1. The Causes of Weather May 2013

2. Air Masses  The air over a warm surface can be heated causing it to rise above more dense air.  Air Mass: A very large mass of air that has nearly uniform properties such as temperature, humidity and pressure.

3. High Pressure Systems  When an air mass cools over an ocean or a cold region of land, a high pressure system forms.  As the air mass cools, the air mass becomes more dense.  When the air mass contracts, it draws in surrounding air from the upper atmosphere.

4. Low Pressure Systems  Air masses that travel over warm land or oceans may develop into low pressure systems.  When an air mass warms, it expands and rises. As it rises, it cools.  Water vapour in the air may condense, producing clouds or precipitation.

5. Trying to breathe on Mt. Everest

6. Land and Sea Breezes  Land and Sea Breezes Land and Sea Breezes  Land breeze : a type of wind that blows from the land to the ocean.  Land breezes usually occur at night.  Air moves because of differences in air pressure over the land.  Winds at the surface flow from high to low pressure creating a land breeze.

7. Land and Sea Breezes  Sea Breeze: A wind from the sea that develops over land near coasts.  Formed by increasing temperature differences between the land and water.  Air temperature gets cooler relative to nearby locations as one moves closer to a large body of water.

8. Land and Sea Breezes  The sea has a greater heat capacity than land and can absorb more heat than the land.  The strength of the sea breeze is directly proportional to the temperature difference between the land and the sea.  (Land and Sea Breezes activity)

9. The Coriolis Effect and Wind  The Coriolis effect is a change in the direction of moving air, water, or any objects on Earth’s surface due to Earth’s rotation.  As Earth rotates, any location at the equator travels much faster than a location near either of the poles.

10. Global Wind Systems  Wind systems are wide zones of prevailing winds. There are three major wind systems, which occur in both hemispheres.  Trade Winds  Prevailing Westerlies  Polar Easterlies

11. Jet Streams  A large temperature gradient in upper-level air, combined with the Coriolis effect, results in strong westerly winds called jet streams.  A jet stream is a narrow band of fast-moving wind.  A jet stream can have a speed up to 300 km/h or greater at altitudes of 10 km to 12 km.  Storms form along jet streams and generate large-scale weather systems

12. Shipwrecks Reveal Ocean Currents

13. Fronts  A front is a zone that develops as a result of the meeting of two air masses with different characteristics.  Each air mass has its own temperature and pressure.  An approaching front means a change in the weather, and the extent of the change depends on the difference between conditions in the air masses.  Fronts usually bring precipitation.

14. Fronts

15. Weather Fronts

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