Because, OF ALL THE ICE!!! Oceanography Lecture 12 How do you know there’s an Ice Age? i. The Ocean/Atmosphere coupling ii.Surface Ocean Circulation Global Circulation Patterns: Atmosphere-Ocean “coupling” 3) Atmosphere-Ocean “coupling” Atmosphere – Transfer of moisture to the Low latitudes: Oceans atmosphere (heat released in higher latitudes High latitudes: Atmosphere as water condenses!) Atmosphere-Ocean “coupling” In summary Latitudinal Differences in Energy Atmosphere – Transfer of moisture to the atmosphere: Hurricanes! 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 Atmospheric – Wind patterns January 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 Easterlies the water surface 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 1) Ekman Spiral Once the surface film of water molecules is set in motion, they exert a Spiraling current in which speed and direction change with frictional drag on the water molecules immediately beneath them, depth: getting these to move as well. Net transport (average of all transport) is 90° to right Motion is transferred downward into the water column (North Hemisphere) or left (Southern Hemisphere) of the ! Speed diminishes with depth (friction) generating wind. ! Direction changes with depth (coriolis) Transport occurs at most down to 100m! 1) Ekman Transport 1) Ekman Transport An example: An example: July January 1) Ekman Transport 2) Geostrophic Flow Surface circulation Large central “gyres” in ocean basins 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 2) Geostrophic Flow Dynamic equilibrium between Coriolis deflection and Western intensification due to transport and vorticity pressure gradient 3) 2) Ekman Transport Grand scheme of things… 1) Downwelling: Surface circulation: Heat transport Convergence zones generate downwelling of water and nutrients The Gulf Stream Ekman Transport Western intensification 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 Grand scheme of things… Upwelling: Peru; California; Africa; Australia Surface circulation: Warm and cold currents Balance of Earth Heat budget.