The June 2012 North American Derecho: A testbed for evaluating regional
and global climate modeling systems at cloud-resolving scales
Abstract
In this paper, we introduce a testbed for evaluating and comparing
climate modeling systems at cloud resolving scales using hindcasts of
the June 2012 North American derecho. The testbed is applied to two
models: the regionally-refined Simple Cloud-Resolving E3SM Atmosphere
Model (SCREAM) at horizontal resolutions ranging from 6.5 to 1.625 km
and the Weather Research and Forecasting (WRF) model with 4 km grid
spacing. We find the simulation results to be highly sensitive to the
initial conditions, initialization time, and model configurations, with
initial conditions from the Rapid Refresh (RAP) producing the best
simulation. Significant improvement is identified in the SCREAM
simulations as horizontal grid spacing is refined. While a propagation
delay of approximately 2 hours is found in both models, SCREAM at 1.625
km simulates the observed bow echo structure of the derecho well and
predicts strong surface gusts that exceed 30 m/s. In comparison, WRF
hardly produces surface wind over 25 m/s, and the derecho wind gust in
WRF is 42-46% lower than in SCREAM. Moreover, WRF has a lower bias in
simulating cold clouds but overestimates the precipitation intensity.
Both models well reproduce the observed outgoing longwave radiation
spatial patterns (Pearson correlation > 0.88) while they
simulate larger areas of composite radar reflectivity > 40
dBZ by up to 4 times and underestimate the precipitating area by
~ 70\% in WRF and 47\%
in SCREAM compared to observations.