1. XBT FALL RATE EQUATION WORKSHOP National Oceanic and Atmospheric Administration Atlantic Oceanographic and Meteorological Laboratory, Miami, FL March 10-12, 2008 Miami, Florida, USA

2. Objectives Bring together members of the technical, operational and scientific community to:  Present and discuss issues related to XBT fall rate equation and coefficients,  Discuss if changes need to be made to these coefficients,  Discuss what changes need to be made to these coefficients,  Propose how to implement these changes together with a timetable.

3. Approximately 60% complete Ocean observing system 57% Total in situ networks January 200758% 100% 40% 82% 43% 72% 48%21% 92% continuous satellite measurements “operational” sustained research funding pilot projects/ research funding

4. 70+ SOOP ships ocean obs 400+ SOOP and VOS ships met bulletins World Meteorological Organization and Intergovernmental Oceanographic Commission Ship of Opportunity Team (SOT) Ship Of Opportunity Programme (SOOP) Voluntary Observing Ship scheme (VOS) Automated Shipboard Aerological Programme (ASAP) Courtesy D. Roemmich

5. XBT (GTS) and Argo observations 2000-2007 (spatial distribution) 2000 20012002 200320042005 20062007

6. XBT and Argo observations 2000-2007 (temporal distribution) (*) Includes additional 4k XBTs per year that are not transmitted into the GTS

7. SOOP XBT deployments High density mode:  1 XBT deployment every 25 km  4 transects per year Frequently repeated mode:  6 XBT deployments per day (1 every 80 km)  18 transects per year Low density mode:  4 XBT deployments per day (1 every 120 km)  12 transects per year  Being replaced by Argo observations Transects need to be continuously revised/assessed

8. Sippican XBTs Deep blue, most commonly used

9. Fall Rate Equation and Coefficients (FREC) Same equation proposed by TSK and Sippican: z (t) = a * t – b * t 2 t in secs and z in m a ~ b * 4000 b correction for mass loss Sources of errors: Fall rate error Thermistor calibration Signal digitization error

10. ISSUES that we need to address in this workshop - 1  What XBT FREC (Fall Rate Equation and Coefficients) are we using ? Are we simultaneously using identical FRECs ?  Time-varying FREC ? Was there a time when FRECs were ok ? When, How and WHY did the FRECs change with time ?  Have XBTs changed with time ? Sippican experts will tell us.  What is the difference between the FRECs currently being used with those obtained from experiments ? New coefficients.  Where is the problem coming from ? Geographical dependency ? Viscosity / temperature (!!!) dependence ? Transient signal ?

11. ISSUES - 2  Are there additional problems related to the data acquisition systems ? If there is a correction due to data acquisition system, we may need to use different FRECs.  Do we have enough experiments to determine new FRECs ? CSIRO (Australia), ENEA (Italy), AOML (USA), NRL (USA), NIO (India), SIO (USA), PMEL (USA), etc. How important is the geographical distribution of these experiments ?  Is there a need for more experiments ? Funding (XBT-CTD comparisons). New platforms (altimetry !). Closer cooperation with Sippican.

12. ISSUES - 3  Do we all agree that there is a problem with the FRECs ? Are all the results obtained from experiments consistent ?  How to implement a change in FRECs ? Can this be done, simultaneously, smoothly ?  Implementation of change of FRECs to old data Which data ? Can we tell what FRECs were used in each profile held by NODC and Coriolis ? Issues with metadata. Is there enough metadata ? Is there good metadata ? New BUFR format. TIMEFRAME to do it.

13. ISSUES - 4  How do we communicate results and findings consistently ? Scientific findings already made the journals. Communicate efficiently (do not use harsh wording) so the scientific community will trust XBT data.  Can we implement the recommendations effectively ? How ? Again, issues with metadata, archives (NODC, Coriolis, GTS). TIMEFRAME to do it.  Scientific implications. Correction of estimates of heat storage and trends. Corrections to already made long term forecasts that used old data.

14. An example: T5 (1800m) FRECs Same equation proposed by TSK and Sippican: z (t) = 6.828 * t – 0.000182 * t 2 t in secs and z in m a ~ b * 4000 b correction for mass loss Kizu et al. proposed new FRECs for TSKs: z (t) = 6.5407 * t – 0.0018691 * t 2 With the TSK proposed equation, the XBTs were going too fast and for Sippican: z (t) = 6.705 * t – 0.001619 * t 2 With the Sippican proposed equation, the XBTs were also going too fast

15. This Workshop Introduction Historic perspective When everything started What we know about XBTs Different XBTs: different FRECs (?) Time varying XBT FRECs Experiments: XBT – CTD – altimetry Why some experiments indicate that XBT FRECs should be different and why some others don’t. Scientific implications Ocean warming Data bases Implications, Metadata, BUFR