Transcript Weather
Meteorology 12.1 The Causes of Weather Weather Meteorology is the study of atmospheric phenomena Weather is the current state of the atmosphere. This is usually measured in minutes, days and weeks Climate Climate 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 Masses An air mass is a large body of air that takes on the characteristics of the area over which it forms. Types of Air Masses Moisture Maritime vs. Continental: Maritime air masses form over waterhave more moisture Continental air masses form over land- they are drier Types of Air Masses Temperature Tropical vs. Polar Tropical air masses form closer to the equator- warm Polar air masses form closer to the poles- cold Arctic air masses are extremely cold Source Regions Combine 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, Mexico Maritime 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 Effect The 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 R Wind Systems Three wind zones in each Hemisphere Trade Winds Prevailing Westerlies Polar Easterlies Wind Zones •The trade winds occur from the equator to 30ºN and 30ºS. The winds at the equator are called the doldrums and the ones at the 30º mark are called the horse latitudes. •The prevailing westerlies are between 30ºN and S up to 60ºN 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 60ºN and S and the poles. (90ºN and S) Jet Stream A stream of air that circulates the globe. Caused by differences in pressure between the wind systems. Trade and Westerlies Westerlies and Easterlies Fronts A front is the narrow region separating two air masses of different densities. These differences are due to differences in temperature, humidity, and pressure. Cold Warm Stationary Occluded Page 308- 309 in RED BOOK! Cold Front – Cold dense air displaces warm air and forces the warm air up along a steep front -Thunderstorms often occur along the front On a weather map: solid blue line with blue triangles that point in direction of the front’s motion Cold Fronts Cold 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 Fronts When 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 precipitation On a map: combination of short segments of cold and warm front symbols Stationary Fronts Stationary 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 precipitation On a map: alternating purple triangles and semicircles that point toward the direction of motion. Occluded Occluded Fronts occur when two cold fronts “pinch” a warm front up. Front Video High Pressure Systems High Pressure SystemsAir sinks, then hits the Earth’s surface and spreads out. Wind blows away from high pressure. Clockwise in N. Hemisphere Associated with fair weather Low Pressure System Low Pressure System- Air rises, must be replaced. Wind blows toward center of low pressure Counter-Clockwise in N. Hemisphere Associated with clouds and precipitation