The Spatial and Temporal Organization of Deep Convective Systems and Its
Impacts on the Production of Anvil Clouds
Abstract
A multi-threshold technique was used to objectively identify the
space-time structure of meso-scale convective systems in the warm pool
region using observations of high-resolution Himawari geostationary
satellites. Several thresholds of the IR brightness temperature were
used to capture the life cycles of cloud clusters with complex behaviors
(merging and breaking) and spatial organizations (inclusion,
aggregation). According to the inclusions between cloud clusters with
different thresholds, cloud clusters were characterized as simple
single-core or complex multi-core systems, more likely represented
isolated systems or aggregated/merged systems respectively. The mixed
depth multi-core clusters existed frequently, even for very cold
brightness temperatures (<230K) and more of them were
associated with the merging process compared to single core clusters.
Thus they were often a mixture of systems at different development
levels. A large amount of convective systems experience merging and
breaking during their lifetime. Merging and breaking processes were
found to result in unrealistic local life stage. These facts questioned
the use of any single threshold technique on determining the life cycle
of deep convective systems as well as that of their anvil clouds. When
the same development height was selected, the multi-core systems
systematically produced less warmer clouds around their cold cores than
that of single-core systems. Thus per the same cold core area the
muti-core systems tended to produce less total cloud coverage and weaker
reduction of the TOA OLR. These phenomena were consistent with previous
studies suggesting that aggregated convection might resulted in less
high cloud coverage and enhanced domain-averaged OLR. The documentation
and understanding about the cause of different organizations of cloud
clusters and their impacts on clouds and radiation are currently
lacking. If these phenomena and effects cannot be effectively documented
and stratified in observations, it will be misleading when applying
observations as a guide for diagnosing and improving models. This study
provided an observational reference to test if current models can
realistically reproduce observed organizations of deep convection along
with its associated anvil and cirri-form clouds.