Characterization of
Regional/Global Aerosol Distributions Using the Assimilation Approach
Aerosols are relatively
short-lived in the atmosphere, with an average residence time of a few days in the
lower troposphere, and are heterogeneous in space and time. It remains
difficult to characterize the large spatial and temporal variations of aerosol
properties, and so integrated research
is required with 
multiple platforms and techniques
(e.g., ground-based networks, satellite remote sensing, computer modeling). The
newly-launched NASA EOS satellites Terra
and Aqua
carry a sensor designed specifically for aerosol remote sensing, namely the MODerate resolution
Imaging Spectroradiometer (MODIS), a
36-band well-calibrated spectroradiometer with
spatial resolution of 250-1000m. This provides an unprecedented opportunity of
study aerosols from space with high accuracy and on a nearly global scale.
However, difficulty with highly reflective arid and snow-covered lands
introduces significant gaps in global or regional coverage (e.g., Saharan
deserts, Mid-east deserts and central Asian deserts) that must be filled with
other means. In collaboration with scientists at GSFC/NASA,
we integrated MODIS retrievals and Georgia
Tech/Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model simulations by using assimilation
approach [Yu et al., 2003],
obtaining an annual cycle
(11/2000-10/2001) of global distributions of aerosol optical depth at 550 nm (panel to the left).
Measurements from AErosol
RObotic Network (AERONET) and the Advanced
Very High Resolution Radiometer (AVHRR) 2-channel retrievals were used for
evaluation and comparisons.
The
work under way is to incorporate the Total
Ozone Mapping Spectrometer (TOMS) aerosol optical depth into the assimilation
and derive spectral variations of optical depth in a self-consistent manner.
The TOMS retrieves aerosols over land by taking advantage of the UV technique,
i.e., small reflection in the UV for most land surfaces (including desert, see left panel). It hence can be used to constrain model
simulations and fill MODIS gaps (right panel) over
deserts.
Aerosol optical depth over
