Spatial and temporal variations in the atmospheric aerosol optical depth at the ARM CART Site Page: 1 of 16
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ORNL/CP-96847
(o+F - Y63-
Spatial and Temporal Variations in the Atmospheric Aerosol
Optical Depth at the ARM CART Site
98-RAC.03P (A143) -
Terra M. Nash and Meng-Dawn Cheng*
Oak Ridge National Laboratory, Environmental Sciences Division, P. O. Box )8; I 38,
Oak Ridge, TN, USA.
ABSTRACT
In an effort to better characterize the inputs to radiative transfer models and research-grade global
climate simulation models (GCMs) the columnar aerosol loading, measured as the aerosol optical
depth (AOD), has been computed for five facilities within the Atmospheric Radiation
Measurement (ARM) Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) Site.
Characterization of the AOD reported here show clear evidence that the spatial and temporal
gradient exists at a much finer linear scale than those of the CART site. The annual variations of
median AOD are on the order of 0.30 at all five facilities. The Spearman correlation and varimax-
rotated PCA indicated the AOD values vary consistently across the CART site. The Northwest
corner facility (EF-1) was the single facility that behaved differently from the rest. This sub-GCM
grid variation can not be ignored if the model it to be used to accurately predict future climate
change.
INTRODUCTION
The issue of global warming had recently held the attention of world leaders and scientists with
the signing of the Kyoto Accord in December of 1997. In the accord many nations agreed to
reduce anthorpogenic emissions of six "greenhouse gases" to the atmosphere because of global
warming predictions by Global Climate Models (GCMs). GCMs divide the Earth's surface into
large grids for calculations. GCMs assume that a grid or sub-grid process is homogenous, and one
average number is used by the models to represent the process state. Many of the input
parameters to the GCMs, like cloud cover, ozone concentration, water vapor, and aerosol
loading, vary on a scale that is much smaller than the current grids. More complex models,
working on a more detailed spatial scale, are needed to better predict the long-term changes of the
global climate'. While researches are needed to improve these models, accurate measurements
are imperative to the models. The Atmospheric Radiation Measurement (ARM) program,
sponsored by the Department of Energy (DOE), is committed to collect, document, and archive
data critical to this research over a long time period (20 years).
Aerosols play a critical role in affecting cloud formation and altering atmospheric radiative
transfer2. These are two key processes, among others, affecting surface temperature and
precipitation. The aerosol optical depth (AOD) has been shown to be one of the most important
parameters in many radiative transfer models. Literature3 indicates variation of 13.5 W/m2 in the
direct-normal solar irradiance would result from a change in the AOD value of 0.01. The
sensitivity of atmosphere radiative calculations to other model parameters such as precipitable
water and ozone was er by an order of magnitude when compared to aerosols
under clear-sky
und er cl"The submitted manuscript has been authorized by a
contractor of the U.S. Government under contract No.
DE-AC05-960R22464. Accordingly, the U.S.
DISTRIBUTION OF THIS DOCUMENT iS tJN!MED Government retains a non-exclusive, royalty-free
license to publish or reproduce the published form of
this contribution, or allow others to do so, for U.S.
Government purposes."
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Nash, T.M. & Cheng, M.D. Spatial and temporal variations in the atmospheric aerosol optical depth at the ARM CART Site, report, February 1, 1998; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc711006/m1/1/: accessed March 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.