The Silver Lining of Disaster

There aren’t many reasons to consider a volcanic eruption a positive event, but if results from recent research by Amato Evan of the University of Virginia are confirmed, residents of hurricane-prone areas, at least, may have a new reason to welcome volcanoes. Evan studied the effects of two major volcanic events–the 1982 discharge of El Chichón and Mount Pinatubo’s eruption in 1991–on Atlantic hurricane activity. He found that hurricane frequency and intensity both decreased by about 50% in the year following the eruptions, as compared to the year preceding the eruptions. Smaller decreases were still detected two and three years after the eruptions.
The finding is not entirely surprising. Major volcanic eruptions can expel large amounts of sulfur dioxide into the stratosphere; the gas then reacts with water to form sulfuric acid aerosols, which reflect light and absorb radiation, cooling tropical ocean waters while warming the lower stratosphere. The combination of these changes would be expected to dampen the frequency, duration, and power of hurricanes, which thrive on the temperature contrast between the sea surface and the atmosphere high above.
Evan’s study (subscription only) runs into complications that will need to be addressed before the volcano-hurricane link is accepted. For instance, both the El Chichón and Mount Pinatubo eruptions were also followed by strong El Niño events, which by themselves are expected to suppress hurricane activity. (On the other hand, some research suggests that El Niños can be caused by volcanic eruptions.) Further study of the dynamics in play is necessary.
Convincing people on the coasts that hurricanes themselves are a positive force in their lives may be a bit more difficult. At the annual Governor’s Hurricane Conference in Florida last week, however, attendees looked back at the 20-year legacy of 1992’s Hurricane Andrew with mixed feelings. While it is still the costliest disaster in the state’s history, the storm brought about many significant positive changes. For one, the state government revised emergency management funding so that each county could have a full-time emergency manager on staff. The institutionalization of emergency plans and outreach to residents has paid off repeatedly in subsequent hurricanes. Hurricane Andrew also led to stiffer enforcement of building codes and rethinking of the ways buildings must withstand high winds.
All in all, the silver lining of disaster isn’t great consolation, but the conference, like Evan’s research, gives hope for continued improvement in hurricane forecasting, preparedness, and response.

Special Session Today on the 2010 Icelandic Volcano Eruptions

Iceland's eruptions, 2010: Getting close safely for measurements was one of the problems with observing the initial eruption conditions that affect plume dispersion modeling.

The Eyjafjallajökull volcano eruption in Iceland lasted from the 15 April to 25 May 2010.  In addition to threatening local people and their livestock, the volcano sent an ash plume to heights of up to 26,000 feet. Due to the weather conditions, the plume spread over a large part of Europe. Because volcanic ash can cause airplane engines to fail, the plume disrupted aviation over several weeks.
Weather Services played a key role in  predicting the spread of the ash and advising the aviation industry. The forecasts were based on safety thresholds for flying through volcanic ash set by the International Civil Aviation Organisation (ICAO) along with the national aviation authorities and aircraft manufacturers.
Scientists modelled the evolution of the ash cloud using dispersion  models and trajectory models. The model predictions were compared with  observations from satellites, aircraft and ground-based networks.
Supplemental ash concentration information from the UK Met Office

The eruption of Eyjafjallajökull presented challenges to the meteorological community, especially in Europe.  The event highlighted the importance of enhanced international coordination to ensure a consistency of approach in the observation, forecasting and dissemination of volcanic ash information and warnings.
At the AMS annual meeting, papers covering the observing, forecasting and warning to the public and especially to the airline industry regarding the effects of the eruption of Eyjafjallajökull will be presented today (Monday) at the Special International Applications Session 1B: The Eyjafjallajökull Volcanic Eruption of 2010 (1:30 pm). At 2 pm Ian Lisk of the UK Met Office talks about how the aviation industry, grounded by safety rules, put pressure on meteorologists to produce ash concentration charts to supplement the normal information from the Volcanic Ash Advisory Centre in the UK. This was an added burden on dispersion modeling services (with the NAME model), but the results proved promising:

The largest uncertainty in the computer modelling of ash dispersion and transport is the ability to accurately reflect the status of the eruption at model initialization. This is less of a modelling issue and much more a case of being able to accurately and safely observe what the volcano is doing in real time, in particular, the:
•Height, diameter and time variance of eruptive column;
•Assessment of ash concentration and particle size/distribution;
•Ash deposition close to the volcano i.e. ash that is not available to be transported.

Unlike atmospheric phenomena, volcanic eruptions are in fixed places and don’t condense or disappear out of thin air, like atmospheric phenomena…but apparently observing them isn’t much easier.