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The balanced radiative effect of tropical anvil clouds

Hartmann, D., and S. E. Berry (2017), The balanced radiative effect of tropical anvil clouds, J. Geophys. Res., 122, doi:10.1002/2017JD026460.
Abstract: 

Coincident instantaneous broadband radiation budget measurements from Clouds and Earth’s Radiant Energy System and cloud vertical structure information from CloudSat-Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations radar-lidar observations are combined to study the relationship of cloud vertical structure to top-of-atmosphere energy balance fluctuations. Varying optical and physical thickness of high ice clouds produces most of the covariation between albedo and outgoing longwave radiation in regions of tropical convection. Rainy cores of tropical convective clouds have a negative impact on the radiation balance, while nonprecipitating anvil clouds have a positive effect. The effect of anvil clouds on the radiative heating profile is to warm near cloud base and cool near cloud top, and to reduce the radiative cooling rate in the clear air below the cloud. The cooling rate in the clear air below the anvil is reduced to small values for moderately thick anvils, and the driving of instability in the anvil itself also saturates for relatively thin clouds. It is hypothesized that the dependence of radiative heating on cloud thickness may be important in driving the distribution of tropical cloud structures toward one that produces net neutrality of the cloud radiative effect at the top-of-the-atmosphere, as is found in regions of deep convection over ocean areas with high and relatively uniform surface temperatures. This idea is tested with a single-column model, which indicates that cloud-radiation interactions affect anvil cloud properties, encouraging further investigation of the hypothesis. Plain Language Summary Satellite data are used to show that tropical convective clouds have a small net effect on the energy balance because the cooling effect of thick tropical clouds is offset by the warming effect of thin upper level clouds that are connected to the thick clouds. Why these two types of clouds cancel each other out nearly exactly in the warm regions of the tropics is unknown. The effect of radiative transfer on the anvil clouds seems to be a possible contributor to the abundance of thin high clouds that give the positive influences on the radiation budget at the top of the atmosphere.

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Research Program: 
Interdisciplinary Science Program (IDS)
Mission: 
Aqua
Terra