Earth Science Chapter 7 Study of the Atmosphere. Introduction The atmosphere was most likely created...

Earth ScienceEarth Science

Chapter 7

Study of the Atmosphere

IntroductionIntroduction

• The atmosphere was most likely created by the process of volcanic outgassing.

• Weather is the state or condition of the atmosphere at a particular location for a short period of time.

• The study of weather is called meteorology.

Electromagnetic EnergyElectromagnetic Energy

• Electromagnetic energy is energy that has the properties of transverse waves.


• All stars, including the sun constantly produce and emit electromagnetic energy.

• Solar energy is the major source of energy for Earth.– Most of the energy from the Sun is in the form of

invisible waves (ultraviolet and infrared). – The sun also gives off visible light that can be

separated into different wavelengths.

• The entire range of wavelengths is known as the electromagnetic spectrum.


– When electromagnetic energy comes in contact with a material, it can be: • refracted, or bent• reflected to a new direction• scattered (refracted and reflected) into

several directions• absorbed by the material


– Half of the energy absorbed by Earth is long-wave (infrared) and half is short-wave (visible and ultraviolet).

– Almost all of the energy released by Earth or re-radiated is long-wave radiation.

Energy Transfer in the AtmosphereEnergy Transfer in the Atmosphere

• There are 3 methods of energy transfer: convection, conduction, and radiation.

– Convection is the transfer of heat energy by movements of fluids (liquids and gasses).

– Conduction is the transfer of heat energy by the collision of atoms with adjoining atoms.

– Radiation is the transfer of electromagnetic energy through space in the form of waves.

Heat Energy and Phase ChangesHeat Energy and Phase Changes

• Normally when heat is added to a substance the temperature will rise.

• The exception is during a change in phase.

• Latent heat is energy taken in or given off by a substance during a change in phase.– These transfers of energy DO NOT result in a

change in temperature.

Atmospheric RelationshipsAtmospheric Relationships

• Temperature– Temperature is greatly affected by intensity

and duration of insolation • INcoming SOLar radiATION.

– The atmosphere receives most of its heat energy by conduction through direct contact with Earth’s surface.

– The amount of reradiated energy absorbed is directly related to the amount of water vapor, carbon dioxide and various other pollutants.


– Factors affecting local temperature• Latitude

–Higher latitude = lower intensity of insolation = lower temperatures

• Altitude–Higher altitude = lower temperatures

• Closeness to large bodies of water–Water heats and cools slower than land,

so large bodies of water regulate temp.


• Moisture– The warmer the air the more moisture it can hold– When the air contains all the moisture it can hold

at a particular temperature it is saturated.• The air is not usually saturated.• To become saturated more water vapor must

be added or the air must be cooled.• The temperature at which condensation

occurs is called the dewpoint temperature.


– Absolute humidity is the actual amount of water vapor in the air.

– Relative humidity is a comparison between the amount of water in the air and the amount the air can actually hold at that temperature.• Example: If the air is holding half as much

water as it could, the relative humidity is 50%.– An instrument called a psychrometer is used to

find dewpoint and relative humidity.


• Air pressure (atmospheric pressure)– The force, or weight, of the air pushing down

on a unit area of a surface.– Air pressure is inversely proportional to

temperature changes.– Air pressure is directly proportional to density

changes.– The instrument used to measure air pressure

is called a barometer.


– Air pressure is inversely proportional to the amount of moisture in the air.• When moist air moves into a region, air

pressure decreases and the barometer “falls”.• A “falling” barometer is an indication that rainy

weather is on the way.– As altitude increases, the number of air

molecules decreases and, thus, pressure decreases.


• Factors affecting rate of evaporation:– Amount of energy available

• More heat energy = more evaporation– Surface area

• More surface area = more evaporation– Amount of moisture in the air

• More moisture = less evaporation


• Large horizontal movements of air near Earth’s surface are called winds.

• Smaller, local horizontal movements are called breezes.

• Winds are named from the direction they come from.


• The primary causes of winds are differences in air temperature, which causes differences in air pressure.

• Air always moves from areas of high pressure to areas of low pressure.

• The rate of change in pressure between two locations is called the pressure gradient. – Close isobars = steep gradient


Local Breezes

Sea Breeze Land Breeze


Planetary Winds


• Jet streams are winds at high altitudes that exert a controlling influence over the direction traveled by air-masses at Earth’s surface.– 7 to 8 miles above Earth’s surface– Avg. speed in summer 35 mph; in winter 75 mph

• Atmospheric transparency is how much or little the Sun’s radiation is scattered or reflected. – Varies inversely with the amount of aerosols

(dust and vapor) in the air.

Clouds and PrecipitationClouds and Precipitation

• Clouds - collections of tiny water droplets or ice crystals suspended in the atmosphere.– Form when moist air expands and cools as it

rises vertically in the atmosphere.– When air cools to the dewpoint temperature, it

becomes saturated & condensation occurs.– When the water droplets or ice crystals in a

cloud grow large enough to fall, precipitation results.

Moisture and Energy TransferMoisture and Energy Transfer

• Adiabatic temperature change – any change in temperature of a system without heat being added or removed from that system. – In the atmosphere, when air descends, it is

compressed by the air around and its temperature increases.

– When air rises, it expands and its temperature decreases.

Moisture and Energy TransferMoisture and Energy Transfer

Forecasting the WeatherForecasting the Weather

• Measurements of atmospheric variables, when combined with similar measurements taken earlier, can provide the information needed to predict the weather.– Since relationships between variables are often

complex, predictions are not always accurate.– These relationships are expressed as the

probability of occurrence.• Example: 40% chance of snow

Weather Maps and ForecastingWeather Maps and Forecasting

• A station model is a recording of weather observations for a particular location


• An air-mass is a huge body of air in the troposphere (diameter up to 2000 km) having similar pressure, moisture, wind, and temperature characteristics throughout.

• Air-masses have definite characteristics that depend on their source region.

• On a weather map air-masses are usually labeled with two letters indicating the moisture and temperature characteristics


– Maritime air-masses (m)• Develop over water and are moist

– Continental air-masses (c)• Develop over land and are dry

– Polar air-masses (P)• Develop in high latitudes and are cool

– Tropical air-masses (T) • Develop in lower latitudes and are warm

– Arctic air-masses (A)• Develop in very high latitudes & are very cold and dry


• Cyclone - low-pressure air mass with winds moving counterclockwise toward its center.– When the moving air converges at the center

of a low, it rises vertically, often producing rain.

• Anticyclone - high-pressure air mass with winds moving clockwise away from its center.– The air descending in their center is often dry

and they usually bring cool, clear weather.


• The boundary between two air-masses is called a front.– Atmospheric conditions at fronts:

• Unstable air• Clouds • Strong winds• Precipitation• Other weather changes


• Warm fronts– Occur when warm air meets and rises over cold

air on the ground.– Have long gentle slopes.

• can be over 1000 km– Bring predictable sequence weather and clouds.– Precipitation may occur ahead of the front


• Cold Fronts– Occur when cold air meets and pushes out

warmer air.– Have short, steep slopes.– Move faster than warm fronts.– No sequence of clouds warning approach.– Precipitation occurs all around the front


• Occluded front– When a faster moving cold front overtakes a

slower moving warm front and lifts the warmer air between the two fronts above the ground.

– Weather is characteristic of both fronts without any gap in the sequence.

• Stationary front– When a warm air-mass and a cold air-mass are

side-by-side, with neither one moving.– Weather is similar to a warm front.


• Mid-latitude cyclones– Mix polar and tropical air-masses.– First develop in areas of low pressure.– The greater the pressure gradient, the faster

the winds move into the low, and the greater the impact of the Coriolis Effect.

– The counterclockwise flow circulates the warm air northward and the cold air southward.

– Fronts occur at the interfaces of air-masses.


• Making predictions– Decreasing air pressure often brings warm

unsettled air and rainy weather– Increasing air pressure brings cool, clear

weather.– Weather systems in the United States

generally move from west to east.– Look at pressure and rate of movement of air-

masses to the west to predict local weather.

Hurricanes and TornadoesHurricanes and Tornadoes

• A hurricane is a doughnut shaped ring of counterclockwise winds exceeding 75 mph around an area of extremely low pressure.– As the air moves closer to the center of the

storm, its velocity increases.– The eye of the hurricane is a relatively calm

area of clear skies in the middle of the hurricane.


• A hurricane is fueled by heat stored in water vapor. – The released heat warms the air and provides

lift for its upward flight.– This reduces the pressure near the surface

and encourages a more rapid inflow of air.– Hurricanes develop in late summer when high

temperatures provide the heat and moisture.– Energy produced in 1 day is equal to US

electrical energy production for 1 year.


• Tornadoes are local storms of short duration that are among nature’s most destructive forces. – Violent windstorms that take the form of a

rotating funnel of air that extends downward from a cumulonimbus cloud.

– Winds can exceed 300 mph.– Pressure drop is usually around 25 mb, but

drops of up to 200 mb have been observed.


• Tornadoes are extremely variable with a small diameter and a short lifetime that are impossible to forecast precisely. – They generally form in the vicinity of intense

cold fronts and squall lines associated with mid-latitude cyclones.

– Throughout spring, cold and dry cP air from the north mix with warm humid and unstable mT air from the Gulf spawning tornadoes.

Earth Science Chapter 7 Study of the Atmosphere. Introduction The atmosphere was most likely created...

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