By Adam Robinson, Undergrad Physics Major/Summer Intern at University of Maryland, Baltimore County (UMBC), and Scott Hannon, Sergio DeSouza-Machado, Larrabee Strow of the Joint Center for Earth Systems Technology/Physics at UMBC
On June 4, 2011 the Puyuhue-Cordón Caulle volcano complex, located 40.59 deg S, 72.12 deg W in Chile, erupted, sending ash clouds 15 km into the atmosphere and on their way around the world. It was the first major eruption by the volcano since 1960. The ash clouds were tracked as they circled the globe using infrared data from AIRS, revealing their position during the day and the night.
The flag we use to detect volcanic ash is similar to the dust flag present in the AIRS L1 and L2 products. In this case, we look for a spectral signature between about 800 and 1200 cm-1 and we focus on the brightness temperature differences between channels near 860 cm-1 and near 960 cm-1.
The movie shows the results of our volcanic ash detection algorithm, using AIRS data between June 4th--June 21st, 2011. The colorbar is related to the brightness temperature differences between 860 cm-1 and 960 cm-1, which is an indicator of the amount of ash in the atmosphere. By looking at the measured brightness temperatures, AIRS can also determine the height of the plume. For example in the spectrum shown above, the approximately 280 K brightness temperatures at 960 cm-1 indicate this ash is at low altitudes (<= 4km). For each day there are two images.
There are two frames displayed for each day. The first frame shows data taken between 12 am and 12 pm UTC (AIRS granules 1-120) and the second frame shows data taken between 12pm and 12 am the next day (AIRS granules 121-240). In general, ascending swaths were taken during daylight hours in the region and descending swaths were taken during the night. June 11th and June 17th--21st do not have the descending images.
We have also detected SO2 emitted from the volcano, and transported around the Southern Hemisphere, using channels in the 1375 cm-1 region. The following figures show the retrieved SO2 amount in dobson units. The amounts of SO2 emitted by the Puyehue eruption are much smaller than the ones emitted in some other eruptions, such as the Aleutian Islands (Okmok) eruption in August 2008, where almost 5-8 times the amount of SO2 was detected.
As the ash circled the globe, airports were forced to cancel flights to avoid flying through the thick ash. Airports from Argentina to Australia and New Zealand had to ground flights since the ash is harmful to aircraft engines.