Julien Delanoë

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The RadOn method and associated error analysis

Delanoë J., Protat A., Bouniol D., Testud J.

Centre d’étude des Environnements Terrestre et Planétaires

CloudNET meeting : Paris

Julien Delanoë4/5th April 2005

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Outline

• RadarOnly Algorithm

• Error analysis

• Retrieval

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Radar Only Algorithm

RadOn Principle of the radar retrieval

method

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Principle of the Radar Algorithm (1)

Z Doppler VelocityVd=Vt+w

Density law and Area diameter relationships

Dm(Vt)

N0*=f(Dm,Z) IWC, , re

Vt retrieval

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First step : Retrieval of VT from VD

Vd=w+Vt

Hypothesis (*) : for a long enough time span tw V

2 methods:•Vt-Z : Statistical relationship between Vd and ZAssuming (*), we obtain Vt from Z (Vt=aZb)

New approach•Running Window: Every 30s we compute the mean Vd over ±10 minutes (like Matrosov) for each radar gate.

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Running Window (20min)

Advantages:•Better resolution than Matrosov method•More variability of Vt than Vt-ZBut instability of RadOn when Vt<5cm.s-1

Vt from Vt-Z relationship

04/14/03 Palaiseau

Retrieval of terminal fall velocity with different methods

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Density and Area diameter relationships

Dm(Vt)


Vt retrieval

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Principle of the radar retrieval method (2)Second step : estimate of the particle density (D) and area A(D) from VT-Z relationship

• Vt-Z relationship obtained from radar is compared to microphysical Vt-Z relationships with different density and area laws.

• Microphysical Vt-Z relationships : (D)=aDb and v(D)=f(m(D),A(D),ad,bd) (Mitchell 1996) Where m(D)=(/6) a D3+b , A= D and ad, bd are the continuous drag coefficients (Khvorostianov and Curry 2002).

From coefficients of Vt-Z radar relationship we estimate the best density diameter and area diameter relationships.

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Example : 04/14/2003 Palaiseau

•black: Vt-Z obtained by the radar•red: The best density and Area relationships

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Dm(Vt)


Vt retrieval

Step unchanged (see Delft presentation)

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Density law and Area diameter relationships

Dm(Vt)


Vt retrieval

Step unchanged (see Delft presentation)Direct relationship:

25 18 1

*0 4

10( / )e m bsc

wN Z F D D dD

K

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Dm(Vt)


Vt retrieval

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Clouds parameters

max

min

( )z

zs ds

3 *0210 ( / )mN F D D D dD

* 4044

wmIWC N D

3

2e

IWCr

Using Dm N0* and Gamma shape => Clouds parameters

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Evaluation of RadOn using the microphysical database

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Evaluation of RadOn using the microphysical database

• Dataset: CLARE 98, CARL 99, EUCREX, ARM SGP, FASTEX, CEPEX, CRYSTALFACE

• We impose a density law and area diameter relationships for a radar at 35 and 95GHz:

A(D)=D with several couples of coefficients

(D)=aDb with several couples of coefficients

We compute Vt, Z, IWC, and re from the in-situ measurements, assuming A(D) and

(D)

RadOn Algorithm

IWC, , re from RadOnIWC, , re micro

Entries of the algorithm :Vt and Ze from in situ data

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bias

bias + std

bias - std

4 « Density diameter relationships »: b=-1.4, -1.1, -0.8, -0.5

5 « Area diameter relationships»

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bias

bias + std

bias - std

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bias

bias + std

bias - std

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RadOn Retrieval:

•14th April 2003: PalaiseauDeep ice cloud•15th April 2003: PalaiseauCirrus case

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Retrieval 14th April 2003

IWC

re

N0*

(D)=0.022D-0.6

A(D)=/4D2

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Retrieval 15th April 2003

IWC

re

N0*

(D)=0.0005D-1.3

A(D)=D1.4

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Future work

• Refine the error analysis

• Run Radon on all the CloudNET sites, for all frequencies

• Statistical study of density, IWC, , re….

• Comparison with Radar/Lidar and other Radar algorithm

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IWC retrieval from different method

1. RadOn with running window

2. RadOn with Vt-Z

3. IWC-Z-T R.J Hogan

4. IWC-Z Protat et al.

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With running window Vt-Z

IWC-Z-T RJH IWC-Z Protat et al.

1 2

3 4

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