Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 18, 691-703, 2018
https://doi.org/10.5194/acp-18-691-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
19 Jan 2018
MLS measurements of stratospheric hydrogen cyanide during the 2015–2016 El Niño event
Hugh C. Pumphrey1, Norbert Glatthor2, Peter F. Bernath3,4, Christopher D. Boone4, James W. Hannigan5, Ivan Ortega5, Nathaniel J. Livesey6, and William G. Read6 1School of GeoSciences, The University of Edinburgh, Edinburgh, UK
2Karlsruher Institut für Technologie, Institut für Meteorologie und Klimaforschung, Karlsruhe, Germany
3Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, VA 23508, USA
4Department of Chemistry, University of Waterloo, Waterloo, ON, N2L 3G1, Canada
5National Center for Atmospheric Research, Boulder, CO, USA
6NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
Abstract. It is known from ground-based measurements made during the 1982–1983 and 1997–1998 El Niño events that atmospheric hydrogen cyanide (HCN) tends to be higher during such years than at other times. The Microwave Limb Sounder (MLS) on the Aura satellite has been measuring HCN mixing ratios since launch in 2004; the measurements are ongoing at the time of writing. The winter of 2015–2016 saw the largest El Niño event since 1997–1998. We present MLS measurements of HCN in the lower stratosphere for the Aura mission to date, comparing the 2015–2016 El Niño period to the rest of the mission. HCN in 2015–2016 is higher than at any other time during the mission, but ground-based measurements suggest that it may have been even more elevated in 1997–1998. As the MLS HCN data are essentially unvalidated, we show them alongside data from the MIPAS and ACE-FTS instruments; the three instruments agree reasonably well in the tropical lower stratosphere. Global HCN emissions calculated from the Global Fire Emissions Database (GFED v4.1) database are much greater during large El Niño events and are greater in 1997–1998 than in 2015–2016, thereby showing good qualitative agreement with the measurements. Correlation between El Niño–Southern Oscillation (ENSO) indices, measured HCN, and GFED HCN emissions is less clear if the 2015–2016 event is excluded. In particular, the 2009–2010 winter had fairly strong El Niño conditions and fairly large GFED HCN emissions, but very little effect is observed in the MLS HCN.

Citation: Pumphrey, H. C., Glatthor, N., Bernath, P. F., Boone, C. D., Hannigan, J. W., Ortega, I., Livesey, N. J., and Read, W. G.: MLS measurements of stratospheric hydrogen cyanide during the 2015–2016 El Niño event, Atmos. Chem. Phys., 18, 691-703, https://doi.org/10.5194/acp-18-691-2018, 2018.
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Short summary
The Microwave Limb Sounder (MLS) is a satellite instrument that has been measuring the amount of various gases in the atmosphere since 2004. In late 2015 and 2016 it observed unusual amounts of hydrogen cyanide (HCN), a gas produced when vegetation is burned. We compare the MLS observations to similar observations from other instruments. The excess HCN is shown to come from fires in Indonesia. There are more fires than usual in 2015–16 due to a drought caused by an El Niño event.
The Microwave Limb Sounder (MLS) is a satellite instrument that has been measuring the amount of...
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