Mexico Fires - May 1998
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National Aeronautics andSpace Administration Goddard Space Flight Center |
Many of the fires were started by farmers, who traditionally clear land
by burning fields. A severe drought, thought to be caused by the effects of
El Niņo, had dried out the typically moist area, making conditions particularly
ripe for wildfires.
Smoke and aerosol particles from large-scale biomass (trees and vegetation)
burning can rise high into the troposphere and be carried long distances by
wind currents. Smoke plumes from Mexico traveled as far north as Wisconsin
and the Dakotas, and as far east as Florida and out over the Gulf Stream.
Smoke and haze caused health alerts to be issued in Texas as residents suffered
scratchy throats and watering eyes and it even grounded aircraft at major
airports in Texas and Mexico.
The Effect of Aerosols on Climate
Aerosols have a two-fold cooling effect on climate. In a clear atmosphere,
they scatter and absorb incoming solar radiation, thereby reducing the amount
of sunlight that reaches the surface. Moreover, aerosols act as "seeds"
- called cloud condensation nuclei causing water vapor to condense and form
cloud droplets. When clouds form in the polluted atmosphere, the clouds' droplets
tend to be smaller and more numerous. Because polluted clouds are typically
comprised of more densely-packed droplets, they are more efficient at absorbing
and reflecting sunlight, again having a cooling effect on the surface.
Aerosols represent one of greatest areas of uncertainty regarding climate
change, both on global and regional scales. Scientists do not fully understand
the magnitude of their cooling influence on climate.
The Images
Sea-viewing Wide Field-of-View Sensor (SeaWiFS) true-color image of the
Southeastern United States and Gulf of Mexico on May 14, 1998. The image is
a combination of three visible wavelengths (412, 555, 670 nanometers) of SeaWiFS
calibrated data as observed by the spacecraft. This color composite highlights
vegetation and clouds. Heavy white areas are clouds and dense aerosols while
the lighter, softer white areas represent smoke and haze. Smoke and haze are
especially noticeable over the western half of the Gulf of Mexico and over
the states of Louisiana, Mississippi, Arkansas, and Missouri. The SeaWiFS
instrument consists of an optical scanner and an electronics module and is
carried by the OrbView-2 spacecraft in a polar orbit at an altitude of 705
km.
National Oceanic and Atmospheric Administration (NOAA) Geostationary Operational
Environmental Satellite (GOES)-8 false-color image of North America (visible
and infrared data) enhanced to show areas of smoke and aerosols. White and
gray areas are clouds; red and green areas represent high and low concentrations
of aerosols, respectively. GOES-8 was launched into a geosynchronous orbit,
which means it orbits the equator at a speed matching the Earth's rotation,
allowing it to hover continuously over one position on the surface, at an
altitude of 35,800 km.
Earth Probe Total Ozone Mapping Spectrometer (TOMS) detection of aerosols
from the fires in Mexico and Central America using the TOMS aerosol index
on May 14, 1998. The aerosol index is a measurement of the amount of ultraviolet
(UV) radiation-absorbing aerosols such as dust, smoke (sulfates), and other
pollution in the atmosphere. The index is (roughly) calculated by subtracting
the opacity of a "dirty" (smoke, dust, etc.) atmosphere from the
opacity of a "clean" atmosphere. Red and black areas indicate a
high percentage of UV-absorbing aerosols while the green areas are representative
of a low percentage of UV-absorbing aerosols. Earth Probe TOMS circles the
Earth in a polar orbit at an altitude of 740 km.
Additional information can be found on the World Wide Web at:
Global Fire Monitoring
http://modarch.gsfc.nasa.gov/fire_atlas
Related NASA Websites
NASA's Earth Science Enterprise
NASA's EOS Project Science Office
NASA's Earth Observatory
http://earthobservatory.nasa.gov
Images courtesy of NASA's EOS Terra (AM-1) Visualization Team, GOES, SeaWiFS,
and TOMS Project Science Offices.