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Cloud liquid water and ice content by
multi-wavelength radar Nicolas Gaussiat
Henri Sauvageot Anthony J. Illingworth
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Dual-Wavelength measurements
For a dual-wavelength pair ( Long, Short)
DWR is due to (1) differential attenuation , (2)
Mie scattering
In clouds, Mie scattering is more often due to
ice. Differential attenuation is dominated by
liquid water
A 95 35 8 dB km-1/g m-3
A 35 3 2 dB km-1/g m-3
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Assuming a gamma distribution of scatterers
the Mie scattering term (F) is a function of D0

25
F3-95
20
F35-95
FdB
15
10
F3-35
5
0
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ARM case study
(1) Cirrus
(2) Stratocumulus
(3) Mixed phase cloud
(3)
(2)
(1)
Excepted in cirrus, LWC content derive from
differential attenuation ignoring Mie scattering
looks good, BUT
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Simulating differential attenuation

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Principle of a triplewavelength method
With 3 frequencies 3, 35, 95 GHz
k 0.2
and
The system is solved using an iterative process

1. First guess DWR3-35 Mie scattering only ? D0
   first estimate
2. With D0 ,Mie scattering term F3-94 is predicted
3. (Observed DWR3-94 predicted F3,94) ?
   Ad3-94 attenuation profile.
4. With Ad3-94 ? correction First guess DWR3-35 is
   now corrected for attenuation

When Ad and F profiles are stables LWC is
derived from Ad3-94
(Ad94 3 10 dB km-1/g m-3 )
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Running triple-wavelength method
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Using triple-wavelength method in mixed phase
clouds
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Dual-wavelength observables
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Merging Mie scattering and attenuation
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Microphysical Parameters Derived From Ad and F