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Charles Chemel

Publications and source records attributed to Charles Chemel.

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The TEAMx Observational Campaign

As part of the international research programme TEAMx (multi-scale transport and exchange processes in the atmosphere over mountains - programme and experiment) a one-year long measurement campaign, the TEAMx Observational Campaign (TOC), was conducted between 2024 and 2025 in a north-south transect through the Alps. Building on the dense operational measurement network in the Alps, the TOC was designed to collect long-term atmospheric observations over the highly complex Alpine terrain. During two six-week long Extended Observational Periods, more than 40 research institutions came together to instrument about 30 sites in the four target areas of the TEAMx domain and study different transport processes, from gravity waves to orographic convection, thermally driven flows, and turbulent exchange. In addition to a suite of ground-based in-situ and remote-sensing instruments, observational activities included airborne measurements with up to three research aircraft and multiple UAS. This paper gives an overview of the science goals and the TOC design, together with preliminary analyses that highlight the potential of the collected dataset.

physics.ao-ph

Numerical Modelling of Neutral Boundary-Layer Flow across a Forested Ridge

Forest canopies have been shown to alter the dynamics of flows over complex terrain. Deficiencies have been found when tall canopies are represented in numerical simulations by an increase in roughness length at the surface. Methods of explicitly modelling a forest canopy are not commonly available in community numerical weather prediction models. In this work, such a method is applied to the community Weather Research and Forecasting model. Simulations are carried out to replicate a wind-tunnel experiment of neutral boundary-layer flow across a forested ridge. It is shown that features of the flow, such as the separated region on the lee slope of the ridge, are reproduced by the roughness length or canopy model methods. Shear at the top of the ridge generates turbulence that spreads vertically as the flow moves downstream in both cases, but is elevated to canopy top where a canopy model is used. The roughness-length approach is shown to suffer several deficiencies, such as an over-prediction of mean wind-speeds, a lack of turbulence over flat forested ground and an insufficient vertical extent of turbulence at all locations of the domain studied. Sensitivity to the horizontal resolution of the simulation is explored. It is found that higher resolution simulations improve reproduction of the mean flow when modelling the canopy explicitly. However, higher resolutions do not provide improvements for the roughness-length case and lead to a reduction in the horizontal extent of the separated region of flow on the lee slope of the ridge.

physics.ao-ph