Snowfall microphysics: insights gained from Doppler radars

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• Anne-Claire Billault-Roux (LTE - EPFL)
• Friday 12 July 2024, 14:00-15:00
• BAS Cambridge Seminar Room 1 and Zoom.

If you have a question about this talk, please contact Siddharth Gumber.

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 of 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 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 and grow. Among different approaches to studying snowfall microphysics, meteorological radars offer decisive insights: the interpretation of radar variables reveals unique information on the microphysical properties of hydrometeors over large spatial areas and along the vertical dimension. In this talk, we investigate snowfall microphysics by relying primarily on measurements from radars transmitting at different frequencies and on radar Doppler spectra. The data stems from a multi-sensor dataset of in situ and remote sensing measurements, which was collected during the ICE GENESIS campaign in the Swiss Jura Mountains in January 2021.

Based on these measurements, we first propose a novel framework to retrieve a number of snowfall microphysical properties from dual-frequency radar Doppler spectra, relying on a two-step, physics-driven deep learning approach. In comparison with existing methods, this framework relaxes the need for certain prior assumptions on microphysical properties, or on perfect beam alignment and non-turbulent atmosphere. We evaluate the retrieval against in situ measurements, and the encouraging (albeit not perfect) results pave the way for advanced characterizations of snowfall properties on larger datasets. Then, we focus on a specific snowfall event of ICE GENESIS . Through a detailed analysis of multi-frequency and Doppler spectral measurements, we propose interpretations of the complex signatures observed, which reveal the occurrence of distinct ice production and growth processes. With this case study, we further illustrate the relevance of radar measurements to improve our understanding of microphysical processes.

This talk is part of the BAS Atmosphere, Ice and Climate Seminars series.

This talk is included in these lists:

• BAS Atmosphere, Ice and Climate Seminars
• BAS Cambridge Seminar Room 1 and Zoom

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