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Observational approaches to understanding cloud microphysics

Observational approaches to understanding cloud microphysics. Microphysical measurement needs. Quantitative characterization of…. Size distribution of liquid hydrometeors from CCN size (0.01 m m) to precipitation size (10000 m m) – 6 orders of magnitude range of size (18 of mass!)

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Observational approaches to understanding cloud microphysics

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  1. Observational approaches to understanding cloud microphysics

  2. 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

  3. 1. Liquid Hydrometeors

  4. Forward Scattering Spectrometer Probe (FSSP) Radius range 1-25 µm NCAR

  5. FSSP Scattered Energy Scattered energy per particle [arbitrary units] 1 10 100 1000 1 10 100 Diameter [microns]

  6. Phase Doppler Particle Interferometer (PDPI) Size range 1-1000 µm

  7. Interferometry

  8. 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

  9. Comparisonof FSSP and OAPs • Problems in overlap zone Baumgardner and Korolev, J Atmos. Ocean Tech., 1997

  10. 2. Ice Hydrometeors

  11. Small ice – the perennial problem • FSSPs can be used, but….

  12. 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

  13. Small ice – the perennial problem …and

  14. The Small Ice Detector (SID) • Examines angular dependence of scattering • Irregular particles University of Hertfordshire, UK

  15. Large ice crystals: OAPs Size range 25-4000 µm • OAP images 1000 microns [1 mm] Field, JAS, 1999

  16. Large ice crystals: Cloud Particle Imager (CPI) Size range 10-4000 µm • CCD camera takes photographs of particles SPEC Inc, Boulder

  17. More common crystals

  18. 3. CCN/IN characterization

  19. 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 supersaturated T e RH

  20. 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

  21. IN characterization • Cannot measure (in-situ): • Contact freezing IN • Immersion freezing IN

  22. 4. Characterization of thermodynamic environment • Temperature • Vapor content • Liquid water content

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

  24. Liquid water content • Hotwire probes • Nevzorov probes • Lyman-alpha, total water content

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