Atmosphere Ocean Science Colloquium

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The Balanced Radiative Effect of Tropical Anvil Clouds

Speaker: Dennis Hartmann, University of Washington

Location: Warren Weaver Hall 1302

Date: Wednesday, April 26, 2017, 3:30 p.m.

Synopsis:

Coincident instananteous broadband radiation budget measurements from CERES and cloud vertical structure information from CloudSat-CALIPSO 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 produce most of the co-variation 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 non-precipitating 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.