1. Contributions to SST Anomalies in the Atlantic Ocean [Ocean Control of Air-Sea Heat Fluxes] Kathie Kelly Suzanne Dickinson and LuAnne Thompson University of Washington, Seattle WA USA SST Science Team, Seattle, WA 2013

2. Motivation
Want to understand origins of low frequency (climate-related) ocean anomalies
Kelly et al 2013

3. Atlantic Multidecadal Oscillation
1st EOF of SST
Tripole structure
Kelly et al 2013

4. Horizontal advection/diffusion
Contributions to SST
Surface heating
Vertical penetration
Upwelling & mixing
Horizontal advection/diffusion
Kelly et al 2013

5. Mixed Layer Heat Budget
Mixed layer temperature (here interchangeable with SST):
Problems:
Heat penetration hp not mixed layer depth
Time varying hp not known
Advection difficult to compute
Temperature below mixed layer not known
Entrainment velocity unknown
Kelly et al 2013

6. Estimate Mixed Layer Heat Budget
compute climatogical penetration depth by regression with net surface flux (Qnet)
ML advection from surface currents
also Ekman layer advection from wind stress
residual of ML heat budget includes vertical contributions and errors
Kelly et al 2013

7. Estimate Penetration Depth
Regress:
Then
Kelly et al 2013

8. Penetration Depth Ratios
Heat penetration deeper than MLD around 20N or 20S
Shallower in center of gyres
Kelly et al 2013

9. Compare Advection Estimates
Total from OSCAR currents and SST
Ekman from wind stress and SST
Kelly et al 2013

10. Mixed Layer Heat Budget
40N, 25W
Kelly et al 2013

11. Relative Term Sizes
Advection too large particularly in energetic current regions
Kelly et al 2013

12. Examine Heat Budget in Tripole Regions
north
middle
south
Kelly et al 2013

13. ML Heat Budget by Region
north middle south
Kelly et al 2013

14. SST Versus Heat Content
SST used in most climate studies (bulk flux formulas)
SST decorrelates seasonally, but heat content does not (Deser et al., 2003)
Interannual air-sea interaction depends on heat content (Kelly et al, 2010)

15. EOFs of SST and Heat Content
First mode of SST and heat content similar
Heat content from SSH has only 20-year record
Kelly et al 2013

16. Water Column Heat Budget
where
No vertical terms
Advection/diffusion estimated as a residual
Kelly et al 2013

17. Compare Heat Budgets
Mixed layer
Total column
Kelly et al 2013

18. Heat Content from Altimetric Sea Level
Assuming sea level anomalies are primarily from heat content
where η is sea surface height anomaly
α coefficient of thermal expansion
ρ density of sea water
cp heat capacity of sea water
Kelly et al 2013

19. Contributions to Altimetric Sea Level
thermosteric sea level
altimetric sea level
mass & salinity
Kelly et al, J. Climate, accepted
Kelly et al 2013

20. Column Heat Budget by AMO Region
north middle south
Kelly et al 2013

21. Meridional Heat Advection
Meridional advection
heat loss in subtropics
Kelly et al 2013, J. Climate, accepted
Gulf Stream regions 2 & 3

22. Summary
Mixed layer budget complicated (vertical distribution of heat in water column)
Mixed layer has large advection terms and large residual (vertical or errors?)
Column heat content budget simple: surface heating vs. advection
EOF 1 (AMO) similar for SST and SSH
AMO dominant term is:
ML: vertical distribution or errors?
Column: advection
Kelly et al 2013

23. Take Home
SST has longest record for computing ocean-related climate indices
Easier to determine contributions to heat content than to SST
Heat content dominates air-sea interaction on longer (climate) time scales
Kelly et al 2013