1. JCOMM SOT-4 April 2007 Revisiting the XBT Fall Rate Equation (Sippican Deep Blue):Implications and Recommendations JCOMM/SOT-4 Derrick Snowden Gustavo Goni Molly Baringer

2. JCOMM SOT-4 April 2007 Outline Introduction to the data XBT Error Partioning Estimating a New Fall Rate Equation Implications for Climate Studies Conclusions and Recommendations

3. JCOMM SOT-4 April 2007 Instruments List System NameLauncher Type Recorder TypeController Software (PC) aomlautoAOML Autolauncher MK-12AOML (DOS 386 PC) devilhandSippican LM- 3A DevilDevil Software (Win XP PC) seasautoAOML Autolauncher MK-21SEAS2000 (WinXP PC) seashandSippican LM- 3A MK-21SEAS2000 (Win XP PC) sioautoSIO Autolauncher MK-21SEAS2000 (Win XP PC) siok98SIO Autolauncher MK-12 366 total profiles

4. JCOMM SOT-4 April 2007 XBT/CTD Profiles

5. JCOMM SOT-4 April 2007 Outline Introduction to the data XBT Error Partioning Estimating a New Fall Rate Equation Implications for Climate Studies Conclusions and Recommendations

6. JCOMM SOT-4 April 2007 Partitioning XBT Error XBT differs from the CTD due to : A: inaccurate depth measurements B: inaccurate temperature measurements AB

7. JCOMM SOT-4 April 2007 Fall Rate Equation a: Change of mass of the probe due to spooling wire. b: Probe geometry and initial terminal velocity c: Describes startup transients i.e. initial conditions Currently used FRE (WMO 1770:52) for Deep Blue probes contains no constant term ( c ).

8. JCOMM SOT-4 April 2007 Fall Rate Error: Initial Conditions Hallock and Teague 1992

9. JCOMM SOT-4 April 2007 Outline Introduction to the data XBT Error Partioning Estimating a New Fall Rate Equation Implications for Climate Studies Conclusions and Recommendations

10. JCOMM SOT-4 April 2007 Determining Depth Offset Focus on the temperature gradient: derivative of temperature with respect to depth Minimize temperature error effect

11. JCOMM SOT-4 April 2007 Depth Offset Prior to Correction

12. JCOMM SOT-4 April 2007 Depth Correction Algorithm Assemble the depth offsets (dZ) Recalculate XBT depths Znew = Zxbt+dZ Back calculate time (t) Fit new fall rate equation to (t) z = at^2 + bt + c

13. JCOMM SOT-4 April 2007 Depth Offset: Post-Correction

14. JCOMM SOT-4 April 2007 Summary of Fall Rate Coefficients ABC Wmocode 52 -0.002256.6910 this study-0.001916.4870 this study-0.002996.639-4.5117 other studies (1) -0.00131 – -0.00329 6.440 – 6.798 0 - 0 1: Taken from Hanawa et al 1995

15. JCOMM SOT-4 April 2007 Outline Introduction to the data XBT Error Partioning Estimating a New Fall Rate Equation Implications for Climate Studies (Wijffels and Thresher 2007) Conclusions and Recommendations

16. JCOMM SOT-4 April 2007 Basin Averaged Offset

17. JCOMM SOT-4 April 2007 Global Trends

18. JCOMM SOT-4 April 2007 Recommendations Future Work: Tropical Atlantic Cruise (May 2007) will conduct additional side by side XBT-CTD comparisons Reinvorgorate research toward understanding fall rate issues Metadata to include coefficients and the form of the equations (it isnt sufficient to list A,B need to know z=at^2 + bt + c + … (including exchange files and metadata servers) Quality flags should be listed level by level not just for the entire profile Communication with the manufacturers to better understand the timing and nature of changes in XBT manufacturing procedures.

19. JCOMM SOT-4 April 2007 Implications for Climate Studies AB