Explosive volcanic eruptions generate huge amounts of ash clouds, inject an avalanche of aerosols, gases and ash into the troposphere, and can even reach into the stratosphere. Major eruptions can cause short-time climate change in case sulfur dioxide is emitted to the atmosphere forming sulfate aerosols with extensive residence times of approximately 1 to 3 years. The impact however depends on the location of the volcano, total mass erupted, the extent of the dispersion due to atmospheric circulation, and the altitude reached by the ash and sulfur dioxide.
Ash clouds pose a threat to aviation considering that they can damage aircraft engines even far away from the eruptions. Therefore, research attention has centered on the enhancement of detection as well as monitoring of volcanic ash clouds. However, observing the density of the ash clouds as a function of height becomes a major challenge considering that values more than 2 mg/m3 could be rendered dangerous for aircraft engines. Previously, this parameter could only be detected by flying into the clouds with all the relevant risks until recently when infrared spectral imaging indicated promising results.
A good understanding of the cloud top altitude is important in order to offer information on ash-free altitude regions for air traffic as well as on potential overshooting and sulfur dioxide spread into the atmosphere. However, the discrimination of ash clouds from other forms of clouds can be challenging. Researchers at the Wegener Center of the University of Graz in Austria, Riccardo Biondi, Andrea Steiner, Gottfried Kirchengast, and Therese Rieckh, in collaboration with Hugues Brenot at the Belgian Institute for Space Aeronomy studied the potential capacity of the radio occultation method for supporting volcanic cloud monitoring and detection. The research team used geographically co-located Global Navigation Satellite System radio occultation profiles in order to detect the top altitude of volcanic clouds and to assess their effect in terms of temperature change signatures. Their research work is published in Advances in Space Research.
The authors adopted, at the first step, radiometric imaging observations in the thermal infrared as well as UV-visible for detecting volcanic ash as well as sulfur dioxide clouds and for isolating against water clouds. In the second step, the authors adopted geographically co-located profile observations from radio occultation for identifying the cloud top altitude and assessing the thermodynamic effect of volcanic clouds.
In their pioneering demonstration study, the researchers used approximately 1300 radio occultation profiles co-located with two eruptions in 2011 (Puyehue and Nabro) and realized that an anomaly method they developed recently for identifying convective cloud tops and analyzing the vertical thermal structure of deep convective systems could be applied for volcanic clouds. “Assessing the atmospheric thermal structure after volcanic eruptions, we found clear cooling signatures induced by volcanic ash cloud tops in the troposphere for the Puyehue case,” says Andrea Steiner, corresponding author from the University of Graz, and her senior author colleague Gottfried Kirchengast adds “Another exciting finding is that for the Nabro case we detected a considerable warming in the stratosphere over several months, implying that we could see the sulfate cloud’s local warming effect.”
The outcomes of their study are impressive for future large-scale implementation of radio occultation data for supporting the detection and monitoring of volcanic clouds as well as their effects on weather and climate.
Riccardo Biondi, Andrea K. Steiner, Gottfried Kirchengast, Hugues Brenot, Therese Rieckh. Supporting the detection and monitoring of volcanic clouds: A promising new application of Global Navigation Satellite System radio occultation. Advances in Space Research, Available online 28 June 2017.Go To Advances in Space Research