Weather IV Hydrosphere

Water Cycle, Ocean Currents,

Humidity

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.

Water Cycle

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.

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.

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.

Global Ocean Currents

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

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

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.

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)