Meteorology

U.E.Q.: How do atmospheric changes create different weather patterns and

how can they be predicted?

Air Composition

• Composition - the combining of distinct parts or elements to form a whole.

• 78% Nitrogen

• 21% Oxygen

• 1% Other

Air Composition

The atmosphere is important because it makes conditions suitable for living things.

Air Pressure

• Properties of Air– Density - the amount of

mass in a given volume– Pressure – force pushing

on an area or surface– Observe: Pressure– Air pressure is the result of

the weight of an air column pushing down on an area

Air Pressure

• Measuring Air Pressure– Barometer is instrument

used – Mercury barometers

• A glass tube open at the bottom and partially filled with mercury

– Aneroid barometers• Without liquid; airtight metal

chamber with thin flexible walls

Air Pressure

– National Weather Service uses millibars as unit for air pressure

– One inch of mercury is equal to 33.87 mb

• Altitude and Air Properties– Altitude is the distance above sea level, or

elevation– As altitude increases, air pressure decreases,

air density decreases

Air Pressure

• Which layer has the highest pressure?

• Which layer has the lowest pressure?

Layers of the Atmosphere

• Observe: Atmosphere Intro• Atmosphere divided into four layers:

– Troposphere– Stratosphere– Mesosphere– Thermosphere

• Troposphere– Where Earth’s weather occurs– Contains almost all of the mass of the atmosphere– Temperature decreases about 6.5 C each km.– 0-12 km from Earth’s surface

Layers of the Atmosphere

• Stratosphere– Contains the ozone layer– Ozone is the three atom form of oxygen– Upper stratosphere is warmer than lower

stratosphere due to ozone reflecting Sun’s radiation

– 12-50 km from Earth’s surface

Layers of the Atmosphere

• Mesosphere– Protects earth from being hit with meteoroids– Temperatures near -90 C– 50-80 km from Earth’s surface

Layers of the Atmosphere

• Thermosphere– The outermost layer of atmosphere– The air is thin, and hot 1800 C– First layer the Sun’s radiation hits– 80 km-?? above Earth’s surface; No outer

limit

Layers of the Atmosphere

• Thermosphere divided into two layers:– Ionosphere (80km-400km)

• Sun’s energy causes particles to be electrically charged, ions

• Observe Aurora Borealis – the northern lights• Exosphere (400km-Beyond)

• Observe: Atmosphere Diagram

Layers of the Atmosphere

Air Pollution

• An air pollutant is any unwanted substance or chemical that contaminate the air that we breathe resulting in a decline in air quality. Air pollutants occur both outdoors and indoors.

Effects of Air Pollution

Pollutant Source Health Effect

Carbon monoxide

Burning fossil fuels Reduced ability of blood to deliver oxygen to the cells

Nitrogen Dioxide Burning fossil fuels Breathing problems, lung damage

Ozone Chemical reaction of certain carbon compounds

Breathing problems, asthma, eye irritation

Particles of dust, smoke, or soot

Burning of wood and fossil fuels, volcanic

eruptions

Respiratory illnesses, nose and throat irritation

Sulfur dioxide Burning of fossil fuels, volcanic eruptions

Breathing problems, lung damage

Energy in Earth’s Atmosphere

• The energy in Earth’s atmosphere comes from the Sun.

• Energy travels as electromagnetic (EM) waves

• Energy from EM waves is called radiation.

Energy in Earth’s Atmosphere

Greenhouse Effect

Greenhouse Effect

• Sunlight travels through Earth’s atmosphere

• Earth’s surface gives off infrared radiation

• The energy is held in by the atmosphere thus warming it

• Observe: Greenhouse Effect

Heat Transfer

• Temperature is the average amount of energy of motion of each particle of a substance

• Thermal Energy is the total energy of motion in the particles of a substance

• Temperature is measured with a thermometer

• Observe: Global Temperature

Heat Transfer

Types of Heat Transfer

Type Means Example

Radiation EM waves microwave

Conduction Direct contact

stove top

Convection Fluid (liquids or gases)

boiling

Winds

• Local WindsLocal Winds– Sea Breezes – blows Sea Breezes – blows

from water to landfrom water to land– Land Breezes – Land Breezes –

blows from land to blows from land to waterwater

Winds

• Global Winds– Doldrums – calm area near equator of rising air– Trade Winds – blow from the horse latitudes toward the equator

in both hemispheres from east to west – Horse Latitudes – 30 degrees north or south of the equator; calm

area of falling air– Prevailing Westerlies – blow from horse latitudes toward the

poles in both hemispheres from west to east– Polar Easterlies – blow cold air away from the poles in both

hemispheres from east to west

• Observe: Global Winds

Water in the Atmosphere

• Is there water in the air?• Observe: Water Cycle

– Evaporation – transformation of water from liquid to gas– Condensation – transformation of water from gas to liquid– Infiltration – flow of water into the ground– Precipitation – condensed water vapor that falls to Earth– Evapotranspiration – evaporation of water from living plants – Run-off – movement of water across land

Water in the Atmosphere

• Water is introduced into the atmosphere through evaporation

• Humidity– The amount of water vapor in the air varies depending

on air temperature and moisture– SPECIFIC HUMIDITY: The actual amount of water

vapor in the air.• Depends on air temp. • Warm air holds more vapor than cool air

– When the air has a maximum amount of water vapor it can hold, it is said to be saturated.

• Saturation is when actual vapor density=saturation vapor density

Water in the Atmosphere

• Air with higher temperatures can hold more water vapor than air at lower temperatures.

– Relative Humidity: How near the air is to saturation.

• Looks at actual vapor density in relation to saturation vapor density for air at a given temperature.

• @ 10 C a cubic meter of air holds at most 8 grams of water vapor

– If there were 8 grams in the air R.H. = 100%– If there were 4 grams in the air R.H. = 50%

Water in the Atmosphere

– Measuring Humidity• Air temperature is measured with a dry-bulb

thermometer• Wet bulb thermometer uses evaporation as a

cooling process.– Drier air has higher rates of evaporation, which causes a

lower wet-bulb temperature.– More moist air has lower rates of evaporation, which

causes a higher wet-bulb temperature.

• Difference between dry-bulb temperature and wet-bulb temperature can give relative humidity.

Water in the Atmosphere

• Humidity and Condensation– Condensation occurs when air becomes

cooler.– Temperature at which condensation occurs

for a given humidity is known as dew point.• Ex.: Wet grass in the morning

Water in the Atmosphere

• Measuring Relative Humidity– Psychrometer

• Has a wet-bulb and dry-bulb thermometer• The bulb of the wet-bulb thermometer has a cloth covering

moistened in water• When slung air blows over both thermometers• The wet-bulb thermometer is cooled by evaporation and the

reading drops below the dry-bulb thermometer reading• The relative humidity can be found by comparing the

temperatures of the wet-bulb and dry-bulb thermometers

Water in the Atmosphere

Clouds• Clouds form from water vapor condensing to

form liquid water or ice crystals

Clouds

• Observe: Dew Point - the temp. at which condensation begins

• For water vapor to condense into clouds, tiny particles must be present so the water has a surface on which to condense– Salt crystals, dust, and

smoke

Clouds

• Observe: Cloud Types

Clouds

• Clouds are classified in three types by their shape:– Cirrus – means curl of hair; wispy, feathery

• Cirrocumulus – rows of cotton balls, mean storms on its way– Cumulus – means heap or mass; fluffy, rounded piles

of cotton• Altocumulus – high altitude faint cumulus clouds• Cumulonimbus – towering clouds that indicate thunderstorms

– Stratus – means spread out; form in flat layers• Altostratus – high altitude faint stratus clouds• Nimbostratus – thick stratus; produce drizzle, rain or snow

Precipitation

• Precipitation - any form of water that: • falls from clouds• reaches Earth's surface

• Types of Precipitation– Rain

• Most common• Drops at least 0.5 mm in Diameter• Smaller drops are drizzle, even smaller are mist

– Sleet• When raindrops fall through a layer of air below 0 C• Ice particles smaller than 5 mm

Precipitation

– Freezing Rain• When raindrops fall through cold air near the

ground• Freeze when they touch the cold surface

– Snow• When water vapor is converted directly into

crystals• Snow flakes have six branches

– Hail• Ice larger than 5 mm in diameter • Only form in cumulonimbus clouds

Precipitation

• Drought - long periods of unusually low precipitation

• Cloud seeding - sprinkling crystals of silver iodide and dry ice from an airplane.

• Rain measurements are done with an open ended tube called a rain gauge.

Air Masses

• Air Mass – huge body of air at any given height that has similar:– Temperature– Humidity– Air pressure

• An Air Mass Could be:– Millions of square kilometers in spread– Up to 10 kilometers deep

Air Masses

• Four major types of air masses for North America:– Maritime Tropical - bring warm, humid air

• From the Pacific Ocean to California and West Coast• From the Gulf of Mexico to the Eastern U.S.

– Continental Tropical - bring hot, dry air • Move in from the Mexico to the Southern Plains

– Maritime Polar - bring cool, humid air• From the Pacific to West Coast• From the Atlantic and Eastern Canada often pushed out to sea by

westerly winds

– Continental Polar – bring cold air • From Central and Northern Canada to Central and Eastern U.S.

Air Masses

Air Masses

• Air masses move by prevailing westerlies and jet streams– Prevailing Westerlies

– wind belts over the continental U.S., blow from west to east

– Bands of high speed winds about 10 km altitude, west to east

El Nino v. La Nina

• El Nino • La Nina

What are the major differences What are the major differences between El Nino and La Nina events?between El Nino and La Nina events?

What kind of weather do you think What kind of weather do you think each event brings to our area?each event brings to our area?

Fronts and Systems

• Fronts – boundary where air masses meet• Four Types of Fronts:

– Cold Fronts• Cold air mass runs into warm air mass• denser cold air mass slides under the lighter warm air mass• Bring colder, drier air; clear skies, shift in wind and lower

temperatures– Warm Fronts

• Warm air mass runs into cold air mass• lighter warm air mass moves over the denser cold air mass• Brings warm humid weather

Fronts and Systems

– Stationary Fronts• Cold and warm air mass meet but neither moves the other• Water vapor in the warm air condenses into precipitation

– Occluded Fronts• Warm air mass gets caught between two cooler air masses• Cool air moves under warm air; Warm air mass is cut off

from the ground• Brings weather that may turn cloudy and precipitate.

Fronts and Systems

• Cyclones– Low pressure centers often moist air– Winds spiral inward from the center– Brings clouds, wind and precipitation

• Anticyclones– High pressure centers of dry air– Winds spiral out from the center– Brings dry, clear weather

Hurricanes• A hurricane is a rotating tropical storm with winds of at least 74

miles (119 kilometers) an hour. – These storms are called:

• hurricanes - Atlantic or eastern Pacific Oceans. • cyclones - Bay of Bengal and the northern Indian Ocean. • typhoons - western Pacific.

• http://www.nationalgeographic.com/forcesofnature/interactive/index.html

• The eye is the low-pressure center of the hurricane. – Air sinks inside the eye, clearing the skies and making it relatively calm. – A ring-shaped eye wall surrounds the eye and carries the storm's most

violent winds and its most intense rains.

Hurricanes• Hurricane season in the Atlantic, Caribbean, Gulf of Mexico, and

central Pacific is from June 1 to November 30. In the eastern Pacific, it is from May 15 to November 30. – Hurricanes can cause floods, flash floods, tornadoes, and landslides.

• Storm surge - an abnormal rise in sea level – usually the most dangerous part of a hurricane– cause beach erosion– wash out roads– decimate homes

• Forecasters at the U.S. National Hurricane Center in Florida track storms with:– satellite imagery– airborne reconnaissance– computer-model projections

Thunderstorms

• Storm – violent disturbance in the atmosphere

• Thunderstorms – form in cumulonimbus clouds; thunderheads

• On hot, humid afternoons• When warm air is forced up a cold front

– Heavy rainfall possibly hail; strong updrafts and downdrafts

– Most common in spring and summer

Thunderstorms

– Lightning• Areas of positive and negative electrical charges build up in

clouds• As charges jump:

– Between parts of a cloud

– Between clouds

– Between the cloud and the ground

– Heats the air to ~30,000 C

– Thunder• The expansion causes an explosion in the air• See the lightning before you hear the thunder

– Floods due to high precipitation

Tornadoes

• Tornadoes– Rapidly whirling, funnel-shaped cloud that touches

earth’s surface– Winds speeds approach 500 km/h– Formation

• From cumulonimbus clouds• Warm moist air flows in at the bottom of a cumulonimbus

cloud and moves upward. • A low pressure system form inside the cloud• The warm air begins to rotate as it meets winds blowing in

different directions at different altitudes• A tornado forms as part of the cloud descends to earth in a

funnel

Tornadoes

• Most tornadoes occur in the United States.

• Supercells - large thunderstorms that have winds already in rotation.

• Most tornadoes in the United States occur in Tornado Alley – from Texas to Nebraska

Tornadoes

• The average twister – about 660 feet (200 meters) wide – moves about 30 mph (50 kmh)

• Meteorologists at the U.S. National Weather Service watch the skies for severe storms and tornadic activity with: – Doppler radar– Satellites– weather balloons– computer modeling

• http://www.nationalgeographic.com/forcesofnature/interactive/index.html

Winter Storms

• If the air is colder than 0 C all the way to the ground, precipitation falls as snow

• Blizzard - a severe winter storm condition characterized by:– winds of 40 km/h (25 mph) or more– have snow or blowing snow– visibility less than 1 km (about 5⁄8 mile)– a wind chill of less than −25 °C (−13 °F), – All of these conditions must last for 4 hours or more

Winter Storms

• Lake-effect snow1. Frigid air flows over warm water and is heated from below.

Moisture evaporates into the air.

2. Warmer more moist air rises downwind of lakes and often forms heavy snow squalls.

Reading Weather Maps

• Meteorologists – scientists who study the causes of weather and try to predict it using:– Maps – Charts– Computer models– Radar– Balloons– Satellites– Surface instruments

Reading Weather Maps

• A weather map is a “snapshot” of the conditions at a particular time over a large area– Isobars – lines joining places with similar pressure– Isotherms – lines joining places with similar temperature

• Symbols on weather maps show:– Fronts– Areas of high and low pressure– Types of precipitation– Temperatures

• Limits to forecasting due to “Butterfly Effect”