WINDS & FRONTS1/30 – 2/3

2012

Prevailing WindsLarger-scale winds that blow in the same direction

60o Warmer, moist air rises and condenses as it cools. The air could travel back to 30o or up to 90o

0o Warm, moist air rises and heads to the cooler upper latitudes. This air cools and water vapor condenses as it rises. This process leads to much rain at this latitude and humid conditions (equator)

30o Air from equator, now cooler and dryer, sinks to the surface. This dry air leads to arid conditions at this latitude. Air travels across the surface, picking up moisture, up to 60o

90o Cooler, dryer air falls at the poles and travels across the surface to 60o (poles)

All these winds DON’T traveldirectly north or south due to the

CORIOLIS EFFECT

smaller-scale, unlike prevailing winds

Sea Breeze – occurs during the DAY along a shore. Land is heated quicker than water so warm air rises over the land. It sinks over the water and blows back into shore

Land Breeze – occurs at NIGHT when the water is warmer than the land. Warm air rises over the water and sinks over the land

Local Winds

Air MassesA large body of air

with similar temperature and humidity throughoutapproximately the size of an ocean or continent

determined by where they are formed

Continental (c) – formed over land, dry airMaritime (m) – formed over water, humid air

Arctic (A) – formed at a very high latitude, very cold airPolar (P) formed at a high latitude, cold airTropical (T) – formed at a low latitude, warm air

m T m Tc T

m Pc Pm P

The point where two air masses meet

Precipitation happens at the front

KEY QUESTION:What are conditions ahead of & behind the FRONT?

F R O N T S

Cold front shoots air up over short area

Occurs when a colder air mass displaces a warmer air mass. Colder air masses move FAST and stay CLOSE TO the ground. Warmer air is forced to rise and condense, causing brief but hard rain, winds, and thunderstorms. After the front passes, winds change direction, pressure rises, and temperatures drop

Warm front spreads air over longer area

Occurs when warmer air displaces colder air. The warmer air is forced above the colder air. As a warm front passes, there is a gradual increase in the thickness of clouds, pressure decreases and a light but constant rain persists. Once the warm front passes the rain stops, wind direction changes, pressure stabilizes, and temperatures increase

Occluded front/midlatitude cyclone – lots of rain over long period

Occurs when a warm and a cold air mass are circling around a low pressure area. The cold air mass completely overtakes the warm air mass, thus forcing the entire warm air mass above the cold. There is usually heavy precipitation with this front.

http://www.youtube.com/watch?v=DkgPZMBKEIs&feature=related

specific animation found at [0:42 – 2:02]