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An evaluation of a hybrid satellite and NWP based turbulent fluxes with TAO buoys

An evaluation of a hybrid satellite and NWP based turbulent fluxes with TAO buoys. ChuanLi Jiang, Meghan F. Cronin, Kathryn A. Kelly, LuAnne Thompson Submitted to JGR, 2004. Outline. 1. Motivation. 2. Method & Data. 3. TAO buoy comparisons. 4. Heat flux map comparisons. 5. Applications.

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An evaluation of a hybrid satellite and NWP based turbulent fluxes with TAO buoys

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  1. An evaluation of a hybrid satellite and NWP based turbulent fluxes with TAO buoys ChuanLi Jiang, Meghan F. Cronin, Kathryn A. Kelly, LuAnne Thompson Submitted to JGR, 2004

  2. Outline 1. Motivation 2. Method & Data 3. TAO buoy comparisons 4. Heat flux map comparisons 5. Applications

  3. Motivation • Intra-seasonal mixed layer heat budget in the equatorial Pacific plays an essential role in studying the physical processes that relate Kelvin wave to the ENSO variability and climate change. (McPhaden, 2002; Kessler et al. 1995; Zhang, 2001). • NWP winds and heat flux products have shown problems. • Satellite measurements provide accurate variables to calculate both momentum and turbulent heat fluxes. • A new turbulent heat flux product calculated from QuikSCAT winds and Microwave SST is promising (Jiang, Cronin, Kelly and Thompson, submitted to J.G.R, 2004).

  4. QuikSCAT winds… • obtain relative wind vector to ocean surface using model function that relates 10m wind vector to surface roughness. • QuikSCAT: TAO & NWP: http://www.ssmi.com/

  5. Passive microwave TMI SST (MW/OI) • Compared to infrared AVHRR, MW/OI can see through clouds, need less atmosphere correction. • 1-2mm SST • 25km resolution • 40S-40N http://www.ssmi.com/

  6. Method • Bulk algorithm: State variables: relative wind speed using skin SST air specific humidity air temperature • Strategy: COARE v3.0 algorithm (Fairall et al.2003) Most accurate state variables as compared to TAO buoys • Ground truth: TAO buoy state variables and turbulent heat fluxes calculated from the COARE v3.0 algorithm

  7. Data • 2-year: Jan.2000 – Dec.2001 • Smooth all variables to 4day, QuikSCAT winds map (Kelly et al. 1999) • Scalar-averaged relative wind speed: • Zonal ocean currentfrom altimeter (Kelly et al. 2004) • Bulk SST is used, instead of skin SST NWP ===> NCEP1,NCEP2, ERA40

  8. + 64 buoys for 38 buoys for TAO buoys

  9. State variables evaluations on TAO buoys: SST

  10. Wind speed comparison… NCEP1 too weak NCEP2 better than NCEP1 ERA40 better than NCEP QuikSCAT best, Strong along 165E & 8N bias=mean(Products -TAO)

  11. Best match NWP lacks high winds Histograms of wind speeds in eastern Pacific

  12. lacks low wind speed Weak zonal currents rain contamination Best match Histograms of wind speed near ITCZ

  13. SST comparison… Bias=mean(Products - TAO) SDD=STD(Products - TAO) NWP SST: warm in the cold tongue; cold off the equatorMW/OI: consistently cold

  14. Air specific humidity comparison… ERA40 has best humidity Dry along 165E NCEP2 worse than NCEP1 Better along 8N NCEP too dry in the east too wet in the west

  15. State variables evaluation averaged over TAO buoys… QuikSCAT Hybrid ERA40 ERA40 MW/OI

  16. LHF[VAR+all other TAO] LHF[all TAO VAR] Sensitivity of LHF to state variables:

  17. 3 1 2 Products Bias SDD Bias SDD Bias SDD Bias SDD NCEP1 2.3 11.6 -0.8 1.4 - 6.3 18.3 15.0 13.0 NCEP2 1.6 11.6 0.2 1.4 -13.1 18.4 2.5 13.8 ERA40 -0.5 10.4 -0.4 1.0 - 4.8 11.0 4.4 8.3 MW/OI 3.7 8.5 QuikSCAT -4.0 6.9 Sens of LHF to variables productsaveraged over TAO buoys… LHF ERRORHUMIDITY+WINDS+SST

  18. LHF evaluation on TAO buoys:

  19. LHF comparison… NCEP1C underestimate NCEP2C overestimate ERA40C good Hybrid best east of 170W Overestimate along 165E,8N

  20. Along 165E… LHF bias Sens to Sens to Sens to ERA40 overcompensates better LHF Hybrid dry humidity+strong winds larger LHF

  21. LHF evaluation averaged over TAO buoys: Fields NCEP1C NCEP2C ERA40C Hybrid Bias SDD Bias SDD Bias SDD Bias SDD LHF 10.7 24.8 -8.9 26.6 -1.5 18.1 -5.8 16.2 Fields NCEP1 NCEP2 ERA40 Bias SDD Bias SDD Bias SDD LHF -4.7 26.8 -28.6 32.0 -13.6 18.1 Algorithm tuned to observation COARE Improved LHF COARE Improved LHF Mean LHF bias is not sensitive to Difference=Algorithm + State variables + Temporal resolution of input variables

  22. Map comparisons in the tropical Pacific:

  23. Wind speed map comparison… NWP winds are weaker than QuikSCAT

  24. SST map comparison… NWP SST warm in the cold tonguecold off the equator

  25. LHF map comparison… Hybrid LHF Larger than NWPC Hybrid LHF is similar to NCEP1 off the equator

  26. Evaluation (TAO BUOYS) U r ERA40 SCAT MW/OI ERA40 VOTE -Hybrid~ERA40C, but better for models -Hybrid~TAO LHF, accuracy 10-15 (Cronin et al. 1997) -COARE improved NCEP2 & ERA40 -NCEP algorithm tuned to NCEP1 variables Conclusion • Evaluation of state variables: • Evaluation of LHF: VOTE -- Hybrid • Map Comparison: -Mean Hybrid structure similar to NCEP1

  27. Application of Hybrid product to intra-seasonal heat budget in OGCM:

  28. Future work

  29. Time-longitude of intra-seasonal QuikSCAT zonal wind stress, TAO SST and 20C isotherm depth…

  30. Special thanks to… • My advisors: Kathryn A. Kelly and LuAnne Thompson • My committee members: Meghan F. Cronin and Steve Emerson • The lab: Suzanne Dickinson, Jordan Dawe and David Darr • Paper discussion group, Steve Riser Thank You

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