SCIENCE FOCUS: ASIAN DUST
SeaWiFS Observes Transport of Asian Dust over the Pacific Ocean
These SeaWiFS images show the development of a large dust storm in China and its interaction with a meteorological system that carried the dust far out into the Pacific Ocean. In the first image, from April 16, 1998, the bright yellowish-brown cloud near the coast is the center of the storm, being pushed by a frontal system. In the subsequent images from April 20-24, the atmospheric circulation around a low-pressure system entrains the dust from the storm and carries it over the north Pacific Ocean. On April 25, dust from this event reached the west coast of North America (image at bottom).
Correction, June 2002: The sequence of events in 1998 was chaotic. Two large dust storms occurred only a few days apart. The smaller of the two storms is seen in the April 16 image above. The larger storm appeared on April 19, and it is the dust from this storm that was carried across the Pacific Ocean.
Washington University in St. Louis is hosting a virtual workgroup to analyze the propagation of this Asian dust event. Their site contains additional analysis and other images of this event.
The paper entitled "The Asian Dust Events of April 1998" by Husar and 28 co-authors (Journal of Geophysical Research - Atmospheres, 106 (D16), 18317-18330, August 27, 2001) discusses these events. The virtual workshop Web site above has a version of this paper. (Our thanks to Rynda Hudman of Harvard University for the correction and reference information.)
|global area coverage
Dust from large deserts that is transported in this manner can be a vital nutrient source for both the oceans and terrestrial ecosystems. Iron in the minerals composing this desert dust will be a vital nutrient in oceanic regions that are deficient in iron. Furthermore, research has shown that the canopy (top layers) of much of the Central and South America rain forest derives much of its nutrient supply from dust that is transported over the Atlantic from the Sahara Desert in northern Africa. Saharan dust occasionally reaches the state of Florida, causing a characteristic high-altitude haziness that obscures the Sun.
Research performed during the Asian Dust Input to the Oceanic System (ADIOS) project showed that dust particles from China's Gobi Desert were transported all the way to Hawaii. (The hemispheric image at right shows the dust just north of Hawaii on April 23, 1998) Some of these dust particles were "giant" particles, much larger than standard models of dust transport indicated could be carried that far. Furthermore, as the dust settled into the waters around Hawaii, the primary productivity of the plankton in the water column increased, just as predicted by John Martin's "iron fertilization" hypothesis. This research took place in the mid-1980's, before ocean fertilization experiments off the Galapagos Islands, providing additional evidence that Martin's idea was correct.
Interestingly, during colder periods in Earth's climate history, desert areas appear to get larger. During these periods, dust from the deserts was likely transported to the oceans, where it augmented photosynthesis, which removed additional carbon dioxide from the atmosphere. In this manner, the global "thermostat" of carbon dioxide in the atmosphere was maintained at a low level, prolonging the cool conditions. Other climatic effects must come into play so that increasing global temperatures can override this feedback mechanism of the global climate. In fact, due to this connection, John Martin suggested that with enough iron added to the oceans, a new "Ice Age" could be created. Though that level of global climate control is still beyond human capabilities, the interaction of land and ocean in moderating global climate was well-illustrated by his statement.
April 20, 1998
April 21, 1998
April 22, 1998
April 23, 1998
April 24, 1998
SeaWiFS image of the west coast of North America on April 25, showing the arrival of airborne dust from China. The dust is visible in the clouds at the center of the left edge of the image, and as streaks of light brown haze over Cape Mendocino on the California coast.
SeaWiFS images produced by Norman Kuring, SeaWiFS Project, NASA GSFC. Page design by Robert Simmon, Research and Professional Services. Accompanying text by James Acker, SSAI.
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