Michael Lai Jon Robson Laura Wilcox Nick Dunstone Conclusions Models agree AMV of 5070 years with greatest variability in the subpolar Polar and subpolar upper OHC driven by ocean advection subtropical OHC driven by surface fluxes cloud changes ID: 935066
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Slide1
Similarities and differences of the internal AMV at 2 resolutions of HadGEM3-GC3.1
Michael Lai, Jon Robson, Laura Wilcox, Nick
Dunstone
Slide2Conclusions
Models agree:
AMV of 50-70 years, with greatest variability in the subpolar.
Polar and subpolar upper OHC driven by ocean advection, subtropical OHC driven by surface fluxes (cloud changes)
Arctic-Atlantic exchanges of S-controlled density anomalies drive subsurface density.
Models disagree:
Ocean circulation changes
N216
: Dominated by latitudinally coherent AMOC changes
N96
: Both AMOC and SPG changes are important
Appears to be explained by subsurface density propagation.
Role of the atmosphere:
N216
: NAO drives Labrador Sea subsurface density
N96
: NAO is not a significant driver of Labrador Sea subsurface density (ocean-only mode?)
Are the differences due to mean state biases or model resolution?
Slide3Characteristics of the AMV
N96ORCA1:
~135km atmosphere, 1
°
ocean
N216ORCA025
:
~60km atmosphere, 0.25
°
ocean
Slide4SST, SLP, AMOC evolution
‘NAO’ leads AMV by 10 years. AMOC leads AMV by 5 years.
AMOC anomalies do not move as far South in N96 compared to N216.
Slide5AMOC highly correlated with AMV in both models.NAO index is significantly correlated with AMV in
N216
but not in
N96
.
SST, SLP, AMOC evolution
Slide6OHT convergence vs Surface Fluxes
Polar and Subpolar T100: Driven by ocean heat transport convergence
Subtropical T100: Driven by surface fluxes
Slide7Ocean circulation changes
N216
SSH: SPG spin-up in the Labrador Sea region. GS extension / NAC SSH consistent with AMOC strengthening.
N96
SSH: Decrease in SSH consistent with SPG strengthening.
Slide8What’s driving the ocean circulation changes?
A source of S-controlled density anomalies moves from the Arctic into the N. At.
Slide9Role of the atmosphere in driving subsurface density changes
Surface fluxes over the Labrador Sea leads surface fluxes over the
Irminger
Sea
N216
: Wind changes drive SHF
N96
: Wind changes unimportant, SHF driven by vertical mixing instead?
Slide10Summary schematic
AMOC strengthens
Positive AMV
Arctic dense anomaly
Positive winter NAO
AMOC strengthens
Positive AMV
Arctic dense anomaly
SPG strengthens
N216
N96