chapter 12 meteorology. section 12-1 the causes of weather objectives: compare and contrast weather...

Chapter 12Meteorology

Section 12-1The Causes of Weather

Objectives:• Compare and contrast weather and climate• Analyze how imbalances in the heating of the

Earth’s 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”.

The Causes of Weather

Three main categories of “meteors”• “Hydrometeors”- precipitation• “Lithometeors” – smoke, dust, and haze

(condensation nuclei)• “Electrometeors” – thunder and lightning

Weather and Climate

• Atmospheric phenomena interact to affect the environment and life on Earth

• Weather is defined as the current state of the atmosphere

• Climate is the average weather over the course of a 30 year period

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.

Why then doesn’t the heat continue to rise at the equator and make it

even warmer than it is?

A Question of Balance

The air/wind and ocean water redistribute the heat around the

globe, the equator is the main entry point.

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.

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)

Source Regions

• North America experiences all five types of air masses and the climate and weather varies greatly.

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. 304

Section 12-2Weather Systems

Objectives:• Describe how the rotation of Earth affects the

movement of air• Compare and contrast wind systems• Identify the various forms of fronts

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 systems

Coriolis Effect

Global Wind Systems

• There are three basic wind systems in each hemisphere–Trade Winds –Prevailing Westerlies–Polar Easterlies

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 complete

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 Canada

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 air

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/h

Jet Stream

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…

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 weather

Four Types of Fronts

• Cold Fronts• Warm Fronts• Stationary Fronts• Occluded Fronts

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 motion

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

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 semicircles

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 motion

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 systems

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 skies

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 rain

Section 12-3Gathering Weather Data and

Analysis

Objectives:• Describe the technology used to collect

weather data• Describe problems with long-term forecasts

Surface Weather Data

• Thermometers use mercury or alcohol that expand when heated are used to measure temperature

• Barometers use mercury to measure air pressure

Surface Weather Data

• Anemometer is used to measure wind speed• Hygrometer measures relative humidity

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 Satellites

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…

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.

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.

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