Effects of ice particles shattering on optical cloud particle probes
Abstract. Recently, considerable attention has been focused on the issue of large ice particles shattering on the inlets and tips of cloud particle probes, which produces copious ice particles that can be mistakenly measured as real ice particles. Currently two approaches are being used to mitigate the problem: (1) Based on recent high-speed video in icing tunnels, probe tips have been designed that reduce the number of shattered particles that reach the probe sample volume, and (2) Post processing techniques such as image processing and using the arrival time of each individual particle. This paper focuses on exposing suspected errors in measurements of ice particle size distributions due to shattering, and evaluation of the two techniques used to reduce the errors. Data from 2D-S probes constitute the primary source of our investigation, however, comparisons with 2D-C and CIP measurements are also included. Analysis of 2D-S data shows that a particle arrival time algorithm is more effective than probe tips designed to reduce shattering, although application of both techniques ought to be complementary. This finding contrasts results from a recent investigation that found that modified probe tips were more effective than an arrival time algorithm when applied to 2D-C and CIP measurements. The reason for these differing results may be linked to the improved ability of the 2D-S to image small ice particles. The analysis techniques in this paper can be used to estimate the effects of shattering. For example, the additional spurious concentration of (small) shattered ice particles can be measured as a function of the mass concentration of (large) ice particles. The analysis provides estimates of upper bounds on the concentration of natural ice, and on the remaining concentration of shattered ice particles after application of the post-processing techniques. However, a comprehensive investigation of shattering is required to quantify effects that arise from the multiple degrees of freedom associated with this process, including different cloud environments, probe geometries, airspeed, angle of attack, particle size and type.