Part II: Where are we going? Like an ocean... The waves crash down... Introducing OCEAN ATMOSPHERE INTERACTION

The North Atlantic Oscillation (NAO) HIGH INDEX PHASE more regional than hemispheric (AO) pressure variations of the Icelandic Low and the Azores High shift in storm tracks and zonal wind Spatial Structure

The North Atlantic Oscillation (NAO) Temporal Structure NAO is found in all seasons NAO more pronounced during the winter (DJFM)- 37% of mthly 500hPa time series time avg. pressure difference (Azores and Iceland) srfc. spatial pattern is defined by regression with SLP

The North Atlantic Oscillation (NAO) HIGH INDEX PHASE 1900s – 30s: NAO high index 1940s – 70s: NAO low index 1980s – present: NAO high index contributed to much of observed warming in past decades (Hurrell, 1995)

The North Atlantic Oscillation (NAO) Spatial Structure regression of SST on the winter NAO index Tri-polar pattern: leading pattern of SST variability SST responding on monthly to seasonal time scales (NAO forcing) WHY? Fig 2a

The North Atlantic Oscillation (NAO) Co-varying patterns regression of SST on to srfc turbulent heat flux Heat fluxes  Tri- polar pattern SST tri-pole most energetic in late winter (needs a month to be forced by NAO) Fig 2b

The North Atlantic Oscillation (NAO) Temporal Structure wintertime NAO spectrum is red tri- pole SST pattern has an even redder spectrum (thermal inertia) increased power in the decadal band cross-equatorial circulation thumbprint on SST ( ΔT GS ) Fig 3

The North Atlantic Oscillation (NAO) Co-varying Patterns Labrador Sea: NAO/ ocean covariance? LSW has cooling/ warming trends consistent with NAO phase variations are large and sustained Fig 5

Tropical Atlantic Variability (TAV) Also known as the Tropical Atlantic SST Dipole dominant low frequency pattern btwn tropical SST and trade winds around the ITCZ positive SST anomalies north of the ITCZ  weak trade winds cold SSTs south of the ITCZ  weak northern trades  smaller ITCZ displacement to the south

Tropical Atlantic Variability (TAV) SST variability north and south are NOT correlated not a see- saw trade wind response is to cross- ITCZ SST differences SST-trade wind feedback? SST and trade wind time series: decadal variability (ΔT EQ )

TAV and the NAO SST tripole (NAO) and interhemispheric SST gradients (TAV) share equatorial/ subtropical anomalies TAV variability of SST is strongest in March- May lagging behind strongest NAO season (JFM) NAO may be an extratropical forcing that can excite the TAV interhemispheric SST gradients  tropical atmosphere Subtropical SSTs  NAO variability?

Meridonal Overturning Circulation (MOC) Also known as the Thermohaline Circulation responsible for poleward transport of water MOC function of upwelling, downwelling, and upper- wind forcing air-sea interaction  cold North Atlantic Deep Water (NADW) NAO is primary modulator of water mass transformation

IMPACTS: The NAO NAO is strongly linked to wintertime temperatures (SST over ocean, srfc air temperature over land) change in synoptic eddy activity and shifts in storm tracks High Index- dry over central/ southern Europe, northern mediterranean western N. Africa (Alps snowcover) wet from Iceland to Scandinavia (Norway glaciers)

IMPACTS: TAV regions dependent on the north-south swings of the ITCZ especially sensitive Nordeste, Brazil: Dry when N. SSTs high, S. SSTs low West Africa: Wet when N. SSTs are positive, S. SSTs are negative

IMPACTS: The MOC and abrupt climate change GHG warming models suggest increased freshening and warming of subpolar seas models suggest NAO/ AO anomalously high combination  weakened MOC (abrupt change?) potential for rapid cooling in northern Europe and NE America