Appel à candidatures | Recherche, Emploi

PhD: Protecting Orchards from Spring Frosts: The Role of Katabatic Winds in Radiation Frost Processes on Slopes

Du 1 octobre 2026 au 30 septembre 2029

Application till 07/06/2026. Starting grant: 01/10/2026 (3 years)
LEGI Grenoble, France

The PhD will focus, on the one hand, on the in situ observation and study of radiative frost events, and, on the other hand, the analysis of technological methods to combat the effects of these frosts in order to characterize their effectiveness, propose avenues for optimization, and devise viable solutions that are financially accessible to fruit growers and universal—and thus applicable to similar situations encountered in vineyards. we will evaluate the passive mixing effect generated by the interaction of the descending katabatic wind and the presence of low walls or hedges transverse to the flow. Another avenue of investigation will be to examine the source of surface radiative cooling by assessing the impact of injecting a water vapor mist at the orchard scale and its ability to inhibit radiative exchange with the atmosphere by reducing its emissivity. This study will be conducted under real-world conditions in the Belledonne massif and in situ in the orchards of Savoie.

Current climate change is leading to an increase in the frequency and intensity of extreme weather events. Among these, spring frosts are increasingly affecting the development of fruit trees. This project aims to leverage the synergy of the various approaches in which LEGI specializes (numerical, experimental, and theoretical) to gain a detailed understanding of the cooling processes at work in orchards during frost events and to analyze the turbulent mixing required to counteract them.
The project has two main objectives:
• To study the phenomenon of spring frosts in order to better understand the thermodynamic and aerodynamic processes involved and their interaction in alpine terrain, under the thermal inversion conditions commonly observed during anticyclonic weather episodes.
• analyze the effectiveness of the control measures implemented in the field, model them, evaluate them, and propose alternative solutions:
◦ Utilizing the Alpine topography and associated katabatic winds to increase turbulent mixing through passive measures (low walls, hedges)
◦ Generating water vapor clouds to reduce or block radiative exchange at the surface
The approaches used in the study are diverse and complementary, and all draw on LEGI’s expertise in the field of fluid mechanics as applied to geophysics (the MEIGE team) and to high-performance computing (HPC) modeling of turbulence (the MoST team):
- In situ studies of spring frost phenomena in orchards in Savoie
- High-performance computing (HPC) 3D numerical modeling of relevant weather events at the
orchard scale, within the regional context and under idealized conditions
- Theoretical analysis of hydrodynamic and thermal instabilities involved in turbulent mixing
processes at the surface layer scale on hillsides
While firmly rooted in basic research on turbulence, the project aims to address a societal issue and, as
such, will involve close collaboration with various stakeholders concerned with the problem of spring frosts :
• an arborist from the SCEA des Vergers de la Ferme du Coteau in Savoie
• the Mont-Blanc Savoie Chamber of Agriculture network
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To carry out this project, the in situ experimental component will be conducted as part of a doctoral thesis supervised by an assistant professor and a researcher from the MEIGE team at LEGI. The purpose of this project is to describe how the thesis, which focuses on in situ observations of turbulence, will contribute to a component of the research project and is expected to: first, improve our understanding of the processes involved in the interaction between downslope winds and radiative frosts in orchards; and second, propose effective and quantifiable solutions to mitigate these frosts.