Abstract
Abstract. A commercial shadowgraph system, the Oxford Lasers VisiSize D30, originally designed to characterize industrial and agricultural sprays, was tested with respect to its application for measuring cloud microphysical properties such as droplet size distribution and number concentration. A laboratory experiment with a dense stream of polydisperse cloud-like droplets indicated a strong dependence of the depth of field, and thus also the sample volume, on particle size. This relationship was determined and a suitable correction method was developed to improve estimations of droplet number concentration and size distribution. The spatial homogeneity of the detection probability inside the sample volume and the minimum droplet diameter providing uniform detection were examined. A second experiment with monodisperse droplets produced by a Flow Focusing Monodisperse Aerosol Generator (FMAG) verified the sizing accuracy and demonstrated reasonable agreement between the instruments. Effects of collisions and the evaporation of droplets produced by the FMAG were observed. Finally, when the instrument was applied to sample atmospheric clouds at a mountain-based observatory, it performed reliably during a 3-week-long field experiment. Based on the laboratory and field tests, recommendations concerning the use of the instrument for cloud droplet measurements were formulated.
Highlights
IntroductionThere are two general approaches to measuring cloud microphysical properties: in situ sampling at airborne platforms or ground-based stations and remote sensing, which involves applying inverse retrieval techniques to data collected by satellites, radars and radiometers
Atmospheric clouds predominantly consist of water droplets
In situ methods often have to account for a dependence of the sample volume on particle size or air flow velocity, nonlinearity of the Mie scattering intensity with respect to droplet size, and aerodynamic effects related to the flow around or inside the instrument or aircraft; they may involve harsh conditions; and they can necessitate the handling of large datasets or instantaneous data processing
Summary
There are two general approaches to measuring cloud microphysical properties: in situ sampling at airborne platforms or ground-based stations and remote sensing, which involves applying inverse retrieval techniques to data collected by satellites, radars and radiometers. In situ methods often have to account for a dependence of the sample volume on particle size or air flow velocity, nonlinearity of the Mie scattering intensity with respect to droplet size, and aerodynamic effects related to the flow around or inside the instrument or aircraft; they may involve harsh conditions (including icing, wetting and temperature changes); and they can necessitate the handling of large datasets or instantaneous data processing. Remote sensing provides information with limited spatial resolution; the microphysical properties they measure represent only averages or integrals over relatively large volumes, which might be too simplistic to characterize inhomogeneous or multilayered cloud fields. The results obtained in situ are used to derive and validate inversion routines to be used in remote-sensing applications
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
