Ch 18 The Atmosphere Vocab: 18.1 – troposphere, temperature inversion, stratosphere, ozone, mesosphere, thermosphere, greenhouse effect 18.2 – water cycle,

Ch 18 The AtmosphereVocab: 18.1 – troposphere, temperature inversion, stratosphere, ozone, mesosphere, thermosphere, greenhouse effect18.2 – water cycle, transpiration, precipitation, humidity, relative humidity, dew point, barometric pressure, Coriolis effect18.3 – air mass, front, isobar, climate, topography

18.1 Characteristics of the Atmosphere

Layers of the AtmosphereEarth’s atmosphere consists of a

variety of gases.• 78% nitrogen, 21% oxygen, trace

gases

Layers – differ in temperature, density, and amount of certain gases

• Troposphere: height 8 km - 18 km

– Closest layer to the crust– Almost all weather occurs in

troposphere– Densest layer because of the weight of

gases above– Temperature decreases (6°C/km) as

altitude increases

–Tropopause= top of troposphere where temperature stops decreasing

–Temperature inversion= sometimes cold air in troposphere gets trapped beneath warm air; this is one reason for smog pollution

• Stratosphere: height 8 km – 50 km

–Contains ozone layer – O3 – absorbs sun’s energy (UV)

–Temperature increases as altitude increases

–Very little water vapor – little weather, no storms

• Mesosphere: height 50 km – 80 km–Temperature decreases as altitude increases

• Thermosphere: height 80 km – 480 km–Very hot layer 980°C; gas molecules are far apart

• Ionosphere– In between thermosphere and mesosphere, where electrically charged ions are formed

–Electrons in ionosphere reflect radio waves, better at night

–Auroras, colorful light displays occur: aurora borealis

• Note: Temperature is the measurement of heat in the atmosphere

• Fahrenheit to Celsius: °C = (5/9)(°F – 32)

• Celsius to Fahrenheit: °F = ((9/5)(°C)) + 32

Changes in the Atmosphere

When Earth solidified – volcanic eruptions released gases and created the atmosphere. Oxygen was not in this early atmosphere. Bacteria and single-celled organisms lived in this early environment.

Photosynthesis: Plants use carbon dioxide to produce oxygen while making energy from sunlight.

Respiration: Animals use oxygen to produce carbon dioxide, making a cycle.

Man-made chemicals can deplete the ozone layer

• 1985 scientists reported a lower concentration of ozone

• Thought to be caused by increase of Chlorofluorocarbons (CFCs); gases used as refrigerants and propellants in spray cans which can break down ozone molecules.

Greenhouse effect= natural condition where atmospheric gases trap sun’s Energy

• If too much heat is trapped, the global temperature will rise. Some scientists say that this is happening and damaging the Earth.

18.2 Water and Wind

Water Cycle• Movement of water in troposphere:

transpiration, evaporation, precipitation, condensation, ground water

Humidity• the amount of water

vapor in the air–water molecules fit between the air molecules

• the amount of water in the air depends on the temperature

• at cooler temperatures air molecules move more slowly allowing the water molecules to condense and fall out of the air

• at warmer temperatures air molecules are moving too fast for the water molecules to join up and fall out of the air

Relative Humidity• measure of the amount of water

vapor that the air is holding compared to the amount that it can hold at a specific temperature

• saturated= when the air contains all the water it can possible hold

–saturated air = 100% relative humidity

• dew point–the temperature at which air is saturated and condensation takes place

–dew point changes with the amount of moisture in the air

Condensation• the change from vapor to liquid• for water vapor to condense, air

must be cooled below its dew point• cooling can happen by

–contacting a colder surface–radiating heat–mixing with colder air–expanding when it rises

• condensing water vapor needs something to hold onto to condense–condensation nuclei – the tiny particles on which water vapor condense•salt – ocean sea spray evaporates

•surfaces and nitrates – natural sources and burning fuel

• condensed liquid is a fine mist as fog when the warm ground meets the cold air

Cloud formation• clouds form when water vapor

begins to condense around small particles of dust, salt and smoke in the atmosphere

• Cloud classification: classified mainly by shape and altitude

3 main types of clouds• Stratus clouds

– appear when layers of air cool below their dew point temperatures

– form at low altitudes: up to 6 km

– smooth even sheets, layered appearance

–associated with both fair weather and precipitation

–drizzle comes when these clouds are low and gray

–fog= when the air is cooled to its dew point and condenses near the ground it forms a stratus cloud at ground level

• Cumulus Clouds– fluffy, white clouds

with flat bases– they form when air

currents rise, and water condenses

– various altitudes from 500 m to 12 km

– associated with fair weather and thunderstorms

• Cirrus Clouds–appear wispy, fibrous or curly

–high altitude: 6,000 – 11,000 km

–contain ice crystals–associated with fair weather and approaching storms

Other clouds are combinations of these 3 main types

• Nimbus Clouds–added to one of the 3 main clouds

–dark clouds associated with precipitation

–they are so full of water that no sunlight penetrates them

Rain capacity• when water droplets combine

and reach the size of 0.2 mm they become too heavy and fall out of suspension in the cloud

Air Pressure - (barometric pressure or atmospheric pressure)

• pressure from air in atmosphere above measuring instrument

• measured in inches mercury, millimeters mercury or hectapasals

• Barometers– Mercury barometer = more accurate– Aneroid barometer = more portable;

no liquid

• overall pressure depends on temperature, density, and amount of water vapor in air– temperature = pressure– temperature = pressure– density = pressure– density = pressure– water vapor = pressure– water vapor = pressure

• high pressure means descending air–when the air can’t rise, clouds can’t form = nice weather

• low pressure means clouds = bad weather

Winds• Pressure gradient: the differences

in pressure that create winds • Air is pushed from high-pressure to

low-pressure• So, winds result from the uneven

heating of the atmosphere• warm air rises faster creating a

pressure gradient force

Differences in pressure causes winds

• heated island surrounded by cooler water becomes a region of low pressure, causing winds to blow toward the land

Land breeze occurs at night

• Winds are named for the direction that they come from: North winds come from the north.

• The Coriolis Effect – change in movement due to rotation

• Winds normally blow from high-pressure areas to low-pressure areas. However, the Earth is rotating as well. Due to this effect, the path of the wind does not move in a straight line relative to land. Winds are turned to the right (counter clockwise) in the North Hemisphere and to the left (clockwise) in the Southern Hemisphere.

• Northern Hemisphere: winds flow clockwise around highs and counterclockwise around lows

Circulation Cells, Pressure Belts, and Wind• Due to Coriolis effect, the earth’s rotation

affects direction of wind• Earth’s rotation= wind starts= wind blows=

• The winds between the pressure zones are named from the directions that they flow from– North + coriolus effect= northeasterlies– South + coriolus effect=

southwesterlies

animation

• Both the Northern and Southern Hemisphere have three wind belts: Polar Easterlies, Westerlies, and tradewinds. The winds move in vertical loops called cells.– Equator has a low-pressure belt,

because hot air rises.– 30° N latitude has a high-pressure

belt– 60° N latitude has a low-pressure

belt

Trade winds: Found between the equator and 30° N and 30° S

• Warm and steady in both direction and speed

Prevailing winds: Winds that blow from the same direction on the average

18.3 Weather and Climate

Weather• present state of the atmosphere

and describes current conditions• caused by the interaction of air,

water, and sun• National Weather Service depends

upon meteorologists and satellites

Meteorologist• Study the weather; specifically

temperature, air pressure, winds, humidity, and precipitation using machines such as satellites, Doppler radar, computers, and instruments attached to weather balloons

• Information weather maps predictions

Air Masses• a large body of air with uniform

temperature and moisture content• has the same properties as the

surface over which it develops–cold usually forms in high altitude

–hot usually forms near tropics–wet usually forms over an ocean–dry usually forms over land

N. American air masses

Fronts• A front is the boundary between

air masses of different densities• Weather occurs at fronts due to

the interaction of the air masses• Air moves from high pressure

systems to low pressure systems

• As the cold air converges into the low pressure system, it pushes the warmer, less dense air upward

• As the warm air rises it cools and reaches its dew point and the water vapor condenses forming clouds

• When a cold front meets a warm front the air does not mix–High pressure - cold air moves under the warm air

–Warm air is pushed higher–Wind begins–Coriolis effect turns the wind and makes it a circle counter clockwise around the low pressure area

• Fronts usually bring a change in temperature and always bring a change in wind direction

• Most changes in weather occur at the 4 major front types

• Front symbols

Cold front• Cold air mass advances and forces

warmer air mass to rise• Rapid speed of advance causes

steeper slopes than warm fronts• Can causes a narrow area of high

winds, violent thunderstorms, and sometimes tornadoes

Cold Front

Warm front• Less dense, warm air mass slides

over a departing cold air mass• Gentle sloping front because of

slower movement• As warm mass rises, it cools and

precipitation can occur over a large area for one to two days

Warm Front

Stationary front• When neither air mass is being

displaced, the front does not move• Pressure differences cause a warm

front or cold front to stop moving for several days

• Light wind and precipitation across the front for one to two days

Occluded front: 3 air masses coming together: 2 types

• Occurs when cold, cool, and warm air come together

• Cold occlusion: a cold front pushes under a cool front and an overlying warm front

• Warm occlusion: a cool front slides in between a cold front and an overlying warm front

• Both cause warmer air to rise; strong winds and heavy precipitation

Occluded Front

Precipitation• Rain, sleet, snow, hail• When air rises high enough and

in large enough quantities, precipitation occurs

• Warmer air holds more precipitation

• Higher the air rises, the more moisture it can drop

• Rainy areas of the Earth (NW coast of USA) –windward side of mountain range

–storm areas•hurricanes, typhoons, low pressure zones, and fronts

•warm air rises, cools, and drops water

• areas favored by the global wind belts at the equator where air has no choice but to rise causing daily thunderstorms

Thunderstorms• Heavy rain, lighting flashes,

thunder and sometimes hail• Occur inside warm, moist air

masses and at fronts

• Warm, moist air moves upward rapidly, cools, condenses, and forms cumulonimbus clouds up to 10 km high–Water droplets fall, collecting other drops

–The falling rain causes downdrafts which form strong winds

• Lightning= a large spark caused by a rapid uplift of air resulting in a build up of electrical charges (+ & -); can travel easily through water

• Thunder–Results from the rapid heating of the air around the bolt of lightning then its cooling

–Moving molecules cause sound waves: 25° C to 30,000° C

Tornadoes• Violent whirling wind that moves

in a narrow path over land and through the clouds

• Most form along fronts in severe thunderstorms as warm air rises, and begins to rotate

• Wind shears: differences in wind direction and speed: causes funneling

• Most common in the United States during spring and early summer

• Begins as a funnel cloud of water droplets

Hurricanes• A large, swirling, low pressure

system that forms over tropical oceans; also called cyclones (Indian Ocean) and typhoons in (Pacific)

• Warm ocean water evaporates; warm water vapor rises causing tropical depressions (low-pressure area) that can gain strength

• As water vapor rises, it condenses into clouds… releases energy

Hurricane

• Occur when SE tradewinds meet up with NE tradewinds in North Atlantic

• Start in the north hemisphere between 5° and 20° latitude; move slowly and are powerful

Weather Maps• Map showing weather conditions

including precipitation, wind speed, and cloud coverage.

Isotherm• Line that indicate temperature• Connects points of the same

temperature–“iso” = same–“therm” = temperature

Isobar• Line drawn to connect points of

equal atmospheric pressure• You can tell how fast the wind is

blowing in an area by how close the isobars are; closer isobars = faster winds

• When isobars create a closed loop, this is the pressure center–Remember lows usually mean clouds and precipitation

–Highs mean fair weather

Climate = the average weather of a region measured over years

• The Sun • The sun is the driving force

behind weather… it supplies the energy for air and water to heat and move which causes winds

• Winds move in attempt to equalize pressure and temperature… but cause changing weather.

• Temperatures are closer to the equator because of the direction of sunlight

• Earth’s tilt and rotation cause the seasons–Northern hemisphere has summer when it is tilted towards the sun… Southern hemisphere is on opposite seasons

– June 21 summer solstice – longest day

–December 21 winter solstice – shortest day

–March 21 vernal (spring) equinox – day and night are equal

–September 22 autumnal (fall) equinox – day and night are equal

Topography affects climate• Hills, mountains, valleys etc affect

pressure systems and climate• Air masses must rise to pass over

mountains… it cools, precipitation falls on windward side.

• Deserts often form on the leeward side of a high mountain range

• Broad flat surfaces (Great Plains) have winds and air masses converge and create thunderstorms and tornadoes