Influence of cloud-radiation interaction
on simulating tropical intraseasonal oscillation with an atmospheric
general circulation model
Lee, M.-I., I.-S. Kang, J.-K. Kim, and B.E. Mapes
JGR, 106, 14219-14233.
ABSTRACT
The influence of cloud-radiation interaction in simulating the
tropical intraseasonal oscillation (ISO) is examined using an aqua
planet general circulation model (GCM). Two types of simulation are
conducted: one with prescribed zonal mean radiation and the other with
fully interactive clouds and radiation. In contrast to the fixed
radiation case, where the ISO is simulated reasonably well, the
cloud-radiation interaction significantly contaminates the eastward
propagation of the ISO by producing small-scale disturbances moving
westward with the easterly basic winds. The small-scale disturbances
are persistently excited by a strong positive feedback through
interaction between cumulus-anvil clouds and radiation. The longwave
interaction is shown to play a bigger role in contaminating the ISO
than the shortwave interaction does. The anvil clouds reduce the
longwave cooling significantly in the lower troposphere while
releasing latent heating in the upper troposphere. To moderate the
strong cloud-radiation feedback, the large-scale condensation scheme
in the GCM is modified by reducing the autoconversion timescale,
needed for cloud condensates to grow up to rain drops. In addition,
upper air ice cloud contents are reduced to change the cloud
albedo. These modifications make a more realistic simulation of the
ISO similar to the observed.