Drift-corrected Odin-OSIRIS ozone product: algorithm and updated stratospheric ozone trends

Adam E Bourassa,Chris A Mclinden,Daniel J Zawada,Landon A Rieger,Douglas A Degenstein,Chris Z Roth

doi:10.5194/amt-11-489-2018

Abstract

Abstract. A small long-term drift in the Optical Spectrograph and Infrared Imager System (OSIRIS) stratospheric ozone product, manifested mostly since 2012, is quantified and attributed to a changing bias in the limb pointing knowledge of the instrument. A correction to this pointing drift using a predictable shape in the measured limb radiance profile is implemented and applied within the OSIRIS retrieval algorithm. This new data product, version 5.10, displays substantially better both long- and short-term agreement with Microwave Limb Sounder (MLS) ozone throughout the stratosphere due to the pointing correction. Previously reported stratospheric ozone trends over the time period 1984–2013, which were derived by merging the altitude–number density ozone profile measurements from the Stratospheric Aerosol and Gas Experiment (SAGE) II satellite instrument (1984–2005) and from OSIRIS (2002–2013), are recalculated using the new OSIRIS version 5.10 product and extended to 2017. These results still show statistically significant positive trends throughout the upper stratosphere since 1997, but at weaker levels that are more closely in line with estimates from other data records.

Highlights

Satellite observations have been used for over 3 decades to measure, diagnose, and monitor stratospheric ozone variability and long-term trends
It was noted by Bourassa et al (2014) that the derived positive trends were somewhat higher than those reported from a similar merging analysis by Kyrölä et al (2013), using the Stratospheric Aerosol and Gas Experiment (SAGE) II and Global Ozone Monitoring by Occultation of Stars (GOMOS) measurements
We identify the source of the drift in the Optical Spectrograph and Infrared Imager System (OSIRIS) ozone product as a small systematic error in the limb pointing knowledge of the instrument that is nominally determined by on-board star trackers

Summary

Introduction

Satellite observations have been used for over 3 decades to measure, diagnose, and monitor stratospheric ozone variability and long-term trends. The conclusion of Bourassa et al (2014) was that from 1997 to 2013 (the end of the OSIRIS data set analysed at that point) there was a statistically significant recovery of 3–8 % per decade throughout the stratosphere, except in the tropical lower stratosphere, where small but significant negative trends persisted It was noted by Bourassa et al (2014) that the derived positive trends were somewhat higher than those reported from a similar merging analysis by Kyrölä et al (2013), using the SAGE II and Global Ozone Monitoring by Occultation of Stars (GOMOS) measurements. The effectiveness of the pointing correction is demonstrated through comparison of the time series with MLS measurements, and revised SAGE II-OSIRIS trend results are presented, showing recovery throughout the upper stratosphere that is still statistically significant, but at weaker levels than previously reported

Pointing correction technique

Impact on trends

Findings

Summary and conclusion