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

Status of improving the use of MODIS and AVHRR

polar winds in the GDAS/GFS

David Santek, Brett Hoover, Sharon Nebuda, James JungCooperative Institute for Meteorological Satellite Studies

University of Wisconsin - Madison

12th JCSDA Workshop on Satellite Data AssimilationNCWCP

College Park, Maryland23 May 2014

Outline

• Polar Winds product: MODIS and AVHRR

• Current QC method

• New approach

• Forecast impact

• Verification at 1800 UTC

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

• Verify 00 UTC forecast run

• Two Seasons

1. 1 September to 25 October 2012 (own analysis)

2. 1 April to 31 May 2012 (consensus analysis)

Experiments

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) AVHRR replaces MODIS

1 April to 31 May 2012

1. Control Current QC with operational data

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

MODIS: Northern HemisphereForecast Impact: 500 hPa ACC

Heights

LNVD (red) Control (black)

• First season:10 September to 24 October 2012 (45 days)

• Neutral Impact

MODIS: Southern HemisphereForecast Impact: 500 hPa ACC

Heights

LNVD (red) Control (black)

Significant

• First Season:10 September to 24 October 2012 (45 days)

• Significant impact at Day 4 and 5

MODIS: Northern HemisphereForecast Impact: 500 hPa ACC

Heights

LNVD (red) Control (black)

• Second Season:9 April to 16 May 24 2012 (38 days)

• Neutral Impact

MODIS: Southern HemisphereForecast Impact: 500 hPa ACC

Heights

LNVD (red) Control (black)

• Second Season:9 April to 16 May 24 2012 (38 days)

• Neutral Impact

AVHRR: Northern HemisphereForecast Impact: 500 hPa ACC

Heights

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

• 10 September to 13 October 2012 (30 days)

• Neutral Impact

• Good news because AVHRR replaced MODIS

AVHRR: Southern HemisphereForecast Impact: 500 hPa ACC

Heights

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

• 10 September to 13 October 2012 (30 days)

• Neutral Impact

• Good news because AVHRR replaced MODIS

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 of MODIS LNVD Experiment

• One-month period (23 Sep - 24 Oct 2012)

00 UTC VerificationNorthern Hemisphere 500 hPa Height

ACC

Generally a neutral impact (Control slightly better)Experiment dropout on Day 1; Control dropout on Day

4

Red: LNVDExperiment

Blue:Control

18 UTC VerificationNorthern Hemisphere 500 hPa Height

ACC

Generally a neutral impact (Experiment slightly better)

Red: LNVDExperiment

Blue:Control

Wind RMSE ChangeGlobal: 00 UTC vs. 18 UTC

Green: Reduce vector RMSE Red: Increase vector RMSE

Note: Color scales are different

00 UTC 18 UTC

Summary• Results are encouraging for using the LNVD quality

control: Reject more slow winds; Accept more fast winds

• AVHRR-only winds have a neutral forecast impact compared to MODIS-only winds: AVHRR, VIIRS are future

• Forecast verification of MODIS polar winds with 18 UTC model run worth additional investigation

• Working with Iliana Genkova to get code checked into NCEP SVN

• This project ends on 31 May 2014

NOAA: NA10NES4400011