Evolution of stratospheric ozone and water vapour time series studied with satellite measurements

A Jones,D Degenstein,H Bovensmann,J Urban,A Rozanov,T Sonkaew,A Bourassa,C Haley,J Burrows,C Von Savigny,S Brohede,P Eriksson,D P Murtagh

doi:10.5194/acp-9-6055-2009

Abstract

Abstract. The long term evolution of stratospheric ozone and water vapour has been investigated by extending satellite time series to April 2008. For ozone, we examine monthly average ozone values from various satellite data sets for nine latitude and altitude bins covering 60° S to 60° N and 20–45 km and covering the time period of 1979–2008. Data are from the Stratospheric Aerosol and Gas Experiment (SAGE I+II), the HALogen Occultation Experiment (HALOE), the Solar BackscatterUltraViolet-2 (SBUV/2) instrument, the Sub-Millimetre Radiometer (SMR), the Optical Spectrograph InfraRed Imager System (OSIRIS), and the SCanning Imaging Absorption spectroMeter for Atmospheric CHartograpY (SCIAMACHY). Monthly ozone anomalies are calculated by utilising a linear regression model, which also models the solar, quasi-biennial oscillation (QBO), and seasonal cycle contributions. Individual instrument ozone anomalies are combined producing an all instrument average. Assuming a turning point of 1997 and that the all instrument average is represented by good instrumental long term stability, the largest statistically significant ozone declines (at two sigma) from 1979–1997 are seen at the mid-latitudes between 35 and 45 km, namely −7.2%±0.9%/decade in the Northern Hemisphere and −7.1%±0.9%/in the Southern Hemisphere. Furthermore, for the period 1997 to 2008 we find that the same locations show the largest ozone recovery (+1.4% and +0.8%/decade respectively) compared to other global regions, although the estimated trend model errors indicate that the trend estimates are not significantly different from a zero trend at the 2 sigma level. An all instrument average is also constructed from water vapour anomalies during 1991–2008, using the SAGE II, HALOE, SMR, and the Microwave Limb Sounder (Aura/MLS) measurements. We report that the decrease in water vapour values after 2001 slows down around 2004–2005 in the lower tropical stratosphere (20–25 km) and has even shown signs of increasing until present. We show that a similar correlation is also seen with the temperature measured at 100 hPa during this same period.

Highlights

Since the 1987 Montreal Protocol, important steps have been taken in order to halt the decrease of stratospheric ozone, which has been a main environmental concern for the last couple of decades (WMO, 2006)
The instruments that contribute during this time, SAGE I+II, Solar BackscatterUltraViolet-2 (SBUV/2), and HALogen Occultation Experiment (HALOE) show consistency with each other during overlapping periods, the SBUV/2 anomalies are slightly larger than anomalies calculated for the whole SAGE I period, and for SAGE II during 1988–1991
The trend line after 1997 indicates a slowing down of ozone depletion and that there is even an increase (1.4%/decade ±2.3%, i.e. not statistically significant at the 95% confidence level). It can be seen visibly from 2001 that HALOE, Sub-Millimetre Radiometer (SMR), Optical Spectrograph InfraRed Imager System (OSIRIS), and SCIAMACHY all show a slight increase in ozone in this bin if one just considers the respective anomalies

Summary

Introduction

Since the 1987 Montreal Protocol, important steps have been taken in order to halt the decrease of stratospheric ozone, which has been a main environmental concern for the last couple of decades (WMO, 2006). The largest estimates of ozone loss (of 6–8%/decade) are reported in the upper stratospheric mid-latitudes, typically between 35–45 km (Newchurch et al, 2003; Steinbrecht et al, 2004; Cunnold et al, 2004), which is a result of ozone-depleting halogen gases being released at the surface and slowly travel to the stratosphere. As a result of the protocol’s directives, halogen loading has reduced and recent studies have reported a slowing down of ozone depletion in the upper stratosphere (Newchurch et al, 2003; Steinbrecht et al, 2004, 2006), there is still some uncertainty over how much recovery is masked by natural. Ozone depleting substance levels are thought to have reached their peak in between 1995 and 2000 in the upper stratosphere, but are not expected to return to pre 1980 values until 2050–2060, ozone’s recovery is as long (WMO, 2006). Recent estimations suggest that the Antarctic ozone hole will recover to pre 1980 values around 2068 (±10 years) (Newman et al, 2006)

Methods

Results

Discussion

Conclusion