MLS measurements of stratospheric hydrogen cyanide during the 2015-2016 El Niño event

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 Nino 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 Nino period to the rest of the mission. HCN in 20152016 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.