What is meteorology? Meteorology: the study of atmospheric processes and events….”meteor” means high in the air.

What is meteorology?What is meteorology?

• Meteorology: the study of atmospheric processes and events….”meteor” means high in the air

What is the difference between weather and climate?What is the difference between weather and climate?

• Weather: current state of the atmosphere….it changes daily!!!

• Climate: long-term variations in weather over a geographic area– The angle (and intensity) of sunlight is the major factor

that determines climate• More direct at Equator = tropics

• More indirect at Poles = arctic region

What is an air mass?What is an air mass?

• Air mass: large body of air that is influenced by the area over which it forms– Continental tropical (cT): warm and dry– Maritime tropical (mT): warm and humid– Continental polar (cP): cold and dry– Maritime polar (mP): cold and humid– Arctic (A): same as cP, but MUCH colder!!

What is an air mass?What is an air mass?

• All of these air masses MOVE and INTERACT, which causes WIND, STORMS, and all other WEATHER!!!

What are weather systems?What are weather systems?

• There are many types of weather systems….

• 1) Permanent wind systems– Trade winds– Prevailing winds– Polar easterlies

What are weather systems?What are weather systems?

• 2) Jet streams: narrow bands of high-altitude, fast-moving winds

• 3) Fronts: narrow region separating two DIFFERENT air masses– Cold fronts: causes clouds, rain– Warm fronts: causes clouds, rain– Stationary fronts: two fronts collide and “stall”– Occluded fronts: warm air mass trapped between two

cold air masses.

What are weather systems?What are weather systems?

• 4) Pressure systems: cause pressure changes that allow air to move in a rotating motion

– High pressure system: usually good weather– Low pressure system: usually stormy weather

WeatherWeatherWeather: A Brief Introduction:

WeatherWeather is short-term atmospheric conditions in an area. It is typically is short-term atmospheric conditions in an area. It is typically considered in hours or days.considered in hours or days.

Much weather activity is due to interactions between leading edges Much weather activity is due to interactions between leading edges or or frontsfronts of moving masses of of moving masses of warmwarm or or cold aircold air..

Jet streamsJet streams are near the top of the troposphere and circle the are near the top of the troposphere and circle the Earth. They have a strong influence on weather patterns.Earth. They have a strong influence on weather patterns.

WeatherWeatherA A cold frontcold front is an advancing is an advancing

mass of cold air that mass of cold air that stays close to the stays close to the ground. It is often ground. It is often associated with associated with thunderstorms and high thunderstorms and high winds. Cooler, clear winds. Cooler, clear weather is the result.weather is the result.

A warm front is the boundary between a warm mass of air and the cooler air it replaces. It often results in cloudy, rainy days.

WeatherWeather

What causes precipitation?What causes precipitation?

• Coalescence: small water droplets combining to form larger droplets that then FALL out of the cloud by the act of gravity

WeatherWeatherWeatherWeatherChanges in atmospheric Changes in atmospheric

pressure also affect pressure also affect weather.weather.

Atmospheric pressure is Atmospheric pressure is greater near the earth's greater near the earth's surface. A surface. A high-pressurehigh-pressure air mass (a high “air mass (a high “HH”) ”) contains cool, dense air contains cool, dense air that warms as it descends. that warms as it descends. Fair weather is the result.Fair weather is the result.

A A low-pressurelow-pressure air mass (a air mass (a low “low “LL”) produces cloudy, ”) produces cloudy, stormy weather. The stormy weather. The center of the low rises due center of the low rises due to the low density of air. If to the low density of air. If condensation nuclei are condensation nuclei are present with cooler present with cooler conditions, there will be conditions, there will be rain.rain.

What are thunderstorms?What are thunderstorms?

• At any point in time, about 2,000 thunderstorms are occurring on Earth!!!

• 3 conditions are needed for formation…– 1) Lots of moisture in lower atmosphere

– 2) Air must be lifted/cooled so moisture can condense into liquid water

– 3) The moist air mass must be unstable so it can continue to rise (so that the cloud gets big!)

What are thunderstorms?What are thunderstorms?

• 3 stages of a thunderstorm…

– 1) Cumulus stage: air rises and cools so that moisture condenses into liquid drops

– 2) Mature stage: precipitation forms and downdrafts/updrafts (winds) form

– 3) Dissipation stage: winds/energy/ precipitation “run out” and the thunderstorm ends

What are thunderstorms?What are thunderstorms?

• Air-mass thunderstorms (temperature differences between 2 air masses)– Mountain thunderstorms– Sea-breeze thunderstorms

• Frontal thunderstorms (produced by advancing cold fronts)

What other weather occurs along with thunderstorms?What other weather occurs along with thunderstorms?

• Supercells: the most SEVERE thunderstorms with high winds

• Lightning: electricity caused by rapid air movement within cumulonimbus clouds– 5 times hotter than the sun!!!

Supercell ThunderstormSupercell Thunderstorm

What other weather occurs along with thunderstorms?What other weather occurs along with thunderstorms?

• Hail: frozen water droplets that form within clouds

• Floods: occur when storm systems move SLOWLY

• Tornadoes: occur when wind speed and direction change suddenly– Fujita scale: F1 (least) to F5 (most severe)

Extreme WeatherExtreme WeatherTornadoes and tropical Tornadoes and tropical

cyclonescyclones are extremes are extremes of weather that cause of weather that cause much damage. much damage. Tornadoes form over Tornadoes form over land, and tropical land, and tropical cyclones form over cyclones form over warm ocean waters.warm ocean waters.

TornadoesTornadoes are most prevalent are most prevalent in the United States and in the United States and Australia. They are Australia. They are funnel-shaped clouds funnel-shaped clouds that form when dry, cold that form when dry, cold air from Canada meets air from Canada meets humid air from the Gulf humid air from the Gulf of Mexico, (tornado of Mexico, (tornado alley) alley) Oklahoma CityOklahoma City experienced 58 experienced 58 tornados in one day . tornados in one day . Most tornadoes occur in Most tornadoes occur in the spring.the spring.

Tropical StormsTropical Storms

• Tropical cyclones: large, rotating, low-pressure storms

Tropical StormsTropical Storms

• Steps in tropical storm formation…

– 1) Warm ocean water evaporates, then condenses to form clouds

– 2) Low pressure area develops in the middle of clouds

– 3) Pressure differences cause rotating winds to form

Tropical StormsTropical Storms

Tropical StormsTropical Storms

• Saffir-Simpson scale: categorizes hurricanes– Category 1 (weak) Category 5 (strong)

– Storm Surge: winds drive a mound of ocean water over land

Tropical cyclonesTropical cyclones are formed by low-are formed by low-pressure cells of air pressure cells of air moving over warm moving over warm tropical seas. tropical seas. Cyclones forming Cyclones forming over the over the Atlantic Atlantic Ocean are called Ocean are called hurricanes; those ; those forming over the forming over the Pacific Ocean are Pacific Ocean are called called typhoonstyphoons..

Forces of Forces of hurricanes and hurricanes and typhoons can kill typhoons can kill and injure people and injure people and damage and damage property.property.

Hurricanes also flush out excess nutrients from land runoff, dead Hurricanes also flush out excess nutrients from land runoff, dead seagrasses, and rotting vegetation from coastal bays and marshes. This seagrasses, and rotting vegetation from coastal bays and marshes. This results in increased productivity of commercially important species of results in increased productivity of commercially important species of shellfish and fish as well as reduced explosive growth of algae.shellfish and fish as well as reduced explosive growth of algae.

Extreme WeatherExtreme Weather

Other Weather EventsOther Weather Events

• Droughts: extended periods of well-below-normal rainfall

• Heat waves: extended periods of hot weather• Cold waves: extended periods of cold weather

– Wind-chill factor: takes into account the effect of winds on temperature

How is weather analyzed?How is weather analyzed?

• Isobar maps: “topographic maps” for pressure differences– The closer together the ‘isobar lines’, the faster

the wind speed!!!

– How accurate are weather forecasts? • ACCURATE from 1-3 days• INACCURATE from 4-7 days (or more)

Weather DataWeather Data

• Thermometer: measures temperature (a liquid expands when heated and fills up a tube)

• Barometer: measures air pressure– Pressure drop = future storm!

Weather DataWeather Data

• Anenometer: measures wind speed

• Hygrometer: measures humidity

• Ceilometer: measures height of cloud layers

Weather DataWeather Data

• Radar: radar waves bounce off of large raindrops (but not small droplets within clouds)

• Satellite: tracks clouds (but not necessarily rain)

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