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Nicolas Gaussiat and Robin Hogan Progress meeting 4 – Toulouse – 20-21 Oct 2003 Dual wavelength retrieval of LWC and IWC at Chilbolton.

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Presentation on theme: "Nicolas Gaussiat and Robin Hogan Progress meeting 4 – Toulouse – 20-21 Oct 2003 Dual wavelength retrieval of LWC and IWC at Chilbolton."— Presentation transcript:

1 Nicolas Gaussiat and Robin Hogan Progress meeting 4 – Toulouse – Oct 2003 Dual wavelength retrieval of LWC and IWC at Chilbolton

2 LWC from dual-wavelength radar Retrieval technique In Rayleigh scattering conditions, 1. The reflectivity difference measured by at two frequencies equals the cumulative differential attenuation. 2.The differential attenuation is proportional to LWC => LWC is obtained by taking the derivative of the reflectivity, difference (DWR)

3 LWC from dual-wavelength radar Why getting maximum sensitivity is crucial Reflectivity at 1 km

4 LWC from dual-wavelength radar Why getting maximum sensitivity is crucial Reflectivity at 1 km

5 LWC from dual-wavelength radar Results using ARM data

6 The technique works and scripts are ready to use the data issue from the categorization. The accuracy of the retrieval depends strongly on the absolute sensitivity of the dual-wavelength radar. With a new antenna 46 cm -> 2.4 m +15 dB of sensitivity, we will produce LWC with an accuracy of +/- 0.1g cm^-3 within most of the liquid clouds (assuming 30 s averaging and 60 meters). LWC from dual-wavelength radar Conclusions

7 IWC from dual-wavelength radar Retrieval technique

8 IWC from dual-wavelength radar First results using Galileo and Copernicus

9 IWC from dual-wavelength radar Solving the density problem DmDm DaDa D = D m Brown and Francis ( 1995 )  (D) = 0.07D -1.1 g.cm -3 D = D a Francis et al. ( 1998 )  (D) = 0.175D g.cm -3

10 IWC from dual-wavelength radar Simultaneous DWR and  V D in cirrus cloud

11 IWC from dual-wavelength radar DWR versus  V D in cirrus cloud Brown and Francis (1995) density relationship  (D)=0.07D -1.1 gives the best agreement between radar observations of DWR vs  V D and theoretical calculations.

12 The technique works and scripts are ready to use the data issue from the categorization but the data gathered by the 35 GHz Copernicus needs to be checked. Extra sensitivity at 35 GHz will allow to resolve IWC calculation in thinner cirrus clouds. We suggest that on the basis of the DWR vs  V D analysis, Brown and Francis density relationship should be use for CloudNet calculations of IWC from reflectivity measurements. Further work is currently done to see how this result is changed by considering spheroids instead of spheres IWC from dual-wavelength radar Conclusions


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