A comparison of airborne in-situ cloud microphysical measurements with ground C and X band radar observations in African squall lines E. Drigeard 1 , E. Fontaine 1 , W. Wobrock 1 , A. Schwarzenböck 1 , E.R. Williams 2 , F. Cazenave 3 , M. Gosset 4 , A. Protat 5 and J. Delanoë 6 ICCP 2012, July 30 – August 03, Leipzig, Germany 1 2 3 4 5 6
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A comparison of airborne in-situ cloud microphysical measurements with ground C and X band radar observations in African squall lines E. Drigeard 1, E.
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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
• 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.
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
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.