Observational approaches

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Observational approaches to understanding cloud
microphysics
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Microphysical measurement needs

• Quantitative characterization of.
• Size distribution of liquid hydrometeors from CCN
  size (0.01 mm) to precipitation size (10000 mm)
  6 orders of magnitude range of size (18 of mass!)
• Size/mass distributions and habits of ice-phase
  hydrometeors (1-10000 mm)
• Efficacy of aerosols to act as CCN and IN
• Thermodynamic and dynamic environment in which
  hydrometeors form, exist, grow, and evaporate

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1. Liquid Hydrometeors
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Forward Scattering Spectrometer Probe (FSSP)
Radius range 1-25 µm
NCAR
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FSSP Scattered Energy
Scattered energy per particle arbitrary
units 1 10 100 1000
1 10
100 Diameter microns
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Phase Doppler Particle Interferometer (PDPI)
Size range 1-1000 µm
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Interferometry
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Larger particles D?

• Optical Shadow Probes (Optical Array Probes, OAPs)

Size range 10-10000 µm
Examples 260-X 2D-C 2D-P HVPS
Baumgardner and Korolev, J Atmos. Ocean Tech.,
1997
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Comparisonof FSSP and OAPs

• Problems in overlap zone

Baumgardner and Korolev, J Atmos. Ocean Tech.,
1997
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2. Ice Hydrometeors
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Small ice the perennial problem

• FSSPs can be used, but.

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Interarrival times in ice clouds

• Bursts of particles observed
• Shattering of large ice giving impression of many
  small xtals

Field et al., J Atmos. Ocean Tech., 2003
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Small ice the perennial problem

• and

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The Small Ice Detector (SID)

• Examines angular dependence of scattering
• Irregular particles

University of Hertfordshire, UK
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Large ice crystals OAPs
Size range 25-4000 µm

• OAP images

1000 microns 1 mm
Field, JAS, 1999
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Large ice crystals Cloud Particle Imager (CPI)
Size range 10-4000 µm

• CCD camera takes photographs of particles

SPEC Inc, Boulder
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More common crystals
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3. CCN/IN characterization
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Thermal diffusion chamber

• Supersaturation maximizes in center of chamber
  and can be controlled by ?T
• Subject aerosols to known supersaturation and
  check for rapid growth using a droplet counter
• Vary ?T and obtain a CCN spectrum

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Thermal diffusion chambers

• New designs allow for
• continuous flow in chamber
• Multiple supersaturations simultaneously

• Can be used at between ice and water saturation
  to characterize heterogeneous deposition nuclei

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IN characterization

• Cannot measure (in-situ)
• Contact freezing IN
• Immersion freezing IN

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4. Characterization of thermodynamic environment

• Temperature
• Vapor content
• Liquid water content

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Humidity

• High concentrations
• Optical (Lyman-alpha)
• Tunable diode laser
• Dewpoint Hygrometer
• Low concentrations
• Fluorescence hygrometer

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Liquid water content

• Hotwire probes
• Nevzorov probes
• Lyman-alpha, total water content