Flux Measurements on Top of the Research Station Jungfraujoch in Switzerland

Measurements of the microphysics of orographic clouds were conducted over a 4-week period on top of the high-alpine Jungfraujoch research station in Switzerland during 2017. The goal of the measurements was to investigate the discrepancy between high ice number concentrations previously measured at the site and those predicted by primary ice nucleation parametrizations. Farrington et al. (2016) used the Weather Research and Forecasting model (WRF) to show that secondary ice processes, as well as an increase in Ice Nucleating Particles (INPs), could not explain the observed concentrations. One suggestion is that ice crystals generated from surface hoar frost may account for the high concentrations (Lloyd et al. 2015). By implementing a surface flux parametrization into WRF they found that this could account for the observed concentrations.

The measurements in 2017 at the Jungfraujoch station aimed to confirm the existence of these vertical fluxes from the surface and their contribution to the measured number concentration of ice particles. For this goal, the well-adapted and previously used system of a rotation wing that points instruments into the mean wind field was reused in 2017. The list of instruments involved a 3 View-Cloud Particle Imager (3V-CPI). A combined probe of a two-dimensional stereoscopic (2DS) shadow imaging probe and a cloud particle imager (CPI). Furthermore, a cloud droplet probe (CDP) on the wing measured size distributions of liquid droplets, providing a combined particle range of 3 to 1250 μm.

Ice crystal fluxes were calculated using eddy covariance calculated from the wind direction and speed near the inlet of the 3V-CPI. This provides data for the first particle flux calculations for particles over the range of 3 to 1250 μm. The first results show the presence of increased upward but also downward fluxes of both liquid supercooled droplets and larger ice particles which were often composed of pristine plate crystals.

Keywords Schledewitz, Lloyd, Choularton, Gallagher, Eddy-Covariance, Fluxes, Number Concentrations, Cloud Microphysics, Orographic Clouds, Meteorology

References

• R. J. Farrington et al. (2016). Comparing model and measured ice crystal concentrations in orographic clouds during the INUIAQ campaign, Atmos. Chem. Phys., 16 4945-4966.
• G. Lloyd et al. (2015). The origins of ice crystals measured in mixed-phase clouds at the high-alpine site Jungfraujoch, Atmos. Chem. Phys., 15 12953-12969