4 Summary and Discussion
This study examines the impact of radiative interactions on the spatial
organization of convection, the distribution of clouds and relative
humidity, and extreme daily precipitation events. We show that
suppressing radiative interactions does not alter the mean circulation
much but reduces the degree of convective aggregation. The reduction in
the degree of aggregation is associated with an increase in high cloud
coverage and relative humidity in the free troposphere and a decrease in
the boundary layer. These differing responses of cloud and humidity are
found to be sensitive to radiative interactions and, to some extent,
independent of variations in the degree of aggregation.
Additionally, a less aggerated state due to suppressed radiative
interactions is associated with a decrease in the frequency of extreme
precipitation events due to a reduction in the dynamic contribution,
i.e., a weakening of the strongest updrafts. At regional scales,
suppressing radiative interactions diminishes the horizontal gradient of
radiative cooling from dry to moist regions, weakening the upgradient
transport of energy and reducing the degree of aggregation. However, the
mean ITCZ width shows little difference with and without radiative
interactions.
While our results show that the impact of radiative interactions on the
degree of aggregation and extreme precipitation is not overwhelmed by
the presence of realistic SST gradients, it is worth mentioning that the
model response to suppressed radiative interactions shows considerable
spatial variability. Overall, stronger signals are found in the tropics
than those at mid to high latitudes. Signals over sea surfaces are also
more robust than those over land ones. These spatially heterogeneous
responses indicate that local environment may play a role in determining
the extent to which radiative interactions impact extreme weather
extremes and convective aggregation. In addition, our simulations are
performed with prescribed SSTs, which essentially excludes the possible
impact of changes in the degree of aggregation on SSTs. It remains
unclear whether and how changes in the degree of aggregation affect
SSTs, and if yes, how changes in SSTs would feedback onto interactions
between radiation and convection. Future studies may explore these
issues using fully coupled GCMs.