Earth Observation Data Group

Abstract:

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a polar orbiting high resolution mid-infrared emission stratospheric limb sounder with a nominal vertical resolution of 3 km. Work to extend the list of interesting, routinely retrieved species led to the examination of SF6, a potent greenhouse gas and a useful tracer species. We demonstrate the feasibility of profile retrievals in the range 6-30 km based on single scans. Additionally, we investigate latitudinal variation using coaddition to improve signal-to-noise. A mean mid-latitude profile shows tropospheric (4.32 +/- 0.03 pptv, 6-12 km) and stratospheric (3.50 +/- 0.03 pptv, 21-30 km) regimes, in September 2002, similar to accepted values. The global mean contains an interhemispheric variability of the order of 0.3 pptv in the lower stratosphere, in line with age of air. Finally, the continuation of acknowledged global trends in atmospheric concentration, is estimated at +0.28 pptv yr(-1) (6.5 +/- 1.3% yr(-1)).

Abstract:

We present a new method to determine mesospheric electron densities from partially reflected medium frequency radar pulses. The technique uses an optimal estimation inverse method and retrieves both an electron density profile and a gradient electron density profile. As well as accounting for the absorption of the two magnetoionic modes formed by ionospheric birefringence of each radar pulse, the forward model of the retrieval parameterises possible Fresnel scatter of each mode by fine electronic structure, phase changes of each mode due to Faraday rotation and the dependence of the amplitudes of the backscattered modes upon pulse width. validation results indicate that known profiles can be retrieved and that chi(2) tests upon retrieval parameters satisfy validity criteria. Application to measurements shows that retrieved electron density profiles are consistent with accepted ideas about seasonal variability of electron densities and their dependence upon nitric oxide production and transport. (C) 2004 Elsevier Ltd. All rights reserved.

Abstract:

During recent years ozone depletion has been detected not only over polar regions but also over mid-latitude areas. This study analyzed daily total ozone (TO) data from three south-western European locations in order to detect long-time TO trends by means of a filtering technique. Correlation analysis with atmospheric circulation patterns was carried out to explain the decreasing trends observed. Results appear to show a strong correlation between TO decrease and the North Atlantic Oscillation and Arctic Oscillation Indices throughout recent decades. On the other hand, the trends also indicate that, at least during the last ten years, TO variations cannot be explained solely by natural atmospheric cycles over the studied area.