What is meteorology?• Meteorology: the study of atmosphericprocesses and events….”meteor” meanshigh in the air
What is the difference betweenweather and climate?• Weather: current state of the atmosphere….itchanges daily!!!• Climate: long-term variations in weather over ageographic area– The angle (and intensity) of sunlight is the major factorthat determines climate• More direct at Equator = tropics• More indirect at Poles = arctic region
What is an air mass?• Air mass: large body of air that isinfluenced 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?• All of these air masses MOVE andINTERACT, which causes WIND,STORMS, and all other WEATHER!!!
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?• 2) Jet streams: narrow bands of high-altitude,fast-moving winds• 3) Fronts: narrow region separating twoDIFFERENT 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 twocold air masses.
What are weather systems?• 4) Pressure systems: cause pressurechanges that allow air to move in a rotatingmotion– High pressure system: usually good weather– Low pressure system: usually stormy weather
WeatherWeather: A Brief Introduction:Weather is short-term atmospheric conditions in an area. It is typicallyconsidered in hours or days.Much weather activity is due to interactions between leading edgesor fronts of moving masses of warm or cold air.Jet streams are near the top of the troposphere and circle theEarth. They have a strong influence on weather patterns.
WeatherA cold front is an advancingmass of cold air thatstays close to theground. It is oftenassociated withthunderstorms and highwinds. Cooler, clearweather is the result.
A warm front is theboundary between a warmmass of air and the coolerair it replaces. It oftenresults in cloudy, rainy days.Weather
What causes precipitation?• Coalescence: small water dropletscombining to form larger droplets that thenFALL out of the cloud by the act of gravity
WeatherChanges in atmosphericpressure also affectweather.Atmospheric pressure isgreater near the earthssurface. A high-pressureair mass (a high “H”)contains cool, dense airthat warms as it descends.Fair weather is the result.A low-pressure air mass (alow “L”) produces cloudy,stormy weather. Thecenter of the low rises dueto the low density of air. Ifcondensation nuclei arepresent with coolerconditions, there will berain.
What are thunderstorms?• At any point in time, about 2,000 thunderstormsare 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 condenseinto liquid water– 3) The moist air mass must be unstable so it cancontinue to rise (so that the cloud gets big!)
What are thunderstorms?• 3 stages of a thunderstorm…– 1) Cumulus stage: air rises and cools so thatmoisture condenses into liquid drops– 2) Mature stage: precipitation forms anddowndrafts/updrafts (winds) form– 3) Dissipation stage: winds/energy/precipitation “run out” and the thunderstormends
What are thunderstorms?• Air-mass thunderstorms (temperaturedifferences between 2 air masses)– Mountain thunderstorms– Sea-breeze thunderstorms• Frontal thunderstorms (produced byadvancing cold fronts)
What other weather occurs alongwith thunderstorms?• Supercells: the most SEVEREthunderstorms with high winds• Lightning: electricity caused by rapid airmovement within cumulonimbus clouds– 5 times hotter than the sun!!!
What other weather occursalong with thunderstorms?• Hail: frozen water droplets that form withinclouds• Floods: occur when storm systems moveSLOWLY• Tornadoes: occur when wind speed and directionchange suddenly– Fujita scale: F1 (least) to F5 (most severe)
Extreme WeatherTornadoes and tropicalcyclones are extremesof weather that causemuch damage.Tornadoes form overland, and tropicalcyclones form overwarm ocean waters.Tornadoes are most prevalentin the United States andAustralia. They arefunnel-shaped cloudsthat form when dry, coldair from Canada meetshumid air from the Gulfof Mexico, (tornadoalley) Oklahoma Cityexperienced 58tornados in one day .Most tornadoes occur inthe spring.
Tropical Storms• Steps in tropical storm formation…– 1) Warm ocean water evaporates, thencondenses to form clouds– 2) Low pressure area develops in the middle ofclouds– 3) Pressure differences cause rotating winds toform
Tropical Storms• Saffir-Simpson scale: categorizeshurricanes– Category 1 (weak) Category 5 (strong)– Storm Surge: winds drive a mound of oceanwater over land
Tropical cyclonesare formed by low-pressure cells of airmoving over warmtropical seas.Cyclones formingover the AtlanticOcean are calledhurricanes; thoseforming over thePacific Ocean arecalled typhoons.Forces ofhurricanes andtyphoons can killand injure peopleand damageproperty.Hurricanes also flush out excess nutrients from land runoff, deadseagrasses, and rotting vegetation from coastal bays and marshes. Thisresults in increased productivity of commercially important species ofshellfish and fish as well as reduced explosive growth of algae.Extreme Weather
Other Weather Events• Droughts: extended periods of well-below-normalrainfall• Heat waves: extended periods of hot weather• Cold waves: extended periods of cold weather– Wind-chill factor: takes into account the effect ofwinds on temperature
How is weather analyzed?• Isobar maps: “topographic maps” forpressure differences– The closer together the „isobar lines‟, the fasterthe wind speed!!!– How accurate are weather forecasts?• ACCURATE from 1-3 days• INACCURATE from 4-7 days (or more)
Weather Data• Thermometer: measures temperature (aliquid expands when heated and fills up atube)• Barometer: measures air pressure– Pressure drop = future storm!