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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
05 Jul 2017
Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.
MLS measurements of stratospheric hydrogen cyanide during the 2015–16 El Niño event
Hugh C. Pumphrey1, Norbert Glatthor2, Peter F. Bernath3,4, Christopher D. Boone4, James 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
3Old Dominion University, USA
4University of Waterloo, Canada
5National Center for Atmospheric Research, Bolder, CO, USA
6NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
Abstract. It is known from ground-based measurements made during the 1982–83 and 1997–98 El Niño events that atmospheric HCN tends to be higher than usual during such years. The Microwave Limb Sounder (MLS) on Aura has been measuring HCN mixing ratios since launch in 2004; the measurements are ongoing at the time of writing. The winter of 2015–16 has seen the largest El Niño event since 1997–98. We present MLS measurements of HCN in the lower stratosphere for the Aura mission to date, comparing the 2015–16 El Niño period to the rest of the mission. HCN in 2015–16 is higher than at any other time during the mission, but ground based measurements suggest that it may have been even more elevated in 1997–98. As the MLS HCN data are essentially un-validated, 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 GFED (V4.1) database are very much greater during large El Niño events and are greater in 1997–98 than in 2015–16, thereby showing good qualitative agreement with the measurements. Correlation between ENSO indices, measured HCN and GFED HCN emissions is less clear away from the 2015–16 event. In particular, the 2009–10 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., Ortega, I., Livesey, N. J., and Read, W. G.: MLS measurements of stratospheric hydrogen cyanide during the 2015–16 El Niño event, Atmos. Chem. Phys. Discuss.,, in review, 2017.
Hugh C. Pumphrey et al.
Hugh C. Pumphrey et al.


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Short summary
The Microwave Limb Sounder (MLS) is a satellite instrument which 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 which has been measuring the amount...