  We analyze the applicability of convolutional neural network (CNN)
architectures for downscaling of short-range forecasts of near-surface winds on
extended spatial domains. Short-range wind field forecasts (at the 100 m level)
from ECMWF ERA5 reanalysis initial conditions at 31 km horizontal resolution
are downscaled to mimic HRES (deterministic) short-range forecasts at 9 km
resolution. We evaluate the downscaling quality of four exemplary model
architectures and compare these against a multi-linear regression model. We
conduct a qualitative and quantitative comparison of model predictions and
examine whether the predictive skill of CNNs can be enhanced by incorporating
additional atmospheric variables, such as geopotential height and forecast
surface roughness, or static high-resolution fields, like land-sea mask and
topography. We further propose DeepRU, a novel U-Net-based CNN architecture,
which is able to infer situation-dependent wind structures that cannot be
reconstructed by other models. Inferring a target 9 km resolution wind field
from the low-resolution input fields over the Alpine area takes less than 10
milliseconds on our GPU target architecture, which compares favorably to an
overhead in simulation time of minutes or hours between low- and
high-resolution forecast simulations.
