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Table of contents
1 INTRODUCTION
1.1 North Atlantic subtropical stratication
1.1.1 EDW subduction and obduction
1.1.1.1 Subduction at southern ank of EDW bulk
1.1.1.2 Subduction estimates
1.1.2 Air-sea heat uxes
1.1.3 Geostrophic heat advection
1.1.4 Ekman current
1.1.5 Mesoscale eddies at the Gulf Stream northern ank
1.1.6 Mesoscale/submesoscale eddies at the southern ank
1.2 Air-sea coupling near Gulf Stream
1.2.1 Impact by NAO
1.2.2 Feedback to NAO
1.3 Preconditioning
2 Data and Method
2.1 Datasets
2.2 Domain of study
2.3 Heat budget calculation
2.3.1 Equations
2.3.2 Terms
2.3.3 Geostrophic current
2.3.4 Ekman current
2.3.5 Volume change estimate due to SSH variability
2.3.6 Closing the heat budget: inverse model approach
2.3.6.1 Our model
2.3.6.2 Stochastic inversion
2.3.6.3 Validation
2.4 Gulf Stream positioning
2.5 To identify EDW
2.5.1 Temperature criteria
2.5.2 Density-stratication criteria
2.5.2.1 Ventilated EDW volume
2.6 Interannual time scales
2.6.1 Signal decomposition
2.6.2 Time ltering
2.7 Denition of extremes
2.8 Buoyancy Budget
2.8.1 Fixed-domain buoyancy content anomaly BCASep
2.8.2 Relative September buoyancy content anomaly
2.9 Weather Regimes
3 Heat Budget
3.1 Abstract
3.2 Introduction
3.3 Direct Results
3.3.1 Periods with and without OHC extremes
3.3.2 Interannual Variability
3.3.3 Major contributing factors to OHC variability
3.3.4 Frequency component of OHC and its major contributing factors
3.3.5 OHC explained variance
3.3.6 Recirculation gyre
3.3.7 Gulf Stream positioning
3.3.8 Air-sea heat uxes
3.3.9 OHC extreme occurrences
3.4 Discussion
3.4.1 AMOC: the 1990s sudden increase and 2009-2010 slowdown .
3.4.1.1 Two periods of OHC extreme absence
3.4.2 Meridional heat transport due to mesoscale / submesoscale eddies
3.4.3 Interannual band-pass lter
3.5 Summary
4 Eighteen Degree Water extreme formation years
4.1 Abstract
4.2 Introduction
4.2.1 Extreme years in EDW freshly ventilated volume
4.2.2 Ekman current
4.2.3 EDW subduction and obduction
4.2.4 EDW formation volume
4.3 Results
4.3.1 Extreme occurrences over a multi-decadal period
4.3.2 EDW renewal spatial distribution
4.3.3 Interannual variability of EDW ventilated volume
4.3.4 OHC of the September-March period
4.3.5 Air-sea heat ux
4.3.6 Ekman eects
4.3.7 NAO
4.3.8 Preconditioning
4.3.9 A brief summary of the direct results
4.4 Discussion
4.4.1 Ventilated Volume and Subducted Volume
4.4.2 Wind-driven Heaving
4.4.3 EDW outcropping volume
4.4.4 Annual maximum outcropping area
4.4.5 Geostrophic transport at 30oN
4.4.6 Uncertainty of geostrophic transport at 30oN
4.4.7 EDW convection due to the Ekman term
4.4.7.1 OHC and EDW volume
4.5 Summary
5 Conclusions and Future Work
5.1 Conclusions
5.2 Future Work
A Weather conditions and Weather regimes
A.1 Introduction
A.2 Results
A.2.1 Impact of NAO through Ekman heat divergence
A.2.1.1 Atmospheric states
A.2.1.2 Weather conditions
A.2.2 Winter storm watch
A.2.2.1 Strong EDW formation years: 2005, 2010, and 2013 .
A.2.2.2 Weak EDW formation years: 2008, 2012, 2014, and 2015
A.2.2.3 Intermediate EDW formation years: 2011 and 2018 .
A.2.2.4 Surface wind stress curl
A.2.3 Impact of Atlantic Ridge/Blocking through Air-sea heat uxes
A.2.3.1 10m surface wind speed
A.2.3.2 Air-sea surface heat uxes
A.2.3.3 EDW volume composites
A.2.3.4 Impact of NAO through Gulf Stream
A.3 Discussion
A.3.1 Wind stress curl
A.3.2 Zero-year lag impact
A.3.3 Lagged correlation
A.4 Summary
B Buoyancy Budget
B.1 A hybrid buoyancy model
B.1.1 Results
B.2 Fixed-domain BCASep
B.2.1 Role of preconditioning for extreme years
B.3 Discussion
B.3.1 Seasonal cycle
B.3.2 Interannual variability
B.3.3 BCA
Sep v.s. xed-domain BCASep
C Eective Resolution
C.1 Signal smoothing: Gaussian kernel optimization
D Heat budget climatology and seasonal cycle
D.1 Climatology
D.2 Seasonal cycle
E Heat budget error estimates
E.1 2002-2019 time series
E.2 Interannual variabilities
