Regional And Mesoscale Meteorology Team
Daily Satellite Discussion
Tuesday August 12, 1997
Today's feature focuses on one of the many recent violent explosions of the active volcano on Soufriere Hills, Montserrat. Volcanic ash is an aviation hazard, as it can cause serious damage to aircraft engines. The detection of the plume both day and night is very important. Figure 1. depicts hourly imagery from 1515-1815 UTC on 7 August 1997. Montserrat is located at the center of each of the images and is depicted by a yellow dot. Notice the umbrella shaped cloud at 1615 UTC and the movement of the ash cloud in both easterly and westerly directions in the following 2 hours. The 10.7-12.0 micrometer difference product for the same time period is shown in Figure 2. The 12.0 micrometer channel is sensitive to low level moisture and certain types of aerosols. Volcanic ash particles have a higher radiative emissivity in 12.0 than in 10.7. At low levels in the atmosphere during the day, the 12.0 micrometer channel will be colder than the 10.7 micrometer channel due to moisture and ash absorption. If the ash reaches into the trade wind inversion above the moist layer, the 12.0 micrometer will appear warmer than the 10.7 micrometer imagery. In the 10.7-12.0 micrometer difference product, the blue indicates that 10.7 is colder than 12.7 by more than 3 degrees, while the change from black to gray indicates 10.7 is 0-3 degrees colder than 12.7. When the unbrella cloud forms above the island at 1615 UTC, the 10.7-12.0 micrometer difference is strongly negative indicating that the cloud has reached the trade wind inversion. Reports from Government of Montserrat and the Montserrat Volcano Observatory (http://www.geo.mtu.edu/volcanoes/west.indies/soufriere/govt/) indicate the ash reached 15,000 to 20,000 feet asl quickly. In the following hours, as the ash cloud spread out and mixed with the environment and the temperature difference decreased. Here we have given an example of the more obvious detection during the day. The 10.7-12.0 difference product can also be used at night.
For further information, check out the NEW Volcanic Ash section in the RAMM/CIRA 3.9 micrometer tutorial.
and Selected Presentations: 1) GOES Imagery for Alaska Workshop by Stan Kidder 2) Aviation and Marine Applications by Gary Ellrod 3) Polar Satellite Images by Gary Hufford from the COMET SatMet Class
Bernadette Connell