Current Weather

Introduction to Air-Sea interactions

Ekman Transport

Sub-tropical and sub-polar gyres

Upwelling and downwelling

Return Exam I

For Next Class: Read Moran Ch. 8 (pp. 253-264)

Climate and Air-Sea Interactions

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Driving Question

How do interactions between the ocean and atmosphere impact worldwide climate and short-term climate variability?

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Air/Sea Interactions

The ocean influences radiational heating and cooling of the planet

Primary control of the amount of solar radiation absorbed at Earth’s surface

Contributes to non-radiative latent heat and sensible heat fluxes at the air/sea interface

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Air/Sea Interactions

Ocean and atmosphere are closely coupled Variations in atmospheric conditions can

impact temperatures and wind-driven currents Ocean surface currents strongly influence

climate Broad scale patterns of sea-surface

temperature strongly influence the location of major features of the atmosphere’s planetary scale circulation

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Mean State of Ocean Circulation

Ekman Transport Ekman spiral: simplified model

of the three-dimensional current pattern caused by a steady horizontal surface wind• Indicates that the direction of water

movement changes with increasing depth

• Each successively lower layer moves more toward the right and at a slower speed

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Mean State of Ocean Circulation

Ekman Transport Net transport of water due to the coupling

between the surface wind and water is known as Ekman transport• Piles up surface waters in some areas of the

ocean and removes surface waters from other areas

Produces variations in the height of the sea surface, causing it to slope gradually

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Mean State of Ocean Circulation

Geostrophic Flow and Ocean Gyres Horizontal movement of surface water arising

from a balance between the pressure gradient force and the Coriolis Effect is known as geostrophic flow• Characterizes gyres, large-scale roughly circular

surface current systems in the ocean basins

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Mean State of Ocean Circulation

Geostrophic Flow and Ocean Gyres Subtropical gyres are centered near 30° latitude in the

North and South Atlantic, the North and South Pacific, and the Indian Ocean

Ekman transport causes waters to converge from all sides toward the central region of a subtropical gyre

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Mean State of Ocean Circulation

Upwelling and Downwelling Coastal upwelling occurs where Ekman

transport moves surface waters away from the coast• Surface waters are replaced by water that wells up

from below

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Mean State of Ocean Circulation

Upwelling and Downwelling Where Ekman transport moves surface

waters toward the coast, the water piles up and sinks in the process known as coastal downwelling

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Mean State of Ocean Circulation

Upwelling and Downwelling Upwelling is most common along the west

coast of continents bordering the subtropical gyres

Upwelling and downwelling also occur in the open ocean where winds cause surface waters • Diverge from a region

causing upwelling• Converge toward a region

causing downwelling

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Mean State of Ocean Circulation

Upwelling and Downwelling Equatorial upwelling occurs

when surface waters are moved away from the equator and replaced by upwelling waters

Upwelling and downwelling influence ocean temperatures, biological activity, weather, and climate

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Mean State of Ocean Circulation

Thermohaline Circulation Deep-ocean circulation driven by variations in

density• Caused by variations in temperature and salinity

Significant in the Earth system because• Contributes to poleward heat transport• Modifies climate