XBT FALL RATE EQUATION WORKSHOP

National Oceanic and Atmospheric AdministrationAtlantic Oceanographic and Meteorological Laboratory, Miami, FL

March 10-12, 2008Miami, Florida, USA

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.

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

70+ SOOP ships ocean obs400+ 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

XBT (GTS) and Argo observations2000-2007 (spatial distribution)

2000 2001 2002

2003 2004 2005

2006 2007

0

25000

50000

75000

100000

125000

# o

bs

erv

ati

on

s

Argo 7934 12210 20237 32420 48035 72203 95520 105000

XBTs (*) 12968 20592 19999 23303 26371 24098 21944 28000

2000 (inc)

2001 2002 2003 2004 2005 2006 2007

XBT and Argo observations2000-2007 (temporal distribution)

(*) Includes additional 4k XBTs per year that are not transmitted into the GTS

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

Sippican XBTs

Deep blue, most commonly used

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 ma ~ b * 4000b correction for mass loss

Sources of errors:Fall rate errorThermistor calibrationSignal digitization error

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 ?

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.

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 dataWhich 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.

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.

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 ma ~ b * 4000b 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

This Workshop

Introduction

Historic perspectiveWhen everything started

What we know about XBTs Different XBTs: different FRECs (?)Time varying XBT FRECs

Experiments: XBT – CTD – altimetryWhy some experiments indicate that XBT FRECs should be different and why some others don’t.

Scientific implicationsOcean warming

Data basesImplications, Metadata, BUFR