Defense Announcement: Morgan Stessman

Wednesday, May 5, 2021 9:30am

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Using CloudSat and MERRA-2 to Examine the Characteristics and Variability of Individual Cloud Types Associated with Intertropical Convergence Zone Extremes

Diabatic heating is often inaccurately represented in weather forecast and global climate models (GCMs). These problems are compounded at low latitudes where diabatic heating strongly affects the large-scale circulation and other tropical and subtropical weather phenomenon. Previous work has primarily focused on the diabatic heating from precipitating systems, even though non-precipitating systems also play a role in the redistribution of late heat or modifying radiative and sensible heat fluxes. One of the largest sources of latent heat in the tropics is the Intertropical Convergence Zone (ITCZ), which is the intense band of clouds and precipitation resulting from the convergence of the surface trade winds in the tropics. The seasonal migration of the ITCZ has been well studied and multiple dynamical theories can explain this behavior. Changes to the ITCZ width, however, are less understood despite being of equal importance to regional water budgets and the expansion of dry zones in the tropics and subtropics.

This study uses orbital data from CloudSat’s Cloud Profiling Radar (CPR) to create a gridded climatology of cloud and precipitation characteristics for individual cloud types. CloudSat orbital data is spatially and temporally matched to sub-daily reanalysis temperature tendency data to create conditional average profiles of diabatic heating and its subterms for each of the cloud types at the specific heights, locations, and times they occur. In addition to creating cloud climatologies and conditional heating profiles, this study examines potential links between changes in ITCZ width and the properties of individual low-latitude cloud types by matching the ITCZ location database from Wodzicki and Rapp (2016) with monthly CloudSat anomalies. Deep convective clouds, which have the strongest overall latent heating and highest conditional precipitation rates, experience positive frequency of occurrence and geometric thickness anomalies when the ITCZ is wide. Deep convection also shows a decrease in conditional precipitation rates when the ITCZ is wide, which may be related to differences in ITCZ core and flank precipitation. Through bettering our understanding of the properties of individual cloud type characteristics and their relationship with changes in ITCZ width, we increase the potential to evaluate theories such as the shallow cumulus moisture throttle of Neggers et al. (2007) with satellite observations.

  • Dave Gnojek

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