Transcript wind stress & wind forcing

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 Salinity & Air-Sea Fluxes
Global Salinity
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
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