novel application of this modeling system, we used (LS)2D to study
surface solar irradiance variability, as this quantity directly links
land-surface processes, turbulent transport, and clouds, to radiation.
At a horizontal resolution of 25 m, the setup reproduces satisfactorily
the solar irradiance variability down to a timescale of seconds. This
demonstrates that the coupled LES-ERA5 setup is a useful tool that can
provide details on the physics of turbulence and clouds, but can only
improve on its host reanalysis when applied to meteorological suitable
conditions.