S. Godin

Upper-Stratospheric Ozone Trends 1979-1998

Extensive analyses of ozone observations between 1978 and 1998 measured by Dobson Umkehr, Stratospheric Aerosol and Gas Experiment (SAGE) I and II, and Solar Backscattered Ultraviolet (SBUV) and (SBUV)/2 indicate continued significant ozone decline throughout the extratropical upper stratosphere from 30–45 km altitude. The maximum annual linear decline of −0.8±0.2 % yr−1 (2σ) occurs at 40 km and is well described in terms of a linear decline modulated by the 11-year solar variation. The minimum decline of −0.1±0.1% yr−1 (2σ) occurs at 25 km in midlatitudes, with remarkable symmetry between the Northern and Southern Hemispheres at 40 km altitude. Midlatitude upper-stratospheric zonal trends exhibit significant seasonal variation (±30% in the Northern Hemisphere, ±40% in the Southern Hemisphere) with the most negative trends of −1.2% yr−1 occurring in the winter. Significant seasonal trends of −0.7 to −0.9% yr−1 occur at 40 km in the tropics between April and September. Subjecting the statistical models used to calculate the ozone trends to intercomparison tests on a variety of common data sets yields results that indicate the standard deviation between trends estimated by 10 different statistical models is less than 0.1% yr−1 in the annual-mean trend for SAGE data and less than 0.2% yr−1 in the most demanding conditions (seasons with irregular, sparse data) [World Meteorological Organization (WMO), 1998]. These consistent trend results between statistical models together with extensive consistency between the independent measurement-system trend observations by Dobson Umkehr, SAGE I and II, and SBUV and SBUV/2 provide a high degree of confidence in the accuracy of the declining ozone amounts reported here. Additional details of ozone trend results from 1978 to 1996 (2 years shorter than reported here) along with lower-stratospheric and tropospheric ozone trends, extensive intercomparisons to assess relative instrument drifts, and retrieval algorithm details are given by WMO [1998].

Dual lidar observations of mesoscale fluctuations of ozone and horizontal winds

A case study is presented of 6.5 h of simultaneous colocated stratospheric Differential Absorption Lidar (DIAL) measurements of ozone concentration and Rayleigh-Mie Doppler (RD) lidar measurements of horizontal wind velocity from the Observatoire de Haute Provence (OHP), France (44°N, 6°E). The RD lidar observations reveal a distinct gravity wave motion at ∼12–18 km, while the DIAL data show laminated ozone structures in the same height range. We combine these data to show that advection due to the gravity wave cannot produce the large ozone lamina at ∼14km.

Correlation of ozone loss with the presence of volcanic aerosols

Statistically significant reductions of ozone compared to a climatological profile have been measured above the Observatoire de Haute Provence (OHP) in Southern France (43.9 deg N, 5.7 deg E) during the months of July and August, 1992. Lidar profiles of ozone, temperature and aerosols were recorded on 25 separate nights during that time. The change in the ozone profile is correlated with the presence of volcanic aerosols from the eruption of Mt. Pinatubo. The total ozone loss amounts to approximately a 10% reduction in the total ozone column over OHP.

Interannual changes of temperature and ozone: Relationship between the lower and upper stratosphere

Changes of stratospheric dynamical structure and ozone are investigated in observations of the lower stratosphere, from meteorological analyses and Total Ozone Mapping Spectrometer (TOMS) ozone, and in contemporaneous observations of the upper stratosphere and mesosphere, from the French lidar at Observatoire de Haute-Provence (OHP). Interannual changes in the lower stratosphere are shown to be accompanied by coherent changes in the upper stratosphere and mesosphere. Over the 1980s and 1990s, both operate coherently with anomalous forcing of the residual mean circulation. Changes of temperature and ozone at OHP have sign and structure consistent with interannual changes of meridional transport. They reflect a poleward expansion and contraction of warm ozone-rich air, compensated by opposite changes of the polar-night vortex.

Vertical short-scale structures in the upper tropospheric and lower stratospheric temperature and ozone at la Réunion Island (20.8°S 55.3°E)

The distribution and the nature of vertical short-scale structures observed in ozone and temperature are investigated in the upper troposphere and the lower stratosphere at La Reunion Island located in the vicinity of the southern subtropical barrier by using wavelet-based methods. A climatology of dominant wavelike patterns with short vertical wavelengths reveals the presence of localized structures on both the ozone and the temperature perturbations, extracted from ozonesonde and temperature data, up to the middle stratosphere. Some case studies are presented to identify the nature of short-scale structures with 1- to 5-km vertical wavelengths in the troposphere and the stratosphere. A climatology of short-scale structures induced by gravity waves and the horizontal advection shows that short-scale structures are mainly detected in the middle and upper troposphere and in the lower stratosphere. The weak value of the coefficient R(z) that links the ozone and temperature perturbations induced by gravity waves is a major limit to detecting such short-scale structures above 21-km altitude. Some structures with vertical wavelengths ranging from 1 to 5 km are attributed to gravity waves produced by convection in summer and the subtropical jet in winter, or quasi-horizontal large-scale motions from both sides of the subtropical barrier.

Doppler Wind Lidar in the Stratosphere: Sensitivity to High Mie Scattering and Self-Correction

A Rayleigh Doppler Lidar is operated at the Observatoire de Haute-Provence (OHP) (44°N, 6°W) for winds measurement in the stratosphere. The instrument has been designed to run in presence of large amount of particles [1]. However, for lower altitudes and high Mie/Rayleigh scattering ratio, recent measurements have revealed that the residual errors can reach several m/s, order of the magnitude of the wind perturbations under study. A correction is applied coupling estimates of scattering ratios within the clouds, observed winds and theoretical calculation. An illustration of the possible use of the wind Lidar is given through simultaneous Lidar measurements of wind, ozone and temperature perturbations as produced by gravity waves processes.