Research / Research Highlights

Land surface influences on vertical velocity spectra in a convective mixed layer

Submitter

Williams, Ian N — Iowa State University

Area of Research

Surface Properties

Journal Reference

Williams I and S Qiu 2022. "Long‐term observations of turbulence vertical velocity spectra in a convective mixed layer: Dependence on land‐surface forcing in the U.S. Southern Great Plains." Journal of Geophysical Research: Atmospheres, 127(24), e2022JD037137, 10.1029/2022JD037137.

Science

Cumulus clouds are coupled to the land surface, but the physical processes are not adequately understood. We used seven years of ARM Doppler lidar and surface observations to understand how surface processes affect updrafts relevant to cloud development.

Impact

The influence of the land surface on boundary-layer updrafts is scale dependent and occurs at larger scales than previously considered, with potentially greater impacts on boundary-layer cumulus clouds.

Summary

We found significant variability in vertical velocity at the largest scales of boundary-layer turbulence, indicating potential influence of organized boundary-layer circulations on updraft properties at the cloud base. An increase in friction velocity (wind stress) was correlated with larger integral scales (updraft widths) and a greater proportion of energy in the mesoscale regime. The role of wind stress suggests that updrafts are organized by shear instabilities, and implies that existing variance-based turbulence closures may not be adequate for capturing the effects of the land surface on cloud-base updrafts.