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

Atmospheric chemistry and physics

Rozanov, Alexey^1¹  Galytska, Evgenia^1,2,3²  Chipperfield, Martyn P.^4,5³  Arosio, Carlo^1⁴  Weber, Mark^1⁵  Dhomse, Sandip. S.^4⁶ 

[1]Department of Meteorology and Climatology, Taras Shevchenko National University of Kyiv, Kyiv, Ukraine^2

[2]Institute of Environmental Physics, University of Bremen, Bremen, Germany^1

[3]Invited contribution by Evgenia Galytska, recipient of the EGU Atmospheric Sciences Outstanding Student Poster and PICO Award 2018.^3

[4]National Centre for Atmospheric Science, University of Leeds, Leeds, UK^6

[5]National Centre for Earth Observation, University of Leeds, Leeds, UK^5

[6]School of Earth and Environment, University of Leeds, Leeds, UK^4

DOI  :  10.5194/acp-19-767-2019

学科分类：大气科学

来源: Copernicus Publications

【 摘 要 】

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 ( NO_y ), which are a result of a longer residence time of the source gas N₂O and increased production via N₂O + O( ¹ D). 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 NO_y , which enhances O₃ loss. During winter months (January–February) there are negative AoA changes, indicating faster N₂O transport and less NO_y 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.

【 授权许可】

CC BY