Positive Volcanic Clouds

There are several reasons why a volcanic cloud may be characterized by a positive, rather than negative, band 4-5 brightness temperature difference. The most common reason is that the cloud is still opaque. The temperature difference method relies upon radiation from the surface beneath the cloud passing through the cloud, and being scattered and absorbed by particles in the cloud. If it is opaque to thermal radiation, the signal seen by the satellite comes from emission from the cloud top. At the temperatures of typical clouds, this results in a positive temperature difference. If the cloud is positive due to its opacity, one would expect that it would become negative over time, and thus be able to be discriminated using the band 4-5 temperature difference.


This page maintained by Dave Schneider (djschnei@mt u.edu)