AIR MASSES AND FRONTS By: Ms. Nail

Air Masses An air mass is a large body of air that develops over a particular region. Warm air forms over tropical regions near the equator. Has low air pressure. T- Tropical Cold air forms over polar regions. Has high air pressure P- Polar Wet air masses form over oceans. m- maritime Dry air masses from over land. c- continental

Air masses Moisture content is noted by the first letter. m – maritime – wet c – continental – dry Temperature is noted by the second letter. P – polar – cool T – tropical - warm

Air Masses mP- maritime polar cP – continental polar mT – maritime tropical cT – continental tropical

Fronts A front is a boundary between air masses. Cold front Warm front Four types of fronts and map symbols Cold front Warm front Occluded front Stationary front

COLD FRONT What is a cold front? A cold front forms when a cold air mass pushes under a warm air mass. Bring thunderstorms, rain or snow. This produces cumulonimbus clouds. Cold front followed by cooler drier air.

Cold Front

WARM FRONT What is a warm front? A warm front forms when a warm air mass moves up and over a cold air mass. This produces stratus and cirrus clouds. Brings drizzly precipitation. Followed by clear warm weather.

Warm Front

STATIONARY FRONT What is a stationary front? A stationary front forms when a warm air mass and a cold air mass meets but neither advances. Many days of cloudy, wet weather.

Stationary Front

OCCLUDED FRONT What is an occluded front? An occluded front forms when a fast moving cold air mass overtakes a slower warm air mass. The warm air is caught between two cooler air masses. The cool dense air moves under the warm less dense air and cuts the warm air mass off. Brings cool temperatures with large amounts of rain or snow

Occluded Front

Quiz: Take this on the paper provided. 1. Describe a maritime polar (mP) air mass, in terms of moisture and temperature. 2. What is the name of an air mass that forms over water? 3. What is the name of an air mass that forms over land? 4. What is the name of an air mass that forms in a cold region? 5. What is the name of an air mass that forms in a warm region? 6. Describe a continental tropical (cT) air mass, Moisture and temperature. 7. The boundary between two air masses is called a ______________________. 8. A cold air mass meets and pushes a warm air mass out of the way. What type of front am I? 9. A warm air mass is trapped between to cold air masses. 10. A warm air mass meets and pushes a cold air mass out of the way. 11. I am a front that brings drizzly rain and am followed by warm clear weather. Name me 12. A cold air mass meets a warm air but neither is very strong. They are separated and many days of wet , cloudy weather occur.

Pressure Systems What is air pressure? The force that a column of air applies ON the air or a surface below it. Air flows from areas of: HIGH pressure to areas of low pressure. Air pressure is the same thing as saying Barometric Pressure.

What is a HIGH pressure system? Circulating air with HIGH pressure at it’s center and lower Pressure outside of the system. In the center of a HIGH pressure system, what happens to the density of the air? It increases & thickens. The density of the air sinks and move to areas of low pressure. What does the level of density cause the air to do? Move away from the center What kind of weather does a high-pressure system bring? Clear skies and fair weather. High pressure = Happy weather.

What kind of air mass has a HIGH pressure? Cool Air Masses How do the air molecules circulate in a high-pressure system? CLOCKWISE. AND what does it cause the air to do in terms of the center of the system? Move DOWN & AWAY from the center of the system. What is the weather map symbol for a high-pressure system? (USE YOUR colors)

What is a LOW pressure system? Circulating air with LOW pressure at it’s center and higher Pressure outside of the system. In the center of a LOW pressure system, what happens to the density of the air? It decreases & gets lighter; Rises and moves to areas of high pressure. What does the level of density cause the air to do? Move toward the center What kind of weather does a low-pressure system bring? Clouds, rain or snow. Low pressure = Lousy weather.

What kind of air mass has a LOW pressure? Warm Air Masses How do the air molecules circulate in a LOW-pressure system? COUNTER CLOCK-WISE AND what does it cause the air to do in terms of the center of the system? Move UP & TOWARD the center of the system. What is the weather map symbol for a low-pressure system? (USE YOUR COLORS)

What weather instrument is used to measure air pressure in the atmosphere? Barometer, Air pressure is the SAME thing as saying Barometric pressure. What unit of measure is used when measuring air pressure? MILLIBARS (mb) or INCHES OF MERCURY (in.HG)

Compare/Contrast Chart High and Low Pressure High Pressure Low Pressure Moving inward on isobars… Pressure Increases Pressure Decreases Density of air Higher Lower Representation on a map H (typically blue) L (typically red) Motion of air Clockwise, air sinks Counterclockwise, air rises Also known as… Anticyclone Cyclone Motion of air causes a zone of… Divergence Convergence Stability of atmosphere Stable Unstable

High Pressure

LOW PRESSURE