The Coherence of Upper Ocean Heat Transport in the Western North Atlantic

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The Coherence of Upper Ocean Heat Transport in
the Western North Atlantic

• Kathryn A. Kelly
• LuAnne Thompson
• Suzanne Dickinson
• University of Washington
• Ocean Sciences Meeting
• Orlando, FL
• March 2008

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Outline

• Data
• AVISO merged altimeter SSH anomalies, 1/4 degree,
  weekly
• Definitions of transport
• Jet, eastward or net
• Surface transport coherence
• Temperature transport
• Subtropical/subpolar gyre connection

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Mean SSH (Drifters, Hydrography GRACE)

• Maximenko and Niiler, GRL, 2003

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Definitions of Transport
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Transport Schematic SSH
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Transport Schematic Velocity
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Gulf Stream Transport Statistics
Note seasonal cycle removed from all time series
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Decorrelation Spatial Scales

• Upstream all variables decorrelated by 6 degrees
  longitude
• Downstream hmaxS and hminN (eastward) remain
  correlated
• Need to spatially average

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Transport Correlations

• Jet and eastward correlated in both regions
• Net transport uncorrelated with others
• Upstream and downstream transports uncorrelated
  (even allowing time lag)

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Gulf Stream Inflow

• Transports at 33N and 28N marginally correlated
• Transport at 33N marginally correlated with
  upstream box eastward flow

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Subpolar/Subtropical Gyre Connection

• GS inflow correlated with subtropical gyre flow
  (connected)
• NAC is anticorrelated with subtropical gyre

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Gyre Connection The Switch

• Direct model increase in GS flow increases NAC
  flow

Erratic gyre connection Lavender et al 2004
Bower Lozier float studies
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Upper Ocean Thermodynamic Model to Estimate Heat
Transport

• Specify surface currents and vertical profile
• Force with heat flux
• Estimate volume and temperature transport

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Volume and Temperature Transports

• Volume transport correlations mimic surface
  transport
• Temperature transport
• GS/subtropical gyre correlated
• NAC anticorrelated with Azores (but not
  subtropical)

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Summary

• Analysis of transports in the western North
  Atlantic
• GS Transports zonal average of jet or eastward
• Florida Current is marginally correlated with
  Gulf Stream (and alongstream)
• Gulf Stream well correlated with subtropical
  gyre flow
• Subtropical/subpolar gyre connection NAC
  increases at the expense of subtropical gyre (the
  switch)
• Temperature transport also shows evidence of
  switch
• What controls the transport switch?