Post on 05-Jun-2018
8-3: Air Masses and Fronts
• An air mass is a huge body of air that has similar temperature, humidity, and air pressure, up to 10 km deep.
Air Mass
8-3: Air Masses and Fronts
• There are four major types of air masses that influence the USA.
1. Tropical
2. Polar
3. Maritime
4. Continental
Types of Air Masses
8-3: Air Masses and Fronts
• Tropical air masses form in the tropics and have low pressure.
Tropical Air Masses
8-3: Air Masses and Fronts
• Polar air masses form above 50 degrees latitude (north or south).
• They are cold and have high pressure.
Polar Air Masses
8-3: Air Masses and Fronts
• If the air mass formed over water, it is called maritime – and it is humid (no surprise right?)
• If it formed over land it is called continental – and it is dry – makes sense.
Moist or Dry?
8-3: Air Masses and Fronts
• Maritime tropical air is warm and moist.
• They move north into the southern USA and the west coast.
Maritime Tropical
8-3: Air Masses and Fronts
• Maritime polar air is cold and humid.
• Brings fog and cool temperatures to the west coast of the USA.
Maritime Polar
8-3: Air Masses and Fronts
• Continental Tropical air is hot and dry!!
• They move northeast from Mexico bringing hot, dry weather to the Great Plains.
Continental Tropical
8-3: Air Masses and Fronts
• Continental polar air is cold and dry.
• They move south from Canada into the USA and collide with maritime tropical air, producing storms.
Continental Polar
8-3: Air Masses and Fronts
• Air masses move as they are pushed around by prevailing westerlies and the jet stream, from west to east.
How Air Masses Move
8-3: Air Masses and Fronts
• Where two different air masses collide, a front forms, where weather is changing.
• For kinds exist:
1. cold fronts
2. warm fronts
3. stationary fronts
4. occluded fronts.
Fronts
8-3: Air Masses and Fronts
• When a cold air mass is moving into a warm air mass, a cold front forms.
• Cold air pushes warm air up, causing clouds and heavy rain.
Cold Fronts
8-3: Air Masses and Fronts
• When a warm air mass is moving into a cold air mass, a warm front forms.
• Warm air rises up over the cold air, causing cirrus and stratus which can produce a gentle rain.
Warm Fronts
8-3: Air Masses and Fronts
• When a warm and cold air mass are next to each other, but not moving, it is called a stationary front.
• If the warm air is humid, condensation can form and a gentle rain may fall.
Stationary Front
8-3: Air Masses and Fronts
• When a cold air mass catches up to another cold air mass, the warm air gets trapped and pushed up, creating an occluded front.
• This sometimes creates some of the most violent thunderstorms.
Occluded Front
8-3: Air Masses and Fronts
Cyclones / Anticyclones
• When a front starts to bend, the air can start to rotate counter clockwise around a developing low pressure – called a cyclone.
• Air rises and cools and rain can develop.
8-3: Air Masses and Fronts
• Anticyclones are the opposite of a cyclone, high pressure causes air to spiral outward clockwise.
• Air is sinking, warming, and drying. So high pressures are associated with fair weather.
8-3: Air Masses and Fronts
• In the southern hemisphere, lows and highs rotate opposite of what they do in the northern hemisphere.
• Global Video Link
• Cyclone in northern hemisphere.