Meteorology12.1 The Causes of Weather

WeatherMeteorology is the study of atmospheric phenomenaWeather is the current state of the atmosphere. This is usually measured in minutes, days and weeks

ClimateClimate is the weather for a long period of time for a given location.

Usually averaged over 30 or more years.

Ex. The climate is hot and humid in Miami, but it is snowing there today.

Air MassesAn air mass is a large body of air that takes on the characteristics of the area over which it forms.

Types of Air MassesMoistureMaritime vs. Continental:Maritime air masses form over water- have more moistureContinental air masses form over land- they are drier

Types of Air MassesTemperatureTropical vs. PolarTropical air masses form closer to the equator- warmPolar air masses form closer to the poles- coldArctic air masses are extremely cold

Source RegionsCombine Moisture and Temperature titles to name air masses. Name them after the regions where they form.Continental Tropical(cT) will form over land near the equator. Ex. Brazil, MexicoMaritime Tropical(cM) will form over water near the equator. Ex. Gulf of Mexico

Examples:Continental Polar(cP)Continental Tropical(cT)Maritime Polar(mP)Maritime Tropical(mT)Arctic(A)

Coriolis EffectThe Earth spins on its axis. This causes air particles to deflect to the left in the N. Hemisphere & to the right in the S. Hemisphere

RRLL

Wind SystemsThree wind zones in each HemisphereTrade WindsPrevailing WesterliesPolar Easterlies

Wind ZonesThe trade winds occur from the equator to 30N and 30S. The winds at the equator are called the doldrums and the ones at the 30 mark are called the horse latitudes. The prevailing westerlies are between 30N and S up to 60N and S in a pattern opposite of the trade winds. They are responsible for moving most weather across the US and Canada.

The polar easterlies are between 60N and S and the poles. (90N and S)

Jet StreamA stream of air that circulates the globe. Caused by differences in pressure between the wind systems. Trade and WesterliesWesterlies and Easterlies

FrontsA front is the narrow region separating two air masses of different densities. These differences are due to differences in temperature, humidity, and pressure. ColdWarmStationaryOccluded

Cold Front Cold dense air displaces warm air and forces the warm air up along a steep front-Thunderstorms often occur along the front

Page 308- 309 in RED BOOK!On a weather map: solid blue line with blue triangles that point in direction of the fronts motion

Cold FrontsCold Fronts occur when a cold air mass runs into a warm air mass, forcing the warm mass to rise.(notice cloud types!)

Warm Front Advancing warm air displaces cold air- Extensive cloudiness and precipitation

On a map: solid red line with regularly spaced, solid red semicircles pointing in the direction of the front's motion.

Warm FrontsWhen warm masses run into cold masses and slowly displaces it. (notice clouds!)

Stationary Front Two air masses meet and neither advances; air masses stall- Light wind and precipitationOn a map: combination of short segments of cold and warm front symbols

Stationary FrontsStationary Fronts occur when front run in parallel opposite directions

Occluded Front Cold air mass moves so rapidly that it overtakes a warm front- Strong winds, heavy precipitationOn a map: alternating purple triangles and semicircles that point toward the direction of motion.

OccludedOccluded Fronts occur when two cold fronts pinch a warm front up.

Front Video

High Pressure SystemsHigh Pressure Systems- Air sinks, then hits the Earths surface and spreads out. Wind blows away from high pressure.Clockwise in N. HemisphereAssociated with fair weather

Low Pressure SystemLow Pressure System- Air rises, must be replaced.Wind blows toward center of low pressureCounter-Clockwise in N. HemisphereAssociated with clouds and precipitation