ARM Data Improves Understanding of Shallow Cumulus Clouds over Land


Fair-weather shallow cumuli are often observed over land in the summer. They are small and short lived but cause a significant net radiative surface cooling. U.S. Department of Energy 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 cumulus. They found strong observational support for theories involving the increase of humidity in the first 1–2 kilometers above the surface leading to larger vertical development of shallow cumulus clouds. They also confirmed the effect of atmospheric thermodynamic variability and surface heat transport into the atmosphere in limiting cloud development. This study is among the first to comprehensively validate these theories over land and investigate the relationship between various meteorological conditions and the vertical development of shallow cumulus clouds using observational data. These results will improve convective cloud representation in global climate models, addressing their well-known problem with simulating the diurnal cycle of shallow cumulus over land.


Zhang, Y., and S. Klein. 2013. “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,” Journal of the Atmospheric Sciences 70(4), 1297–1315. DOI: 10.1175/JAS-D-12-0131.1.