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Abstract.A new snow melting parametrization is presented for the non-hydrostatic limited-area COSMO ("consortium for small-scale modelling") model. In contrast to the standard cloud microphysics of the COSMO model, which instantaneously transfers the meltwater from the snow to the rain category, the new scheme explicitly considers the liquid water fraction of the melting snowflakes. These semi-melted hydrometeors have characteristics (e.g., shape and fall speed) that differ from those of dry snow and rain droplets. Where possible, theoretical considerations and results from vertical wind tunnel laboratory experiments of melting snowflakes are used as the basis for characterising the melting snow as a function of its liquid water fraction. These characteristics include the capacitance, the ventilation coefficient, and the terminal fall speed. For the bulk parametrization, a critical diameter is introduced. It is assumed that particles smaller than this diameter, which increases during the melting process, have completely melted, i.e., they are converted to the rain category. The values of the bulk integrals are calculated with a finite difference method and approximately represented by polynomial functions, which allows an efficient implementation of the parametrization. Two case studies of (wet) snowfall in Germany are presented to illustrate the potential of the new snow melting parametrization. It is shown that the new scheme (i) produces wet snow instead of rain in some regions with surface temperatures slightly above the freezing point, (ii) simulates realistic atmospheric melting layers with a gradual transition from dry snow to melting snow to rain, and (iii) leads to a slower snow melting process. In the future, it will be important to thoroughly validate the scheme, also with radar data and to further explore its potential for improved surface precipitation forecasts for various meteorological conditions.

Accurate numerical weather prediction of intense snowfall events requires the correct representation of dynamical and physical processes on various scales. In this study, a specific event of high-impact wet snowfall is examined that occurred in the northwestern part of Germany in November 2005. First, the synoptic evolution is presented, together with observations of precipitation type and vertical temperature profiles, which reveal the existence of a so-called potential melting layer during the early period of wet snowfall. During the main part, the performance of the operational forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF) is investigated. It is shown that only the short-term predictions captured the snowfall event, whereas earlier forecasts were in error concerning the phase and/or amount of precipitation. However, even the short-term forecasts produced the onset of surface snowfall too late (i.e., during the dry snowfall period). Reasons for the misforecasts are errors on various scales. For the early forecasts, they include an inaccurate representation of the upper-level trough and a misplacement of the surface cyclone. For the later forecasts, a slight overestimation of the depth of the potential melting layer and a potentially too fast snow melting process in the model lead to the erroneous prediction of surface rainfall during the wet snowfall period. Hindcast experiments with the high-resolution Consortium for Small-Scale Modeling (COSMO) model also point to the necessity of improving its snow melting parameterization in order to provide useful predictions of potentially high-impact wet snowfall events.

Many scientific institutions are faced with the question of how they should inform their scientists and scientific coordinators about the option of publishing open access. This task is one that libraries have taken upon themselves: libraries are familiar with the market participants and have years of experience in teaching information and publication literacy. This case report looks at two approaches taken by the Central Library of Forschungszentrum Jülich in 2017. It highlights the motivation, strategy, resources and implementation, as well as the first evaluation of both approaches. The first approach was a redesign of the training courses offered by the Central Library with a focus on the target groups and new contents. The second approach was implemented as part of International Open Access Week and involved offering an information event tailored to each scientific institute. The event was customized to meet the needs of the target group defined by each institute, the institute itself, and was organized individually. As a result of these efforts, the open access rate increased over the last few months and at 48% open access in 2017, Forschungszentrum Jülich is well on its way to achieving the open access goals set by the Helmholtz Association.