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Sensitivity of climate simulations to radiative effects of tropical anvil structure

  • Author(s): Zender, Charles S.
  • Kiehl, J. T.
  • et al.
Abstract

Climate sensitivity to the representation of tropical anvil is investigated in a version of the National Center for Atmospheric Research Community Climate Model. Common features of tropical anvil generation and structure, consistent with observations and cloud resolving models, are incorporated into a simple prognostic anvil parameterization. These features include anvil convective origin, vertical profile, phase, areal extent, and life span. Two numerical climate integrations are forced by 1985–1989 sea surface temperature (SST): the control, with simple diagnostic anvil, and the experiment, which simulates tropical anvil structure prognostically. The prognostic anvil formulation enhances ice and reduces liquid in the tropics. Increase in hydrometeor size associated with anvil weakens cloud radiative extinction per unit mass by factors of 1–3. The weaker mass extinction efficiency approximately balances enhanced ice amount so that anvil ice mass quadruples without biasing the mean radiative energy balance but significantly alters the vertical distribution of radiative effects. Enhanced anvil perturbs the tropical upper troposphere temperature structure more strongly in winter, when the column is clearer and anvil radiatively heats the troposphere above 200 mbar. In the summer tropics, enhanced anvil reduces radiative cooling up to 200 mbar and enhances cooling above that. The prognostic anvil formulation improves longwave cloud radiative response to SST cooling but worsens response to warming >2°C. The net response of convection is a shift toward the winter hemisphere in solstice months. These changes lead to a significant response in the extratropical height field in January. These results emphasize the importance of representing tropical anvil structure in climate simulations.

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