Measuring Cloud Microphysical Properties

Cloud water content, droplet/particle size distribution and effective radius, extinction, and liquid water path are critical for a variety of applications including:

• Characterizing/investigating cloud-aerosol interactions
• Understanding aerosol chemical and wet-removal processes
• Investigating cloud formation processes and radiative characteristics
• Validating satellite retrievals and model predictions

LARGE deploys the following instruments to determine key cloud microphysical properties.

Water Content

• Multi-element water content probe (SEA WCM-2000)
  • Directly measures total (TWC) and liquid water content (LWC)
  • Ice water content (IWC) and median volume diameter (MVD) derived
  • 0-6 g/m3, TAS < 230 m/s, SL - 45,000 ft
  • http://scieng.com/produtcs/multi.htm
• Hot-wire liquid water content sensor (DMT, LWC/CAPS)
  • 0-3 g/m3, TAS <200 m/s, SL – 41,000 ft
  • http://www.dropletmeasurement.com/products/airborne/LWC-200
• Axial-flow Cyclone Cloud Collector (AC3; built at LaRC)
  • Collects liquid cloud water for subsequent analysis (e.g. ion chromatography)
  • Variable droplet cut size depending on instrument configuration
  • Improvement on the instrument described by Straub and Collett, 2004
    (http://journals.ametsoc.org/doi/pdf/10.1175/JTECH-1670.1)

Size Distributions

• Forward-Scattering Spectrometer Probes (FSSP-300, FSSP-100; PMS/DMT)
  • Open sample cavity, wing-mounted optical particle counters
  • Derive size of spherical particles from forward scattering light intensity
  • 30 size channels over the 0.3 to 20 µm (FSSP-300) or 2 to 47 µm size range (FSSP-100)
  • Flown on NASA aircraft since 1970s to measure aerosol/cloud-droplet concentrations
  • https://www.eol.ucar.edu/instruments/forward-scattering-spectrometer-probe-model-100
• Cloud Droplet Probe (CDP-2, DMT)
  • Open sample cavity, wing-mounted forward-scattering optical particle counter
  • 30 size channels over the 2 to 50 µm diameter range
  • Probe arms designed to minimize particle shattering
  • http://www.dropletmeasurement.com/products/airborne/CDP-2
• Cloud and Aerosol Spectrometer (CAS/CAPS, DMT)
  • Open sample cavity, wing-mounted optical particle counter
  • Derives size of particles from forward scattering light intensity
  • Measures backscattering to provide refractive index information
  • 30 size channels over the 0.5 to 50 µm diameter range
  • Flown on NASA aircraft since 2000 to measure aerosol/cloud-droplet concentrations
  • http://www.dropletmeasurement.com/products/airborne/CAPS#Specifications
• Cloud Particle Spectrometer with Polarized Detection (DMT CPSPD)
  • Open sample cavity, wing-mounted optical particle counter w/anti-shattering tips
  • Derives size of particles from forward scattering light intensity
  • Measures single-particle polarization ratios to discriminate ice from water droplets
  • 20 size channels over the 0.65 to 30 µm diameter range
  • i.e., http://www.dropletmeasurement.com/products/airborne/CPSPD
• Cloud Imaging Probe (CIP/CAPS, DMT)
  • Optical array probe with 64 element CCD
  • 62 size channels over 15 to 930 µm size range
  • Onboard airspeed and temperature sensors
  • Stores individual gray-scale particle images
  • http://www.dropletmeasurement.com/products/airborne/CAPS#Specifications