Assessing Cloud Fraction in the Canadian Regional Climate Model Over
North America Using Satellite Data and a Satellite Simulator Package
Abstract
Clouds are crucial to Earth’s climate system, influencing radiation and
contributing to climate projection uncertainties. Here, the simulated
cloud fraction by the sixth version of the Canadian Regional Climate
Model (CRCM6/GEM5) was evaluated using CALIPSO lidar retrievals and the
second version of the Cloud Feedback Intercomparison Project (CFMIP)
Observation Simulator Package (COSP2) for the years 2014 and 2015.
Horizontal and vertical distributions of clouds in the CRCM6/GEM5 model
were evaluated using cloud profiles and four cloud categories (total,
high-, mid- and low-level clouds) derived directly from the CRCM6/GEM5
model and treated using the COSP2 satellite simulator. A seasonal
analysis was conducted across specific regions in North America. Results
showed that the use of COSP2 is essential for comparing CRCM6/GEM5
outputs against satellite data to account for variable definitions and
signal attenuation of active instruments (e.g., Cloud-Aerosol Lidar with
Orthogonal Polarization: CALIOP). Spatial and vertical cloud
distributions and seasonal patterns were generally well represented by
the CRCM6/GEM5 for both winter (December-February) and summer
(June-August). High- and low-level clouds were particularly
well-represented, especially in winter. The CRCM6/GEM5 model
demonstrated some difficulty producing enough clouds to accurately
represent those at mid-level. Cloud fraction representation was
systematically better during winter than summer. The CRCM6/GEM5
generally performed well over the whole North American domain for the
four cloud categories and COSP2 was confirmed to help mitigate
discrepancies in variable definitions. These results contribute to a
better understanding of the CRCM6/GEM5 cloud representations and the use
of COSP2 with high-resolution models.