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Because, OF ALL THE ICE!!! How do you know there’s an Ice Age? Global Circulation Patterns: 3) Atmosphere-Ocean “coupling” Low latitudes: Oceans High latitudes: Atmosphere Oceanography Lecture 12 i. The Ocean/Atmosphere coupling ii.Surface Ocean Circulation Atmosphere-Ocean “coupling” Atmosphere – Transfer of moisture to the atmosphere (heat released in higher latitudes as water condenses!) Atmosphere-Ocean “coupling” Atmosphere – Transfer of moisture to the atmosphere: Hurricanes! In summary Latitudinal Differences in Energy www.weather.com Amount of solar radiation received annually at the Earth’s surface Latitudinal Differences in Salinity Latitudinal Differences in Density Structure of the Oceans Heavy Light T has a much greater impact than S on Density! Atmospheric – Wind patterns January Atmospheric – Wind patterns January Westerlies Easterlies Easterlies Westerlies High/Low Pressure systems: Heat capacity! High/Low Pressure systems: Wind generation Wind drag Zonal Wind Flow Wind is moving air Air molecules drag water molecules across sea surface (remember waves generation?): frictional drag Westerlies If winds are prolonged, the frictional drag generates a current Easterlies Only a small fraction of the wind energy is transferred to the water surface Easterlies Westerlies Any wind blowing in a regular pattern? High/Low Pressure systems: Wind generation by flow from High to Low pressure systems (+ Coriolis effect) 1) Ekman Spiral Once the surface film of water molecules is set in motion, they exert a frictional drag on the water molecules immediately beneath them, getting these to move as well. Motion is transferred downward into the water column ! Speed diminishes with depth (friction) ! Direction changes with depth (coriolis) 1) Ekman Spiral Spiraling current in which speed and direction change with depth: Net transport (average of all transport) is 90° to right (North Hemisphere) or left (Southern Hemisphere) of the generating wind. Transport occurs at most down to 100m! 1) Ekman Transport An example: July 1) Ekman Transport An example: January 1) Ekman Transport Surface circulation Large central “gyres” in ocean basins 2) Geostrophic Flow Ekman transport is limited to ~100m! How come the Gulf Stream extends down to 500-800m?. Pressure or geostrophic gradients (P = ! gh) 1) 2) Geostrophic Flow Dynamic equilibrium between Coriolis deflection and pressure gradient 2) 2) Geostrophic Flow Western intensification due to transport and vorticity 3) Ekman Transport 1) Downwelling: Convergence zones generate downwelling of water and nutrients The Gulf Stream Western intensification Grand scheme of things… Surface circulation: Heat transport Ekman Transport 2) Upwelling: If wind blows parallel to a shore in the proper direction Ekman transport moves near-surface water offshore. Water must then rise from below to compensate for seaward surface flow. 1) Ekman Transport Upwelling: Peru; California; Africa; Australia Grand scheme of things… Surface circulation: Warm and cold currents Balance of Earth Heat budget