Statistical Quantification of Secondary Ice Occurrence Using Long-Term Remote Sensing Observations in the Arctic

Secondary ice production is a process important to the prediction of ice crystal number concentrations at temperatures warmer than -10 C, and the subsequent influence on the precipitation mass flux and evolution of cloud systems. A number of aircraft-based observations have provided sufficient evidence for enhanced ice crystal number concentrations in this temperature regime that cannot be attributed to primary ice production alone. Recently, a growing body of episodic (case-study) radar-based observations using polarimetric and spectral information have been added to the evidence supportive of enhanced ice crystal concentrations being due to secondary ice, with explanations of possible underlying mechanisms.

Here, a novel, multi-sensor technique is applied to the continuous long-term ground-based cloud radar Doppler spectra dataset collected by the U.S. Department of Energy ARM User Facility at the North Slope of Alaska. For the first time, we are able to quantify, with uncertainty estimates, the frequency of occurrence of rime splintering and drizzle fragmentation in the natural environment with respect to several controlling physical parameters. Our results shed new light on existing laboratory studies (e.g. Hallett and Mossop) and recent in situ aircraft observations of drizzle fragmentation, bringing new intriguing questions to the table for further investigation.