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PhD Defense

Robin Wing (LATMOS)

Title : Studies of decadal variations in the temperature of the middle atmosphere.

Date and time : The 21-02-2019 at 14h00

Type : thèse

Université qui délivre le diplôme : UVSQ

Location : Bâtiment d'Alembert, salle des thèses (2ème étage), 5-7 Boulevard d'Alembert, 78280 Guyancourt.
Members of jury :

Chantal Claud, Directrice de recherche, Laboratoire de Météorologie Dynamique, Présidente

Nathalie Huret, Professeure, OPGC / Université de Clermont-Ferrand, Rapporteure

Alexis Le Pichon, Directeur de recherche, CEA-DAM, DASE, Rapporteur

Wolfgang Steinbrecht, Professeur, Deutscher Wetterdienst, Examinateur

Alain Hauchecorne, Directeur de recherche, CNRS, Directeur de thèse

Philippe Keckhut, Professeur, Université de Versailles Saint-Quentin-en-Yvelines, Co-directeur de thèse

Albert Hertzog, Maître de conférences, Laboratoire de Météorologie Dynamique, Invité

Summary :

The Earth’s middle atmosphere is a pristine natural laboratory for the study of geophysical fluid dynamics and optics in neutral gasses. Research in this region has long been  limited by a lack of long-term observations which are capable of covering the entire region from the troposphere to the upper mesosphere and lower thermosphere. Past decades have seen the construction of many ground based observatories and launches of satellite based instruments in an effort to provide the measurements needed to understand the chemistry, dynamics, and long-term climactic changes in the middle atmosphere. Both groundbased and space-based atmospheric remote sensing have clear strengths as well as limitations; the former being able to provide high resolution, well calibrated measurements at a single site and the latter allowing for global coverage at the cost of resolution and some degree of certainty in calibration. For this work we are using temperature measurements produced from a Rayleigh-scatter lidar ground-based remote sensing technique and making systematic comparisons to temperature profiles produced from three passive scanning satellite-based remote sensing instruments: Microwave Limb Sounder on the Aura satellite (MLS), Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), and Global Ozone Monitoring by Occultation of Stars (GOMOS). This manuscript has three main results : 1a) Results of several improvements to the lidar temperature algorithm resulting in a cooling of the mesospheric temperatures by up to 20 K at 90 km. 1b) Better agreement between the cooled lidar temperatures and temperature profiles from SABER and MLS between 70 km and 90 km. 1c) A cross-validation between temperatures from a co-located Rayleigh temperature lidar and ozone lidar which provides confidence in the stability of the lidar technique and justification for the use of lidar temperatures as a reference database for satellite validation. 2a) Presentation of a decadal comparison between the validated lidar temperatures and the temperatures produced by SABER and MLS. 2b) We show a cold bias in the satellite measurements with respect to the lidar (-6 K for SABER and -17 K for MLS) in the stratopause region, a warm bias (6 K near 60 km) in the summer mesosphere, and a vertically structured bias for MLS (-4 to 4 K) which spans the middle atmosphere. 2c) We reduce the magnitude of the bias by vertically shifting the height of the satellite stratopause and see an improvement in the resulting lidar-satellite temperature comparison. This result has important implications for the reporting of satellite temperatures as a function of geopotential height. 3a) Comparison of lidar temperature profiles with the newly created GOMOS temperature data base shows that satellite geometric altitudes can be better estimated by occultaion techniques than by inference of pressure levels from radiometric data 3b) The effect of tides on lidar to satellite temperature comparisons when the satellite overpass is temporally offset from the lidar measurement can be on the order of 2 to 4 K depending on the phase of the solar hour.

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