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.