1. Air pressure Fronts
Science 10 – Weather Unit

2. Air Pressure
Air Pressure is a measure of the force of the air pressing down on the Earth’s surface. It can vary at any particular point on the Earth depending on the density of the air.
Warm air is less dense than cool air. Warm air rises. Cool air sinks.
Air at high altitudes is less dense than air at lower altitudes.

3. Factors That Affect Air Pressure
Temperature – A measurement that indicates how hot or cold something is.
Water Vapor – Water in its gaseous state.
Elevation – A rise, or the raising of something.
Ex: Mountains have an elevation based on how high they are.
*Air pressure is measured by an instrument called a barometer. Units are mm of Hg (mercury) or kPa (kilopascals).

4. Pressure Systems High Pressure System Low Pressure System
A region where air is descending and thus exerting more pressure on the region below.
As the high air pressure sinks, it becomes warmer and drier.
High pressure systems often bring clear skies.
Low Pressure System
A region were rising air is leaving less dense air below.
As the air rises, it cools, causing water vapour to condense and produce clouds and precipitation.
Often brings wet weather.

5. Fronts
Fronts happen when two different air masses meet BUT they do not mix together. There are four different types:
Cold Front
Warm Front
Occluded Front
Stationary Front

6. How Do Air Masses Move?
Cold air, which is more dense, always sinks under warm air, which is less dense.
So what is the difference between the 4 types of fronts?
Which air mass takes over the other! Its a battleground.
One air mass is pushing the other out of the way because it does not want to mix!
Video on Air Masses:

7. Cold Front What happens?
A fast moving cold air mass runs into a slow moving warm air mass, pushing the warm air up quickly to form clouds.
Weather forecast: Cooler temperatures and dryer weather. Can also have rain on the warm front side.

8. Warm Fronts What happens?
A fast moving warm air mass collides with a slowly moving cold air mass. Warm air slowly moves over the cold air.
Weather forecast: Slow, steady rain!

9. Stationary Front What happens?
A cold air mass and warm air mass meet, but neither air mass has enough force to move the other air mass.
Weather forecast: Clouds and rain for multiple days.

10. Occluded Front What happens?
A cold air mass moves so fast that it overtakes a warm front, forcing the warm air up. The advancing cold air mass collides with the first cold air mass.
Weather Forecast: Usually rain – light to heavy.

11. Homework For homework, please read the following:
Pages for review about the seasons. We will not go into anymore detail than the book, so ensure you read it.
Page 30 on the Coriolis Effect. We will be talking about this tomorrow and doing a group activity, so please ensure you read it.
Project is due, in full, by the end of the day April 14th. Any submissions brought into class on April 15th will be marked late and will effect your project grade.
Unit Test: April 17th. Outline is posted on my website. You will have a review/study class on the 16th.