Cloud radiative forcing at the Atmospheric Radiation Measurement Program Climate Research Facility: 2. Vertical redistribution of radiant energy by clouds

Abstract

Documentation of the effects of clouds on the radiant energy balance of the surface and atmosphere represents a shortcoming in the set of observations that are needed to ascertain the validity of climate model simulations. While clouds are known to cool the climate system from top of atmosphere (TOA) radiation budget studies, the redistribution of energy between the surface and atmosphere and within the atmosphere by clouds has not been examined in detail with observations. Using data collected at the Atmospheric Radiation Measurement Program (ARM) Southern Great Plains (SGP) site, we use measurements of cloud occurrence and structure together with a scheme to characterize the cloud microphysical and radiative properties to estimate the uncertainty in our ability to calculate the radiative forcing and effect of clouds at the top of atmosphere, the surface and within the atmosphere. We find that overcast clouds during 2000 tended to have a small net influence on the atmosphere (6 W m−2 ± 3 W m−2 of heating) with net TOA and surface cooling (25 W m−2 ± 3 W m−2 and 32 ± 3 W m−2, respectively). These statistics mask a significant redistribution of radiant energy within the atmosphere by clouds where low overcast clouds resulted in strong atmospheric cooling (37 W m−2 ± 9 W m−2), and thin high clouds resulted in warming (21 W m−2 ± 6 W m−2) suggesting that accurate prediction of the phasing of these cloud types within meteorological features is important for capturing the essential feedbacks by clouds to the general circulation.