Dynamically controlled ozone decline in the tropical mid-stratosphere observed by SCIAMACHY

Evgenia Galytska,John P Burrows,Martyn P Chipperfield,Sandip S Dhomse,Wuhu Feng,Mark Weber,Carlo Arosio,Alexey Rozanov

doi:10.5194/acp-19-767-2019

Abstract

Abstract. Despite the recently reported beginning of a recovery in global stratospheric ozone (O3), an unexpected O3 decline in the tropical mid-stratosphere (around 30–35 km altitude) was observed in satellite measurements during the first decade of the 21st century. We use SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) measurements for the period 2004–2012 to confirm the significant O3 decline. The SCIAMACHY observations show that the decrease in O3 is accompanied by an increase in NO2. To reveal the causes of these observed O3 and NO2 changes, we performed simulations with the TOMCAT 3-D chemistry-transport model (CTM) using different chemical and dynamical forcings. For the 2004–2012 time period, the TOMCAT simulations reproduce the SCIAMACHY-observed O3 decrease and NO2 increase in the tropical mid-stratosphere. The simulations suggest that the positive changes in NO2 (around 7 % decade−1) are due to similar positive changes in reactive odd nitrogen (NOy), which are a result of a longer residence time of the source gas N2O and increased production via N2O + O(1D). The model simulations show a negative change of 10 % decade−1 in N2O that is most likely due to variations in the deep branch of the Brewer–Dobson Circulation (BDC). Interestingly, modelled annual mean “age of air” (AoA) does not show any significant changes in transport in the tropical mid-stratosphere during 2004–2012. However, further analysis of model results demonstrates significant seasonal variations. During the autumn months (September–October) there are positive AoA changes that imply transport slowdown and a longer residence time of N2O allowing for more conversion to NOy, which enhances O3 loss. During winter months (January–February) there are negative AoA changes, indicating faster N2O transport and less NOy production. Although the variations in AoA over a year result in a statistically insignificant linear change, non-linearities in the chemistry–transport interactions lead to a statistically significant negative N2O change.

Highlights

Stratospheric ozone (O3) is one of the most important components of the atmosphere
The European Space Agency (ESA) Environmental Satellite (Envisat) mission carried 10 sensors dedicated to Earth observation, which were operational from the launch of the satellite in March 2002 until it failed in April 2012, doubling the planned lifetime of 5 years
To further improve our understanding of age of air” (AoA) changes, we show in Fig. 9 a seasonal analysis of AoA linear changes from the multiple linear regression (MLR) model during January 2004– April 2012 based on TOMCAT control run (CNTL) simulation for DJF, March–April–May (MAM, panel b), June–July– August (JJA, panel c), and September–October–November (SON, panel d)

Summary

Introduction

Stratospheric ozone (O3) is one of the most important components of the atmosphere It absorbs ultraviolet solar radiation, which is harmful to plants, animals, and humans, and thereby plays a key role in determining the thermal structure and dynamics of the stratosphere (Jacobson, 2002; Seinfeld and Pandis, 2006). The amount of O3 in the stratosphere is controlled by a balance between photochemical production and loss mechanisms. E. Galytska et al.: Ozone decline in the tropical mid-stratosphere these photochemical and chemical reactions take. To set the scene for our understanding of chemical O3 variations in the tropical mid-stratosphere, we briefly discuss the mechanism of O3 production and loss via catalytic NOx (NOx = NO + NO2) cycle and the role of nitrous oxide (N2O)

Methods

Results

Conclusion