A comparison of airborne in-situ cloud microphysical measurements with ground C and X band radar observations in African

squall lines

E. Drigeard1, E. Fontaine1, W. Wobrock1, A. Schwarzenböck1, E.R. Williams2, F. Cazenave3, M. Gosset4, A. Protat5 and J. Delanoë6

ICCP 2012, July 30 – August 03, Leipzig, Germany

1 2 3

4 5 6

Introduction : The Megha-Tropiques mission

• French-Indian satellite (launched on the 11/10/12)– To improve our knowledge of the processes linked to the

tropical convection and precipitation

• 2 ground validation campaigns (Niger & Maldives)– Aircraft measurements with the French Falcon 20

(CIP, PIP, 2DS probes, cloud radar RASTA)

Introduction : The Megha-Tropiques mission

• French-Indian satellite (launched on the 11/10/12)– To improve our knowledge of the processes linked to the

tropical convection and precipitation

• 2 ground validation campaigns (Niger & Maldives)– Aircraft measurements with the French Falcon 20

(CIP, PIP, 2DS probes, cloud radar RASTA)

– 2 ground radars : MIT & Xport

Objective : comparing ground based radar reflectivity with those

calculated from in-situ microphysical observations

MIT & Xport radar : Data description

• Volumetric protocol :– 3D spatial distribution of the reflectivity every 12 minutes

• Elevations : - Xport : 12 anglesfrom 2 to 45°

- MIT : 15 anglesfrom 2 to 24°

MIT & Xport radar : Data description

• MIT radar :– On the Niamey airport– C-band (5.5 GHz)– Range of 150km

• Xport radar :– 30 km SE of the airport– X-band (9.4 GHz)– Range of 135km

• To compare radar data and in-situ observations :

Co-localization of the 2 ground radars data

and the aircraft position Δ Xport radar+ MIT radar

90 km

MIT & aircraft trajectory

Co-localization radar-aircraft : Method• Use of all scans collected during a observationnal period

• Steady state hypothesis of the reflectivity field during this period (increasing the vertical resolution)

• Spatial interpolation (Inverse Distance Weighting) using 8 observation points

23

14

5

6

7

8250 m

1° 1- 7°

250 m

Radar

Co-localization : Validation

• Comparison of observed and calculated RHI scans for the MIT radar

– Differences increase with distance (deterioration of the vertical resolution of the volumetric data)

– Statistical analysis : standard deviation = 3dBZ

Calculated RHI(15 scans)

Measured RHI(300 scans)

± 3dBZ

Co-localization : Validation

Good agreement between co-localized MIT reflectivity and airborne radar RASTAVery similar pattern for the airborne and the ground observation

5.5 GHz

95 GHz

Calculation of reflectivity from in-situ microphysics

In-situ probes (PIP, CIP, 2DS) show cloud particles from 50µm to 5mm.The cloud particles have irregular shapes (graupel, aggregate)

To calculate the equivalent reflectivity Ze, a power mass law m=αDβ is applied:

Example for number distribution averaged during 10s during

the flight #20

Calculation of reflectivity from in-situ microphysics

In-situ probes (PIP, CIP, 2DS) show cloud particles from 50µm to 5mm.The cloud particles have irregular shapes (graupel, aggregate)

To calculate the equivalent reflectivity Ze, a power mass law m=αDβ is applied:

α is determined by matching the reflectivity calculated by Mie theory with measurements of the cloud radar RASTA at 95GHz

0.001 < α < 0.1; and β = 2.1The mass law obtained in this way is applied again to calculate the reflectivity of the precipitation radars MIT and Xport (using Rayleigh approximation)

Co-localization radar-aircraft : Results

- Calculated reflectivity is in good agreement with observations of both ground radars

- Best results in regions where aircraft < 8000 m and range < 80 km

Co-localization radar-aircraft : Results

• Some periods with differences between signals• Statistically : MIT - microphysics Xport - microphysics

Mean 1.44 dBZ -0.96 dBZ

Standard deviation 4.76 dBZ 5.51 dBZ

Conclusions

• Reflectivity observed by precipitation radar can be recalculated from in-situ cloud microphysical measurements, if a mass-diameter relationship in a form of m=αDβ is applied (instead of m~D3)

• Limits :– mixte phase clouds and predominantly cold clouds (in the levels

from -5 to -30°C)– where reflectivity prevails from 15 to 35 dBZ.

DYNAMO

Mesures microphysiques :enregistrement d’images 2D.

• Tailles des hydrométéores mesurés [50 6400]µm

déduction de la distribution en tailles des hydrométéores (et surface)

max max( )m D D maxprojectedArea D

( )?f

•Numerical simulations to •retrieve β =f°(σ) relation

• Projection 2D

•V(Dmax) A(Dmax)

Estimation de la masse, densité, et loi masse-diamètre

1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.20.5

1

1.5

2

2.5

3

3.5

4

4.5

Relation -

y = 1.9*x - 1.1

y = 2.3*x2 - 6*x + 5.5

y = 10*x3 - 50*x2 + 82*x - 43

CubeSpheresHexagonal platesHexagonal columnsStars type 1Stars type 2Sphere Agregates test 1Sphere Agregates test 2Sphere Agregates test 3Capped columns plates+platesCapped columns plates+starsCapped columns stars+starsRosettes test 1Rosettes test 2Rosettes test 3Hexagonal plates + rimed spheresHexagonal columns + rimed spheresStars type 2 + rimed spheres--- table from D.Mitchell 1995 --- linear quadratic cubichexagonal plates 15µm<D<100µmhexagonal plates 100<D<3000µmhexagonal columns 30<D<100µmhexagonal columns 100<D<300µmhexagonal columns D>300µmRimed long columns 200<D<2400µmCrystal with sector-like branches(P1b) 10<D<40µmCrystal with sector-like branches(P1b) 40<D<2000µmbroad-branched crystal (Plc) 10<D<10µmbroad-branched crystal (Plc) 100<D<1000µmStellar crystal with braod arms (P1d) 10<D<90µmStellar crystal with braod arms (P1d) 90<D<1500µmdensely rimed dendrites (R2b) 1800<D<4000µmside planes (S1) 300µm<D<2500µmBullet rosettes, 5 branches at -42°C 200<Dw1000µmAggrgates of side planes 600<D<4100µmAggregates of side planes, columns & bullets (S3) 800<D<4500µmAssemblages of planar polycrystals in cirrus clouds 20<D<450µmLump graupel (R4b) 500<D<3000µmHail 5000<D<25000µm

Résultats pour MT2010

Pour MT2 ?

T > 0

T<0

MT-DYNAMO 2011

DYNAMO

- Meilleure journée pour les données microphysiques : 27/11/2011:Vols #45 et #46

- Radars présents : - RASTA (95 GHz)- SPol (2.80 GHz)- SMART-R (5.63 GHz)

DYNAMO

Vol #45

DYNAMO

Radar SPol : - Protocole volumique de 5 minutes toutes les 15 minutes - 8 élévations (entre 0.5 et 11°)

DYNAMO

Vol #46

DYNAMO

DYNAMO

• Travail en cours : Radar SMART-R – Protocole volumique de 7.5min toutes les 10 minutes– 26 élévations (entre 0.5 à 33°)– Protocole difficile à décoder

Vertical Structure

800

900

1000

500

600

700

200

300

400

100

150

0° 10° 20° 30°

4 5 10 20 (g /kg)

1 0 m /sNiamey (Niger) Gan-Island (Maldives)

• strong wind shear in 850 hPa

• significant instability at the surface

• strong wind shear in 300 hPa

• weaker instability

800

900

1000

500

600

700

200

300

400

100

150

0° 10° 20° 30°

4 5 10 20 (g/kg)

20 m/s

Megha-Tropiques, Niger 2010

Ice and water field after 7 h

250 km

Ice and water field after 7 hIce and water field after 7 hFields of ice supersaturation andwater supersaturation

Fields of ice supersaturation andwater supersaturationFields of ice supersaturation andwater supersaturation and LWC

Megha-Tropiques, Niger 2010

Microphysics

Microphysical instrumentation onboard the French F-20:

- 2DS, CIP, PIP, 2D-C+P and a cloud radar (see poster P.12.29 by Fontaine et al.)

100 1000diameter (µm)

0.0001

0.001

0.01

0.1

1

10

dN

/dlo

d D

m odeled spectra6-7 km

7-8 km

8-9 km

100 1000d iam ete r (µm )

0.0001

0.001

0.01

0.1

1

10

dN

/dlo

g D

observations 6-7 km

7-8 km

8-9 km

18 Aug. 2010, Niger

Microphysics

10 100 1000 10000

diam eter (µm )

1E-008

1E-007

1E-006

1E-005

0.0001

0.001

0.01

0.1

1

10

100

1000

dN

/dD

(lit

er-1

µm

-1)

w ater drops

ice crystals (spheres)

10 100 1000 10000

diam eter (µm )

1E-008

1E-007

1E-006

1E-005

0.0001

0.001

0.01

0.1

1

10

100

1000

dN

/dD

(lit

er-1

µm

-1)

w ater drops

ice crystals (spheres)

w ater + ice

10 100 1000 10000

diam eter (µm )

1E-008

1E-007

1E-006

1E-005

0.0001

0.001

0.01

0.1

1

10

100

1000

dN

/dD

(lit

er-1

µm

-1)

w ater drops

ice crysta ls (spheres)

w ater + ice

ice m ass = 0 .02 D 2.2 (aggregates)

Explanation for the second mode in the hydrometeor spectra:

model

-4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9vertica l w ind (m /s)

0.0001

0.001

0.01

0.1

1

TW C > 0.5 g/m 3

all c loud points

-5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9vertica l w ind (m /s)

0.0001

0.001

0.01

0.1

1

freq

uenc

y

Dynamics - Niger

Frequency analysis of the vertical wind field in cloudy air

measurements

max.35% max.73%

all cloudy points

TWC >0.5 gm-3

Maldives (MT2 – Dynamo)

• Data processing not completed

• Nov./ Dec. 2011 – only few MCS encountered

Measurements in convective cloudsAfrica versus Maldives

g/m

3g/

m3

1200 1800 2400 3000 3600 4200 4800 5400 6000 6600 7200 7800 8400 9000 9600 10200

tim e (s)

0

1

2

3

4

1

2

3

4

Condensed water content during 3 hours of flight

Niger

Maldives

flight #2018 aug ’10

flight #4627 nov ‘11

(km)

17.5

14

10.5

7

3.5

Water and Ice field

Model set-up: Maldives

Identical with the African set-up – however: stronger latent heat fluxes and weaker sensible heat fluxes

(km)

17.5

14

10.5

7

3.5

Water field350 km

Dynamics and Microphysics

Frequency analysisof vertical wind

Cloud particle spectra

-5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8vertica l w ind (m /s)

0.001

0.01

0.1

1

freq

uenc

y

M ald ivesm odelA frican M C S

-5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8vertica l w ind (m /s)

0.001

0.01

0.1

1

freq

uenc

y

M ald ivesm odelA frican M C S

100 1000d iam eter (µm )

0.0001

0.001

0.01

0.1

1

10

dN

/dlo

g D

6 -7 km8-9 km

100 1000d iam eter (µm )

0.0001

0.001

0.01

0.1

1

10

dN

/dlo

g D

6 -7 km8-9 kmm odel 6-7 kmm odel 8-9 km

100 1000d iam eter (µm )

0.0001

0.001

0.01

0.1

1

10

dN

/dlo

g D

6 -7 km8-9 kmm odel 6-7 kmm odel 8-9 kmAfrica: 8-9 km

« Pristine » range fit(80 µm,300 µm)

« pré-precipitation » range fit(300 µm,1000 µm)

Precipitation range fit(1000 µm,3000 µm)

Tail of big hydrometeors(D>3000 µm) (not fitted in log-log)(fitted with exponential decrease law)

Statistical studies of the shape of PSD using different in-situ imaging probes (2DS,CIP,PIP)

Three ranges of hydrometeore size are used to fit the PSD shape in log-log unit ( i.e. looking for the best power law fit in each diameter ranges)The largest size range (D>5 mm) is fit in lin-log unit (exponnential decrease)This mean description of PSD shape is estimated at small scale (200 metres) and is used:1- To compare the different probes in common range (wathever exact concentration measurements)2- To quantify the variability of PSD shapes in MCS, compare this variability with mesoscale model results and test some normalisation approach to fit PSD.

Pente « d’équilibre » P=-3

Mode d’accumulation

TransitionPré, précipitation

Fit log-log