The Indian Ocean Experiment (INDOEX) had as a primary objective
determining the radiative forcing due to anthropogenic aerosols over
climatologically significant space and time scales: the Indian Ocean during the
winter monsoon, January-March. During the winter monsoon, polluted, low-level
air from the Asian subcontinent blows over the Arabian Sea and Indian
Ocean. As part of INDOEX, aerosol optical depths were derived from Advanced
Very High Resolution Radiometer (AVHRR) data for the cloud-free ocean regions.
The AVHRR radiances were first calibrated using the interior zone of the Antarctic
and Greenland ice sheets, which proved to be radiometrically stable calibration
targets. Optical depths were derived by matching the observed radiances to
radiances calculated for a wide range of optical depths and viewing geometry.
Optical depths derived with the AVHRR were compared with those derived with
NASA's Aerosol Robotic Network (AERONET) CIMEL instrument at the Center
for Clouds, Chemistry, and Climate's Kaashidhoo Observatory, as well as with
other surface and shipboard observations taken in the INDOEX region. The
retrieved and surface-based optical depths agreed best for a new 2-channel, 2-
aerosol model scheme in which the AVHRR observations at O·64 and O·84 microns
were used to determine relative amounts of marine and polluted continental aerosol
and then the resulting aerosol mixture was used to derive the optical depths.
Broadband radiative transfer calculations for the mixture of marine and polluted
continental aerosols were combined with the 0·64 and 0·84-micron AVHRR
radiances to determine the radiative forcing due to aerosols in the INDOEX region.
Monthly composites of aerosol optical depth and top of the atmosphere, surface,
and atmospheric radiative forcing were derived from calibrated AVHRR radiances
for January-March 1996-2000. An inter-annual variability in the magnitude and
spatial extent of high value regions is noted for derived optical depths and radiative
forcing, with highest values reached in 1999, particularly in the Bay of Bengal
which during the IFP was covered by plumes from Indochina. Frequency
distributions of the optical depth for 1⁰ x 1⁰ latitude-longitude regions are well
represented by gamma distribution functions. The day-to-day and year-to-year
variability of the optical depth for such regions is correlated with the long term
average optical depth. Interannual variability of the monthly mean optical depths
for such regions is found to be as large as the day to day. / Graduation date: 2001
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28702 |
| Date | 02 February 2001 |
| Creators | Tahnk, William Richard |
| Contributors | Coakley, James A. Jr |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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