Aerosol effects on atmospheric radiation are a leading source of
uncertainty in predicting future climate. TARFOX was designed to reduce this
uncertainty by measuring and analyzing aerosol properties and effects in the
U.S. eastern seaboard, where one of the world's major plumes of industrial haze
moves from the continent over the Atlantic Ocean.
The TARFOX Intensive Field Campaign was conducted July 10-31, 1996. It
included coordinated measurements from four satellites (GOES-8, NOAA-14, ERS-2,
LANDSAT), four aircraft (ER-2, C-130, C-131A, and a modified Cessna), land
sites, and ships. A variety of aerosol conditions was sampled, ranging from
relatively clean behind frontal passages to moderately polluted with aerosol
optical depths exceeding 0.5 at mid-visible wavelengths. Gradients of aerosol
optical thickness were sampled to aid in isolating aerosol effects from other
radiative effects and to more tightly constrain closure tests, including those
of satellite retrievals. Early results from TARFOX include demonstration of the
unexpected importance of carbonaceous compounds and water condensed on aerosol
in the US mid-Atlantic haze plume, chemical apportionment of the aerosol
optical depth, measurements of the downward component of aerosol radiative
forcing, and agreement between forcing measurements and calculations. A wide
variety of closure studies is currently in progress.
Aerosol particles can change the Earth's radiation budget both directly by
scattering and absorption and indirectly by affecting cloud properties.
Changing the net flux of radiation above or within the atmosphere changes the
energy available for driving climatic processes. Hence, such a net flux change
is termed a radiative forcing of climate. Negative forcings tend to cool the
climate, and positive forcings tend to warm it. Current estimates of the
global, annually-averaged, direct radiative forcing by anthropogenic aerosols
(e.g., sulfates, soots, mineral dust, biomass smokes) range from about -0.3 to
-1.0 W m-2, with an uncertainty factor of about two. Analogous, but
even less certain, estimates for the indirect effect are 0 to -1.5 W
m-2. These values are comparable in magnitude, but opposite in
sign, to the current estimates of +2.1 to +2.8 W m-2 for the forcing
caused by increases in greenhouse gases over the past century.
Because of the great spatial variability in aerosol concentrations that
results from their short lifetime, there are many regions - principally over
and downwind of major source areas - where the best estimates of aerosol
negative forcing exceed the greenhouse positive forcing. Some studies show that
aerosol effects appear to be present in global and regional twentieth-century
temperature records, and that inclusion of aerosol effects in numerical models
improves agreement with observed temperature patterns in both time (decadal and
diurnal) and space. Although these studies suggest that anthropogenic aerosols
can play an important role in determining current and future climates, their
results are far from conclusive. Major questions remain about the realism with
which models represent the great diversity of actual aerosol properties,
processes, and radiative effects. Error analyses show that the uncertainty in
the aerosol radiative forcing is unacceptably large - larger, in fact, than the
uncertainty in climate forcing by all greenhouse gases released over the past
century.
As a result of both the potential importance of aerosols and the large
uncertainties in their radiative effects, the International Global Atmospheric
Chemistry (IGAC) Project has established a Focus on Atmospheric Aerosols (FAA)
and endorsed a series of aerosol field campaigns. TARFOX is the second in the
IGAC/FAA series. TARFOX was designed to reduce uncertainties by measuring and
analyzing a wide range of aerosol properties and effects in the US eastern
seaboard. This is the region where one of the world's major plumes of
industrial haze moves from the continent over the Atlantic Ocean (see Section
3).
The overall goal of TARFOX is to reduce uncertainties in the effects of
aerosols on climate by determining the direct radiative impacts, as well as the
chemical, physical, and optical properties, of the aerosols carried over the
western Atlantic Ocean from the United States. Subsidiary objectives of TARFOX
are to:
Perform a variety of closure studies by using overdetermined data sets
to test the mutual consistency of measurements and calculations of a wide range
of aerosol properties and effects.
Use the results of the closure studies to assess and reduce
uncertainties in estimates of aerosol radiative forcing, as well as to guide
future field programs on this subject.
An important component of the closure studies is tests and improvements of
algorithms that retrieve aerosol properties and effects from satellite and
aircraft radiometers. The resulting validated algorithms will permit extensions
of the TARFOX results to other times and locations that have aerosol properties
similar to those of the TARFOX Intensive Field Campaign (IFC).
Langley DAAC User and Data Services Office
NASA Langley Research Center
Mail Stop 157D
Hampton, Virginia 23681-2199
USA
Telephone: (757) 864-8656
FAX: (757) 864-8807
E-mail: larc@eos.nasa.gov
Contact Information:
Langley DAAC User and Data Services Office
NASA Langley Research Center
Mail Stop 157D
Hampton, Virginia 23681-2199
USA
Telephone: (757) 864-8656
FAX: (757) 864-8807
E-mail: larc@eos.nasa.gov
Philip B. Russell
NASA Ames Research Center
Mail Stop 245-5
Moffett Field, CA 94035-1000
USA
Telephone: 415-604-5404
FAX: 415-604-3625
E-mail: prussell@mail.arc.nasa.gov
Philip B. Russell
NASA Ames Research Center
Mail Stop 245-5
Moffett Field, CA 94035-1000
USA
Telephone: 415-604-5404
FAX: 415-604-3625
E-mail: prussell@mail.arc.nasa.gov
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