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Diurnal differences in tropical maritime anvil cloud evolution
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  • Blaž Gasparini,
  • Adam B. Sokol,
  • Casey J. Wall,
  • Dennis L. Hartmann,
  • Peter N. Blossey
Blaž Gasparini
University of Vienna, University of Vienna

Corresponding Author:[email protected]

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Adam B. Sokol
University of Washington, University of Washington
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Casey J. Wall
Scripps Institution of Oceanography, Scripps Institution of Oceanography
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Dennis L. Hartmann
University of Washington, University of Washington
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Peter N. Blossey
University of Washington, University of Washington
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Satellite observations of tropical maritime convection indicate an afternoon maximum in anvil cloud fraction that cannot be explained by the diurnal cycle of deep convection peaking at night. We use idealized cloud-resolving model simulations of single anvil cloud evolution pathways, initialized at different times of the day, to show that tropical anvil clouds formed during the day are more widespread and longer lasting than those formed at night. This diurnal difference is caused by shortwave radiative heating, which lofts and spreads anvil clouds via a mesoscale circulation that is largely absent at night, when a different, longwave-driven circulation dominates. The nighttime circulation entrains dry environmental air that erodes cloud top and shortens anvil lifetime. Increased ice nucleation in more turbulent nighttime conditions supported by the longwave cloud top cooling and cloud base heating dipole cannot overcompensate for the effect of diurnal shortwave radiative heating. Radiative-convective equilibrium simulations with a realistic diurnal cycle of insolation confirm the crucial role of shortwave heating in lofting and sustaining anvil clouds. The shortwave-driven mesoscale ascent leads to daytime anvils with larger ice crystal size, number concentration, and water content at cloud top than their nighttime counterparts.
01 Mar 2022Published in Journal of Climate volume 35 issue 5 on pages 1655-1677. 10.1175/JCLI-D-21-0211.1