Using radar observations to evaluate 3-D radar echo structure simulated by the Energy Exascale Earth System Model (E3SM) version 1
2021
Abstract. The Energy Exascale Earth System Model (E3SM) developed
by the Department of Energy has a goal of addressing challenges in
understanding the global water cycle. Success depends on correct simulation
of cloud and precipitation elements. However, lack of appropriate evaluation
metrics has hindered the accurate representation of these elements in
general circulation models. We derive metrics from the three-dimensional
data of the ground-based Next-Generation Radar (NEXRAD) network over the
US to evaluate both horizontal and vertical structures of precipitation
elements. We coarsened the resolution of the radar observations to be
consistent with the model resolution and improved the coupling of the Cloud
Feedback Model Intercomparison Project Observation Simulator Package (COSP)
and E3SM Atmospheric Model Version 1 (EAMv1) to obtain the best possible
model output for comparison with the observations. Three warm seasons
(2014–2016) of EAMv1 simulations of 3-D radar reflectivity features at an
hourly scale are evaluated. A general agreement in domain-mean radar
reflectivity intensity is found between EAMv1 and NEXRAD below 4 km
altitude; however, the model underestimates reflectivity over the central
US, which suggests that the model does not capture the mesoscale
convective systems that produce much of the precipitation in that region. The
shape of the model-estimated histogram of subgrid-scale reflectivity is
improved by correcting the microphysical assumptions in COSP. Different from
previous studies that evaluated modeled cloud top height, we find the model
severely underestimates radar reflectivity at upper levels – the simulated
echo top height is about 5 km lower than in observations – and this result
is not changed by tuning any single physics parameter. For more accurate
model evaluation, a higher-order consistency between the COSP and the host
model is warranted in future studies.
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