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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 University of Washington May,11 2005. Method. QuikSCAT winds : ; TAO & NWP :

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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 University of Washington May,11 2005

  2. Method • QuikSCAT winds: ; TAO & NWP: • Microwave SST (MW/OI) can see through clouds, compared to AVHRR. • Bulk algorithm: • State variables: ; ; • Strategy: COARE v3.0 algorithm Most accurate state variables evaluated by TAO buoys

  3. + 64 buoys for 38 buoys for TAO buoys

  4. Data • 2-year: Jan.2000 – Dec.2001 • Smooth all variables to 4day, QuikSCAT winds map (kelly et al. 1999) • Vector-averaged relative wind speed: • Zonal ocean currentfrom altimeter (kelly et al. 2004) • Bulk SST is used, instead of skin SST

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

  6. lacks low wind speed Weak zonal currents rain contamination match best Histograms of wind speed near ITCZ

  7. Air specific humidity comparison… ERA40 has best humidity Dry along 165E NCEP2 worse than NCEP1 Better along 8N

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

  9. 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 -3.1 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 Errors of LHF to variables productsaveraged over TAO buoys… LHF ERRORHUMIDITY+WINDS+SST

  10. LHF evaluation on TAO buoys:

  11. LHF comparison… Fields NCEP1C NCEP2C ERA40C Hybrid NCEP1C underestimate Bias SDD Bias SDD Bias SDD Bias SDD NCEP2C overestimate LHF 10.7 24.8 -8.9 26.6 -1.5 18.1 -5.8 16.2 ERA40C good Fields NCEP1 NCEP2 ERA40 Hybrid best in the east Overestimate along 165E,8N Bias SDD Bias SDD Bias SDD LHF -4.7 26.8 -28.6 32.0 -13.6 18.1

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

  13. Evaluation (TAO BUOYS) U r ERA40 SCAT MW/OI ERA40 VOTE -Hybrid~ERA40C, but better for models studies -Hybrid~TAO LHF, accuracy 10-15 (Cronin et al. 1997) -COARE improved NCEP2 & ERA40 -NCEP algorithm tuned to NCEP1 variables Summary • Evaluation of state variables: • Evaluation of LHF: VOTE -- Hybrid • Map Comparison: -Mean Hybrid structure similar to NCEP1 • Combining QuikSCAT winds and microwave SST to • produce turbulent heat fluxes products is promising.

  14. Outline 1. Motivation 2. Method & Data 3. TAO buoys comparisons 4. Heat flux maps comparisons 5. Applications (See Thompson et al. poster)

  15. Motivation • Intra-seasonal mixed layer heat budget in the equatorial Pacific plays an essential role in studying the physical processes that contribute 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, under revision to J.G.R).

  16. QuikSCAT winds… • Obtain relative wind vector to ocean surface using model function that relates 10m wind vector to surface roughness. • QuikSCAT: TAO & NWP: 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

  17. Data • 2-year: Jan.2000 – Dec.2001 • Smooth all variables to 4day, QuikSCAT winds map (kelly et al. 1999) • Vector-averaged relative wind speed: • Zonal ocean currentfrom altimeter (kelly et al. 2004) • Bulk SST is used, instead of skin SST

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

  19. match best NWP lacks high winds Histograms of wind speeds in eastern Pacific

  20. Error of LHF to state variables: Error to VAR=mean{LHF(VAR+all other TAO)-LHF(all TAO variables)}

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

  22. 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 Same algorithm as NCEP1 COARE algorithm improved Difference=Algorithm + State variables + Temporal resolution of input variables

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