Abstract submitted for oral presentation at the
EUMETSAT conveference, 21-25 September 2008, Bath.

An alert system for volcanic SO₂ emissions using satellite measurements

 
Volcanic eruptions pose a major threat to human health and safety. Local population is primarily affected by lava and pyroclastic flows. Finer ash particles can be a threat further away from the volcano, depending on the elevation of the volcanic cloud. Ash reaching high altitudes can be transported over large distances before descending to the ground. Ash high up in the atmosphere is also a hazard to aviation, ranging from obstruction pilot views and clogging aircraft sensors to disruption the engines.

Apart from ash (aerosols), volcanic eruptions also release a number of trace gases into the atmosphere. The most important of these after water vapour and CO2 is sulphur dioxide (SO₂), which is readily measurable with modern sensors. Since the background level of SO₂ (away from sources) is negligible, the presence of SO₂ is a tell-tale sign of possible volcanic activity (or anthropogenic activity, the location of which is usually well-known). SO₂ itself is also a hazard to aviation, as it reacts with water to form sulphuric acid (H₂SO₄), which is highly corrosive and may lead to sulphate deposits in aircraft engines.

Monitoring of SO₂ concentrations on a global scale from satellite, with an automated notification of exceptional concentrations of SO₂, can therefore be very useful, in particular since not all volcanoes are monitored well on a regular basis.

SO₂ is measured from satellite by UV/Visible (GOME-2, SCIAMACHY and OMI) and IR (IASI) instruments, thus providing several data points during the day (all instruments) and an additional one during the night (IASI). Though IASI is less sensitive than UV/Visible instruments to SO₂ close to the surface, it has the potential of providing information on the vertical distribution of the SO₂. The added use of forward and backward particle trajectory analysis in case of an alert can aid in determining the origin of the volcanic cloud and its future motion.

The alert service is primarily designed to support the Volcanic Ash Advisory Centres (VAACs) in their official task to gather information on volcanic clouds. On the basis of this, the VAACs issue advice and alerts to airline and air traffic control organisations on the possible danger of volcanic clouds. Other users of the service are, for example, local Volcanic Observatories.

The presentation will give a description of the alert system and a number of examples.

 
Website for alert service and data archive: http://sacs.aeronomie.be