Scatterometer Winds

1
Scatterometer Winds

• An Operational Perspective

Andrew Burton BoM (WA) Based on a presentation by
Roger T. Edson and Jeff Hawkins
2
Scatterometer Winds

• Sources of scatterometer data and how they differ
• Good data
• Bad data
• Getting Good from Bad

3
Conclusions - a sneak peek

• Provides coverage over data sparse areas.
• Wind speeds generally good useful for areas of
  gales etc.
• Use the data if it makes sense.
• Be aware of low skill areas and different
  ambiguity removal processes (compare!).
• Do not use in isolation.

4
Where to Get Scatterometer Data

• NRL Monterey
• http//kauai.nrlmry.navy.mil80/sat-bin/tc_home
• NOAA/NESDIS QuikSCAT http//manati.wwb.noaa.gov/q
  uikscat
• FNMOC
• http//www.fnmoc.navy.mil/PUBLIC
• Remote Sensing Systems
• http//www.ssmi.com

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Where to Get Scatterometer Data

• NRL Monterey
• http//kauai.nrlmry.navy.mil80/sat-bin/tc_home
• NOAA/NESDIS QuikSCAT
• http//manati.wwb.noaa.gov/quikscat
• Storms page includes ambiguities
• http//manati.wwb.noaa.gov/cgi-bin/qscat_storm.p
  l
• Alternative NOAA site, with SSMI wind
  speeds
• http//polar.wwb.noaa.gov/winds/globdata.html
• FNMOC
• http//www.fnmoc.navy.mil/PUBLIC
• Remote Sensing Systems
• http//www.ssmi.com

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NRL Monterey http//kauai.nrlmry.navy.mil80/sat
-bin/tc_home
7
NOAA/NESDIS QuikSCAT http//manati.wwb.noaa.gov/q
uikscat
8
FNMOChttp//www.fnmoc.navy.mil/PUBLIC
FNMOC Ambiguity Removal over SSMI
Near Real-Time Ambiguity Removal
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Remote Sensing Systemshttp//www.ssmi.com
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Differences

• Wind retrieval
• RSS uses KU-2000 wind retrieval method
• Others use QuikSCAT1 wind retrieval method
• Rain Flags
• Generally Multidimensional Histogram (MUDH)
  procedure a statistical method based on
  noisiness of data
• RSS has similar approach though it is less
  conservative and hence rain affected areas are
  often smaller

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Rain Flags MUDH vs RSS
RSS
Less Coverage
TC Ando
FNMOC-NOGAPS
FNMOC-NRT
Same Coverage
12

• Ambiguity Removal
• FNMOC Near Real Time (NRT) plots and others use
  the US AVN model to nudge the selection
  process.
• FNMOC Ambiguity Removal over SSMI plots use
  NOGAPS
• Solutions buddy-checked with median filter
• Must pick one of these solns

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• FNMOC NRT
• Ambiguity removal - AVN

• FNMOC over SSMI
• Ambiguity removal - NOGAPS

04/02/02 0220Z
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• Ambiguity Selection
• NOAA/NESDIS use rain flagged data in ambiguity
  selection process
• FNMOC does not rain flagged data is put in as
  is after ambiguity removal.

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What is it GOOD for?

• Detection of circulations and determination of
  windspeeds.

X
09/04/02 0922Z TC Bonnie in its early stages.
Note gales on the southern side.
16
Small system (X) could be followed for 3 days
--no help from NWP model
20S
170W
170W
O
O
X
X
X
O
25 Jan 1800Z 26 Jan 0517Z
26 Jan 1800Z
170W
160W
170W
160W
O
X
O
27 Jan 1712Z
28 Jan 0427Z
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What is it GOOD for?

• Location of fronts/troughs.
• Wind speeds in data sparse areas.

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When is it BAD?

• Edge of swath ( 7 wind vector cells)
• Rain effects
• Sensitivity to errors in NWP
• Practical wind regime 5-45 m/s (problems with
  both very light and very strong winds)
• Resolution (25km) impact in tight gradients
• Ambiguity Removal Process and rain flag process
  can affect final solution

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Edge Problems
Along the whole edge or small
portion
FNMOC DISPLAY
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Rain Flags
RSS
TC Chris 05/02/02 0937Z
Rain flagged areas
NRL
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Typical Rain Patterns
Rain effects Cross swath vectors Higher wind
speeds
Some intense rain not flagged
RSS slide
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Rain Effects
One or two bad wind solutions may affect
neighboring wind vector cells through
buddy-checking system causing a rain contagion
effect.
TC Chris 05/02/02 0937Z
Direction of swath
Rain block direction perpendicular to swath Do
not use direction speed may be OK
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Rain Effects
Default direction seems to be perpendicular to
the swath direction
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Errors in NWP
TC Guillaume 19/02/02 1341Z
Wrong Model Position?
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Getting Good Stuff From Bad

• Sort the good from the bad
• Streamline method
• Isotach method
• Comparing different solutions

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Rain Effects tear drop
In tear drop shapes try to position using the
curvature outside of the rain block
region. Usually found closer to the curve vs.
pointed side. Look for good north-south winds.
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Streamlines
TC Chris 03/02/02 0914Z
Beware of winds perpendicular to the swath, even
when they are not flagged
X
Look for non-rain flagged winds
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Isotachs
TC Chris 04/02/02 1002Z
X
Look for min speed near centre
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Comparing Different Solutions
FNMOC-NOGAPS
FNMOC-NRT
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Where is TC HUDAH?No circulation!
Try to fix in trough equator-ward of the
strongest winds
?
Max Winds 95 knots
31
Model initialisation errors
In this case, poor model initialization combined
with a lower skill nadir position, picks proper
wind speed, but NO circulation center
20/2356Z
AVN 19/12Z tau 24
(Light winds?) -----low skill
c
10S
c
10S
?
Max Wind 55 KTS
?
20S
TC Paul
20S
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Analysis Methods - Summary

• Ignore the bad - streamline the good
• Tear-drop curved end
• TCs equatorward side of max wind
• Compare different solutions
• Isotach method ignore direction

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Conclusions

• Provides coverage over data sparse areas
• Wind speeds generally good useful for areas of
  gales etc
• Use the data if it makes sense
• Be aware of low skill areas and different
  ambiguity removal processes (compare!)
• Do not use in isolation