Dual-Doppler Wind Retrieval from two operational Doppler radars

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Dual-Doppler Wind Retrieval from two operational
Doppler radars
Yong Kheng Goh, Anthony Holt University of Essex,
U. K. for CARPE DIEM, Bologna 29 Nov 03 Dec 2004
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Dual Doppler Wind Retrieval

• DDWR Procedure
• Terrain analysis establish area amenable to
  dual-Doppler analysis.
• Data gridding interpolating polar data into
  Cartesian data.
• Wind field calculation.
• Verifying wind field

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SMR Radar
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SMR Radars

• Locations- Po Valley, Italy
• Gattatico (44o 47' 30'', 10o 30' 30'')
• S. Pietro Capofiume(44o 39' 17'', 11o 37' 25'')
• C-band/5.5GHz
• Synchronised scan strategy every 15 minutes 3
  volumes
• 4 elevs (4 mins, Dual PRF, Nyquist 49 m/s, 0.5
  deg, 1.4 deg, 2.3 deg, 3.2 deg)
• 12 elevs (8 mins, Single PRF, Nyquist 16 m/s)
• 5 elevs (3 mins, Long range, non-Doppler)

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Height Profile
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Terrain Analysis Po Valley
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Location of Po Valley study region
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Calculating wind field

• Three Fundamental Equations
• Radial Velocities (from each radar)
• Mass Continuity

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Numerical procedures

• Iterative method
• horizontal components
• vertical component
• Boundary conditions
• zero vertical velocity on ground
• zero horizontal velocity gradient on ground
  (optional simplify computation w/o loss of
  accuracy)

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Case I stratiform
Examples of Retrieval

• 2002 Dec 17 (1915 hr)

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Radar Gattatico Date 2002 Dec
17 Elevation 1.4 deg Field Z Threshold 0 dBZ
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Checking the wind field
How do we know that the wind field is correct?

• comparing with VAD
• calculating convergence factor for vertical wind
  component
• by reconstructing radial velocity PPI and
  comparing with original PPI
• comparing along-track components

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Velocity-Azimuth Display (VAD)
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Convergence factor

• Typical convergence factor

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along-track components
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Case II Convective Storm
Examples of Retrieval

• 2003 Jul 31 (1730 hr)

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Radar S. Pietro C. Date 2003 Jul
31 Elevation 1.4 deg Field Z Threshold 0 dBZ
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Radar S. Pietro C. Date 2003 Jul
31 Elevation 1.4 deg Field V Threshold 0 dBZ
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Triple-Doppler Analysis

• We have obtained data from Teolo.
• In theory, 3 radars should give 3 wind
  components, but ...
• 3 radars scanning at low elevation -gt large error
  in vertical component.
• However, 3 radars allow us to do
• Validate dual-Doppler technique
• Improve horizontal wind extraction using
  along-track method.

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Teolo data(positive vel. away from radar)
Problem Radial wind PPI do not agree between
Teolo and Gattatico (or SPC).
A.D.Fontana (TEO) we are working with EEC to
solve this problem, that seems to correlated to a
bad functioning of unfolding processing of
velocity ....
Gattatico(positive vel. toward radar)
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Reconstruction from DDWR
Observation
Reconstruction (GAT SPC)
Gattatico
S. P. Capofiume
Teolo
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Wind fields from DDWR
GATSPC
SPC TEO
wind speed
wind field
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Along-track comparison
DDWR using GAT SPC
Along-track using GATSPCTEO
wind direction
wind speed
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Reconstruction of 'AT' wind
Observation
Reconstruction
Gattatico
Teolo
S.P.Capofiume
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Summary

• Dual Doppler wind retrieval with operational
  weather radars.
• Useful and reliable in both uniform windfields
  and convective storms.
• Expect to extend the study to triple Doppler
  Analysis when suitable datasets from Monte Grande
  are available.
• Will be comparing results with output from NWP
  analysis by our Carpe Diem partners.