Evaluation of a New Method to Quality Control Satellite-

derived Polar Winds in the NCEP GDAS/GFS

David Santek, Brett Hoover, Sharon NebudaCooperative Institute for Meteorological Satellite Studies

University of Wisconsin - Madison

Second Symposium on the Joint Center for Satellite Data AssimilationAtlanta, Georgia06 February 2014

J5.4

Outline

• Polar Winds product: MODIS and AVHRR

• Current QC method

• New approach

• Forecast impact for one-season experiment

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.

MODIS Polar Winds QCCurrent Thinning criteria

qcU = qcV = 7 ms-1

(O-B)U > qcU OR (O-B)V > qcV

Within 50 hPa of the tropopauseWithin 200 hPa of the surface, if over land

Special case

qcU = qcV = (ObsSpd + 15)/3

(IR wind within 200 hPa of surface OR WV wind below 400 hPa) AND

(GuessSpd +15)/3 < qcU

New Approach• Goal: One method for screening all polar winds

•MODIS, AVHRR, VIIRS

• Wind speeds vary over 3 orders of magnitude (1, 10, 100 ms-1)

•Normalize vector departure by Log of speed

•Log Normalized Vector Departure (LNVD)

Polar Winds QCCandidate Thinning criteria

Discards winds when Log Normalized Vector Departure (LNVD)

exceeds a threshold

SQRT ( (Uo-Ub)2 + ( Vo – Vb)2 ) / log(ObsSpd) > Threshold

Within 50 hPa of the tropopauseWithin 200 hPa of the surface, if over land

LNVD Threshold

Discard winds LNVD > 3

•Compared to control:

•Similar number of vectors discarded

•Discard more slow winds

•Retain more high speed winds

9 – 26 October 2012

Log Normalized Vector Departure

ObsSpd* Log(ObsSpd) VecDif

------ ----------- ----------

3 1.1 3.3

10 2.3 6.9

50 3.9 11.7

100 4.6 13.8

*Speed in ms-1

LNVD Threshold = 3

Current QC vs. LNVD3 ms-1

• Purple dots represent the end point of vectors that will be retained

Current LNVD

Opposite Direction!

Current QC vs. LNVD60 ms-1

• Blue arrow represents the wind vector at 60 ms-1

• Purple dots represent the end point of vectors that will be retained

• Purple vector is one possible AMV that would be retained

CurrentLNVD

Experiments • Running r29119 hybrid GDAS/GFS on S4

• 00 UTC forecast run

• 1 September to 25 October 2012

1. Control Current QC with operational data

2. MODIS LNVD => VecDiff / Log(Obs_spd) < 3

3. AVHRR (NOAA-15, 16, 18, 19, Metop-A)

a) Current QC

b) AVHRR replaces MODIS

MODIS: Northern HemisphereForecast Impact: 500 hPa ACC

Heights

LNVD (red) Control (black)

MODIS: Southern HemisphereForecast Impact: 500 hPa ACC

Heights

LNVD (red) Control (black)

Significant

AVHRR: Northern HemisphereForecast Impact: 500 hPa ACC

Heights

AVHRR-only (red) MODIS-only (black)

AVHRR: Southern HemisphereForecast Impact: 500 hPa ACC

Heights

AVHRR-only (red) MODIS-only (black)

AVHRR: Southern HemisphereForecast Impact: 700 hPa Heights

RMSE

AVHRR-only (red) MODIS-only (black)

Significant

Different Verification Time• Forecast impact typically measured with 00 UTC

model run

•Most input data

• What is AMV impact when radiosondes not available?

• Examine impact for 18 UTC model run

• Initial results using a 10-day period (1-10 October 2012)

MODIS: Northern HemisphereForecast Impact: 500 hPa Wind RSME

Green: Reduce vector RMSE Red: Increase vector RMSE

Note: Color scales are different

00 UTC 18 UTC

MODIS: Southern HemisphereForecast Impact: 500 hPa Wind RSME

00 UTC 18 UTC

Green: Reduce vector RMSE Red: Increase vector RMSE

Summary• First season results are encouraging for using the LNVD quality control: Reject more slow winds; Accept more fast winds

• AVHRR-only winds have a similar forecast impact as MODIS-only winds using current quality control: AVHRR, VIIRS are future

• Running a second season

• Forecast verification for 18 UTC model run shows increased forecast impact due to MODIS AMVs (conflict with RAOBs?)

NOAA: NA10NES4400011