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
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