What Makes the Temperature Region between -10 and -20°C so Interesting in Terms of Ice Microphysics?

The temperature region between -10 and -20°C is not only the part of clouds where beautiful dendritic crystals grow (hence this region is often called the dendritic growth zone, DGZ). Single ice crystals grow there also most rapidly by vapor deposition. Their specific branched structure is known to favor fast and efficient formation of aggregates. Laboratory experiments revealed that fragmentation of those delicate structures also occurs preferably in this temperature regime which might be an important source process for new ice particle formation. A profound understanding of the interplay of all those processes is crucial considering that several studies already indicated that a majority of the precipitation reaching the ground is generated inside the DGZ.

In this contribution we will present an overview of the various processes and potential feedback mechanisms in this fascinating temperature regime with a special focus on the fingerprint of those processes in modern cloud radar observations. Based on combined multi-frequency, polarimetric, and Doppler spectral radar datasets including observations from the Arctic to mid-latitudes, we will illustrate the surprising coincidence of several radar signatures at very distinct temperatures. In addition, we will demonstrate based on a recent study on Arctic clouds, that also dynamical effects such as turbulence inside clouds have a measurable impact on collisional ice processes such as aggregation and riming.