Dr. Anne-Claire Billault-Roux awarded for her Ph. D. thesis
Dr. Anne-Claire Billault-Roux has been awarded by EDCE Committee with the "EPFL Outstanding Ph. D. Thesis Distinction in Civil and Environmental Engineering" for her Ph. D. thesis on "Snowfall microphysics: a dual-frequency and Doppler spectral radar perspective" defended during the past academic year.
The Ph. D. thesis was funded by H2020 European project « ICE GENESIS ».
Snowfall is an essential component of the hydrological cycle, as it is involved in most precipitation on Earth, either directly as snow falling to the ground or indirectly as rain melted from snow. At the same time, the ice phase in clouds and precipitation is a key contributor to the Earth’s radiative budget, making it a crucial aspect of climate-oriented research. Properly modeling snowfall for both weather and climate applications requires knowledge of the “microphysics of snowfall”, that is, a microscale description of snow particles and of the mechanisms by which they form, grow, and decay.
Among different approaches to studying snowfall microphysics, remote sensing techniques and, in particular, meteorological radars, offer decisive insights. The goal of my thesis was to investigate the microphysical properties and processes of snowfall by relying primarily on measurements from radars transmitting at different frequencies and on radar Doppler spectra – which disclose how radar signals are distributed between large, fast-falling, and small, slow-falling particles.
One aspect of my work consisted in collecting a multi-sensor dataset of in situ and remote sensing measurements of snowfall, during a field campaign in the Swiss Jura mountains. I then introduced new methods to retrieve cloud and snowfall properties from remote sensing measurements, making use of cutting-edge machine-learning techniques. With a slightly different perspective, I then focused on a specific snowfall event: there, we showed that a lot could be learnt, using radar measurements, about certain ice growth and multiplication mechanisms which are still poorly understood. Overall, this work sheds a new light on remote sensing studies of snowfall microphysics, both in terms of quantifying snowfall properties, and understanding the complex processes at work.
As a postdoctoral researcher at the Environmental Remote Sensing laboratory, I am currently working on a continuation of the research questions I explored during my thesis. My goal is to better characterize the intrinsic limitations and uncertainties of such radar-based studies of cloud and precipitation microphysics, to understand how far we can hope to take them.