The influence of cloud droplets on the measurement of ice particle concentrations with a Particle Measuring System's 2DC optical array probe

The Particle Measuring System's 2DC optical array probe has been used as a primary instrument to measure ice particle concentrations since its introduction in 1976. In certain mixed-phase clouds containing cloud droplets in size ranges 30-100 μm, the 2DC has been found to respond to both liquid and ice particles. This is of real concern, since ice crystals occur naturally in tens per liter, while supercooled droplets in this size range can occur in tens to hundreds per liter. In this note, the effect of cloud droplets on the measurement of ice particle concentrations with the 2DC probe is discussed. An example is presented where supercooled droplets overwhelm the probe, making accurate measurements of ice particle concentrations difficult to obtain.