MOC related activities at NOC Joël Hirschi, Elaine McDonagh, Brian King, Gerard McCarthy Stuart Cunningham, Harry Bryden, Adam Blaker SAMOC workshop, Rio de Janeiro 11 th – 13 th May 2010

Outline Some thoughts about SAMOC Hydrography in the South Atlantic Imprints of eddies and internal waves on MOC

Thoughts about SAMOC What is the added value of having an observing system in the South Atlantic? How and where should we make measurements?

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

Heat budget of tropical Atlantic?

MOC anomalies: April 2004 – April 2008 MOC anomalies: deseasoned, 2-month running average

Lag correlation between MOC anomalies and SSTs: MOC leads SSTs by 6 months Influence on North Atlantic Storm Track Origin of North Atlantic Hurricanes

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

Changes at 30ºS: Max. Anom at 13ºC in Eastern Basin Salinification of Thermocline and Intermediate Water in the East

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

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

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

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

Imprint of eddies and internal waves on MOC

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)

Two passes through 1958 to 2001 forcing: Influence of initial conditions Pass 1 Pass 2 Atlantic MOC at 26°S at 1000 m depth

Red: pass 2 Blue: pass 1 Atlantic MOC 1100 m depth: 26N

MOC in 1/4° NEMO spinup: mean MOC [Sv]‏

Standard deviation of MOC (5-day averages) Sv

Snapshots of sea surface height in passes 1 and 2 Pass 1, 21-25/12/1980Pass 2, 21-25/12/1980 m

SSH difference between passes 2 and 1 [m]

Std. dev.of MOC variability due to eddies & waves Sv

Ratio between chaotic and total MOC variability

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