This loop of GOES-8 InfraRed (IR) difference product 1 (or "split window" product) shows the volcanic ash plume following the eruption of the Guagua Pichincha Volcano at 12:07 UTC on 07 October 1999. This product is created by taking the difference in brightness temperatures between the 10.7 micrometer "IR window" and 12.0 micrometer "dirty IR window" channels. Differences in the emissivity of silicate particles within the ash plume at these two wavelengths leads to brightness temperature differences of 1-5 degrees Kelvin (cyan to blue enhancement). This IR difference product shows the ash plume very well initally, but as the plume becomes thinner and more diffuse with time it loses its identity on the IR difference product after about 16:00 UTC. Vigorous pre-mature convective cloud growth can also show a similar signature on this IR product 2 -- note the appearance of negative differences (blue enhancement) the end of the loop (17:15 UTC) as deep convective clouds begin to develop over eastern portions of the region.
1 "Observations of volcanic ash clouds in the 10-12 micrometer window using AVHRR/2 data", A.J. Prata, Int. J. Remote Sensing, 10, 751-761 (1989)
2 "Negative 11 micron minus 12 micron brightness temperature differences: a second look", C.C. Moeller, S.A. Ackerman, K.I. Strabala, W.P. Menzel, W.L. Smith, 8th Conference on Satellite Meteorology and Oceanography, Jan 28 - Feb 2, 1996, Atlanta, GA, AMS, 313-316.