MOC related activities at NOC Joël Hirschi, Elaine McDonagh, Brian King, Gerard McCarthy Stuart...
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Transcript of MOC related activities at NOC Joël Hirschi, Elaine McDonagh, Brian King, Gerard McCarthy Stuart...
![Page 1: MOC related activities at NOC Joël Hirschi, Elaine McDonagh, Brian King, Gerard McCarthy Stuart Cunningham, Harry Bryden, Adam Blaker SAMOC workshop, Rio.](https://reader036.fdocuments.in/reader036/viewer/2022062409/5697bf721a28abf838c7e91f/html5/thumbnails/1.jpg)
MOC related activities at NOC
Joël Hirschi, Elaine McDonagh, Brian King, Gerard McCarthyStuart Cunningham, Harry Bryden, Adam Blaker
SAMOC workshop, Rio de Janeiro 11th – 13th May 2010
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Outline
• Some thoughts about SAMOC
• Hydrography in the South Atlantic
• Imprints of eddies and internal waves on MOC
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Thoughts about SAMOC
• What is the added value of having an observing system in the South Atlantic?
• How and where should we make measurements?
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What value can SAMOC add?
• Heat budget in tropical Atlantic
• Lead/lag relationship between heat fluxes at 26/32°S, 26°N and the development of anomalous heat content/SSTs
• Better understanding of southern vs northern influences on Atlantic MOC
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Heat budget of tropical Atlantic?
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MOC anomalies: April 2004 – April 2008
MOC anomalies: deseasoned, 2-month running average
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Lag correlation between MOC anomalies and SSTs:MOC leads SSTs by 6 months
Influence onNorth AtlanticStorm Track
Origin of NorthAtlantic Hurricanes
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Hydrography in the South Atlantic
Focus on Repeat Zonal Hydrography in the Subtropics
• At 24ºS– 2009: JC032– 1983: OC133– 1958: IGY Section
• At 30ºS– 2003 & 1993
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Changes at 30ºS: 2003 - 1993
Max. Anom at 13ºC in
Eastern Basin
Salinification of Thermocline and Intermediate Water in the East
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Interannual Variability at 30ºS
• Salinity Anomalies with large temporal amplitude are seen in the Eastern Basin – peak to trough comparable with cruise changes
• Salinity anomalies appear to propagate westwards with speeds of ~ 5cm/s recalling anomalies seen highlighted by Biastoch (2008) in satellite and model data
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• Salinity Anomalies with large temporal amplitude are seen in the Eastern Basin – peak to trough comparable with cruise changes
Raw Argo salinity on 13ºC
F
S
F
Interannual Variability at 30ºS
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• Salinity Anomalies with large temporal amplitude are seen in the Eastern Basin – peak to trough comparable with cruise changes
• Salinity anomalies appear to propagate westwards with speeds of ~ 5cm/s recalling anomalies seen highlighted by Biastoch (2008) in satellite and model data
Interannual Variability at 30ºS
![Page 13: MOC related activities at NOC Joël Hirschi, Elaine McDonagh, Brian King, Gerard McCarthy Stuart Cunningham, Harry Bryden, Adam Blaker SAMOC workshop, Rio.](https://reader036.fdocuments.in/reader036/viewer/2022062409/5697bf721a28abf838c7e91f/html5/thumbnails/13.jpg)
• Salinity Anomalies with large temporal amplitude are seen in the Eastern Basin – peak to trough comparable with cruise changes
• Salinity anomalies appear to propagate westwards with speeds of ~ 5cm/s recalling anomalies seen highlighted by Biastoch (2008) in satellite and model data
Interannual Variability at 30ºS
![Page 14: MOC related activities at NOC Joël Hirschi, Elaine McDonagh, Brian King, Gerard McCarthy Stuart Cunningham, Harry Bryden, Adam Blaker SAMOC workshop, Rio.](https://reader036.fdocuments.in/reader036/viewer/2022062409/5697bf721a28abf838c7e91f/html5/thumbnails/14.jpg)
Imprint of eddies and internal waves on MOC
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NEMO (Nucleus of European Modelling of the Ocean)
• NEMO ¼° global
1958 to 2001 run
• 64 Vertical levels
• 6-hourly forcing for
wind, heat and
freshwater fluxes
Madec (2008) http://www.nemo-ocean.eu
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Two passes through 1958 to 2001 forcing:Influence of initial conditions
Pass 1 Pass 2
Atlantic MOC at 26°S at 1000 m depth
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Red: pass 2Blue: pass 1
Atlantic MOC 1100 m depth: 26N
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MOC in 1/4° NEMO spinup: mean MOC 1976-2001 [Sv]
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Standard deviation of MOC 1976-2001 (5-day averages)
Sv
Sv
Sv
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Snapshots of sea surface height in passes 1 and 2
Pass 1, 21-25/12/1980 Pass 2, 21-25/12/1980m
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SSH difference between passes 2 and 1 [m]
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Std. dev .of MOC variability due to eddies & waves
Sv
Sv
Sv
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Ratio between chaotic and total MOC variability
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• Importance to clearly define benefits of SAMOC
• Hydrographic measurements at 30°S suggest large interannual variability – difficult to detect trends
• Imprint of eddies and internal waves varies from 1-2 Sv std.dev. (Tropics to mid-latitudes) to more than 5 Sv std.dev. at the equator
• Model results suggest similar “chaotic” variability at 25°S and 32°S
• Inferred “chaotic” variability likely to be a lower limit as eddies are likely to be too “predictable” in ¼° model
Conclusions