Pristine areas (ultraclean regions, low aerosol content) are of fundamental importance in the understanding of the changing climate because they are far from anthropogenic and terrestrial sources of contamination and so are good proxys of the natural component of the climate. This natural component is still far to be understood. For instance, due to the low aerosol optical depth (AOD < 0.1), the cloud aerosol interactions in pristine areas are highly sensitive to small variations of the AOD and of the humidity, and may have important nonlinear impacts on cloud formation and properties (cloud base altitude, height, microphysical content, lifetime, cloud field structure, etc.).
In this PhD Thesis, the pristine areas under consideration are oceanic ones, with a special attention paid to the Indian Ocean. It has been recently the topic of a paper  examining statistically, through almost a decade, the AOD distribution and variability, and highlihting the interest of the Southern Indian Ocean for cloud and aerosol physics as well as climate change investigations.
The Indian Ocean is currently the place of a field campaign (Dec. 2018 → Apr. 2019) devoted to characterize the marine aerosol, humidity and cloud properties around the Reunion Island and offshore. Several laboratories are involved in this campaign (LOA, LaCy, Leeds University) and a large instrumentation is operating: (1) microwave and infrared radiometers for very-high time resolved temperature and humidity profiles, (2) Doppler polarimetric radar for wind and cloud detailed properties, (3) lidar and photometer for aerosol characterization. This campaign is funded by the CNRS-INSU (LEFE project) and data will be used in addition in the frame of three ANR project (ReNovRisk, BIO- MAIDO, CONCIRTO).
The PhD student will have to analyse the data acquired during this campaign (AOD, humidity, cloud properties) in order to understand more thoroughly how sea-air exchanges (heat, aerosols, humidity, momenta) occur and to quantify them precisely. The underlying question is the deep characterization of the cloud aerosol interactions in this pristine Ocean to better quantify the natural component of the changing climate. This experimental part of the PhD thesis will be accompanied by a theoretical part in which the PhD student will have to develop a statistical model (Ising-like) of cloud formation. Comparisons with other pristine areas (Atlantic, Pacific) will be performed.
 Mallet P.E, Pujol O., Brioude J., Evan S., Jensen A., 2018: Marine aerosol distribution and variability over the pristine Southern Indian Ocean, Atm. Env., 182, 17-30
Please send your application (cover letter and CV) to firstname.lastname@example.org
Supervisors : Olivier Pujol (Dir.) & Jérôme Brioude (LaCy, co-Dir.)
Laboratory : Laboratoire d’Optique Atmosphérique, UMR CNRS 8518
Fundings : Labex CaPPA (WP5)