?INFORMATION CONTENT IN LOW DENSITY
XBT TRANSECTS RELATIVE TO OCEANIC GYRES
ROBERT L. MOLINARIFORMERLY: NOAA/AOML
PRESENTLY: UNIVERSITY OF MIAMI- CIMAS
CARMEN ALEXUNIVERSITY OF MIAMI- CIMAS
OUTLINE1) OBJECTIVES
2) SUMMARY OF LOW DENSITY NETWORK RELATIVE TO GYRE STRUCTURE INCLUDING BASIC CHARACTERISTICS AND HYPOTHESIS TESTING
3) IN VIEW OF RECENT QUESTIONS ABOUT STABILITY OF FALL-RATE EQUATION ARE RESULTS
REPRESENTATIVE OF ACTUAL GYRE CHARACTERISTICS?
4) SUMMARY AND RECOMMENDATIONS
OBJECTIVES (LIMITED BY TIME OF TALK TO NORTH ATLANTIC SUBTROPICAL GYRE)
1) WHAT INFORMATION RELATIVE TO THE TIME DEPENDENT STRUCTURE OF THE NORTH ATLANTIC SUBTROPICAL GYRE CAN BE DISCERNED FROM LINES PROVIDING 40+ YEARS OF OBSERVATIONS (E.G., IS THE GYRE SLOWING?)
2) IN VIEW OF THE QUESTIONS RECENTLY RAISED ABOUT THE FALL RATE EQUATION OF XBT’S, IS THE INFORMATION VALID?
3) WHAT FUTURE STEPS SHOULD BE TAKEN?
TYPES OF XBT AVAILABLE AT NODC
DEPTH FIX RECOMMENDED:A) Insufficient meta-data available: 16,442B) Hanawa fix applied: 106,267C) Hanawa fix required: 649,941
DEPTH EQUATION APPLIED:A) Original Sippican equation: 658,795B) Hanawa: 113,557C) Unknown: 0
INSTRUMENT TYPE:A) Unknown XBT type (I.e., Sippican, Spartan, etc): 421,742B) Sippican T7: 75,672C) Sippican T4: 200,064
DATADepth range: MBT: 150 to 200m Early XBTs: 450m Post 1970 XBTs: 750 m Sampling: Pre WOCE-TOGA: regional oceanographic surveys WOCE-TOGA: occupation of low-density network (LDN) shown in Figure 1.Types of LD lines for purposes of this poster: Real lines, VOS transects regularly (once/month) occupied from one end to the other (blue lines Figure 1) Imaginary lines: given a WOCE-TOGA number but not regularly occupied by a VOS (red lines Figure 1). Extensive data can exist along an imaginary line because of other transects crossing the section (e.g., A6 is crossed by A5, A7, A11, A12, A15, A20). Imaginary lines will not be considered in this presentation.
anomaly
Wijffels et al. (2008)
Wijffels et al. (2008)
ISHII AND KOMOTO (2008)
GOURETSKI (2008)
Gouretski(2008)
Wijffels et al. (2008)
ISHII AND KIMOTO (2008)
EXAMPLES OF FALL RATE CORRECTIONS
Sippican depth Hanawa Ishii WijffelsDepth Error (2%) For Sippican T7 For all T7s 1976 1987 1976 1987
450 +/-9m 465 465 455 459 460
750 +/-15m 775 775 758 765 768
SUMMARY
1) SEVERAL DIFFERENT DATA SETS AND METHODS HAVE BEEN USED TO DERIVE A VARIETY OF NEW FALL RATE EQUATIONS RANGING FROM PROBE SPECIFIC (I.E., FOR SIPPICAN T4’S AND T’7S AND SPARTON PROBES) TO ONE GLOBAL EQUATION.
2) DATA SET LIMITED PARTICULARLY IN THE 1970’S TO DETERMINE WHICH EQUATIONS ARE BEST.
3) PRELIMINARY RESULTS SUGGEST THAT MOST FIXES ARE CAPABLE OF PRODUCING CORRECTIONS SUITABLE FOR STUDIES OF LARGE-SCALE OCEAN FEATURES, BUT NOT FOR CLIMATE VARIABILITY AND CHANGE REQUIREMENTS (PART OF PROBLEM THESE HAVE NOT BEEN DEFINED FOR TOTAL OCEAN VOLUME)
Additional Problems1) Temperature biases: Kizu and
Hanawa (2002), up to 1C2) Recorder biases:Snowden et al.
(2008), below manufacturers error3) Limited data: Wijffels et al.
(2008), particularly southern oceans
4) Incomplete meta-data:Wijffels et al. (2008), particularly pre-1990
5) Data location biases: Thadathil et al. (2002), cold water bias
RECOMMENDATIONS1) CONTINUE PRESENT METHOD OF STORING XBT
DATA AT NODC (I.E., DO NOT APPLY NEW CORRECTIONS, EXCEPT HANAWA)
2) IMPRESS ON DATA COLLECTORS THE IMPORTANCE OF PROVIDING REQUIRED META-DATA
3) ASSEMBLE A WORKING GROUP OF MODELERS AND OBSERVATIONSALISTS TO DEVELOP A PLAN FOR DEFINING CLIMATE CRITERIA FOR SUBSURFACE TEMPERATURE DATA AND FOR CORRECTING HISTORICAL XBT DATA TO MEET THESE CRITERIA
(SIMILAR TO APPROACH USED FOR SST)
