Effects of ice crystals shattering on probe tips

Description

Ice particles shattering on the inlets and tips of cloud particle probes produce small ice artifacts that can be erroneously included in measurements of ice particle size distributions. While the issue surrounding ice particles shattering on the inlets and tips of optical particle probes (hereafter referred to simply as “shattering”) has been known since the 1970s, it has only been recently that the magnitude of the effect has been brought to the attention of the cloud physics community. Advances in high-speed digital videography and cloud particle probes have provided new insights into the shattering process. High-speed videography of ice particles shattering on probe tips in the icing research tunnel (IRT) at the National Aeronautics and Space Administration (NASA) Glenn Research Center (GRC) showed some remarkable results. Dr. Alexei Korolev of Environment Canada (EC) has shown digital videography of millimeter-size ice particles shattering on probe tips, with small ice particles bouncing several mm upstream into the 100 m s airflow, and then traversing up to 3 cm across the airflow into the probe sample volume. Advances in the electro-optics of linear-array cloud particle probes have provided new insights into measurements of cloud particle size distributions. In particular, the 2D-S probe has been demonstrated to have 10-µm pixel resolution at airspeeds exceeding 200 m s^-1. This presentation is focused on exposing suspected errors in measurements of ice particle size distributions due to shattering and evaluation of techniques used to reduce the errors. Korolev recently evaluated shattering effects on 2D-C and CIP probes and suggested that that specially modified tips were more effective than an arrival time algorithm in reducing the effects of shattering. In our work it is seen that when considering the newer technology 2D-S probe, we find the opposite; i.e., an arrival time algorithm is more effective in reducing the apparent effects of shattering than modified tips. Measurements are compared from two 2D-S probes, one with standard tips and one with modified tips. The two probes were installed side-by-side on the SPEC Learjet for the recent DOE ARM SPARTICUS field project. While modified tips did reduce the number of shattered particles, the arrival time algorithm was more effective in removing effects of shattering, regardless of whether the tips were modified or not. 2D-C, CIP, and 2D-S data from the recent Airborne Icing Instrumentation Evaluation (AIIE) field experiment are presented and discussed. Finally, an improved algorithm for removing shattered particles from Fast FSSP and Fast CDP instruments is discussed.