Wednesday, 26 July 2017
Kona Coast Ballroom (Crowne Plaza San Diego)
Cloud lines are often seen in satellite and radar imagery and are of many types such as long thin lines of small cumuli, shallow convective clouds, or deep convective elements on the leading or trailing edges. Convective initiation from cloud rolls associated with the cloud lines will be sensitive to atmospheric humidity in ways that need to be understood to represent convection in global models. We simulate multiple cases of cloud lines observed during January 2016 over northeastern Australia using the Weather Research and Forecasting (WRF) Model (version 3.7.1), initialized by and nudged to reanalysis data. The simulations were evaluated with satellite imagery, humidity observations from satellite (Megha-Tropiques), and radiosondes at 8 different sites. The current version of Megha-Tropiques appears to be too moist in the lowest retrieved layer by up to 30% over the dry continental interior, though mostly accurate to within ± 10% otherwise. Overall, WRF skilfully simulated convergence lines driven by sea breezes since large-scale circulation were properly resolved, however the associated roll clouds and convective elements of the cloud lines were not properly captured by the model. Unperturbed WRF simulations for the test case examined here were 10-20% too dry in the region where cloud lines were observed. Compensating for the bias in RH via the model initialization produced more realistic simulations of roll clouds and convection. This result highlights the importance of accurate observations of water vapor, especially in the lower troposphere, for properly constraining simulations of convective environments, as well as the value of satellite data in providing spatial coverage.
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