Intercomparison of holographic imaging and single-particle forward light scattering in situ measurements of liquid clouds in changing atmospheric conditions

[摘要] Upon a new measurement technique, it is possible to sharpen thedetermination of microphysical properties of cloud droplets using highresolving power imaging. The shape, size, and position of each particleinside a well-defined, three-dimensional sample volume can be measured withholographic methods without assumptions of particle properties. In situcloud measurements were carried out at the Puijo station in Kuopio, Finland,focusing on intercomparisons between cloud droplet analyzers over 2 months in September–November 2020. The novel holographic imaging instrument(ICEMET) was adapted to measure microphysical properties of liquid clouds,and these values were compared with parallel measurements of a cloud dropletspectrometer (FM-120) and particle measurements using a twin-inlet system.When the intercomparison was carried out during isoaxial sampling, ourresults showed good agreement in terms of variability between theinstruments, with the averaged ratios between ICEMET and FM-120 being 0.6  ±  0.2, 1.0  ±  0.5, and 1.2  ±  0.2 for the total numberconcentration ( N d ) of droplets, liquid water content (LWC), and medianvolume diameter (MVD), respectively. This agreement during isoaxial samplingwas also confirmed by mutual correlation and Pearson correlationcoefficients. The ICEMET-observed LWC was morereliable than FM-120 (without a swivel-head mount), which was verified bycomparing the estimated LWC to measured values, whereas the twin-inlet DMPSsystem and FM-120 observations of N d showed good agreement both invariability and amplitude. Field data revealed that ICEMET can detect smallcloud droplets down to 5  µ m via geometric magnification.

[学科分类] 内科医学