Dual-Doppler Wind Retrieval from two operational Doppler radars Yong Kheng Goh, Anthony Holt...
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![Page 1: Dual-Doppler Wind Retrieval from two operational Doppler radars Yong Kheng Goh, Anthony Holt University of Essex, U. K. for ERAD04, Visby.](https://reader031.fdocuments.us/reader031/viewer/2022012922/56649d425503460f94a1d032/html5/thumbnails/1.jpg)
Dual-Doppler Wind Retrieval from two operational Doppler radars
Yong Kheng Goh, Anthony Holt
University of Essex, U. K.
for
ERAD04, Visby
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Acknowledgment
Carpe Diem (EVG-CT-2001-0045) is supported by
European Commissionunder
5th Framework Programme
Thanks toP.P. Alberoni
A.R.P.A – SMRBologna,Italy
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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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Terrain Analysis – Po Valley
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Location of Po Valley study region
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Data Gridding
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Data Gridding● Radar data
– Polar data – 4 elevation
angles(deg) 0.5, 1.4, 2.3, 3.2
– ray resolutions 0.25km x 440 bins, beam width: 0.9 deg
● Gridded data– Cartesian data– 4 layer altitudes (km) ~
0.5, 1.4, 2.3, 3.2– horizontal resolutions
cell spacing: 0.5 km, no. of cells: 60 x 60
e.g. Doppler Vel.
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Calculating wind field
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Calculating wind field
● Three Fundamental Equations:– Radial Velocities (from each radar)
– Mass Continuity
2,1,sin
sincoscoscossinˆ
iVWv
wvu
iitr
iiiii
i
vri
0
vvvtt
t
i
r
W
V
vi
wvu
i
velocity,terminal
velocity,radialnet
,radar at t measuremenlocity Doppler ve
,, vector,(velocity) wind v
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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)
iterationth -,, 11 nwDCvwBAu nnnn
ln where,0dz
dw
z
w
y
v
x
u
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Case I: stratiform2002 Dec 17 (19:15 hr)
Examples of Retrieval
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Radar: GattaticoDate: 2002 Dec 17Elevation: 1.4 degField: ZThreshold: 0 dBZ
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Radar: GattaticoDate: 2002 Dec 17Elevation: 1.4 degField: VThreshold: 0 dBZ
tangential
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3D representation not very helpful
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Wind travelling to the East-North-Eastat the centre
Vel. (m/s)
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Vel. (m/s) Thresholded at 15 dBZ
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How do we know that the wind field is correct?
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Checking the wind field● comparing with VAD● calculating convergence factor for vertical
wind component● by reconstructing radial velocity PPI and
comparing with original PPI ● comparing “along-track” components
How do we know that the wind field is correct?
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Velocity-Azimuth Display (VAD)
Gattatico: minimum ~ 60 degwind travel to East-North-East
gat windowspc window
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Convergence factor● Typical convergence factor
030.0)1(
,,)(,,
)(,,
)1(,,
max
nkji
nkji
nkji
nkji
ww
ww
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Comparison of reconstructed radial velocity field and radar measurement
Gridded data Reconstructed
Gattatico
S. PietroCapofiume
Doppler windmeasurement
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“along-track” components
v
r1r2
r12
(obs)
(obs)(obs)
nd,Doppler wi measured
vector, windcalculated
where
1% deviation, relative Typical
0
12
ir
rr
v
vv
(cal)
12(cal)
1212(cal)
1212
v
rv
rrrv
rrrv
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Magnitude of “along-track” component
(height = 1.4 km)
12(cal) rv
rr (obs)2
(obs)1 21 rr vv
12(cal)
12(cal)
rv
rv
derived from measurement
from calculation
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L1 L2 L3 L4
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Case II: Convective Storm2003 Jul 31 (17:30 hr)
Examples of Retrieval
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Radar: S. Pietro C.Date: 2003 Jul 31Elevation: 1.4 degField: ZThreshold: 0 dBZ
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Radar: S. Pietro C.Date: 2003 Jul 31Elevation: 1.4 degField: VThreshold: 0 dBZ
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VAD is not very helpful in this case
Seen from S. Pietro C.wind changes direction
reflectivity
Doppler vel.
gat window
spc window
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Vel. (m/s)Thresholded at 0 dBZ
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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.