Weather and Climate

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Chapter 24

• Weather and Climate

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24.1 The Atmosphere

• Its the protective layer that surrounds Earth
• It protects Earth from UV rays
• It moderates the temperature
• It contains gases that are essential for life.

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Composition of Atmosphere

• 78 is nitrogen
• 21 is oxygen
• The remaining 1 is a mixture of water vapor and
  other gases

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Air Pressure

• The force of gravity pulling the atmosphere
  toward Earth causes air pressure.
• It is equal to 101,325 Newton per square meter at
  sea level
• Pressure decreases as altitude increases
• Density decreases as altitude increases

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Barometer

• Air pressure is measured with a barometer
• A mercury barometer measures pressure at sea
  level at 760 mm Hg
• It uses a column of Hg to measure pressure

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Aneroid Barometer

• More portable than a mercury barometer
• It uses a metal chamber to measure pressure

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Atmospheric layers

• Temperature drops as altitude increase
• Changes in temperatures define the layers in the
  atmosphere

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Troposphere

• Lowest layer
• Contains almost all of the water vapor and
  suspended particles
• Weather happens here
• 9 km at poles 12 km at the equator
• Temperature decreases by 6.5 per km

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Stratosphere

• Next Layer
• 12 km to 50 km above the earth
• Temperature remains the same near the boundary of
  the troposphere then increase after about 20km
• The ozone layer warms the upper stratosphere by
  absorbing UV radiation

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Mesosphere

• The layer above the stratosphere
• 50km to 80km
• Gets cooler the higher it gets
• Most meteoroids burn up in this layer

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Thermosphere

• Outer most layer
• Gets warmer as it gets further from earth
• Starts at -90C and goes to 1000C
• It has no upper boundary but instead gradually
  enters outer space

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Ionosphere

• Not a layer but instead a region of charged
  particles that covers the thermosphere
• AM radio waves bounce back to earth from the
  ionosphere
• Aurora is a colorful display at night occurs when
  charged particles from the sun are attracted to
  Earths Magnetic poles

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24.2 The Sun and the Season
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Rotation

• Spinning of Earth on its axis
• Takes 24 hours

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Revolution

• The movement of one body in space around another
• Earths movement around the sun
• Takes 365 days

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Latitude Zones
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The Season

• Earth is on a tilt of 23.5 N
• It is the cause of the season
• Seasons are NOT caused by the distance from the
  sun. In fact, the Earth is closest to the sun
  during winter in the Northern hemisphere

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Solstices

• Occurs when the Sun is directly overhead at 23.5
  N and 23.5 S
• Northern hemisphere it occurs on June 21st
• Daylight hours are longest in the northern
  hemisphere and shortest in the southern
  hemisphere
• December 21st is the winter solstice and the
  reverse occurs

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Equinoxes

• Days are about equal darkness and light
• Occurs approximately half way between solstices
• Neither hemisphere is tilted toward the sun
• Vernal equinox occurs on March 21
• Autumnal equinox occurs September 22

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24.3 Solar Energy and Winds

• Most of the energy that heats the troposphere is
  radiated from Earth
• The greenhouse effect reflects that energy back
  toward the Earth

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Wind

• Caused by differences in air pressure
• Differences in air pressure caused by unequal
  heating of Earths surface
• Warm air expands and rises
• Cooler air is denser and moves to take its place

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Local Winds

• Wind that occurs in a small area
• Caused by unequal heating in a small area
• Sea breezes are an example

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Global Winds

• Winds that blow in specific direction
• Move in bands called convection bands
• Examples are trade winds, westerlies and polar
  easterlies

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• The rotation of the Earth causes the winds to
  turn Coriolis effect

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Monsoons

• Characterized by reversal in weather over a large
  region for a large amount of time.

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Jet Stream

• Fast moving stream of air that occur because of
  great differences in air pressure that develop at
  high altitudes

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24.4 Water in the Atmosphere

• Humidity amount of water vapor in the air
• Relative humidity is the ratio of the amount of
  water vapor in the air
• Expressed in percentage
• Cooler air holds less water vapor than warm air
• Dew point is the temperature at which water
  condenses

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Cloud Formation

• Form as warm, moist air rises and water vapor
  condenses in the atmosphere
• Must have solid suspended particles to form
• When water vapor is cooled below its dew point,
  water vapor condenses onto these particles

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Precipitation

• Rain, sleet, snow, hail, and freezing rain
• Rain forms in nimbostratus clouds or cumulonimbus
  clouds
• Hail is ice of more than 5 mm in diameter
• Sleet is ice smaller than 5mm
• Freezing rain is rain that freezes after it hits
  the surface

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24.5 Weather Patterns

• Consists of
• Warm Fronts
• Stationary Fronts
• Occluded Fronts
• cold Fronts

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Air Masses

• Large body of air that covers a large area and
  has uniform properties
• They are classified by how they are formed over
  land or water and the latitude where they form

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Fronts

• After air masses form, they move
• When they move they meet other air masses and
  form a front
• Cold front
• Warm front
• Stationary front
• Occluded front

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Cold Fronts

• Fronts when a cold air mass overtakes a warm air
  mass
• Produces cumulus and cumulonimbus clouds
• Produces severe thunderstorms, precipitation, and
  strong winds

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Warm Fronts

• Occurs when a warm air mass overtakes a cold air
  mass
• Stratus clouds forms
• May have a steady rain, may have some
  thunderstorms
• Temperature rises after the front passes

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Stationary Fronts

• Occur when two unlike fronts meet but do not
  overtake one or the other
• May results in clouds and steady rain or snow for
  several days

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Occluded Fronts

• Forms when a warm air mass is caught between two
  cooler air masses.
• The cooler masses cut the warm air mass off from
  the ground. The warm air rises and cools
• Results in cloudy skies and precipitation

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Cyclones

• Low air pressure in the center
• Rotates counterclockwise in the Northern
  Hemisphere
• Doesnt stay in one place
• Associated with strong winds and precipitation

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Anticyclones

• Center is a high air pressure
• Rotate clockwise in the Northern hemisphere
• Has clear skies, very little precipitation, and
  generally calm conditions

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Storms

• Thunderstorms
• Tornadoes
• Tropical Storms and Hurricanes

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Thunderstorms

• Small weather system that includes thunder and
  lightning
• Accompanied by strong winds and heavy rain or
  hail
• Occur when columns of air rise within a
  cumulonimbus cloud

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Lightning

• Sudden electrical discharge in the atmosphere
• Positive charges accumulate at the top of the
  cloud, negative charges at the bottom
• When there is enough difference in charge,
  lightning flashes

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Thunder

• Occurs from the expansion of gases that results
  from the extreme heat the released when lightning
  discharges
• You hear thunder after you see lightning because
  light travels faster than sound

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Tornadoes

• A small but intense windstorm that is a rotating
  column of air that touches the ground
• Usually occur at the leading edge of an advancing
  cold front
• Occurs in a thunderstorm
• Wind can reach 500 km/hr usually 150km/hr

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Hurricanes

• Cyclone that develop in the tropics
• Hurricane is a large tropical cyclone with winds
  of at least 110 km/hr

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24.6 Predicting the Weather

• Meteorologists study Earths weather
• They use
• Doppler radar
• Automated weather stations
• Weather satellites
• High- speed computer

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Doppler Radar

• Bounces radar waves off the clouds
• Measure the frequency of the waves that return
• Speed of the storm can be calculated

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Weather Stations and Satellites

• Have sensors that measure
• Temperature
• Precipitation
• Winds speed
• Direction

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High Speed Computers

• Used to predict weather
• Accurate from 12 hrs to 3 days
• Large weather systems 3-7 days
• Difficult to predict beyond 7 days

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Weather Maps

• Temperatures
• Sun, cloud symbols
• Cloud cover
• Drawings of rain or snow

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Isotherm

• Line on a map that connects points of equal air
  temperature

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Isobar

• A line on a map that connect points of equal air
  pressure

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24.7 Climate

• Long term- weather conditions
• Natural
• Ice Ages
• El Nino
• Caused by Humans
• Global Warming

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Temperature

• Latitude
• Distance from large bodies of water
• Ocean currents
• altitude

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Precipitation

• Latitude
• Distribution of air pressure systems
• Global winds
• Existence of a mountain barrier

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desert

• Receive less than 25 cm of rain per year
• Can be hot or cold
• Direction of prevailing winds

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Natural Climate Change

• Possible causes are
• Variations in Earths orbit around the sun
• Changes in the angle of Earths axis
• Global levels of volcanic activity

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El Nino

• Occurs about every 3-8 years
• The cold water upwelling fails to occur off the
  coast of Peru causing a warming tend

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Global Warming

• Possibly caused by human activities
• Burning of fossil fuels raises CO2 levels
• 1990s hottest decade on record
• Hotter temperatures cause the oceans to swell
  which floods low lying areas causing many
  peoples homes to be flooded