1. Section 12.1 – The Causes of Weather
8th Grade Earth and Space Science
Class Notes

2. What is Meteorology? Study of atmospheric phenomena
Meteorologist – scientist who studies atmospheric phenomena

3. Weather vs. Climate
Weather – short-term variations in atmospheric phenomena
Climate – long-term,
average variations in
atmospheric phenomena
Determined by 30 year
averages

4. Heating the Earth’s Surface
Solar radiation is constantly heating some portion of the Earth’s surface.
The way solar radiation is distributed ultimately determines weather.

5. Imbalanced Heating
Earth’s axis is tilted to different parts of the Earth receive different amount of sunlight at different times of the year.

6. Imbalanced Heating
The Earth is a sphere so different places on Earth are at different angles to the sun.
Some places receive more direct, concentrated sunlight

7. Thermal Energy Redistribution
Air and water are constantly moving among the Earth’s surfaces, oceans, and atmosphere.
This constant circulation keeps the same average temperatures in a particular area over time.

8. Air Masses
Air mass – large volume of air with the same characteristics
Source region – area over which an air mass forms

9. Types of Air Masses

10. Tropical Air Masses
Maritime tropical – form over tropical bodies of water
In the summer they bring hot, humid weather to the eastern 2/3 of North America
Continental tropical –
form over the southwestern
US and Mexico

11. Polar Air Masses
Maritime polar air masses – form over the North Atlantic and North Pacific
Continental polar air masses – form over the interior of Canada and
Alaska

12. Arctic Air Masses
Form over regions north of 60 latitude in Siberia and the Arctic Basin
During part of the winter these areas receive almost no solar radiation and become extremely cold!

13. Air Mass Modification
Air masses move and as they move they transfer thermal energy.
As energy is transferred, the air masses characteristics change as they exchange thermal energy and moisture with the area they travel over.

14. Air Mass Characteristics
Air Mass Type
Weather Map Symbol
Source Region
Winter Characteristics
Summer Characteristics
Arctic A
Siberia, Arctic Basin
Bitter cold, dry
Cold, dry
Continental polar cP
Interiors of Canada and Alaska
Very cold, dry
Continental tropical cT
Southwest US, Mexico
Warm, dry
Hot, dry
Maritime polar mP
North Pacific
Mild, humid
North Atlantic
Cold, humid
Maritime tropical mT
Gulf of Mexico, Caribbean Sea, tropical and subtropical Atlantic and Pacific Ocean
Warm, humid
Hot, humid