02/01/2013
Impact of Local Climate on Cloud Systems
Summary
Researchers took advantage of cloud system observations in two very different environments to study factors that influence tropical convective cloud system development. The Atmospheric Radiation Measurement (ARM) program conducted field studies in two different tropical locations—Darwin, Australia, and Niamey, Niger. Darwin is a tropical coastal site, while Niamey is an arid site fairly close to the Sahara desert. The researchers used radiosonde observations from ARM and other international agencies to initialize high-resolution model simulations and compared the resulting cloud fields to radar and satellite observations to determine whether the model was correctly capturing the cloud properties. The model was able to reproduce characteristics of the observed mesoscale convective systems (MCSs) in both locations. The African cloud systems had a scale of nearly 400 km, while the Australian systems were much smaller (approximately 100 km). Once satisfied with the model simulation quality, the researchers performed sensitivity studies to understand what environmental aspects led to cloud system variations at the two locations. The model experiments found that the Australian cloud systems had stronger convective updrafts, while the African clouds had stronger mesoscale ascent outside of the convective areas. Differences in vertical wind shear and larger amounts of dust aerosol at Niamey also contributed to the variations found in the two regions. The high-resolution model simulations enabled quantitative descriptions of water transport between the convective, stratiform, and anvil regions of the cloud systems and quantification of water sources and sinks from microphysical processes, providing information that can be used to help determine parameters in cloud parameterizations used in general circulation models (GCMs).
References
Zeng, X., W.-K. Tao, S. W. Powell, R. A. Houze, P. Ciesielski, N. Guy, H. Pierce, and T. Matsui. 2013. “A Comparison of the Water Budgets Between Clouds from AMMA and TWP-ICE,” Journal of the Atmospheric Sciences 70(2), 487–503. DOI: 10.1175/JAS-D-12-050.1.