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The Atmosphere • Wind Field – Drives upper layer flows of the major gyres • Net Heat & Freshwater Exchanges – Drives buoyancy flows (like the conveyor belt) • Chapter 2 - Ocean Circulation (we will skip parts) Stupid things that drive Dave crazy... • Easterly winds are from the east (to the west) • Westward winds are to the west (from the east) • Oceanographers say westward winds • Meteorologists say easterly winds – I’m right... Major Features of the Global Wind Field • Trades to Westerlies to Easterlies (toward poles) • Convergence of trades leads to ITCZ – Ascending moist air at equator – Drying & subsidence leads to a high over the subtropical ocean • Polar front is another region of convergence Global Wind Field Hadley Cells Major Features of the Global Wind Field • Winds blow from high to low pressure • BUT Earth rotation turns them to the right (left) in the northern (southern) hemisphere • Hence, winds are mostly zonal (along zones of constant latitude) Earth Rotation • Earth’s rotation gives rise to a fictitious force called the Coriolis force • It accounts for the apparent deflection of motions viewed in our rotating frame • Analogies – throwing a ball from a merry-go-round – sending a ball to the sun Earth Rotation Earth Rotation • Motions in a rotating frame will appear to deflect to the right (NH) • Deflection will be to the right in the northern hemisphere and to the left in the southern • No apparent deflection right on the equator Real Winds • Real winds are not zonal – Land masses mess this up • Seasonal changes happen – intensification in high latitudes – monsoons July climatology January climatology Real Winds • Location of ITCZ shifts seasonally • Seasonal changes in the monsoon – SW in July – NE in January • Driven in large degree by greater seasonal heating on the land Cyclones/Anticyclones • Mid-latitude storms do most of the atmospheric heat transport • Cyclones – low pressure & CCW (NH) rotation • Anticyclones – high pressure & CW rotation Cyclones/Anticyclones Cyclone Anticyclone Cyclones/Anticyclones Combination of cyclones & anticyclones lead to poleward heat transport Cyclones/Anticyclones Cyclones/Anticyclones Air Sea Interactions • We’ve seen this. • Warming of ocean leads to high SST • High SST leads to warm atmosphere • Tropics - High SST corresponds to regions of rising moist air
