Review - Precipitation is caused by the uplift of moist air Air rising along the ITCZ or weather fronts (convergence) Convection caused by intense surface heating (not always accompanied by rain) Orographic uplift (rain deposited on windward side of mountains)
Relative Scales of Cloud-Forming Processes
Water Vapor Warm air can hold move water vapor What happens when you cool air? Undersaturated Supersaturated
Global Circulation Where will rain fall?? High Pressure or Low Pressure
Global air circulation Garrison 2.069
Ocean circulation Surface currents –The Gulf Stream Upwelling –El Niño Vertical structure of the water column Deep water currents –The conveyor belt
Surface currents top m 10% of ocean volume is involved Wind drives the currents –Mostly trade winds and westerlies Water doesn’t get blown directly downwind –Friction of wind over water and Coriolis effect combine –Net transport at 45 o angle to wind direction. Ekman spiral
Trades and westerlies drive gyres G9.1, ,154
Surface circulation patterns Net effect is to cause rotational current systems Trade winds drive water east and away from equator Westerlies drive water west and toward equator
Global surface currents Duxbury 8.5
Currents and climate Miller 2.167
Gulf Stream from space – sea surface temperature G
Energy Transport Surface ocean currents transport energy Especially effective in moving heat from the tropics The Gulf Stream
Structure of the water column Typical verticle profile Top is “mixed layer” Water is stratified –Temperature –Salinity Most dense water on the bottom!
Wind-induced upwelling / downwelling Offshore wind blows away the warm surface layer Brings up deeper waters. Deep waters are nutrient-rich Good fishing! Onshore wind suppresses upwelling
Upwelling off South America 9.12a 2.209
Sea surface temperatures off South America
El Niño Trade winds falter (3-8 year cycle), normal offshore winds disappear. Lack of upwelling. Indicated by a rise in sea surface temperatures
El Niño year 9.12b 2.207
El Niño sea temperature
Deep water currents Driven by density’ Dense (cooler, more saline) water sinks
Ocean Temperatures Temperature varies N-S Solar energy inputs Variations due to currents
Ocean Salinity High where evaporation high Low where it rains, river inputs and ice melt from caps
Deep Water Formation Transport warm saline water north by Gulf Stream Cools in arctic Sea ice increases salinity Becomes dense - sinks
The conveyor belt Flows along the ocean bottom to Antarctica, into the Pacific Ocean, and upwells in the north Pacific.