Long‐term evolution of upper stratospheric ozone at selected stations of the Network for the Detection of Stratospheric Change (NDSC)

Abstract

The long‐term evolution of upper stratospheric ozone has been recorded by lidars and microwave radiometers within the ground‐based Network for the Detection of Stratospheric Change (NDSC), and by the space‐borne Solar Backscatter Ultra‐Violet instruments (SBUV), Stratospheric Aerosol and Gas Experiment (SAGE), and Halogen Occultation Experiment (HALOE). Climatological mean differences between these instruments are typically smaller than 5% between 25 and 50 km. Ozone anomaly time series from all instruments, averaged from 35 to 45 km altitude, track each other very well and typically agree within 3 to 5%. SBUV seems to have a slight positive drift against the other instruments. The corresponding 1979 to 1999 period from a transient simulation by the fully coupled MAECHAM4‐CHEM chemistry climate model reproduces many features of the observed anomalies. However, in the upper stratosphere the model shows too low ozone values and too negative ozone trends, probably due to an underestimation of methane and a consequent overestimation of ClO. The combination of all observational data sets provides a very consistent picture, with a long‐term stability of 2% or better. Upper stratospheric ozone shows three main features: (1) a decline by 10 to 15% since 1980, due to chemical destruction by chlorine; (2) two to three year fluctuations by 5 to 10%, due to the Quasi‐Biennial Oscillation (QBO); (3) an 11‐year oscillation by about 5%, due to the 11‐year solar cycle. The 1979 to 1997 ozone trends are larger at the southern mid‐latitude station Lauder (45°S), reaching −8%/decade, compared to only about −6%/decade at Table Mountain (35°N), Haute Provence/Bordeaux (≈45°N), and Hohenpeissenberg/Bern(≈47°N). At Lauder, Hawaii (20°N), Table Mountain, and Haute Provence, ozone residuals after subtraction of QBO‐ and solar cycle effects have levelled off in recent years, or are even increasing. Assuming a turning point in January 1997, the change of trend is largest at southern mid‐latitude Lauder, +11%/decade, compared to +7%/decade at northern mid‐latitudes. This points to a beginning recovery of upper stratospheric ozone. However, chlorine levels are still very high and ozone will remain vulnerable. At this point the most northerly mid‐latitude station, Hohenpeissenberg/Bern differs from the other stations, and shows much less clear evidence for a beginning recovery, with a change of trend in 1997 by only +3%/decade. In fact, record low upper stratospheric ozone values were observed at Hohenpeissenberg/Bern, and to a lesser degree at Table Mountain and Haute Provence, in the winters 2003/2004 and 2004/2005.

Analysis of HCl and ClO time series in the upper stratosphere using satellite data sets

“…Recent ozone trends calculated for 1997 onwards in this altitude region have shown signs of a small recovery (but not significantly different from a zero trend), although the magnitudes found are typically smaller than those of the chlorine species reported here. Jones et al (2009) reported that ozone is increasing at ∼1.7 % (± ∼ 2.0 % decade −1 ) at mid-latitudes based on linear trends from 1997-2008, while Steinbrecht et al (2006) suggest a 1997-2005 trend for Hawaii to be increasing by 1.9 % ± 1.9 % decade −1 . Both of these examples show trend magnitudes to be less than the trend values estimated here using HCl and ClO.…”

“…By being able to separate the relative contributions of known variation (by the process of linear regression), we will be left with the unexplained variability of the monthly mean signal to which a linear trend can be applied. We follow similar approaches to that of Newchurch et al (2003), and Steinbrecht et al (2004Steinbrecht et al ( , 2006, where we firstly remove the seasonal cycle from the HCl time series. This is simply done for each instrument by finding the difference between each monthly mean value from their corresponding average (climatological) annual cycle.…”

“…Large peaks observed between 7-9, 16-22, and 26-32 months in the resulting FFT power spectrum give an estimate to those cycles that are due to the QBO and are used as P QBO (i)in the regression model. We then compare the summed QBO component to zonal wind data provided at 10 hPa over Singapore to ensure that the modeled QBO component has the correct degree of phasing, such that there will be a phase shift in the modeled QBO output due to the delay in the transport of air from the tropics (typically 6-18 months Stiller et al, 2008).…”

“…It has been estimated that the total inorganic loading of tropospheric Cl peaked in 1993 (Rinsland et al, 2003) and has decreased by ∼5 % through early 2002 (O' Doherty et al, 2004). As it is estimated that it takes 3-6 years for air to be transported into the middle and upper stratosphere (Stiller et al, 2008), then peak stratospheric values are suggested to be somewhere between and 1999(WMO, 2006. Based on assumptions that the international agreements are adhered to, it is proposed using the equivalent effective stratospheric chlorine (EESC) parameter that total Cl values will reach pre 1980 levels around 2040 (Newman et al, 2007).…”

A climatology of the diurnal variations in stratospheric and mesospheric ozone over Bern, Switzerland

“…GROMOS is part of the Network for the Detection of Atmospheric Composition Change (NDACC), and its data set is used for cross-validation of satellite experiments, studies of ozone-climate interactions and middle atmospheric dynamics, as well as for long-term monitoring of the ozone layer in the stratosphere (Peter and Kämpfer, 1995;Peter et al, 1996;Calisesi et al, 2001;Dumitru et al, 2006;Hocke et al, 2006;Steinbrecht et al, 2006;Hocke et al, 2007;Flury et al, 2009;Steinbrecht et al, 2009;Studer et al, 2012;Hocke et al, 2013).…”