Evaluation of ozone total column and vertical distribution recovering trends at NDACC Northern mid-latitude station
Résumé
Since the mid-eighties, stratospheric ozone has been monitored at Observatoire de Haute-Provence (OHP - 44°N, 6°E) by a variety of instruments. Ozone total column measurements are provided by Dobson and DOAS spectrometers since respectively 1983 and 1992 while ozone vertical distribution is obtained by lidar, sondes and Umkehr measurements since respectively 1985, 1984 and 1983. In addition to the ozone data obtained at OHP, satellite ozone measurements from SAGE II, MLS and GOMOS are used for the study of the short term and long term evolution of ozone total column and vertical profile at the station. First, the coherence of ozone time series is evaluated from the analysis of the differences with satellite and ground-based coincident ozone records. This analysis shows generally non significant drifts between the various measurements, especially in the 20 - 40 km range. The stratospheric ozone total column and vertical profile trends are then estimated using the equivalent effective stratospheric chlorine (EESC) time series and two linear trend functions to simulate the change in the trends of ozone depleting substances. To that aim, a multiple linear regression model is used with different explanatory variables such as the quasi-biennial oscillation (QBO), the Northern Atlantic oscillation (NAO), solar flux, eddy heat flux, stratospheric aerosols optical depth and trend function. The computed trends from the ozone column at OHP indicate a clear signal of ozone recovery after 1997. Likewise, significant positive trends of the ozone vertical distribution are estimated in the 15 - 45 km altitude range after 1997. The influence of the various proxies on the medium and short term ozone variability is also analyzed, indicating that the QBO and eddy heat flux have contributed to the large ozone levels observed in 2010. In the lower stratosphere, the regression model is less efficient in reproducing ozone variability and other proxies are tested such as equivalent latitude in order to represent the advection of polar and tropical air masses over OHP during the winter and springtime.