Wind Tunnel Tests of the Airborne PVM-100A Response to Large Droplets

The Gerber Scientific, Inc. Particle Volume Monitor (PVM) is widely used to measure the liquid water content (LWC) and droplet effective radius (reff) of water clouds. The LWC response of the airborne version of this instrument, the PVM-100A, was evaluated in two independent wet wind tunnel experiments under well-controlled conditions. Earlier studies predict that the PVM-100 (the ground-based version of the PVM) theoretical response to monodisperse droplets diminishes for droplet diameters larger than about 40 mm. However, results from the wind tunnel experiments presented in this paper show that the response of the PVM-100A to monodisperse droplets begins to decrease when the droplet diameter is between 20- and 30-mm diameter. For polydisperse droplet populations (such as those found in natural clouds) the efficiency of the airborne PVM-100A for sensing LWC begins to decrease when the median volume diameter (MVD) of the droplet size distribution is above 20 mm, falling to 50% efficiency for an MVD of 50 mm. Therefore, measurements of LWC obtained from the PVM-100A in natural clouds with broad droplet size distributions (and large values of MVD) should be treated with caution.

[1]  R. Knollenberg,et al.  Techniques for probing cloud microstructure , 1981 .

[2]  Jim Swithenbank,et al.  A Laser Diagnostic Technique for the Measurement of Droplet and Particle Size Distributions , 1976 .

[3]  H. Gerber,et al.  Microphysics of Marine Stratocumulus Clouds with Two Drizzle Modes , 1996 .

[4]  G. McFarquhar,et al.  Measurements of wave‐cloud microphysical properties with two new aircraft probes , 1998 .

[5]  M. Wendisch A Quantitative Comparison of Ground-Based FSSP and PVM Measurements , 1998 .

[6]  M. Wendisch,et al.  The great dun fell cloud experiment 1993: An overview , 1997 .

[7]  H. Gerber Comments on `A comparison of optical measurements of liquid water content and drop size distribution in adiabatic regions of Florida cumuli' , 1999 .

[8]  H. Gerber,et al.  Ground-Based FSSP and PVM Measurements of Liquid Water Content , 1999 .

[9]  A. Kowalski,et al.  Deployment and Evaluation of a System for Ground-Based Measurement of Cloud Liquid Water Turbulent Fluxes , 1997 .

[10]  Manfred Wendisch,et al.  Drop size distribution and LWC in Po valley fog , 1998 .

[11]  L. Dodge,et al.  Performance comparison of Malvern instruments laser diffraction drop size analyzer , 1986 .

[12]  M. Facchini,et al.  The Po Valley Fog Experiment 1989 , 1992 .

[13]  H. Gerber,et al.  Direct measurement of suspended particulate volume concentration and far-infrared extinction coefficient with a laser-diffraction instrument. , 1991, Applied optics.

[14]  W. L. Wilcock,et al.  Light scattering measurements of particle distributions. , 1976, Applied optics.

[15]  C. Bowman,et al.  A Laser Diagnostic Technique for the Measurement of Droplet and Particle Size Distribution , 1977 .

[16]  H. Gerber,et al.  New microphysics sensor for aircraft use , 1994 .

[17]  Martin Gallagher,et al.  Measurement and modelling of cloudwater deposition to a snow-covered forest canopy , 1992 .

[18]  M. Wendisch,et al.  Discrepancies between measured and modeled solar and UV radiation within polluted boundary layer clouds , 1999 .

[19]  M. Wendisch,et al.  Overview of the Po valley fog experiment 1994 (CHEMDROP) , 1998 .

[20]  K. Noone,et al.  Comparison of techniques for measurements of fog liquid water content , 1992 .

[21]  W. Winiwarter,et al.  The Kleiner Feldberg Cloud Experiment 1990. An overview , 1994 .

[22]  David S. Lee,et al.  The Great Dun Fell experiment 1995 : an overview , 1999 .

[23]  H. Gerber,et al.  Liquid Water Content of Fogs and Hazes from Visible Light Scattering , 1984 .

[24]  T. A. Cerni Determination of the Size and Concentration of Cloud Drops with an FSSP , 1983 .

[25]  L G Dodge,et al.  Drop-size measurement techniques for sprays: comparison of Malvern laser-diffraction and Aerometrics phase/Doppler. , 1987, Applied optics.

[26]  W. Bachalo Method for measuring the size and velocity of spheres by dual-beam light-scatter interferometry. , 1980, Applied optics.

[27]  A. Blyth,et al.  A comparison of optical measurements of liquid water content and drop size distribution in adiabatic regions of Florida cumuli , 1998 .

[28]  An optical device for the measurement of liquid water content in clouds , 1984 .