Attribution of stratospheric ozone trends to chemistry and transport: a modelling study

Abstract

Abstract. The decrease of the concentration of ozone depleting substances (ODSs) in the stratosphere over the past decade raises the question to what extent observed changes in stratospheric ozone over this period are consistent with known changes in the chemical composition and possible changes in atmospheric transport. Here we present a series of ozone sensitivity calculations with a stratospheric chemistry transport model (CTM) driven by meteorological reanalyses from the European Centre for Medium-Range Weather Forecasts, covering the period 1978-2009. In order to account for the reversal in ODS trends, ozone trends are analysed as piecewise linear trends over two periods, 1979-1999 and 2000-2009. Modelled column ozone (TO3) inter-annual variability and trends are in excellent agreement with observations from the Total Ozone Mapping Spectrometer (TOMS) and Solar Backscatter UV (SBUV/2) as well as the Global Ozone Monitoring Experiment (GOME/GOME2) and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instruments. In the period 1979-1999, modelled TO3 trends at mid-latitudes are dominated by changes in in situ gas-phase chemistry, which contribute to about 50% or more of the TO3 trend in most seasons. Changes in meteorology contribute around 35% to mid-latitude TO3 trends, with strong differences between different seasons. In springtime, export of ozone depleted air from polar latitudes contributes about 35-50% to the modelled TO3 trend at SH mid-latitudes and about 15-30% at NH mid-latitudes. Over the period 2000-2009 positive linear trends in modelled TO3, which agree well with observed TO3 trends, are dominated by changes in meteorology, as expected for the yet small decrease in stratospheric halogen loading over this period. While the TO3 trends themselvesCorrespondence to: G. Kiesewetter (gregor.kiesewetter@iup.physik.uni-bremen.de) are not statistically significant over the period 2000-2009, changes in linear trends between 1978-1999 and 2000-2009 are significant at mid-and high latitudes of both hemisphere during most seasons. However, changes in meteorology have contributed substantially to these TO3 trend changes.

Spatial regression analysis on 32 years of total column ozone data

“…Finally ozone is affected negatively by high values of geopotential height at 500 hPa in southern midlatitudes and northern mid-to high latitudes. The importance of synoptic-scale meteorological variability in understanding extratropical total ozone column variability has long been recognized (e.g., Harris et al, 2008;Kiesewetter et al, 2010;Rieder et al, 2010).…”

A re-evaluated Canadian ozonesonde record: measurements of the vertical distribution of ozone over Canada from 1966 to 2013

“…14). Since stratospheric halogen loading has been decreasing during this period (WMO, 2014), the lack of evident ozone increases may be due to atmospheric variability (Kiesewetter et al, 2010;Chehade et al, 2014), in particular the high values in the early 2000s, possibly caused by changes in the BrewerDobson circulation (Bönisch et al, 2011). However, the standard deviations of the monthly ozone anomalies in the stratosphere at the four long-term stations for the 17 years prior to 1997 average 8-40 % greater than those for the 17-year period 1997-2013, which suggests that the stratosphere has in fact been less variable in the latter period.…”

MIPAS observations of volcanic sulfate aerosol and sulfur dioxide in the stratosphere

“…Sinnhuber et al, 2003;Kiesewetter et al, 2010) is forced by temperature, wind fields, and diabatic heating rates from ERA-Interim (Dee et al, 2011). The model uses isentropes as vertical coordinates.…”