Effects of ice particles shattering on the 2D-S probe

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 the investigation, however, when available comparisons with 2D-C and CIP measurements are also included. Korolev et al. (2010b) report results from a recent field campaign (AIIE) and conclude that modified probe tips are more effective than an arrival time algorithm when applied to 2D-C and CIP measurements. Analysis of 2D-S data from the AIIE and SPARTICUS field campaigns shows that modified probe tips significantly reduce the number of shattered particles, but that a particle arrival time algorithm is more effective than the probe tips designed to reduce shattering. A large dataset of 2D-S measurements with and without modified probe tips was not available from the AIEE and SPARTICUS field campaigns. Instead, measurements in regions with large ice particles are presented to show that shattering on the 2D-S with modified probe tips produces large quantities of small particles that are likely produced by shattering. Also, when an arrival time algorithm is applied to the 2D-S data, the results show that it is more effective than the modified probe tips in reducing the number of small (shattered) particles. Recent results from SPARTICUS and MACPEX show that 2D-S ice particle concentration measurements are more consistent with physical arguments and numerical simulations than measurements with older cloud probes from previous field campaigns. The analysis techniques in this paper can also be used to estimate an upper bound for the effects of shattering. For example, the additional spurious concentration of small 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.