Mean annual SST
EQ WestEast Equatorial Divergence
map view 2˚N 2˚S EQ Trade Winds WestEast Ekman Transport {to right in NH} Ekman Transport {to left in SH} DIVERGENCE Equatorial Divergence
cross-section 2˚N2˚S XXX Trade Winds Ekman Trans. {to left in SH} Ekman Trans. {to right in NH} Equatorial Divergence
cross-section 2˚N2˚S DIVERGENCE XXX Trade Winds UPWELLING Ekman Trans. {to left in SH} Ekman Trans. {to right in NH} Equatorial Divergence
WestEast Warm Surface Layer Cold Deep Ocean Easterly Trade Winds Equatorial upwelling - E vs. W
WestEast Warm Surface Layer Cold Deep Ocean Easterly Trade Winds Thick Warm Surface Layer Thin Warm Surface Layer Thermocline Equatorial upwelling - E vs. W
WestEast Warm Surface Layer Cold Deep Ocean Easterly Trade Winds Thick Warm Surface Layer Thin Warm Surface Layer Thermocline Upwell Cold Water in East Upwell Warm Water in West Bottom of Ekman Layer Equatorial upwelling - E vs. W
Cold Deep Ocean Air-Sea Feedbacks Easterly Trade Winds WestEast H L Upwelling Due to Winds
Cold Deep Ocean Air-Sea Feedbacks Easterly Trade Winds WestEast H L Trade Winds Enhanced by Pressure Gradient Upwelling Due to Winds Upwelling Enhanced by Winds colder
Cold Deep Ocean Air-Sea Feedbacks Easterly Trade Winds WestEast L Trade Winds Enhanced by Pressure Gradient Upwelling Due to Winds Upwelling Enhanced by Winds Stronger H colder Trade Winds Enhanced more by stronger Pressure Gradient Upwelling Enhanced even more by Winds
Mean annual SST
Air-Sea Feedbacks WestEast H L Walker Cell Or Walker Circulation
A big result of Different “Pressure” zones: moisture. WE LOW PressureHIGH Pressure As air rises, it cools, water condenses, lots of rain As air sinks, it warms, lots of evaporation Warm rising air WIND Cold sinking air
“Normal” conditions
Walker Circulation Strong –Trades blow E to W –Thermocline shallow in E –Upwelling of cold water in E –Warm water piles up in W –E to W temperature gradient reinforces trades “Normal” conditions
Walker Circulation Gone, reverse flow WestEast What is an El Niño?
El Niño conditions
Walker Circulation Weak or Gone –Trades very weak or reversed –Thermocline deep in E –Upwelling of warm water in E –Sea level rises in E –E to W temperature gradient reduced or gone El Niño conditions
“Normal” “El Niño”
Annual Average “Normal” Short-lived deviation from “Normal”: El Niño (March 1998)
Walker Circulation Stronger than normal La Niña conditions
Normal conditions El Niño conditions
WestEast H L Walker Cell Or Walker Circulation Normal rainfall
Walker Circulation Gone, reverse flow WestEast El Niño rainfall
La Niña anomaly map
El Niño anomaly map
El Niño impacts - precipitation patterns