Evaluating EAMv2 simulated stratiform mixed-phase cloud properties at
Northern and Southern high latitudes against ARM measurements
Abstract
This study evaluates high-latitude stratiform mixed-phase clouds (SMPC)
in the atmosphere model of the newly released Energy Exascale Earth
System Model version 2 (EAMv2) by utilizing one-year-long ground-based
remote sensing measurements from the U.S. Department of Energy
Atmospheric Radiation and Measurement (ARM) Program. A nudging approach
is applied to model simulations for a better comparison with the ARM
observations. Observed and modeled SMPCs are collocated to evaluate
their macro- and microphysical properties at the ARM North Slope of
Alaska (NSA) site in the Arctic and the McMurdo (AWR) site in the
Antarctic. We found that EAMv2 overestimates (underestimates) SMPC
frequency of occurrence at the NSA (AWR) site nearly all year round.
However, the model captures the observed larger cloud frequency of
occurrence at the NSA site. For collocated SMPCs, the annual statistics
of observed cloud macrophysics are generally reproduced at the NSA site,
while at the AWR site, there are larger biases. Compared to the AWR
site, the lower cloud boundaries and the warmer cloud top temperature
observed at NSA are well simulated. On the other hand, simulated cloud
phases are substantially biased at each location. The model largely
overestimates liquid water path at NSA, whereas it is frequently
underestimated at AWR. Meanwhile, the simulated ice water path is
underestimated at NSA, but at AWR, it is comparable to observations. As
a result, the observed hemispheric difference in cloud phase
partitioning is misrepresented in EAMv2. This study implies that
continuous improvement in cloud microphysics is needed for high-latitude
mixed-phase clouds.