A Comparison of Thermodynamic-Convection Coupling in Observations, Reanalysis, and Models

Abstract:

Variations of moisture and temperature, both in the boundary layer and the lower free troposphere, have been shown to greatly influence tropical convection. Convection, in turn, drives systematic changes in the thermodynamic environment, such that both evolve in tandem. Here we examine the co-evolution of convection, moisture, and temperature using observations, reanalysis, and models.

TRMM precipitation and 100,000+ tropical soundings from the Integrated Global Radiosonde Archive (IGRA) were used to characterize the co-evolution of precipitation and its thermodynamic environment. A comparison of IGRA soundings co-located with ERA5, ERA-interim, and JRA55 reanalyses indicate that reanalysis products systematically underestimate the magnitude of moisture and temperature variations within the boundary layer. When using reanalysis thermodynamic fields, these systematic discrepancies cause boundary layer moisture and temperature to appear much more influential in determining the strength of convection than is suggested by IGRA soundings. Observational benchmarks and process-level diagnostics are developed to help guide model development. When applied to several models, these diagnostics identify shortcomings in both how model convection responds to the thermodynamic environment, as well as how model convection causes the thermodynamic environment to evolve.