mechanisms of decadal variability in the atlanticone.geol.umd.edu/dv/ln/040908.pdf · outline •...
TRANSCRIPT
Mechanisms of Decadal Variability in the Atlantic Thermohaline
CirculationBy
Bill Scheftic
Outline
• Physical Oceanography Review– Ocean Currents and General Properties
– Ekman Pumping
• Dong and Sutton (2005)– Methodology
– Ocean Mechanisms
– Atmospheric Forcing
Ocean Properties: Currents
(Stewart 2005)
Ocean Properties: Salinity
(Stewart 2005)
Ocean Properties: Height
(Stewart 2005)
Ocean Properties: Heat Transport
(Stewart 2005)
Ekman Pumping
(Stewart 2005)
Ekman Pumping
(Stewart 2005)
Ekman Pumping
(Stewart 2005)
Ekman Pumping
Methodology
• HadCM3– Coupled ocean-atmosphere sea-ice GCM
– 1000 yr control run
• THC index– Strength of MOC: 996m, 27.5-32.5N
– 8-65yr bandpass filter (for decadal variability)
• Look at dominant modes of variability of OHT and MOC through EOFs and PCs
Climatology
(Dong and Sutton 2005)
Thermohaline circulation spectrum
(Dong and Sutton 2005)
Mechanisms
Atmosphere
Ocean
(Dong and Sutton 2005)
Ocean Mechanisms
(Dong and Sutton 2005)
Ocean Mechanisms
(Dong and Sutton 2005)
Ocean Mechanisms
(Dong and Sutton 2005)
Ocean Mechanisms
(Dong and Sutton 2005)
Ocean Mechanisms
(Dong and Sutton 2005)
Ocean Mechanisms
(Dong and Sutton 2005)
Ocean Mechanisms
(Dong and Sutton 2005)
Atmospheric Forcing
(Dong and Sutton 2005)
Atmospheric Forcing
(Dong and Sutton 2005)
Global Implications?
(Dong and Sutton 2005)
Summary• ~25 year variability is found in the THC with HadCM3
ocean-atmo GCM• Cold-water accumulates in subpolar gyre, which
strengthens the NAC and advects salty water into the deep convection region which strengthens the THC and subsequent OHT. Finally the subpolar gyre fills in with warmer water leading to a reduction in the THC
• NAO projects onto pattern needed to strengthen subpolar gyre and initiate northeastward saltwater advection.
• Later similar wind stress curl and heat flux anomalies trigger convection in the GIN sea
• DS05 showed that near lag 0 there is a correlation between the THC and tropical precipitation, possibly related to changes in Rossby and Kelvin wave production near the equatorial Atlantic due to ITCZ shifts
References• Dong, B. and R. T. Sutton, 2005: Mechanism of Interdecadal
Thermohaline Circulation Variability in a Coupled Ocean-Atmosphere GCM. J. of Clim., 18, 1117-1135
• Stewart, R. H., 2005: Introduction to Physical Oceanography. Dpt. Of Oceanography, Texas A&M. Available Online at [http://oceanworld.tamu.edu/resources/ocng_textbook/contents.html]