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1st International Summer Snowfall Workshop at University of Cologne

47 scientists from 8 different countries met at the first International Summer Snowfall Workshop, held at University of Cologne's Institute for Geophysics and Meteorology from 28 - 30 June 2017. The workshop was organized by the recently founded Emmy-Noether Group OPTIMIce (Optimal combination of Polarimetric and Triple frequency radar techniques for Improving Microphysical process understanding of cold clouds).

© Stefan KneifelParticipants of the 1st Summer Snowfall Workshop in Cologne, Germany.
Copyright: Stefan Kneifel


Snowfall plays an enormous role in the Global Hydrological Cycle. Especially at higher latitudes, snowfall is the predominant type of precipitation. Today we know from satellites that the majority of raindrops falling to the ground anywhere on the globe, actually started as snowflakes further up in the cloud. The natural variability of snow particle sizes, number concentrations, shapes and densities, makes ice and snow clouds one of the biggest challenges not only for weather and climate modelers but also for observationalists.


Such a complex topic can only be efficiently approached by collaborations between different experts. Motivated by the discussions and recommendations formulated at the last meeting of the International Precipitation Working Group (IPWG), the main objectives of the workshop were:

  • Discuss the progress in developing single scattering databases needed for global snowfall retrievals and data assimilation
  • Define standards and conventions for storing scattering data in order to make them easier accessible to the wider community
  • Discuss applications of these datasets including development of bulk scattering properties and approximations needed for operational users
  • Bridge the gap between scattering models and measured in-situ properties of snowfall and find ways how to evaluate the scattering datasets

Due to the attendance of representatives of all major groups being active in the field of scattering computations for complex snow particles, it was possible to define a first conceptual framework of how to store the multiple scattering datasets. Standards and conventions for specific datasets were defined and a core group agreed on continuing discussions of the data structure in bi-weekly web-conference meetings. Participants from weather organizations and European organizations such as the ECMWF brought important impulses into the discussion what is mostly needed in terms of scattering computations and what is currently missing in our databases. Finally, a large group of experts in the field of in-situ and remote sensing of snowfall properties discussed ways of constraining and evaluating existing scattering datasets.


All participants acknowledged the productive framework of the workshop and expressed their high interest in continuing these dedicated workshops in the future on a biannual basis in between the biannual IPWG workshops. The next snowfall workshop will be organized by the University of Helsinki and will be held in 2019 in Hyytiälä, Finland.


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