Composition, Structure, and Temperature

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Weather and Climate
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Weather and Climate Intro

• Weather the state of the atmosphere for a short
  period of time.
• Climate the generalization of weather conditions
  over a long period of time.

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6 Properties

• Both weather and climate have six properties that
  are measured on a regular basis.
• Air temperature
• Humidity
• Type and amount of cloudiness
• Air pressure
• Type and amount of precipitation
• Speed and direction of the wind

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Properties Continued

• A change in one of these properties will often
  mean a change in one or more of the other
  properties.

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Composition of the Atmosphere

• Air is a mixture of gases as well as liquids that
  are suspended in those gases.
• The composition of air is not a constant.
• Clean, dry air is composed of two main gases.
• Nitrogen- 78
• Oxygen- 21

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Composition of the Atmosphere Continued

• The remaining 1 is a mixture of a number of
  different gases
• Carbon Dioxide is very important because of its
  ability to absorb heat energy to keep that
  atmosphere warm

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There are 3 Variable Components in the Air

1. Water Vapor
2. Dust
3. Ozone

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Water Vapor

• The amount of water vapor in the atmosphere is
  constantly varying
• At some points water vapor can account for up to
  4 percent of the volume
• Water vapor also has the ability to absorb heat
  and solar energy

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Dust

• Some examples of dust particles are pollen,
  spores, and seeds
• Most dust particles are found in the lower
  atmosphere near their source
• Dust particles act as a surface for water vapor
  to condense on
• This is essential for the formation of clouds and
  fog

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Ozone

• Ozone a molecule that has three oxygen atoms
• Ozone is concentrated in the stratosphere,
  between 10 and 50 kilometers
• Ozone absorbs most of the UV rays from the sun

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Height and Structure of the Atmosphere

• Atmospheric changes
• Atmospheric pressure is the weight of the air
  above
• At sea level the average pressure is slightly
  more than 1,000 millibars
• One half of the atmosphere gradually merges with
  outer space

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Height and StructureContinued

• Temperature changes
• The atmosphere is divided into five layers based
  on temperature
• Troposphere
• Stratosphere
• Mesosphere
• Thermosphere
• Exosphere

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Troposphere

• The bottom layer
• Temperature decreases with an increase in
  altitude
• All weather occurs in this layer
• The thickness of the troposphere varies with
  latitude, but the average thickness is 12
  kilometers
• The outer boundary of the troposphere is called
  tropopause

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Stratosphere

• The temperature remains constant to a height of
  20 kilometers then increases until the
  stratopause
• The stratopause occurs at about an altitude of 50
  kilometers
• The reason for the increase in temperature is the
  abundance of ozone

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Mesosphere

• The temperature decreases with altitude until the
  mesopause
• The mesopause is at a height of 80 kilometers

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Thermosphere

• Contains very little of the atmospheres mass
• In this layer the temperature rises as high as
  1,000 degrees Celsius

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Exosphere and Ionosphere

• The Exosphere begins at a altitude of around 400
  kilometers
• A transition zone between earths atmosphere and
  space
• The ionosphere and the exosphere together are
  known as the thermosphere

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The Earth-Sun Relationships

• Solar energy is not distributed evenly over the
  earths surface
• The unequal heating of the earth drives currents
  and creates winds
• Energy from the sun is the most important control
  of our weather and climate

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The Earths Principal Motions

• Rotation is the spinning of the earth on its axis
• The planet rotates once every 24 hours producing
  a daily cycle of daylight an darkness
• Revolution is the movement of earth in its orbit
  around the sun

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The Seasons

• There is an annual shift in the solar angle or
  altitude of the sun

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The Causes of the Seasons

• The tilt on the earths axis is the cause of the
  seasons
• In the northern hemisphere the earth is tilted
  toward the sun in the summer
• In the southern hemisphere the earth is tilted
  away from the sun
• The northern hemisphere receives more sunlight in
  the summer than in the winter
• Distance has no effect of the seasons

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The Angle of the Sun

• The angle of the suns rays also plays a part in
  the seasons
• The angle of the sun makes a difference in how
  many atmospheres that rays have to travel
  through.
• If the sun is directly overhead, the rays only
  have to travel through one atmosphere.
• The angle will change the intensity the suns
  rays will hit the surface.

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Summer Solstice

• In the summer solstice, the sun is directly over
  the Tropic of Cancer, and occurs on June 21 or 22

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Winter Solstice

• The sun is directly over the Tropic of Capricorn,
  and occurs on December 21 or 22

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Autumnal Equinox

• The sun is directly over the equator and occurs
  on September 21 or 22

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Vernal Equinox

• The sun is directly over the equator and occurs
  on March 21 or 22

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Greenhouse Effect

• Most of the solar energy that reaches the earth
  is absorbed or reradiated skyward.
• As well as absorbing solar energy, gases also
  absorb terrestrial radiation.
• As these molecules absorb they heat and warm the
  environment.
• The basis of the greenhouse effect is that
  greenhouse gases were heated in a similar manner.
• The main gases in the atmosphere, carbon dioxide
  and water vapor act like greenhouse gases.

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Greenhouse Effect Animation
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Temperature, Measurement, and Data

• Temperature measurement of how fast molecules
  are moving.
• Every day there is at least two temp. readings,
  minimum and maximum.
• Adding the high temp. and the low temp. and
  dividing by two will give you the daily mean
  temp.
• The temp. mean is calculated by adding all daily
  temp. together and dividing by the number of days
  in the month.

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Temperature, Measurement, and Datacontinued

• Temp. range found by calculating the difference
  between the high and the low in a given day.
• Annual mean 12 month range.
• Annual temp. range difference between the
  highest temp. and lowest temp. achieved during
  the year.

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Temperature Controls

• Temp control is a factor that causes temp to vary
  from place to place and time to time.
• Single greatest influence on temp variations is
  the difference in the receipt of solar radiation.
• Variations in the sun angle and the length of
  daylight are responsible for warmer temp in the
  tropics and colder temp in the poles.

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Important Temperature Factors

• The most important temperature controls are
• Specific heat
• Altitude
• Geographical Position
• Ocean Currents

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Specific Heat

• Land heats more rapidly and to higher temp than
  water and cools more rapidly than water.
• Specific heat watergtland.
• Land surfaces are opaque so heat is only absorbed
  at the surface. Water is transparent so heat
  penetrates for a depth of many meters.

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Water Factors

• Water is constantly mixing warm and colder
  waters.
• Evaporation from water bodies is greater than
  from land surfaces.
• Evaporation from water bodies is greater than
  from land surfaces

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Altitude

• Altitude higher altitudes are generally cooler
  than an elevation that is close to sea level

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Geographical Positions

• Windward coastal location subject to prevailing
  winds experiences considerable different temp.
  from coastal location where prevailing winds are
  directed from the land toward the water.
• Mountains can act as barriers

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World Distribution of Temperature

• Isotherms are lines that connect places of equal
  temp.
• The effectiveness of incoming solar radiation in
  heating the earth and the atmosphere is largely a
  function of latitude.
• Isotherms also reveal the presences of ocean
  currents. Warm currents cause the isotherms to be
  directed pole ward.
• Continental location must endure hotter summers
  and colder winters that a coastal location.

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Air Masses

• Air mass large body of air that is characterized
  by a similar temp, moisture, and a given
  altitude.
• When air moves from the source region it carries
  the temp and the moisture conditions with it.
• Air mass weather is a few days of fairly
  consistent weather conditions.
• The boundary between two air masses is called a
  front.

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Air MassContinued

• Source region is where the air mass acquires its
  characteristic properties or temp and moisture.
• Air masses are always classified according to its
  source region.
• Continental air masses form over land and
  maritime form over water.
• Maritime air is more likely to be moist/humid
• Polar form in the poles are cold, tropical form
  in the tropics and are warm

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Air MassContinued

• 4 basic types of air masses classified by its
  source region.
• Continental polar cold/dry
• Continental tropical warm/dry
• Maritime polar cold/wet
• Maritime tropical warm/wet
• Our weather is mostly influenced by continental
  polar air and maritime tropical air.

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Fronts

• Boundaries that separate air masses of different
  temperature and moisture.
• A front is narrow band running in between two air
  masses (15-200km)
• The warmer less dense air masses are always
  forced upward by the cool dense air mass.

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FrontsContinued

• Warm fronts
• Warm air occupies territory that was formerly
  covered by cooler air.
• Usually cirrus clouds form
• Cold fronts
• Cold air is actively advancing into a region that
  was occupied by warm air.
• Usually heavy down pours and violent weather

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FrontsContinued

• Stationary fronts
• The surface position of the front does not move
• Produces an extended period of widespread
  cloudiness
• Occluded fronts
• An active cold front overtakes a warm front
• Capable of producing precipitation

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FrontsContinued

• The weather along a front line may/ may not
  conform to the idealized picture.
• Descriptions of each of the fronts are
  generalizations

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Middle Latitude Cyclone

• Primary weather producer.
• Large areas of low pressure that generally travel
  from west to east.
• These weather systems have a counter-clockwise
  circulation with air flowing toward the middle.

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4 stages of a typical middle latitude cyclone

• A front develops
• Cyclonic circulation is developed
• Occluded front develops
• Cyclone dissipates

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Thunderstorms

• During the development, there is thermal
  instability in the air.
• Thunderstorm activity is associated with
  cumulonimbus clouds that generate heavy rain,
  thunder, lightening, and some hail.
• At a given time there are about 2,000
  thunderstorms occurring on the surface of the
  earth.

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Thunderstorms Continued

• Majority of these thunderstorms are taking place
  in the tropics.
• Each day about 4,500 take place.
• Require warm, moist air.
• Rapid expansion and collapse of air causes
  thunder.
• Lightening occurs as a huge spark that travels
  between two parts of a cloud.
• Only about 10-20 of the lightening takes place
  between the clouds and the ground.

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3 Stages of Thunderstorms

• Cumulus stage warm air rises until a cumulus
  cloud forms.
• Mature stage cumulonimbus clouds form and an
  anvil is shaped at the top of the cloud. There
  are strong updrafts and downdrafts. Heavy rain
  and sometimes hail form.
• Dissipating stage Thunderstorm dies out due to
  lack of water vapor.

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Tornadoes

• Local storms of short duration
• Greatest frequency of tornadoes occur from April
  through June.
• Tornadoes form is in association with severe
  thunderstorms that produce high winds, heavy
  rainfall, and damaging hail.
• Less than one percent of all thunderstorms
  produce tornadoes.

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Tornadoes Continued

• Tornado formation is associated with interactions
  between strong updrafts in the thunderstorm and
  winds in the troposphere.
• An average tornado has a diameter between 150 and
  600 meters, travels about 30 mph and travels
  around 6 miles.
• Tornados are measured on the Fujita intensity
  scale.

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TornadoesContinued

• Tornados are measured on the Fujita intensity
  scale.
• Majority of tornados are rated as an F1.
• Only about 2 of the total number of tornadoes
  are F4 or F5.
• Tornado watches and warnings
• Watch- conditions are favorable for the formation
  of a tornado.
• Warning- a funnel cloud has been sighted.

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Hurricanes

• Whirling tropical cyclones that on occasion have
  wind speeds attaining wind of speeds of 185 mph.
• Can generate waves reaching 50 feet high.
• Most hurricane damage is due to strong winds and
  flooding.
• Almost all hurricanes form in tropical waters
  between 5 and 20 latitude.

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HurricanesContinued

• Must have winds in excess of 74 mph and on
  average are 375 miles in diameter.
• Amount of energy produced in one day of a
  hurricane is equivalent to the entire electrical
  production of the US in one year.
• Tropical depression winds less than 38 mph.
• Tropical storm winds from 38-74 mph.

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The Eye

• The eye wall
• Doughnut shaped wall of intense convection
  activity surrounding the center of the storm.
• The greatest wind speeds and heaviest rainfall
  occurs here.
• The eye is at the center of the hurricane where
  wind and precipitation subsides.

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HurricanesContinued

• There are 3 reasons that a storm can decrease
  intensity
• Move onto land.
• Move onto ocean water that cannot supply warm
  moist air.
• Reach a location where large scale flow aloft is
  unfavorable.

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HurricanesContinued

• Hurricanes intensity is ranked on a scale between
  category 1-5 on the Saffir-Simpson scale.
• Damages are divided into 3 categories
• Wind damage
• Storm surge
• Inland flooding

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