October 26, 2013
Using Satellites To Track And Improve Volcanic Ash Forecasts
April Flowers for redOrbit.com - Your Universe Online
Frequent travelers can agree that flight delays are all too familiar these days. NASA is looking into a potentially dangerous, though much less frequent, problem that has recently caused major disruptions in flight schedules: volcanic eruptions.
Ash and tiny, jagged particles are expelled from explosive volcanic eruptions. These particulates can be blown thousands of miles away from their source and are dangerous to airplanes, grounding and diverting flights. This has a huge economic impact on travelers and citizens who depend on goods and services delivered by air.
NASA currently has a number of instruments in space with the ability to "see" volcanic ash. Each of these instruments provides the researchers with information about the ash. This data helps detect, locate and characterize the physical and chemical properties of the ash plume. None of the instruments, however, creates a complete enough picture of the ash plume and its constituents to provide effective information to the aviation community about the threat, but that is changing.
A large plume was created over European airspace when the Icelandic volcano Eyjafjallajokull erupted in 2010 grounding more than a hundred thousand travelers. The economic impact was more than a billion dollars, creating a wakeup call to the atmospheric science and aviation communities.
"The Icelandic eruption, such a dramatic event, made us take a hard look at what each of our satellites can tell us," said John Murray, associate program manager for the NASA Applied Sciences Program's natural disasters focus area. "We knew we needed to understand how to integrate them to make better forecasts."
To improve the warning issued by the world's nine operational Volcanic Ash Advisory Centers (VAACs), Murray knew that his team needed to look more closely at the unique capabilities of NASA's satellite imagery. The VAACs use relatively simple representations of atmospheric particles to develop forecasts used to guide decisions about where aircraft can safely fly. Useful short-term information about the volcanic ash distribution is provided by these models, but they lack accurate information about ash plume concentration, layering, and long-term dispersion.
"The dispersion of a volcanic plume in the atmosphere is like ink in water," explained Jean-Paul Vernier, a researcher at NASA's Langley Research Center. "Models, which are used to simulate both, rely on source information like how much ink or ash is introduced and how the flow – either the current or wind – transports the material."
Vernier explained that for longer lasting plumes typically injected at higher altitudes near commercial cruise levels, forecasters need a combination of trajectory models with refresh information about the plume's height and location, which is where the new NASA 3D data comes in.
NASA's CALIPSO (Cloud Aerosol-Lidar and Infrared Pathfinder Satellite Observations) mission is uniquely suited to provide researchers with updated information about ash plume height and location. CALIPSO provides an unprecedented 3D view of atmospheric particles, like volcanic ash, and cloud in the atmosphere using a space-based lidar system since 2006.
MODELING THE PLUME
The research team focused on the volcanic eruption of Puyehue-Cordón Caulle in Chile in June 2011. This eruption disrupted air traffic throughout much of the Southern Hemisphere. This powerful eruption ejected ash in the upper troposphere - 3 to 9 miles above the Earth. Because of the higher ejection, the plume was longer-lasting, circling the globe at least three full times in the southern latitudes.
The data from CALIPSO allowed the researchers to track the plume on its trip around the world. Different channels of the CALIPSO lidar were investigated to be able to differentiate between clouds and ash.
"CALIPSO gives us very accurate information about the 3D location of ash," said Vernier. "However, the CALIPSO lidar data comes to us in curtains and we don't know what's between two curtains. We use trajectory models to fill in those gaps."
Volcanic ash observations from CALIPSO were used as initiation points for the trajectory model. It is possible to produce a more accurate forecast than using a simple dispersion model by accumulating several days of observations transported by the trajectory model forward in time.
A key advancement with this technique, according to Duncan Fairlie, research scientist at NASA's Langley Research Center, was being able to use "cloud clearing" algorithms, or mathematical formulas, developed by Vernier.
Comparing the model results with independent CALIPSO observations showed the team that the model had successfully reproduced the 3D structure of volcanic ash clouds.
"We saw remarkable agreement between the trajectory model and the independent CALIPSO observations," said Fairlie. "To be honest, we were blown away."
The study results were especially compelling for the aviation community in southern Australia and New Zealand. The Darwin, Australia VAAC found the Puyehue-Cordón Caulle plume had persisted during the three weeks following the eruption. The long-term dispersion model, however, forecast the plume becoming increasingly unstable. The Darwin VAAC had to rely heavily on fundamental satellite observations, which can't always see through the clouds to locate ash plumes.
"Our model, however, provided additional information about the 3D structure of the volcanic plume, especially the extension of the plume’s forward trajectory that was not available to the Darwin VAAC at the time of their advisories," said Murray. "For example, the model clearly showed the head of the volcanic ash cloud crossing the southern part of Australia directly east of the Darwin VAAC’s advisory area on June 21."
The team is currently working with the international volcanic ash community to aid in the integration of CALIPSO data trajectory modeling to the VAAC modeling process to help the aviation community’s efforts to operate more safely and efficiently when volcanic ash events occur. Because much of the VAAC workload consists of making judgment calls between potential ash and false alarms, this process is especially challenging with low ash concentrations like those seen in this study.
"The combination of CALIPSO observations of volcanic ash clouds and a Lagrangian trajectory model offers a potential new capability that VAACs could use to improve aviation safety worldwide," said Murray.
"Additionally," said Vernier, "future NASA missions, such as SAGE III on ISS, will be useful to continue monitoring the dispersion of volcanic ash in the atmosphere."