Global Wind Patterns and Ocean Currents
The ocean and atmosphere act as one interdependent system. What happens in one causes changes in the other.
Characteristics of Water
•Polarity, dipole
•Hydrogen bonds
1 Heat Capacity of Water
Phases of Water and Energy Transfer
2 • The Earth climate system maintains a balance between solar energy absorbed and IR (blackbody) energy radiated to space. Ie., the heat budget for the planet is balanced.
GLOBAL ATMOSPHERIC ENERGY BUDGET
reflected solar Incoming solar radiation Outgoing radiation 342 W m2 longwave 107 W m2 radiation 235 W m2 40 Reflected by clouds, 30 aerosol & atmosphere 165 77 emitted by atmosphere Absorbed by atmosphere 67 24 78 350 back radiation 324 Reflected by 198 40 surface 30
168 24 78 390 324 Absorbed by Evapo- Surface radiation surface Absorbed by surface thermals transpiration
Large-scale wind patterns
3 Uneven heating results in large-scale atmospheric circulation
Convection Current
Theoretical Wind Patterns
4 Coriolis Effect
Clockwise Flow
Counterclockwise Flow
Revision
90 Ferrel Cell 60 Polar Cell
30
0 Heat Transport 30 Net Radiation
60 90
Idealized model of atmospheric circulation. N.B. actual circulations are not continuous in space or time.
SOEE3410 : Coupled Ocean & Atmosphere Climate Dynamics
5 Small-scale winds
Cold air is dry, dense and creates zones of high pressure.
Warm air is moist, less dense and creates zone of low pressure.
Which direction will two air masses flow if they meet?
6 Sea or Lake Breeze
Land Breeze
Mountain Breeze
7 8 Surface Currents
North Pacific Gyre
North Atlantic Gyre
Indian Ocean Gyre
South Atlantic Gyre Antarctic Circumpolar Current South Pacific Gyre
Western Boundary Currents
Fastest and deepest currents are found along the western boundaries of ocean basins. They move warm water poleward.
The Gulf of Mexico is the largest boundary current. It can move >160 km/day and its flow is 300 times the Amazon River!
9 Eastern Boundary Currents
Eastern boundary currents are on the eastern edge of ocean basins; they are slow and diffuse. They move cold water toward the equator.
Surface Currents Affect Local Weather and Climate
“The coldest winter I ever spent was a summer in San Francisco.” Mark Twain
Why is Washington D.C., located at about the same latitude as San Francisco, hot in the summer?
Horizontal Structure of Water
Low in Nutrients Mixed Layer Thermocline/ Pycnocline
Deep Ocean
High in Nutrients
10 Equatorial and Coastal Upwelling
Thermohaline Circulation
• Driven by differences in density rather than by wind energy
• Therme (heat) + halos (salt)
• Deep water currents transport about 90% of the Earth’s ocean water
• Entire ocean is involved
Based on temperature and salinity (density) water masses have unique characteristics
11 Different Water Masses Don’t Like to Mix!
Antarctic Bottom Water
• The most distinctive of the deep water masses. • Salinity = 34.65 ppt • Temperature = -0.5 C • Density = 1.0279 g/cm3 • Slowly sinks to bottom and spreads into all ocean basins. Takes a 1000 years to return to surface!!
12 • For every liter of water that sinks, a liter of water must rise to the surface (another equilibrium).
• http://www.youtube.com/watch?v=L9zjmC8InKA
Where is an example where water rises to the surface?
What are two reasons that upwelling is important?
Take-home Message
Pole 90 60
30 If the equator receives excess solar energy and
0Equator the poles receive deficit solar energy, why doesn’t
Heat Transport the equator boil and the 30
Net Radiation poles freeze solid year-
60 round? 90 Pole
13 Ocean currents and global winds carry heat away from tropics (incoming energy > outgoing energy) to the polar regions (outgoing energy > incoming energy).
The atmosphere transfers about 2/3 of the total heat and the ocean transfers about 1/3 of the heat.
What would happen if the patterns of wind and currents change?
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