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)
Water Vapor
• Warm air can hold move water vapor
• What happens when you cool air?Undersaturated
Supersaturated
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 50-100 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 45o angle to wind direction.
Ekman spiral
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
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
El Niño
• Trade winds falter (3-8 year cycle), normal offshore winds disappear.
• Lack of upwelling.
• Indicated by a rise in sea surface temperatures
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