Évolution de la colonne totale d'ozone à deux stations tropicales : observations et modélisation

While the tropics cover a large part of the globe, few long-term ozone observations data exist in this region. In addition, the tropics are the regions where most of the stratospheric ozone is formed. Indeed, the tropical region is the main entry point for tropospheric chemical species and water vapor in the stratosphere, subsequently redistributed at mid-latitudes by the Brewer-Dobson circulation. Monitoring the evolution of the ozone layer in these regions is based on observations (satellite, ground-based and aircraft instruments). This monitoring allows the quantification of stratospheric ozone variability and trends to understand past changes and validate the models used to predict the ozone evolution in these regions. In this perspective, the work of this thesis is divided into two parts: firstly, the analysis and comparison between the UV-Visible SAOZ spectrometer data and those of 10 satellite instruments in the tropics above the Bauru stations (22.18S, 49.06W) in Brazil and Reunion Island (21.11S, 55.53E) in the Indian Ocean. The ozone columns show a negative average bias (-0.84%) between the satellite columns and SAOZ (SAT-SAOZ) in Bauru unlike Réunion (0.75%), where the bias is positive. Moreover, we observe an increase in this bias from 2004 in Bauru of -1.78% / decade, less important in Reunion (-0.8% / decade). The study of this drift has shown that the latter is correlated with an uplift of the vertical ozone profile at equatorial latitudes characterized by an equivalent latitude drift of the Bauru station, which is not considered in the calculation of the Air Mass Factor (AMF) used to convert the slant column measured by SAOZ into vertical column (TOC). Subsequently, the capacity of 9 CCMI-derived climate-chemistry models to reproduce the observed columns, its variations and external forcing on variability was evaluated by comparing the simulations with those of SAOZ and the monthly mean satellites at both stations. The models show a good restitution of the variability of the ozone column with however an overestimation of 3% at both stations compared to the observations. The analysis of the forcings shows a contribution dominated by QBO (~ 40%), followed by ENSO (~ 20%), solar activity (~ 20%), equivalent latitude drift > 10% at Bauru and 10% à Bauru et <10% à La Réunion et plus faible pour les aérosols (