Weather

What is weather?

The condition of the air (or atmosphere) at a given location at

a given time

Climate

“Typical” weather in region; the average weather or the regular variations in weather in a region over a period of years

• includes temperature, air pressure, humidity, days of sunshine, etc...

• drastically affected by water & mountains– coastlines have cooler summers and warmer winters– mountains greatly slow down winds and weather

AtmosphereBlanket of air surrounding the earthAir – the mixture of gases, mainly nitrogen

and oxygen, that forms the Earth’s atmosphere

• 78% Nitrogen• 21% Oxygen• 1% Argon• 1% Other stuff : Carbon dioxide,

water vapor, ozone, dust, ash, smoke, etc.

Structure of the

Atmosphere

Lower LayersTroposphere – the layer of the atmosphere that is

closest to the earth’s surface, where all weather phenomenon occurs.

8 km thick at the poles16 km thick at the equator;

(air temperature normally decreases with height)Stratosphere - upper layer of air 8 - 16 km to

about 50 km and top of the stratosphere contains the ozone layer; almost completely free of clouds.

Middle and Upper layers

Mesosphere – the layer of air, 50km to 80km where temperature begins to decrease with height, mainly because ozone in the stratosphere absorbs energy from the sun, principally ultraviolet radiation

Thermosphere - where air temperatures can exceed 1000° C (1800° F), 80km to 9600 km, primarily due to oxygen absorbing the sun’s energetic rays

Upper-Upper layersIonosphere – the region within the

atmosphere containing ionized molecules, layers of ionized air in the atmosphere extending from almost 60 km above the surface of the earth to altitudes of 1000 km and more.

Exosphere - The region beyond the thermosphere, which extends to about 9,600 km, the outer limit of the atmosphere.

Conditions of the Air

Temperature – amount of hotness or coldness relative to something else

•Thermometer – an instrument that measures relative hotness or coldness•Dew Point temperature – The temperature at which air becomes saturated

•Temperature scales:1°C = 1.8°F or 1°F = 5/9 ° C

Heat transfer

• Conduction – the movement of heat from molecule to molecule

• Convection – the movement of heat by warm and cold currents

• Radiation – the release and transfer of energy in wavelengths of heat and light

How is the atmosphere is heated?

Draw

Draw on back of notes

PressureAir pressure - the downward pressure exerted by

the weight of the overlying atmosphere or the “weight” of the atmosphere per unit AREA.

• Barometer – an instrument used to measure air pressure

Measured in inches of Measured in inches of mercury in a columnmercury in a column• Or millibars (metric Or millibars (metric conversion)conversion)• Average air pressure Average air pressure at sea level is 1013 millibarsat sea level is 1013 millibars

Water in the atmosphereWater Vapor

• Humidity – the amount of water vapor in the air

• Relative humidity – the actual amount of water vapor in the air compared to the greatest amount the air can hold

Precipitationwater or ice that condenses in the air and falls

to the ground as:• Rain- liquid water that falls to the ground• Snow - ice crystal flakes; water vapor in the

atmosphere that froze into ice crystals and falls to the ground in the form of flakes

• Sleet -partially melted grains of ice• Hail - pellets made of layers of ice and snow• Freezing rain –rain that freezes into ice as it hits

the ground

Evaporation

the process of changing from liquid to gas; molecules in a liquid state GAIN energy to change into a gaseous state

(latent heat energy is the stored in molecules through evaporation)

Evaporation DRIVES the water cycle

Condensation • the process of changing from gas to liquid;

molecules in a gaseous state that LOSE energy to change into a liquid state.

Clouds

• a visible mass of dense water vapor or ice suspended in the atmosphere; formed by surface heating & convection and/or warm air lifted by rising over mountains

Wind Air moving at a speed fast enough to be noticed…Air moving at a speed fast enough to be noticed…• Low pressure – air is de-compressed (allowed to Low pressure – air is de-compressed (allowed to

expand) and sucks air toward.expand) and sucks air toward.• High pressure – air is compressed (contracted) High pressure – air is compressed (contracted)

and flows away. and flows away.

high pressure moves to low pressure high pressure moves to low pressure

Winds are named by the direction they come Winds are named by the direction they come FROMFROM

Instruments:Instruments:• WeatherWeather VaneVane – measures wind direction – measures wind direction• AnemometerAnemometer – measures wind speed – measures wind speed

LOCAL WINDS: Sea breeze

Sea breezewind blowing from sea to land during the

day when the sun warms the land faster and cool air from above the water forces the warm air above the land to rise

Draw diagrams

LOCAL WINDS: Land Breeze

LOCAL WINDS: Land Breeze

wind blowing from land to sea at night because the land cools faster than the sea

Draw diagrams

• Draw diagrams

• High pressure – air is compressed (contracted) and flows away.

• Low pressure – air is de-compressed (allowed to expand) and sucks air toward.

– Add the Coriolis Effect and you get ‘cyclonic’ and ‘anticyclonic’ flow.

Coriolis Effect the effect of Earth’s rotation on movement

of air masses

• http://www.youtube.com/watch?v=_36MiCUS1ro (people on turn table)

• http://www.youtube.com/watch?v=BPNLZyBNPTE&feature=fvwrel• http://www.youtube.com/watch?v=mcPs_OdQOYU• http://www.youtube.com/watch?

NR=1&v=Kk7sXkzmtp0&feature=endscreen • http://www.youtube.com/watch?v=49JwbrXcPjc&feature=related• http://www.youtube.com/watch?v=DHrapzHPCSA – hadley cells

(belts)• http://www.youtube.com/watch?v=KadsPCOudt0&feature=fvwrel -

belts

Coriolis Effect on a Synoptic Scale• Low pressure… air moves:

– Up– In– Counter clockwise

• High pressure … air moves:– Down– Out– Clockwise

Global Winds

Draw next page

Air Mass A large region of air with similar properties

throughout (ie. temperature, humidity)

Major Air Masses

• cA – Continental Artic – dry, very cold

• cP – Continental Polar – dry and cold

• cT – Continental Tropical – dry and warm

• mP – Maritime Polar – moist and cold

• mT – Maritime Tropical – moist and warm

• Draw next page

http://www.youtube.com/watch?v=UmyfkXSFiZA&feature=related

Relative Humidity

Comparison of the specific humidity and the maximum amount of water vapor that the air can hold at a given temperature and pressure

Unit is in percentage = %

Relative humidity = specific humidity X 100%

maximum capacity 100% Rel. Hum. – saturated air

0% Rel. Hum. – dry air

Psychrometer

Dry air - greater evaporation

- greater cooling

- greater the difference in the 2 temperatures

High humidity – no evaporation (saturated air)

- temperatures of the 2 bulbs will be the same or

very close

Psychrometer

Instrument to measure humidity

Dry bulb – measures air temp.

Wet bulb – has a water soak wick around the bulb – water evaporates – cools the air

Rain Shadow (Orographic Lifting)

• As a parcel of air rises up the windward side of a mountain range, the water vapor in the air condenses to liquid water and creates clouds and precipitation.

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• When the air begins to flow over the mountain and down the leeward side of the mountain, it is dry (lost all of its moisture).

• As the cool air descends, it heats and compresses (increased pressure), reducing its possibility of precipitation.

Frontthe boundary between two different air masses– Cold front – a front that moves so that cold air

replaces a warmer air mass– Warm front – a front that moves so that warm air

replaces a cooler air mass– Occluded front – a front formed when a cold front

overtakes a warm front– Stationary front – a front that is not moving– Polar front – the low pressure zone where polar and

tropical air masses meet

• Manifestation of low pressure:

Jet Stream

• Jet streams are fast flowing, narrow air currents found in the atmosphere. The main jet streams are located near the tropopause and the stratosphere.

http://en.wikipedia.org/wiki/Jet_streamen.wikipedia.org/wiki/Jet_stream

Jet Stream

http://www.youtube.com/watch?v=CgMWwx7Cll4&feature=related

http://www.youtube.com/watch?v=CgMWwx7Cll4&feature=fvwrel

Greenhouse effectthe ability of the atmosphere to let much

sunlight in, but little infrared radiation (heat) to escape.

Greenhouse effect

Greenhouse gasses: carbon dioxide (CO2), water vapor, methane (CH4), nitrous oxide, hydrochlorofluorocarbons, or HCFCs, & chlorofluorocarbons or CFC’s; CFC’s are chemicals used in refrigerators, air conditioners, etc. and aerosol spray cans that destroy ozone molecules

Causes of the Greenhouse effect

• burning oil, natural gas and coal (increasing CO2 levels)

• deforestation - burning of cleared forests release more CO2; no trees to convert CO2 to oxygen

• Air Pollutant – any harmful matter added to the air

• Ozone – a three-atom form of oxygen that absorbs ultraviolet sunlight

http://ozoewatch.gsfc.nasa.gov/monthly/http://ozoewatch.gsfc.nasa.gov/monthly/monthly_1990-07.htmlnmonthly_1990-07.htmln

• What everything means

For wind direction – For wind direction – this example is a this example is a NE wind (going to NE wind (going to the SW) and the the SW) and the speed is 20 knotsspeed is 20 knots

•

Warm frontWarm front

OccludedOccluded frontfront

Cold front

• Unequal heating – currents

• http://www.youtube.com/watch?v=KadsPCOudt0&feature=fvwrel

• Collapsing (large) can

• http://www.youtube.com/watch?v=JsoE4F2Pb20&feature=related

• http://www.youtube.com/watch?v=Uy-SN5j1ogk&feature=related

http://kids.britannica.com/thunderstorms_tornadoes/ocliwea124v4.html