Thermodynamic and radiative structure of stratocumulus-topped boundary layer

 

Authors

Virendra Prakash Ghate — Argonne National Laboratory
Mark A. Miller — Rutgers University
Bruce A. Albrecht — University of Miami

Category

Cloud Properties

Description

Boundary-layer stratocumulus clouds cool the surface underneath them by reflecting greater incoming shortwave radiation compared to the underneath surface, while emitting longwave radiation comparable to the underneath surface. The turbulence within a stratocumulus-topped boundary layer is thought to be maintained primarily through the cloud-top radiative cooling. Since the same parameterization is used in global climate models (GCM) to represent stratocumulus clouds and their linkage to the boundary-layer turbulence both over land and over the oceans, it is important to highlight the similarities and the differences between the two.

In this study, we have analyzed the thermodynamic and radiative structure of stratocumulus-topped boundary layer using 166 soundings launched at the Southern Great Plains (SGP) site, 202 soundings launched during the ARM Mobile Facility (AMF)’s deployment at the island of Graciosa, Azores, and 158 soundings launched during cruises conducted in the South-East Pacific region. In addition to the general thermodynamic properties like Convective Available Potential Energy (CAPE), Convective Inhibition (CIN), inversion strength, etc., the associated cloud macro-physical properties like cloud boundaries, liquid water path, and surface turbulent fluxes are also quantified. The associated radiative fluxes and radiative heating rates were estimated using the Rapid Radiative Transfer Model (RRTM) at a 20-meter resolution within the boundary layer and at a 500-meter resolution above that. Profiles of thermodynamic and radiative properties will be presented using a height scale normalized by the inversion base height. The soundings will be further classified into coupled (well-mixed) and decoupled soundings using the difference between the cloud base height and lifting condensation level (LCL). The differences between the structure of coupled and decoupled boundary layer will be quantified, and an attempt will be made to explore the causes of these differences.