Extreme rain events in the Tropics : what are the key atmospheric controlling factors ? - Précipitations extrêmes tropicales : quels sont les indicateurs atmosphériques clé ?

Tropospheric moisture is a central element of the global climate and its variability, from the boundary layer up to the stratosphere, water vapor acts as the main greenhouse gas, transports heat and is tightly linked to the formation and dissipation of clouds. For instance, the moistening of the lower troposphere is necessary to trigger convection, while mid-tropospheric intrusions of dry air in the vicinity of a mesoscale convective system (MCS) yield to inhibit its development. In the Tropics, rainfall is an essential component of the economy and is brought by these MCSs that organize during the monsoon.
Since several years tremendous work has been carried out by the modelling community to assess and understand how these MCSs develop and dissipate and why some of them are associated to extreme events. The path to a better understanding of these extreme events requires to dig further into the observation system : this will help to study how the physical processes will define the observed properties.

The project of this internship will focus on the rainfall monitored over the Sahelian region. Indeed, this area is a nice test-bed since it has been studied thoroughly thanks to numerous field campaigns, such as the 2006 international AMMA campaign (African Monsoon Multi-disciplinary Analysis), associated to numerical experiments.
The recent study of Taylor et al (2017) highlighted the intensification of Sahelian MCSs since the 1980s and further questioned the role of the low-level moisture. However, questions remain on how far do we need to describe the atmospheric column in order to best constrain rainfall models used to predict extreme rainfall events.

The objective of the present project is to use the available observations of surface rainfall, provided by a network of rain-gauges (namely AMMA-CATCH), together with satellite (the Megha-Tropiques satellite) estimates of vertically-resolved atmospheric moisture. This study will analyze the hydrological cycle observed at the local scale, and is expected to provide a first-order understanding on the atmospheric constraints on the development of MCSs associated to extreme rainfall.

The funding will rely on the Megha-Tropiques “Groupement de Recherche” and the internship will make the bridge between LATMOS, with the expertise on the Megha-Tropiques measurements, and IGE, with the expertise on the rain-gauge measurements.

References :

• Taylor C and co-authors (2017) : Frequency of extreme Sahelian storms tripled since 1982 in satellite observations, Nature Research Letter, 544, 475-480, doi:10.1038/nature22069
• AMMA-CATCH : http://www.amma-catch.org
• Megha-Tropiques : http://meghatropiques.ipsl.polytechnique.fr/

Pour candidater : - A letter of motivation stating the suitability of the candidate’s profile for the project and the reasons for his interest in the subject.
– A detailed CV.
– A transcript of the M1 grades (or M2 if available).
– The coordinates of a reference person.