Investigating the Causes and Impacts of Convective Organization in a
High Resolution Atmospheric GCM
Abstract
A ~ 50 km resolution atmospheric general circulation
model (GCM) is used to investigate the impact of radiative interactions
on spatial organization of convection, the model’s mean state, and
extreme precipitation events in the presence of realistic boundary
conditions. Mechanism-denial experiments are performed in which
synoptic-scale feedbacks between radiation and dynamics are suppressed
by overwriting the model-generated atmospheric radiative cooling rates
with its monthly-varying climatological values. When synoptic-scale
radiative interactions are disabled, the annual mean circulation and
precipitation remain almost unchanged, however tropical convection
becomes less aggregated, with an increase in cloud fraction and relative
humidity in the free troposphere but a decrease in both variables in the
boundary layer. Changes in cloud fraction and relative humidity in the
boundary layer exhibit more sensitivity to the presence of radiative
interactions than variations in the degree of aggregation. The less
aggregated state is associated with a decrease in the frequency of
extreme precipitation events, coincident with a decrease in the
dynamical contribution to the magnitude of extreme precipitation. At
regional scales, the spatial contrast in radiative cooling between dry
and moist regions diminishes when radiative interactions are suppressed,
reducing the upgradient transport of energy, degree of aggregation and
frequency of extreme precipitation events. However, the mean width of
the tropical rain belt remains almost unaffected when radiative
interactions are disabled. These results offer insights into how
radiation-circulation coupling affects the spatial organization of
convection, distributions of clouds and humidity, and weather extremes.