The Causes of Weather Objectives Compare and contrast weather and climate Analyze how imbalances in the heating of the Earths surface create weather Describe how and where air masses form Meteorology is the study of atmospheric phenomena from the ancient Greek meteor high in the air ID: 743495
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Slide1
Chapter 12
MeteorologySlide2
Section 12-1
The Causes of Weather
Objectives:Compare and contrast weather and climateAnalyze how imbalances in the heating of the Earth’s surface create weatherDescribe how and where air masses formSlide3
Meteorology is the study of atmospheric phenomena, from the ancient Greek meteor “high in the air”. Slide4
The Causes of Weather
Three main categories of “meteors”
“Hydrometeors”- precipitation“Lithometeors” – smoke, dust, and haze (condensation nuclei)“Electrometeors” – thunder and lightningSlide5Slide6Slide7Slide8Slide9
Weather and Climate
Atmospheric phenomena interact to affect the environment and life on Earth
Weather is defined as the current state of the atmosphereClimate is the average weather over the course of a 30 year periodSlide10
A Question of Balance
The Sun heats the surface of the Earth as its rays hit, some rays hit directly and some hit the Earth at a low angle. Slide11
Why then doesn’t the heat continue to rise at the equator and make it even warmer than it is?
A Question of BalanceSlide12
The air/wind and ocean water redistribute the heat around the globe, the equator is the main entry point. Slide13
Air Masses
An air mass is a large area of air that takes on the characteristics of the area over which it forms. The land or water area is called the source region.
The characteristics that the air mass can have are humidity, dryness, hot, or cold. Slide14
Classifying Air Masses
Warm and dry continental tropical (
cT)Warm and humid maritime tropical (mT)Cold and dry continental polar (cP)
Cold and humid maritime polar (
mP
)
Arctic (A)Slide15
Source Regions
North America experiences all five types of air masses and the climate and weather varies greatly.Slide16
Air Mass Modification
Air masses do not stay in one place for very long, as they move they transfer heat from one area to another and they begin to acquire the characteristics of the source region that they travel to.
Table 12-1 pg. 304Slide17
Section 12-2
Weather Systems
Objectives:Describe how the rotation of Earth affects the movement of airCompare and contrast wind systemsIdentify the various forms of frontsSlide18
The Coriolis Effect
The Earth rotates from East to West as it spins, this has an effect on the air, the air is deflected to the right in the northern hemisphere and to the left in the southern hemisphere.
This effect forms very specific and distinct global wind systemsSlide19
Coriolis EffectSlide20
Global Wind Systems
There are three basic wind systems in each hemisphere
Trade Winds Prevailing WesterliesPolar EasterliesSlide21Slide22
Trade Winds
Wind that occurs from equator to 30 N and 30 S
Air sinks, warms, and moves toward the equator in a westerly direction when it reaches the equator, it rises again and goes toward 30 N and 30 S again…cycle completeSlide23
Prevailing Westerlies
Winds between 30 and 60 north and south
The surface winds move toward the poles in a generally easterly direction (the blow from west to east, hence the name)This wind is responsible for the weather patterns that move across the United States and CanadaSlide24
Polar Easterlies
Winds that occur from 60 N and 60 S and the north and south poles
In both hemispheres the winds are characterized by cold airSlide25
Jet Streams
Wind, temperature, and pressure are all related and effect climate and weather
Differences in temperature and pressure create wind high up in the atmosphere that can reach 185 km/hSlide26
Jet StreamSlide27
Large Scale Weather Systems
Despite the jet streams high altitude, it has a dramatic effect on weather, it pushes air across the globe quickly if the air get caught up in the current. It is a hit and miss situation…Slide28Slide29
Fronts
A front is a narrow region separating two air masses of different densities. The density differences can be caused by differences in temperature, pressure, and humidity.
The interaction between colliding air masses can bring dramatic changes in weatherSlide30
Four Types of Fronts
Cold Fronts
Warm FrontsStationary FrontsOccluded FrontsSlide31
Cold Fronts
In a cold front, cold dense air pushes warm air up steeply. As the warm air rises, it begins to cool and thereby lose its moisture…clouds, showers, and thunderstorms are associated with cold fronts
Solid blue line with blue triangles pointing in the direction of the fronts motionSlide32
Warm Fronts
A warm front occurs when warm air displaces cold air near the surface, the air ahead of a warm front moves slowly and because of less land friction can gradually push up the cold air
Cloudiness and precipitation Solid red line with semicircles pointing in the direction of the front’s motion Slide33
Stationary Fronts
When two similar air masses collide sometimes neither can advance or overtake the other this results in a stationary front or a stall.
Solid blue line with alternating blue triangles and red semicirclesSlide34
Occluded Fronts
A warm front that gets wedged in between two cold fronts, the warm air gets pushed upward and rain is common on both sides of the cold air boarder
A purple line with alternating purple triangles and semicircles pointing in the direction of motionSlide35
Pressure Systems
Rising air is associated with low pressure and sinking air is associated with high pressure
Rising and sinking air combined with the Coriolis Effect result in rotating high and low pressure systemsSlide36
High-Pressure Systems
In a high pressure system, air is sinking…so when it finally hits the surface of the Earth it spreads out pushing everything away.
This clears the skiesSlide37
Low-Pressure Systems
As air rises, it creates space beneath it that is usually filled in by dense colder air. Low-pressure systems pull air in to the Earth’s surface as they rise.
This forms clouds and rainSlide38
Section 12-3
Gathering Weather Data and Analysis
Objectives:Describe the technology used to collect weather dataDescribe problems with long-term forecastsSlide39
Surface Weather Data
Thermometers use mercury or alcohol that expand when heated are used to measure temperature
Barometers use mercury to measure air pressureSlide40
Surface Weather Data
Anemometer is used to measure wind speed
Hygrometer measures relative humiditySlide41
Upper-Level Data
While surface data is important, the weather that we experience is caused by changes that take place in the upper atmosphere
Weather Radar including Doppler Radar and Vipir Radar along with Weather SatellitesSlide42
Short-Term Forecasts
In the early days of weather forecasting, meteorologists simply observed what was going on currently and compared it to the last couple of days and tried to predict the future based upon that…Slide43
Short-Term Forecasts
The key to unlocking the weather forecast puzzle is to understand that the atmosphere acts much like a fluid, so we can apply concepts like temperature, density and pressure to understand it.Slide44
Digital Forecast
High speed computers can analyze large amounts of data very quickly and enable meteorologists to make more dependable forecasts…the more available data, the better the forecast.Slide45
Long-Term Forecasts
The further into the future that you try and predict the weather, the less accurate the forecasts become.
Too many variables to predict accurately over a long period