Hélène Brogniez: understanding the atmospheric water cycle
Hélène Brogniez is a professor at the Université de Versailles - Saint-Quentin-en-Yvelines (UVSQ), a researcher in atmospheric sciences and meteorology at the Laboratory for Climate and Environmental Sciences (LSCE - Univ. Paris-Saclay/French Alternative Energies and Atomic Energy Commission, CEA/National Centre for Scientific Research, CNRS/UVSQ) and director of the Geosciences, Climate, Environment, Planets Graduate School at Université Paris-Saclay. A specialist in atmospheric physics, her research focuses on the remote sensing of atmospheric properties in tropical regions, mainly storm systems, and their representation in climate models.
"When I started studying physics at the University of Lille, what interested me more than the fundamental dimension of my discipline was its practical applications," explains Hélène Brogniez. This appetite for the practical was reinforced during a master's internship in the United States, in a laboratory characterising satellite sensors for radiation measurements. "Discovering that satellites could be used for something other than telecommunications or surveillance was when things first clicked for me," recalls the lecturer, who then decided to focus on Earth observation.
Once this decision had been made, she joined Pierre and Marie Curie University, completing a DEA (now equivalent to a 2nd year master’s degree) in physics-based remote sensing methods. Her subsequent thesis, followed by a post-doctorate at the University of Chicago, concentrated on the use of these remote sensing methods to provide a better characterisation of the distribution of water vapour in the atmosphere. "What really inspired me at the time, and was also an important turning point in my career, was the realisation that the measurements and data we were collecting with our satellites could also be used to evaluate climate models and thus, in a way, serve other areas of understanding," explains the lecturer.
On completing her post-doc, she was recruited as a lecturer at UVSQ in 2006, becoming a professor in 2021. After eighteen years at the Atmospheric Space Observations Laboratory (LATMOS - Univ. Paris-Saclay/CNRS/UVSQ/Sorbonne Univ.), she joined the Laboratory of Climate and Environmental Sciences (LSCE - Univ. Paris-Saclay/CEA/CNRS/UVSQ).
From infrared to microwaves
Since completing her DEA, Hélène Brogniez's research has focused on understanding the atmospheric water cycle, and more specifically the processes involved in water vapour distribution. "To advance this understanding, I'm trying to develop methods for estimating atmospheric water vapour using remote sensing measurements," she explains.
Her thesis exploring the tropical troposphere was based on infrared measurements, but she soon realised that there was a major obstacle with processing the data in this spectral range; the presence of clouds influencing infrared radiation. "I began my post-doctorate at the University of Chicago at a time when microwave sensors were proving very effective and interesting for monitoring atmospheric water, such as humidity, clouds and rain. So I changed my approach slightly and decided to continue my research in the microwave field and exploit its benefits," explains Hélène Brogniez. It was a turning point that furthered her understanding of atmospheric transport processes and, from then on, she continued to use this measuring range.
Megha-Tropiques Mission: from algorithms to atmospheric physics
Based on this expertise in the microwave range, once Hélène Brogniez had taken up her position at UVSQ, she was invited to join the team working on the French-Indian Megha-Tropiques space project. The mission's main objective was to study the energy exchanges taking place within the tropical belt. "In 2009, I took over responsibility for the operation and definition of analysis algorithms for future Megha-Tropiques measurements. Once the satellite launched in 2011, I also organised a field measurement campaign in Burkina Faso, along the satellite's ground track, to validate the algorithmic part that I had contributed to developing," explains the lecturer.
This mission helped to collect a huge amount of data during Megha-Tropiques' twelve-year flight, and in the years that followed, Hélène Brogniez worked with engineers and doctoral students to gain a better understanding of the mechanisms driving atmospheric water evolution in the context of climate change. "One of the challenges of this type of research is comparing our observational diagnoses with different climate models, so as to aid modellers in their efforts to improve the representation of atmospheric processes," explains the lecturer.
C2omodo Mission: understanding storm dynamics
Hélène Brogniez's career took a new turn in 2019, when she accepted the position of lead scientist on the C2omodo (Convective core observations through Microwave derivatives in the tropics) mission, scheduled for launch in 2028. Developed by the French space agency, CNES, as part of the international Atmospheric Observing System (AOS) programme led by NASA, this mission aims to use a tandem of two identical microwave instruments following each other at one-minute intervals. These will provide measurements of the rapid dynamics of thunderstorm development, improving their understanding and subsequent numerical representation.
"In practical terms, once the mission has launched, the idea will be to try and see how the humidity around clouds modifies the lifespan or intensity of thunderstorms. The objective is to compare numerical models with observational data and, ultimately, to work towards improving weather and climate models. But at the moment, we're mainly working on how we're going to manage the data and, inevitably, the communication around this future mission," explains the lecturer.
Dialogue as a common theme
If there's one constant in Hélène Brogniez's career, it's dialogue! "Since I began my research, I've been fortunate, as a member of the observation community, to be in constant dialogue with the modelling community," she explains. For several years, Hélène Brogniez has also helped to foster this dialogue between researchers at the Geosciences, Climate, Environment, Planets Graduate School at Université Paris-Saclay.
Bringing together seven research laboratories with a total workforce of around 650 individuals, this Graduate School is characterised by its use of multiple, complementary approaches, such as fieldwork, laboratory measurements, remote sensing, space missions, numerical modelling and experimental simulation. "Although this collective is immensely strong, it should not duplicate the work being carried out within the Institute Pierre Simon Laplace, to which many of our members also belong. That's why we're still considering our positioning, so that with Université Paris-Saclay, we can offer something distinctive. The adventure is only just beginning," concludes the lecturer.
