1. Weather IV Hydrosphere
Water Cycle, Ocean Currents,
Humidity

2. Recall Weather needs a heat imbalance and a medium to flow through.
Water exists in all three phases on Earth.
Water is a good heat sink since it has high specific and latent heat capacities.
The prevailing winds are caused by a combination of the Coriolis effect and convection.

3. Water Cycle

4. Ocean Currents
Ocean currents are a very important way for the Earth to regulate its heat.
Since water is such a good heat sink.
Two Types – Warm surface currents and cold deep currents.

5. Warm Surface Currents
The main cause of surface currents are the prevailing winds which blow the surface water into the same direction.
Additionally, surface currents also experience the same effects as the prevailing winds such as convection and the Coriolis effect.
However, surface currents are also blocked by continents.

6. Deep Ocean Currents
Caused by thermo-haline differences with the surrounding water and convection.
As equatorially warmed waters travel north because of convection, they become saltier as more water evaporates or freezes.
As it cools in the far north, it becomes denser still due to cooling.
Net result is that it will sink in the North and travel southward to replace the water flowing northward from the equator.  Ideally
In reality, the currents are more complex due to the continents and seasons.

7. Global Ocean Currents

8. Consequences of Ocean Currents
Without ocean currents, the equator would be MUCH warmer, the poles would be MUCH cooler
The currents take energy from the equator and move it to the poles
Some areas are much wetter than others
Warm ocean currents tend to bring warm, moist air above them  areas near warm ocean currents have wet climates (rain forests)‏
Cool ocean currents tend to bring cool, dry air above them  areas near cool ocean currents have dry climates (deserts)‏
Areas near oceans are more temperate
The high heat capacity of water and the constant flow of water means coastal areas have milder winters and cooler summers
The lagging of seasons
Water causes the seasons to lag behind the light hours changes

9. Ocean Currents Example 1
United Kingdom’s climate is much more moderate than that of James Bay even though they are similar latitudes due to the warm surface currents which bring equatorial warmth to the country.
Without that current, the UK would rapidly freeze over.
The past
Today

10. The Past Could Ocean Currents Change?
ScienceDaily (Aug. 15, 2007)
Records from ice cores show that around 8,200 years ago the Northern Hemisphere's climate abruptly cooled.
Many scientists link this event to the final drainage of Lake Agassiz, a large glacial lake covering much of central Canada that formed at the foot of North America's continental glaciers.
This drainage is thought to have freshened waters in the northern Atlantic Ocean, slowing down the density-driven oceanic circulation that helps to distribute heat.

11. And Today…? Study shows weakening of heat- transporting ocean currents
Usha Lee McFarling, Los Angeles Times
Thursday, December 1, 2005
Striking Deep Current Reversal In The Tropical Pacific Ocean
ScienceDaily (Nov. 17, 2006)‏
Scientists probing a dying current bring worst climate fears to the surface
The Australian (December 05, 2005)‏