A Comparison of In-Cloud Measurements Obtained with Six PMS 2D-C Probes

Abstract

During a preparatory experiment (PREICE) for the field campaign of the International Cirrus Experiment (ICE), six different Particle Measuring Systems (PMS) 2D-C probes belonging to five research organizations were intercompared. Three of these probes were original versions (2D-C), the three others being updated instruments (2D2-C version). The comparisons were performed using data obtained during flights in various types of warm and glaciated clouds. The probe-by-probe comparisons show that relative particle-size response is in good agreement for all the probes and a variety of particle shapes. Similarly, measurements of the mean volume particle size agree to within about 10%. There are, however, noticeable discrepancies up to a factor of about 1.5 in values of the particle concentration. This can lead to similar large uncertainties in values of derived parameters, such as ice water content (IWC) and extinction coefficient. These differences are found to be related primarily to the probe version. the updated 2D2-C instruments appear to detect some 50% more images than the original version (2D-C). Large differences may also be obtained when two different but common methods of calculation of the sample time are applied to data from a single probe. This appears to be related to timing errors within the probe data stream. There is a need for the standardization of processing schemes, where possible, in order to reduce the uncertainties in results obtained during multiaircraft cooperative experiments.