Status of improving the use of MODIS, AVHRR, and VIIRS polar winds in the GDAS/GFS

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Status of improving the use of MODIS, AVHRR, and
VIIRS polar winds in the GDAS/GFS

• David Santek, Brett Hoover, Sharon Nebuda, James
  Jung
• Cooperative Institute for Meteorological
  Satellite Studies
• University of Wisconsin - Madison

11th JCSDA Workshop on Satellite Data
Assimilation NCWCP College Park, Maryland 06 June
2013
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Outline

• Polar Winds
• What happened to Expected Error (EE)?
• New approach
• Status of MODIS, AVHRR, and VIIRS

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Satellite-derived Polar Winds
Unlike geostationary satellites at lower
latitudes, it is not be possible to obtain
complete polar coverage at a snapshot in time
with one or two polar-orbiters. Winds must be
derived for areas that are covered by three
successive orbits The gray area is the overlap
between three orbits.
Three overlapping Aqua MODIS passes, with WV and
IR winds superimposed. The white wind barbs are
above 400 hPa, cyan are 400 to 700 hPa, and
yellow are below 700 hPa.
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MODIS Polar Winds QCCurrent Thinning criteria
Within 50 hPa of the tropopause Within 200 hPa of
the surface, if over land
qcU qcV 7 ms-1 (O-B)U gt qcU OR (O-B)V gt qcV
Special case qcU qcV (ObsSpd 15)/3 (IR wind
within 200 hPa of surface OR WV wind below 400
hPa) AND (GuessSpd 15)/3 lt qcU
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QC Approach (2012)Expected Error

• Least square regression is used to compute the
  RMSE (ms-1) from the summed EE components as
  compared to co-located RAOBs.
• EE Components Terra NH cloud drift
• Five QI values -0.1 to -2.8
• Wind speed 0.1
• Wind shear 0.03
• Temperature shear -0.01
• Pressure level -0.003
• Constant 8.4

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Difference HistogramAccepted Observations
(Normalized_EE Control)
More slow winds (5 ms-1) are rejected more
mid-speed winds retained.
Few additional winds rejected that deviate lt 7
ms-1 from background. More accepted when O-B gt 7
ms-1.
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Southern Hemisphere
500 hPa ACC EERAT (red) Control (blue)
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What happened to EE?

• EE only available for GOES and MODIS winds
• Not for AVHRR nor VIIRS (initially)
• The EE is dependent on the forecast background
• More so for MODIS winds than GOES
• MODIS EE coefficients vary significantly

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New Approach

• One method for screening all polar winds
• Wind speeds vary over 3 orders of magnitude (1,
  10, 100 ms-1)
• Normalize departure by Log of speed
• Log Normalized Vector Departure (LNVD)

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Polar Winds QCCandidate Thinning criteria
Within 50 hPa of the tropopause Within 200 hPa of
the surface, if over land
Discards winds when Log Normalized Vector
Departure (LNVD)exceeds a threshold SQRT (
(Uo-Ub)2 ( Vo Vb)2 ) / log(ObsSpd) gt Threshold
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LNVD Threshold

• Discard winds LNVD gt 3 Similar to EE ratio gt 1.33
• Compared to control
• Similar number of vectors discarded
• Discard more slow winds
• Retain more high speed winds

9 26 October 2012
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Log Normalized Vector Departure
LNVD Threshold 3
ObsSpd Log(ObsSpd) VecDif ------ -----------
---------- 3 1.1 3.3 10
2.3 6.9 50 3.9 11.7
100 4.6 13.8
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LNVD
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Experiments

• Running current hybrid GDAS/GFS on S4
• Early October into December 2012
• Control Current QC with operational data
• MODIS LNVD gt VecDiff / Log(Obs_spd) lt 3
• AVHRR (NOAA-15, 16, 18, 19, Metop-A) LNVD lt 3
• MODIS IR-only (discard water vapor winds)
• Preliminary O-B and O-A statistics 9 26
  October 2012
• Very preliminary forecast impact 9 - 20 October
  2012

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MODIS OMB and OMA
Control
LNVD
9 26 October 2012
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MODIS Northern HemisphereForecast Impact
500 hPa ACC LNVD (red) Control (blue)
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MODIS Southern HemisphereForecast Impact
500 hPa ACC LNVD (red) Control (blue)
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O-B AVHRR MODIS
9 26 October 2012
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O-A AVHRR MODIS
9 26 October 2012
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MODIS IR-only

• MODIS winds composed of IR, cloudy water vapor,
  clear-sky water vapor
• Current Terra MODIS water vapor channel has only
  2 good out of 10 detectors, which impacts
• Feature tracking
• Cloud heights for both water vapor and IR winds
• CIMSS will discontinue use of Terra MODIS water
  vapor channel in polar winds production
• Investigating tracking features from
  hyperspectral sounder retrievals of water vapor
  (AIRS, CrIS, IASI, ATMS) NASA

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VIIRS Polar Winds

• Spatial Better resolution than MODIS
• 750 m across swath MODIS degrades to 9 km at the
  edge
• Wider swath 3000 km vs. 2320 km
• Spectral No water vapor channel on VIIRS,
  therefore more similar to AVHRR
• No water vapor winds
• Limits cloud height options
• Routine production at STAR late FY13Q4
• Routine production at OSPO October 2013
• Operational December 2013

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Status and Future Plans

• Completing current experiments on S4
• One-year no cost extension
• Expecting satellite-derived winds from VIIRS
  (Suomi NPP) fall 2013
• NOAA NA10NES4400011