Meteorology

12.1 The Causes of Weather12.1 The Causes of Weather

Weather

MeteorologyMeteorology is the study of atmospheric is the study of atmospheric phenomenaphenomena

WeatherWeather is the current state of the is the current state of the atmosphere. atmosphere. This is usually measured in minutes, days This is usually measured in minutes, days

and weeksand weeks

Climate ClimateClimate is the weather is the weather

for a long period of time for a long period of time for a given location.for a given location.

Usually averaged over Usually averaged over 30 or more years. 30 or more years.

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

Air Masses

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

Types of Air Masses

MoistureMoisture Maritime vs. Maritime vs.

Continental:Continental: Maritime air masses Maritime air masses

form over water- form over water- have more moisturehave more moisture

Continental air Continental air masses form over masses form over land- they are drierland- they are drier

Types of Air Masses TemperatureTemperature Tropical vs. PolarTropical vs. Polar

Tropical air masses Tropical air masses form closer to the form closer to the equator- warmequator- warm

Polar air masses Polar air masses form closer to the form closer to the poles- coldpoles- cold

Arctic air masses are Arctic air masses are extremely coldextremely cold

Source Regions

Combine Moisture and Temperature titles Combine Moisture and Temperature titles to name air masses. to name air masses. Name them after the regions where they Name them after the regions where they

form.form. Continental Tropical(cT) will form over Continental Tropical(cT) will form over

land near the equator. Ex. Brazil, Mexicoland near the equator. Ex. Brazil, Mexico Maritime Tropical(cM) will form over Maritime Tropical(cM) will form over

water near the equator. Ex. Gulf of Mexicowater near the equator. Ex. Gulf of Mexico

Examples:

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

Coriolis Effect The Earth spins on its axis. This causes air The Earth spins on its axis. This causes air

particles to deflect to the left in the N. particles to deflect to the left in the N. Hemisphere & to the right in the S. Hemisphere & to the right in the S. HemisphereHemisphere

RR

L

L

Wind Systems Three wind Three wind

zones in each zones in each HemisphereHemisphere Trade Trade

WindsWinds Prevailing Prevailing

WesterliesWesterlies Polar Polar

EasterliesEasterlies

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 A stream of air

that circulates the that circulates the globe. Caused by globe. Caused by differences in differences in pressure between pressure between the wind systems. the wind systems. Trade and Trade and

WesterliesWesterlies Westerlies and Westerlies and

EasterliesEasterlies

Fronts A A frontfront is the narrow region is the narrow region

separating two air masses of separating two air masses of different densities. These different densities. These differences are due to differences are due to differences in temperature, differences in temperature, humidity, and pressure. humidity, and pressure. ColdCold WarmWarm StationaryStationary OccludedOccluded

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 front’s motion

Cold Fronts Cold Fronts occur when a cold air mass Cold Fronts occur when a cold air mass

runs into a warm air mass, forcing the warm runs into a warm air mass, forcing the warm mass to rise.(notice cloud types!)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 When warm masses run into cold masses

and slowly displaces it. (notice clouds!)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 Stationary Fronts occur when front run in

parallel opposite directionsparallel 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 Occluded Fronts occur when two cold

fronts “pinch” a warm front up. fronts “pinch” a warm front up.

Front Video

High Pressure Systems High Pressure Systems- High Pressure Systems-

Air sinks, then hits the Air sinks, then hits the Earth’s surface and Earth’s surface and spreads out. spreads out. Wind blows away from Wind blows away from

high pressure.high pressure. Clockwise in N. Clockwise in N.

HemisphereHemisphere Associated with fair Associated with fair

weatherweather

Low Pressure System

Low Pressure System- Air rises, must be Low Pressure System- Air rises, must be replaced.replaced. Wind blows toward center of low Wind blows toward center of low

pressurepressure Counter-Clockwise in N. HemisphereCounter-Clockwise in N. Hemisphere Associated with clouds and precipitationAssociated with clouds and precipitation