In the morning of December 3rd, 2015 a series of volcanic eruptions started at the ‘Voragine’ crater of the Etna on Sicily (Italy). This type of eruptions is called paroxysm, which is a synonym for increasing volcanic activity. Paroxysms are characterized by frequent explosions, becoming more and more intense until they come to an end in a final violent eruption.
After the first paroxysm on Dec 3rd, a second and third climax occurred in the morning (9-10h UTC) and evening of the following day (20:30h-21:15h UTC). A fourth paroxysm occurred in the afternoon of Dec 5th. During the eruptions, which are considered as the strongest of the last 20 years, large amounts of ash and sulfur dioxide (SO2) were emitted into the atmosphere. The SO2 emissions are clearly detectable by the GOME-2 instruments on the MetOp-A & -B satellites and have a total vertical SO2 column of more than 20 dobson units (see animation of daily measurements)
The GOME-2 measurements show that the SO2 plume from the first paroxysm was transported eastwards and is even detectable over Japan and the Pacific Ocean five days after the event. The SO2 plume of the second eruption in the morning of Dec. 5th was transported south-west, whereas the two plumes from the Dec. 5th/6th paroxysms were transported northwards. They arrived over southern Germany in the evening of Dec. 7th and morning of Dec. 8th , respectively, where they got detected in-situ at the meteorological institute Schneefernhaus on the Zugspitz-Mountain.
Based on a new algorithm developed at EOC, the SO2 plume height of the current eruption of Etna retrieved from GOME-2 data is in the range from 8 to 10 km (see animation of plume height retrieval results), which could be confirmed by satellite images of the ash cloud from MODIS (NASA/TERA&AQUA) and with measurements of SEVIRI (MSG) and CALIOP (NASA/CALYPSO). This new algorithm for the retrieval of SO2 plume height from GOME-2 data allows a much more precise measurements and forecasts of the volcanic SO2 plumes.
GOME-2 is an ultraviolet spectrometer (290-790 nm) aboard the polar-orbiting satellites MetOp-A (launched in 2006) and MetOp-B (launched in 2012) which takes global measurements of atmospheric composition on a daily basis. GOME-2 provides nadir-view scans with a ground pixel resolution of 40 x 40 km2 (MetOp-A) and 80 x 40 km2 (MetOp-B).
SO2 emissions are a good indicator for volcanic activity, since besides weak anthropogenic emissions there are no other known sources for atmospheric SO2. Furthermore it was found that for some volcanic eruptions SO2 can be a good proxy for the much harder to detect volcanic ash. Volcanic ash can be hazardous not only for the local population because of its impact on respiration but also for aviation since it can cause total engine failure if it melts and then congeals in the engine. Ash is also highly abrasive to engine turbine vanes and propellers, and, in the form of acid rain it may increase oxidation of aircraft components.
EOC provides operational trace gas measurements, including total SO2 columns, in near-real-time (i.e., within 2 hours of recording) in the framework of EUMETSAT’s Satellite Application Facility on Ozone and Atmospheric Chemistry Monitoring (O3M-SAF). Users of the SO2 product include the Volcanic Ash Advisory Centres (VAACs), which issue aviation warnings.