Transcript Ocean circulation - University of Arizona

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
Supersaturated
Undersaturated
• What happens
when you cool
air?
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 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
Trades and westerlies drive gyres
• G9.1,2 2.153,154
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
• G9.11 2.179
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.