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 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.