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Differences of Microphysical Processes in the Melting Layer Found for Rimed and Unrimed Snowflakes Using Cloud Radar Statistics
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  • Markus Konrad Karrer,
  • José Dias Neto,
  • Leonie von Terzi,
  • Stefan Kneifel
Markus Konrad Karrer
Institute of Geophysics and Meteorology

Corresponding Author:[email protected]

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José Dias Neto
Delft University of Technology
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Leonie von Terzi
Institute of Geophysics and Meteorology
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Stefan Kneifel
University of Cologne
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Understanding which microphysical processes are dominant while ice particles pass through the melting layer is essential for precipitation prediction by microphysics schemes and precipitation estimates by remote sensing. Comparing the reflectivity flux at the top and bottom of the melting layer reveals the overall effect of the microphysical processes occurring within the melting layer on the particle population. If the reflectivity flux increases more than expected due to the change in the dielectric factor, growth processes dominate. In contrast, a weaker increase in reflectivity flux indicates that shrinking processes dominate. However, inference of growth or shrinking dominance from the increase in reflectivity flux is only possible if other influences (e.g., vertical wind speed) are negligible or corrected for. By analyzing radar spectra and multi-frequency observations, we correct the reflectivity fluxes for vertical wind speed and categorize the height profiles by the riming degree at the melting layer top. Our statistical analysis shows the slight dominance of growth processes for unrimed and a clearer dominance of shrinking processes for rimed profiles. The reflectivity flux profiles within the melting layer indicate that the difference between unrimed and rimed profiles arises mainly in the upper half of the melting layer, where the melting fraction increases the strongest. We further narrow down which processes might be most important to explain the observed signature by analyzing additional radar variables. We suggest that whether the particle population is overall growing or shrinking depends on the relative importance of aggregation and collisional breakup of melting particles.