Impact of QuikSCAT Surface Marine Winds on Wave Hindcasting

Transcription

1 Impact of QuikSCAT Surface Marine Winds on Wave Hindcasting V. J. Cardone, A. T. Cox, E. L. Harris, E. A. Orelup and M. J. Parsons Oceanweather Inc. Cos Cob, CT and H. C. Graber Rosensteil School of Marine and Atmospheric Sciences U. of Miami Miami, FL

2 Outline Brief Look Back - Scatterometry Accuracy and Dynamic Range of QuikSCAT Scatterometer Winds Application of QuikSCAT to Reduction of Systematic Effects in NWP Reanalysis Products Impact of QuikSCAT on Wave Hindcasting

3 History of Scatterometry Aircraft Experiments - 11/1969 SKYLAB SEASAT ADEOS QuikSCAT 6/1978-9/1978 I: 9/1996-6/1997 II: 12/ /2003 6/1999-

4 Highlighted L to R: Willard Pierson, Manley St. Denis, Vince Cardone Linwood Jones, Willard Pierson, Vince Cardone

5 From N. W. Guinard, 1969: The variation of the RCS of the sea with increasing roughness. Microwave Observations of the Ocean Surface, SP- 152, June 1969, Analyses of the NASA/Navy Review,

6 PBL Wind Profile Variation of Mean Wind With Height: Surface Layer Neutral Stratification Uz U * = log k since τ z z 0 = ρ C z U 2 z where z U * = 0 = τ / ρ roughness parameter 2 C z = k (log z / z0) C z = 2 drag coefficien t Stability Effect U z C z U* z = log k z0 = k 2 ϕ z L log z z ϕ z0 L 2 ϕ = stability function L = stability length ~ H = heat flux U * 3 H C 10n is drag coefficient referred to 10m at neutral stratification

7 Buoys Very useful for calibration and validation of models, analysis schemes, remote sensors Error structure a function of buoy type and payload which are far from standardized Systematic errors may arise above about 25 m/sec

8 Evaluation of QuikSCAT Against Buoys Wind Speed Number of Collocations 48,540 Bias 0.05 m/s RMS Difference 1.00 m/s Correlation Coefficient Wind Direction Number of Collocations 48,519 Bias 1.5º RMS Difference 28.3º Correlation Coefficient Ebuchi et al. (2002); J. Atmos. Oceanic Technol., 19,

9 Buoy during Hurricane Ivan 2004

10 Evaluation of QuikSCAT against Platforms Platform Name Anemometer Height

11 North Cormorant Platform: North Sea

12 Platforms Fixed vertical reference frame Top of derrick mount minimizes flow distortion errors The only potential source of accurate extreme winds (U10 >25 m/s) Heights of 50 m-140 m create new challenges for reduction to 10 m Difficult to use because non-standard reporting practices, confidentiality...

13 Platform Data Processing Platform data arrived already reduced to 10m using onboard power law factor (URed) except K-13, which used KNMI s potential wind speed profile. Two alternative reductions to 10m applied: Cardone (1969): first inverted power law factor to restore wind speeds to anemometer height then computed 10 m neutral wind speed using NCEP air and sea temperatures (WindFN). WindFN Neutral: same as WindFN but assuming air-sea temperature difference =0.

14 North Sea Platforms Used to Evaluate QuikSCAT Platform Location Anemometer Height (m) Water Depth (m) Reduction Factor Measurement Interval Draugen 64.3N 7.8E : 20 min Ekofisk 56.5N 3.2E 116 & & : 20 min Gullfaks 61.2N 2.3E : 20 min : 10 min Heidrun 65.3N 7.3E : 20 min : 10 min : 20 min K N 3.22E ~ : 1-hr (WD last 10-min of preceding hour) Sleipner 58.4N 1.9E : 20 min

15 Comparison of Wind Speed Reduction Factors - Ekofisk Platform

16 Collocation Process Read NASA JPL Level 2B (L2B) file processed using DIRTH. Retrievals flagged for land, rain, or ice were not included in this analysis. Search 100 x 100 km box centered on the platform within a +/- 30 minute time window of the platform wind. Always match the single nearest QuikSCAT wind within the time and space filter. Found 21,454 matches total for all six platforms from

17 Platform Winds Reduced to 10 m using WindFN Platform No. Mean Plat Mean QS Wind Speed (m/s) Diff (Q-P) RMS Error Stnd Dev Scat Index Corr Coeff No. Mean Plat Wind Direction (deg) Mean QS Diff (Q-P) Stnd Dev Scat Index Draugen Ekofisk Gullfaks Heidrun K-13* Sleipner All (except K-13) * K-13 statistics using potential wind speed profile by KNMI

18 Q-Q Plot Data Period : 01-JUL :00:00 to 01-JAN :00:00 Number Mean Mean Diff RMS Stnd Scat Corr Platform Method of Pts Plat QScat (Q-P) Error Dev Index Ratio Coeff Wind Spd. (m/s) All URed Wind Spd. (m/s) All WindFN Wind Dir. (deg) All URed-FN N/A N/A N/A

19 Platform-QS Pairs Where Either Exceeds 25 m/s YYYYMM DDHHMM Platform Quikscat WS Platform WS Quikscat WD Platform WD Sleipner Gullfaks Draugen Heidrun Mean Quikscat WS: m/s Ekofisk Draugen Draugen Ekofisk Mean Platform WS: m/s Mean Diff (Q-P): RMS: Sleipner Stnd Dev: Gullfaks Draugen Draugen Draugen Scat Index: 0.10 Corr Coeff: Draugen Gullfaks Gullfaks Draugen Mean Quikscat WD: º Mean Platform WS: º Mean Diff (Q-P): Heidrun Stnd Dev: Draugen Gullfaks Scat Index: Gullfaks Heidrun Heidrun Sleipner Draugen Draugen

20 Horns Rev

21 Winds Observed in North Sea Hurricane by Horns Rev

22 North Sea Hurricane Kinematic Analysis to QuikSCAT Data 1500 UTC December 3, 1999

23 North Sea Hurricane Kinematic Analysis to QuikSCAT Data 1800 UTC (Revs. At 1714 UTC and 1934 UTC)

24 Alternative SWADE IOP-1 WAM hindcasts compared to buoy measurements

25 Impact of QuikSCAT on Current Practice of IOKA

26 Uncorrected NCEP Reanalysis Project Surface Pressure and 10-m Wind Analysis December 28, 2000

27 QuikSCAT Winds in One Pass

28 Wind Workstation

29 Final IOKA Wind Field

30 Wind Field for 01-Sep Z

31

32

33 Evaluation of GROW hindcast driven by NRA wind fields Evaluation of AES40 hindcast driven by reanalyzed NRA wind fields

34 NCEP Grid - Big Boxes

35 Primary/Secondary Regression Lines on Q-Qs Big Box 6 Date Range: 01-JUL :00:00 to 30-JUN :00:00 Wind Spd. (m/s): Dir Number Mean Mean Diff Stnd Scat Corr Bin of Pts QScat NCEP (H-Q) Dev Index Coeff ALL Wind Dir. (deg): Dir Number Mean Mean Diff Stnd Scat Bin of Pts QScat NCEP (H-Q) Dev Index ALL Box Dir (fr) Init WS (m/s) Adj d Primary Adj d Secondary 6 E S W N

36 Quikscat vs. NCEP Unadjusted 90% Exceedance WS Bias All Dir Combined (N-Q) in m/s

37 Quikscat vs. NCEP Adjusted 90% Exceedance WS Bias All Dir Combined (N-Q) in m/s

38 Sample Level I Base Case Wind Field October 7, Z Sample Level II Wind Field October 7, Z

39 Examples of HS biases in terms of model vs. altimeter Q-Q scatter plots in hindcasts driven by QuikSCAT corrected wind fields Sea of Okhotsk South China Sea Location # Pts Bias (H-Alt) Scat. Ind. Corr Coeff Sea of Okhotsk S. China Sea Irish Sea Irish Sea Offshore Algeria Offshore Algeria

40 Conclusions NRA marine surface winds an improvement over previous operational NWP base products NRA winds may be further improved: -assimilate SCAT winds directly from use SCAT winds to identify and remove systematic effects in historical fields - overlay products of mesoscale models for tropical cyclones and terrain effects

41 Present Focus Producing 5-year global QuikSCAT enhanced winds via IOKA may serve as a reference set for future global wave model validation (e.g. explore subtle southern vs northern ocean wave climate effects) Producing 50-year adjusted NRA winds with systematic errors minimized for third pass at GROW

42 Direct Assimilation of QuikSCAT into Global Wind Fields Currently Underway at Oceanweather