Meteorology – the study of atmospheric phenomena (weather and climate).

•“Meteor” is derived from ancient Greek meaning “high in the air.”

•Clouds, raindrops, fog, and rainbows are atmospheric “meteors.”

Types: hydrometeors, lithometeors, electrometeors.

Weather – the current state of the atmosphere.

What is the weather in our area?

Climate – the long-term average state of atmosphere in a particular area.

What is the climate in Hawaii? Alaska?

What are the “reasons for the seasons?

Air Masses•A large body of air that takes on the characteristics of the area over which it forms. Air masses can cover hundreds of thousands of square miles.

1) (cP) continental polar - cold, dry, stable

2) (cT) continental tropical - hot, dry, stable air aloft--unstable surface air.

3) (mP) maritime polar - cool, moist, and unstable

4) (mT) maritime tropical - warm, moist, usually unstable

1. Polar latitudes P - typically located poleward of 60 degrees north and south Latitude. Cold.

2. Tropical latitudes T - typically located within about 25 degrees of the equator. Warm.

3. continental c - located over large land masses-dry. 4. marine m - located over the oceans----moist

1. Continental Polar (cP): cold temperatures and dry.

•Those who live in northern portions of the United States expect cold weather during the winter months. These conditions usually result from the invasion of cold arctic air masses that originate from the snow covered regions of northern Canada.

2. Maritime Polar (mP): Cool temperatures and rich in moisture.

3. Continental Tropical (cT) – hot and dry.

• The air usually only influences the US in summertime as warm, dry air is pumped up off of the Mexican Plateau.

• It is usually fairly stable and dry, and if it becomes stagnant over the midwest, results in a drought.

• Deaths associated with the 1995 heat wave in the midwest were the result of cT and mT air which stagnated over the central and eastern part of the US this last summer.

4. Maritime Tropical (mT): forms over the ocean near the equator. Warm, moist air. Brings hot & humid weather.

•Maritime tropical air masses originate over the warm waters of the tropics and Gulf of Mexico, where heat and moisture are transferred to the overlying air from the waters below. The northward movement of tropical air masses transports warm moist air into the United States, increasing the potential for precipitation.

Air Mass Characteristics•An air mass can acquire some the characteristics of the surface beneath it. This is known as air mass modification, where the exchange of heat or moisture with the surface occurs.

ObjectivesObjectives DescribeDescribe how the rotation of Earth how the rotation of Earth

affects the movement of air. affects the movement of air. CompareCompare and and contrastcontrast wind systems. wind systems. IdentifyIdentify the various types of fronts. the various types of fronts.

– Coriolis effectCoriolis effect– trade windstrade winds– prevailing prevailing

westerlieswesterlies

– polar polar easterlieseasterlies

– jet streamjet stream– frontfront

VocabularyVocabulary

Weather Systems

Weather SystemsWeather Systems The The Coriolis effectCoriolis effect, which is a result of Earth, which is a result of Earth’’s rotation, s rotation,

causes moving particles such as causes moving particles such as airair & & waterwater to be to be deflecteddeflected to the to the rightright in the in the northernnorthern hemisphere and to the hemisphere and to the leftleft in the in the southernsouthern hemisphere. hemisphere.

The Coriolis effect combines The Coriolis effect combines with the heat imbalance with the heat imbalance found on Earth to create found on Earth to create distinct global wind distinct global wind systems that transport systems that transport colder air to warmer colder air to warmer areas and warmer air areas and warmer air to colder areas. to colder areas.

Coriolis Effect and Weather Systems 2 min

Demo: Coriolis Effect

Global Wind SystemsGlobal Wind Systems

Subpolar low

(High Pressure)

(Low Pressure)

Global Wind SystemsGlobal Wind Systems There are There are threethree basic zones, or wind systems, in basic zones, or wind systems, in

each hemisphere.each hemisphere.

Weather Systems

1. The 1. The trade windstrade winds,, the first major wind the first major wind zone, flows at 30° north and south latitude, zone, flows at 30° north and south latitude, where air where air sinks, warms, and returnssinks, warms, and returns to the to the equator in a westerly direction.equator in a westerly direction.

Around 30° latitude, known as the horse Around 30° latitude, known as the horse latitudes, the sinking air associated with the latitudes, the sinking air associated with the trade winds creates a belt of high pressure trade winds creates a belt of high pressure that in turn causes generally weak surface that in turn causes generally weak surface winds. winds.

Global Wind SystemsGlobal Wind Systems When air converges it is forced upward and When air converges it is forced upward and

creates an area of low pressure in a process creates an area of low pressure in a process called convergence.called convergence.

Weather Systems

Near the equator, convergence occurs over Near the equator, convergence occurs over a large area called the a large area called the intertropical intertropical convergence zone (ITCZ),convergence zone (ITCZ), also called the also called the doldrums. doldrums.

The ITCZ migrates south and north of the The ITCZ migrates south and north of the equator as the seasons change. equator as the seasons change.

The ITCZ is characterized by a band of The ITCZ is characterized by a band of cloudiness and occasional showers. cloudiness and occasional showers.

Global Wind SystemsGlobal Wind SystemsWeather Systems

Other Wind ZonesOther Wind Zones

2. The 2. The prevailing westerliesprevailing westerlies, the second major , the second major wind zone, flows between wind zone, flows between 30°30° and and 60°60° north north and south latitude in a circulation pattern and south latitude in a circulation pattern opposite that of the trade winds. opposite that of the trade winds.

– The prevailing westerlies are responsible for The prevailing westerlies are responsible for much of the movement of weather across the much of the movement of weather across the United States United States and Canada.and Canada.

3. The 3. The polar easterliespolar easterlies, the third major wind , the third major wind zone, lies between 60° latitude and the poles. zone, lies between 60° latitude and the poles.

– In both hemispheres, the polar easterlies are In both hemispheres, the polar easterlies are characterized by characterized by coldcold air. air.

Jet StreamsJet Streams Jet streamsJet streams are narrow bands of high-altitude, are narrow bands of high-altitude,

westerly winds that flow at speeds up to 185 km/h westerly winds that flow at speeds up to 185 km/h at elevations of 10.7 km to 12.2 km. at elevations of 10.7 km to 12.2 km.

– The polar jet stream The polar jet stream separates the polar separates the polar easterlies from the easterlies from the prevailing westerlies.prevailing westerlies.

– The jet stream affects the The jet stream affects the intensity of weather intensity of weather systems by moving air of systems by moving air of different temperatures from different temperatures from one region to another. one region to another.

FrontsFronts In the middle latitudes, air masses with different In the middle latitudes, air masses with different

characteristics sometimes collide, forming a characteristics sometimes collide, forming a frontfront..

A A frontfront is the narrow region separating is the narrow region separating twotwo air masses of different air masses of different densitiesdensities that are that are caused by differences in caused by differences in temperature, pressure, temperature, pressure, and humidityand humidity..

The The interactioninteraction between the between the collidingcolliding airair masses masses can bring dramatic changes in weather. can bring dramatic changes in weather.

There are There are fourfour main types of fronts: main types of fronts: coldcold fronts, fronts, warmwarm fronts, fronts, stationarystationary fronts, and fronts, and occludedoccluded fronts. fronts.

FrontsFronts1. Cold Fronts1. Cold Fronts– In a cold front, In a cold front, coldcold, , densedense air displaces warm air and air displaces warm air and

forces the warm air up along a forces the warm air up along a steepsteep front. front.

– Clouds, showers, and Clouds, showers, and sometimes thunderstormssometimes thunderstorms are are associated with associated with cold fronts. cold fronts.

FrontsFronts

2. Warm Fronts2. Warm Fronts

– In a warm front, advancing In a warm front, advancing warm air displaces warm air displaces cold aircold air..

– The warm air develops a The warm air develops a gradualgradual frontal frontal slopeslope rather rather than a than a steepsteep boundary. boundary.

– A warm front is characterized by extensive A warm front is characterized by extensive cloudiness cloudiness and precipitationand precipitation. .

FrontsFronts3.3. Stationary Fronts Stationary Fronts– A stationary front is the result of two air masses A stationary front is the result of two air masses

meeting and meeting and neither advancingneither advancing into the other into the other’’s s territory, stalling the boundary between them.territory, stalling the boundary between them.

- May rain for days.- May rain for days.

FrontsFronts4. 4. Occluded FrontsOccluded Fronts– An occluded front is the result of a cold air mass An occluded front is the result of a cold air mass

overtakingovertaking a warm front, a warm front, wedgingwedging the warm air the warm air upwardupward..

– PrecipitationPrecipitation is common on both sides of an occluded is common on both sides of an occluded front.front.

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