AIRS observes volcanic ash and desert dust
AIRS reveals persistent release of ash from Puyehue volcano, and dust from Atacama desert
AIRS false-color image of Puyehue, December 17, 2011
1. THE CASE
Icelandic volcano eruptions received generous attention in the news over the past two years. However, at any time on the surface of the Earth there are tens of other erupting volcanoes. Depending on the definition of "active" and "volcano", the number could rise into the hundreds. If "active" implies a pyroclastic cone releasing some material, the Puyehue volcano, in the Chilean Andes, will certainly make the list.
Puyehue (or, Puyehue-Cordón Caulle complex) is part of the Southern Volcanic Zone, which by itself is part of the great Andean Volcanic Belt. Puyehue manifested regular eruptions in the past century, and in June 2011 it awakened again with a spectacular eruption. Readers can find many online photos that fully deserve the time spent to contemplate (from a distance) the effects of this eruption. Not to be outdone in the image gallery department, NASA’s MODIS instrument on the Aqua satellite recorded this image on June 5, 2011.
While not as majestic as in June, Puyehue is still active at this very moment in December, 2011, releasing large amounts of volcanic ash. They are not easily seen, but by using appropriate infrared bands and retrieval techniques, volcanic ash can be detected, even at night, by satellites in space. The Atmospheric Infrared Sensor (AIRS) on board NASA’s Aqua satellite, and the AIRS Science Team, have made this possible (DeSouza-Machado et al., 2010).
Figure 1. AIRS false-color image of the ash plume
released by the Puyehue-Cordón Caulle volcano in Chile,
December 17, 2011. Click image to view full-size.
The AIRS false-color visible image in Figure 1 gives an impression of the size of the ash plume, enclosed in the ellipse in the figure, leeward from the volcano, on December 17, 2011. The prevailing winds aloft are apparently driving the ash cloud eastward.
Puyehue is interesting for at least a couple of reasons. On the one hand, its cone is located at 2236 meters (7336 feet) elevation, and meridionally it is in proximity to the Southern Hemisphere's Polar Jet stream. Thus, the volcano can easily eject dangerous ash to aircraft cruise altitudes, and disperse it over large areas. Thin layers of ash particles can easily go undetected by simple visual inspection of the skies – most certainly so at night.
On the other hand, the proximity of Puyehue-Cordón Caulle to the Atacama Desert to the north makes it possible for ashes from the volcano and dust from the desert to mix. This may impact the accuracy of estimates of solar light extinction in the atmosphere, which is of ultimate importance to the accurate estimation of the heat balance of our planet.
2. THE AIRS DUST SCORE
The animation in Figure 2 demonstrates how the AIRS “Dust Score” reveals the presence of volcanic ash and desert dust during the 10-day period of December 13-22, 2011.
Winds at 700 mb (~9500 ft) are taken from the NASA’s Global Modeling and Assimilation Office GEOS-5 model, and are overlain as vectors that describe the air flow aloft. The “+” symbol indicates the location of the Puyehue volcano. Shades represent dust scores greater than 360, which is indicative of dust particles, during the day and night. Every day-frame in the animation shows an average from the day- and night-pass of AIRS and the average wind field for that day.
It is apparent in the lower portion of the frames of the animation that the Polar Jet has an overwhelming impact on the advection of the volcanic ash plume. While it is primarily transported eastward, the plume advection can follow more complicated paths. For example, on December 14, a combination of low pressure (clockwise circulation) and high pressure (counter clockwise circulation) states aloft was very likely pushing portions of volcanic ashes north, into the Atacama desert.
Figure 2. Animation of AIRS Dust Score (shades), and GEOS-5 winds (vectors) at 700 mb, for the period
December 13-22, 2011. Click image to view full-size.
On the other hand, the December 17-18 period was characterized by northerly winds over the Atacama Desert, which probably lifted large amounts of dust that consequently mixed with the volcanic ash emissions.
Figure 3 demonstrates the cumulative effect of the Atacama Desert dust and Puyehue volcano ash loads to the atmosphere during the 10-day period of December 13-22, 2011.
Most of Chile, and large portions of Argentina, are clearly affected by a mixture of ashes and dust, even though the Puyehue-Cordón Caulle eruption is not at its peak eruptive activity.
In the last frame of the Figure 2 animation (December 22), and in Figure 3, the AIRS Dust Score reveals that portions of the desert dust or volcanic materials – or both – riding on the crest of a jet stream wave, reached as far as 2100 km (1300 mi) east from the volcano, well into the Atlantic Ocean.
In summary, AIRS delivers a wealth of valuable information regarding atmospheric aerosols. The AIRS Dust Score alone can improve our understanding of aerosol sources, types, and dispersion. This topic has considerable scientific significance because of the current level of uncertainty in estimates of the aerosol "radiative forcing" - i.e. their impact on the heat balance on our planet.
Figure 3. AIRS Dust Score larger than 360, averaged
for the period December 13-22, 2011. Click image
to view full-size.
References and Acknowledgments
- DeSouza-Machado, S. G., Strow, L. L., Imbiriba, B., McCann, K., Hoff, R. M., Hannon, S. E., Martins, J. V., Tanre´ , D., Deuze´ , J. L., Ducos, F., and Torres, O.: Infrared retrievals of dust using AIRS: Comparisons of optical depths and heights derived for a North African dust storm to other collocated EOS A-Train and surface observations, J. Geophys. Res., 115, D15201, doi:10.1029/2009JD012842, 2010.
- The AIRS Dust Score can be found e.g. in the AIRIBQAP product, and the granules used in this article can be searched and downloaded using Mirador.
- The AIRS Dust Score and the visible images are also served in Near-Real-Time (NRT) using web map server (WMS) through a couple of portals: AIRS MapViewer, and Land and Atmosphere Near-real time Capability for EOS (LANCE)
- GES DISC provides guidance on using AIRS NRT WMS syntax, sample images and GoogleEarth’s KMZ
- AIRS Near-Real Time data (AIRVBRAD_NRT, AIRIBQAP_NRT) can be downloaded after completing user registration at LANCE.
- AIRS data are distributed by GES DISC at NASA Goddard Space Flight Center. AIRS is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., under contract to NASA. JPL is a division of the California Institute of Technology in Pasadena.
- The GEOS-5 data used in this article have been provided by the Global Modeling and Assimilation Office (GMAO) at NASA Goddard Space Flight Center.