Scientific Colloquium
January 12, 2007
WILLIAM K. M. LAU
NASA GODDARD SPACE FLIGHT CENTER"
"Aerosols,
Clouds, Rainfall, Winds and Climate Change"
Aerosols from both
natural (dust and smoke) and man-made (industrial pollution) sources,
clouds and rainfall are parts of our everyday life. They are
present in the atmosphere in the form of suspended particles of varying
concentration and sizes. These particles constitute the
fundamental building blocks of the atmospheric water cycle, forming
nuclei for condensation of water vapor to clouds, and eventually to
rainfall. In the process, water vapor is converted into liquid or ice
form through deposition, collision, coalescence, and phase-change
processes, which release latent heat of condensation and modulate the
water and energy heat cycles of the earth system. This modulation
in turn changes the general circulation of the atmosphere, and alters
weather and climate patterns. I will discuss how the microphysics
of phase-change in the atmospheric water cycle may be a first responder
to climate change, i.e., changes in the way suspended particles in the
atmosphere interact with the water cycle in an increasing warm, and
polluted global environment. I will give examples of new findings from
NASA earth observing satellites and climate modeling that support this
thesis. These include observations of the changing characteristics in
tropical rainfall and clouds, possible effects of dust and black carbon
on the Asian monsoon water cycle, melting of mountain glacier, possible
dust impact on the recovery of the Sahel drought, and how Saharan dust
might have foiled all predictions of the hurricane season of
2006.