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The global XBT network
Molly Baringer (1), Gustavo Goni (1), and Dean Roemmich (2)
(1) NOAA/AOML, Miami, FL(2) SIO, La Jolla, CA
NOAA Climate Program OfficeClimate Observation Division
8th Annual PI MeetingAnnual System Review Meeting
Washington, DCJune 25-27, 2012
XBT Network:
• Program goals: mesoscale resolving global array of repeated transects, real-time data delivery, providing synergy with other platforms
• U.S. roles in the XBT Program; Ocean Obs ‘09 recommendations, Strategy for meeting the program’s goals.
• Users and uses of XBT data : research, operational applications, ocean/climate assessment
• Challenges for the XBT network, technology improvement
The global XBT networkOceanObs09 Recommended Transects
High Density (HD) – mesoscale resolving, 4 times per year
Frequently Repeated (FR) – 100-150 km spacing, 12-18 times per yearLow Density – no longer recommended
The global XBT networkInternational Collaboration with NOAA
France: AX20, AX01, AX02South Africa: AX25, AX08, AX18Brazil: AX97Argentina: AX18Australia: IX01, IX22Italy: MX01, MX02, MX4
More than fourteen institutions collaborate on collection, quality control, and science from XBT data including:US (NOAA, SIO), France (IRD, UP), Australia (ABOM, CSIRO), South Africa (UCPT), Japan (JMA), Brazil (FURG, Navy), Italy (ENEA), India (NIO), Germany (BSH), Argentina (SHA)
The global XBT networkDeployment/Observations
2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011
XBT 25 23 23 29 25 22 20 21 21 19 18
Argo 7 17 31 47 72 96 110 121 126 121 126
2001 2006 2011
125K
20K
XBTs Deployed (Red); Argo Deployed (Blue)
Number of profiles on the GTS in units of 1,000
Value of the HD (HRX) Network
• Ocean circulation: – The HD (HRX) Network samples the boundary currents and the ocean
interiors at high spatial resolution for transport estimation.– It provides a tool for integrating the observing system.– The combination of XBTs, Argo, and altimetry mitigates the limitations
of the individual datasets.
• Mass, heat, and freshwater budgets: – Estimates of reference velocities, heat storage, vertical advection, and
Ekman transport are all much improved in the past decade.– Time mean balances have good confidence.– Time varying balances remain a challenge, but progress is being made.
HRX transects are sampling:• Kuroshio (3 HRX tracks), Gulf Stream (3 HRX tracks)• Agulhas, Brazil Current, East Australian Current (2 HRX tracks)• Eastern boundary currents (California Current, Leeuwin Current, …)• Low latitude WBCs: Solomon Sea, Indonesian Throughflow• Antarctic Circumpolar Current (3 HRX tracks)• …
AOML status map
: Boundary currents sampled by the HRX Network
1. Global in scope (i.e. all 5 subtropical WBCs)
2. Enhanced BC sampling is highest priority, OO’09.
3. Argo provides complementary absolute and/or deep relative reference level velocities.
4. The HD (HRX) Network integrates the BCs and interior.
The High Resolution XBT (HRX) Network samples the world’s boundary currents - the subtropical WBCs and EBCs, the low latitude WBCs, and the ACC.
Boundary Current Array
Goal: The global networkOf currents from XBTs
Agulhas Current at 28S: IX21 (1994)Leeuwin Current 32S: IX15 (1987)Indonesian Throughflow: IX01 (1987)
Upstream Kuroshio Current: Upstream: PX44 (since 1991)Downstream: PX05 (2009)
East Australian Current: at 27S: PX30 (1991)at 33S: PX34 (1991)
East Auckland Current and Tasman outflow: PX06 (1986)
Solomon Sea current system: PX05 (2009)
California Current System: Undercurrent: PX37 (1991)California Current: PX37 (1991)
Alaska Current: PX38 (1993)
Antarctic Circumpolar CurrentSouth of Tasmania: IX28 (1993)Drake Passage: AX22 (1996)South of South Africa: AX25 (2004)
Gulf Stream: AX10 (1997), AX32 (1981) Florida Current: AX7 (2000)North Atlantic Drift Current: AX01 (1997)Labrador Current: AX02 (2010)Atlantic Ocean Equatorial Current System:
AX08 (2000), AX20 (2010)
Brazil Current: AX97 (2004)Brazil/Malvinas Confluence: AX18 (2002)Benguela Current and Agulhas Current
Rings: AX18 (2002) and AX08 (2000)
Zonal currents in the Tropical Atlantic
NECC
NEUCSEUC
SECC
NEC nSECcSEC
sSEC
Goni and Baringer, 2002
PX37S
Line 90
PX37S
Line 90
Line 90
PX37SArgo
Transport
PX37S
The “real” boundary current is the northward California Undercurrent, not the southward California Current.
Argo Steric Height 0/2000
Integrating the ocean observing system: HD (HRX), Argo, CalCOFI
Courtesy of D. Roemmich
Geostrophic volume transport in subtropical Pacific
Integrated transport:Black: Argo RG high resolutionRed: HRX during Argo era (29 cruises)Dark blue: HRX, all Hong Kong (44 cruises)
Argo era: 29 cruises; mean -12.9 Sv; σ = 3.66 Sv; Std error = 0.7 Sv
Differences between PX37 and Argo: • At high spatial resolution Argo has larger errors in the temporal mean• Argo misses the northward EBC
Courtesy D. Roemmich and J. Gilson
Example: Northward Heat Transport in SA (AX18)
Garzoli and Baringer (2007)Baringer and Garzoli (2007)
Both geostrophic and Ekman transports experience annual cycles, but they are out of phase.
Geostrophic transport controls the total northward heat transport.Geostrophic and Ekman transports experience comparable variability
Total = 0.51 0.15 PWGeos. = 0.40 0.16 PWEkman = 0.11 0.16 PW
…now using altimetry…e.g. Brazil current
On average 23 publications a year are published using XBTs as the primary data source.
The global XBT networkScientific Publications
SIOAOML
NOAA Role in the global XBT network
NOAA funds approximately 60% of XBTs, while international partners aid in the actual deployments
E.g. of the 11 HD transects done by AOML, international partners deploy XBTs on 9 lines.
The Future of XBTs:The Future of XBTs:
15. Create an international science panel for upper ocean thermal observations to support and evaluate recommendations of the integration of the different platforms, including XBTs (XBT Science Team created)
Gouretski and Reseghetti, 2010
1. Fully implement and maintain the XBT network as recommended in OceanObs99 (phase out of LD, increases HD)
2. Expand transects to include interior and marginal seas, such as the Mediterranean Sea and the Gulf of Mexico (Med Sea expansion, no Gulf of Mexico)
8.8. Support technological Support technological improvements (underway)improvements (underway)
9. Implement XBT calibrations based on CTDs (underway)
13.13. Continue XBT data analysis for scientific studies and increase its operational Continue XBT data analysis for scientific studies and increase its operational applications applications
The global XBT networkNew technology
Climate quality XBT with two pressure switches, which trigger signal at predetermined depth (By Sippican)
First test with improved thermal sensor was carried out in 2012 on the Western Boundary Time Series cruise.
< 1 m error
Challenges• Resources: Near level funded has forced a more rapid
transition to HD with a reduction in FR (and all LD).
• Spatial Coverage: Deployment opportunities are limited. For example transects in the Indian Ocean are extremely difficult, Ax18/Ax18* in the South Atlantic.
• Technical failures (e.g. variable fall rate): Quick detection and correction is essential. Important to have synergy of multiple platforms with different, enhancing goals.
• System Integration: Many other platforms require XBT program for logistical support (e.g. Argo float deployments, drifter deployments, pCO2/TSG calibrations and maintenance, weather service Met messages and US Coast Guard Amver alert system).
The global XBT networksummary
1. XBT network provides 20,000 T(z) profiles each year globally.2. Network has transitioned away from LD and FR towards HD.3. Science emphasizes HD transects:
Monitoring currentsMonitoring heat budgets, transport, regional balances
4. In the future:HD (HRX) network forms the backbone of a boundary
current observing systemFRE studies refine corrections for historical XBT dataProbe improvements, T sensors, pressure switches
produce climate quality measurements5. First XBT Science Workshop (Australia, 2011)
Highlight scientific accomplishmentsXBT Science Steering Team