Fair-Weather Clouds, Cooling, and Humidity

ARM data offer insights into shallow cumulus clouds over land.

Image courtesy of Atmospheric Radiation Measurement (ARM) Climate Research Facility
Data from the ARM Climate Research Facility’s Oklahoma site are advancing the understanding of continental cumulus clouds, which will improve their representation in global climate models.

The Science

Fair-weather shallow cumulus clouds often are observed over land in the summer. Although small and short lived, they cause a significant net radiative cooling of the surface. Department of Energy (DOE) scientists used long-term comprehensive observations from the Atmospheric Radiation Measurement (ARM) program’s Oklahoma site to systematically study factors controlling the vertical extent of continental shallow cumuli.

The Impact

These results will improve the representation of convective clouds in global climate models, addressing well-known challenges with simulating the daily cycle of shallow cumulus clouds over land.


Researchers found strong observational support for theories involving the increase of humidity in the first 1 to 2 km above the surface leading to larger vertical development of shallow cumulus clouds. They also confirmed that atmospheric thermodynamic variability and surface heat transport into the atmosphere limit the development of these clouds. This study is among the first to use observational data to comprehensively validate these theories over land and to investigate the relationship between various meteorological conditions and the vertical development of shallow cumulus clouds.


Yunyan Zhang
Atmospheric, Earth, and Energy Division, Lawrence Livermore National Laboratory


This study used data from the DOE ARM Climate Research Facility’s Southern Great Plains site and from the Oklahoma Mesonet. The work was supported primarily by the Atmospheric System Research program of the Office of Biological and Environmental Research within DOE’s Office of Science.


Zhang, Y., and Klein, S. “Factors controlling the vertical extent of fair-weather shallow cumulus clouds over land: Investigation of diurnal-cycle observations collected at the ARM Southern Great Plains site.”  J. Atmos. Sc. 70 (4), 1297–1315 (2013). [DOI: 10.1175/JAS-D-12-0131.1]

Highlight Categories

Program: BER , CESD

Performer: DOE Laboratory , SC User Facilities , BER User Facilities , ARM