observational approaches to understanding cloud microphysics
DESCRIPTION
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!) - PowerPoint PPT PresentationTRANSCRIPT
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Observational approaches
to understanding cloud microphysics
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Microphysical measurement needs
Quantitative characterization of….
1) Size distribution of liquid hydrometeors from CCN size (0.01 m) to precipitation size (10000 m) – 6 orders of magnitude range of size (18 of mass!)
2) Size/mass distributions and habits of ice-phase hydrometeors (1-10000 m)
3) Efficacy of aerosols to act as CCN and IN
4) 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
1 10 100
Diameter [microns]
Sca
ttere
d e
nerg
y p
er
part
icle
[a
rbit
rary
un
its]
1 1
0 1
00 1
000
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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>>
Baumgardner and Korolev, J Atmos. Ocean Tech., 1997
• Optical Shadow Probes (Optical Array Probes, OAPs)
Size range 10-10000
µm
Examples:260-X2D-C2D-PHVPS
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Comparison
of 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
Field et al., J Atmos. Ocean Tech., 2003
• Bursts of particles observed
• Shattering of large ice giving impression of many small xtals
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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
Field, JAS, 1999
Size range 25-4000 µm• OAP images
1000 microns [1 mm]
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Large ice crystals: Cloud Particle Imager (CPI)
SPEC Inc, Boulder
Size range 10-4000 µm
• CCD camera takes photographs of particles
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More commo
n crystals
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3. CCN/IN characterization
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Thermal diffusion chamber
RH
supersaturated
eT
• 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