Boundary Layer Controls on the Shallow-to-Deep Cumulus Transition

Abstract

To improve the representation of convection in climate models we will conduct an observational study of the interactions between boundary-layer and cloud-layer processes. Specifically, we will examine how boundary-layer updrafts interact with cloud-layer stratification during the transition from shallow to deep convection in a continental environment. To do so, we will leverage long term boundary-layer and cloud-layer observations from the Atmospheric Radiation Measurement (ARM) Climate Research Facility Southern Great Plains (SGP) site. Key instruments at SGP include Doppler and Raman lidars, providing observations of vertical velocity and water vapor in the boundary layer, and the Ka-band zenith radar, which determines cloud depth and cloud boundaries. These data will then be contextualized with other collocated remote and in situ observations (e.g., AERI and radiosonde profiles) of the thermodynamic state of the lower troposphere.

The resulting multi-sensor analyses will provide an improved physical basis for testing and refining convective parameterizations, including those used in ACME, CAM, and WRF. In particular, we will examine whether mass-flux and PDF based closure assumptions adequately describe the observed co-variations in boundary-layer and cloud-layer processes during the shallow-to-deep cumulus transition. These analyses will then be leveraged to augment ongoing DOE efforts to refine the representation of convection in earth system and climate models. As such, our study will fill critical knowledge gaps in our fundamental understanding convective initiation as well as contribute to near-term improvements in model representations of convective processes.