The paroxysmal event was the largest volcanic eruption ever detected on planet Earth with satellite data. In general, the ash moves downwind in a direction and at a rate closely matching the prevailing wind. The traditional approach has been to relate plume-top temperatures derived from infrared imagery to environmental temperatures measured by rawinsondes. Simplified approaches fail for large eruptions penetrating into the stratosphere because, above the tropopause, ambient temperature increases with height. Additional problems are introduced by increased transmissivity through thin or thinning ash plumes.
Complications arise when shadows fall on a lower cloud layer or on a dark surface such as the ocean.
The technique is only useful during daytime hours and with solar zenith angles large enough to produce shadows. NOAA has experimented with this technique for estimating the altitude of thunderstorm canopies. The heights used in this paper are all derived from wind correlation. After a 28-h respite, frequent brief eruptions began on June 14 and culminated with the massive eruptions on June 15. Figure 1 .