Weather

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Weather

• Changes in our Atmosphere

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Why Do We Need To Know About the Weather?

• Early humans were greatly affected by the
  weather
• Farming, hunting, and shelter to survive.
• Man is still greatly affected by the weather
• Droughts, floods, winds, lightning, hail, heat
  waves, freezing temperatures, blizzards.

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What is the Atmosphere?

• The atmosphere is a thin layer of gas, dust and
  water vapor that surrounds the Earth.
• The atmosphere is held to the Earth by gravity.
• All weather happens in the atmosphere.
• The atmosphere has layers that each have
  different characteristics.
• Troposphere
• Stratosphere
• Mesosphere
• Thermosphere

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What is Weather?

• Weather is the state of the atmosphere at a
  particular place and time.
• Example what it is like outside right here,
  right now. It is rainy and cold.

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What is Meteorology?

• Meteorology is the study of weather.

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Electromagnetic Energy

• Electromagnetic energy is energy that has the
  properties of transverse waves.
• Parts of waves
• Crest top
• Trough bottom
• Wavelength distance crest to crest
• Frequency of wavelengths per time
• Electromagnetic spectrum is the entire range of
  electromagnetic wavelengths.

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The Electromagnetic Spectrum
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Solar Energy

• Stars, our Sun, produce electromagnetic energy or
  solar energy.
• Doppler effect is an apparent change in wave
  frequency.
• Red Shift a phenomenon observed as a source of
  light moves away from an observer.
• Blue Shift a phenomenon observed as a source of
  light moves away from an observer.

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Matter and Electromagnetic Energy

• When electromagnetic energy comes in contact with
  a material it can interact in several ways. It
  can be
• bent or refracted
• reflected in a different direction
• scattered (refracted and reflected) in
  several directions
• absorbed or taken in

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Energy Transfer in the Atmosphere

• Convection is the transfer of heat energy by
  movement of fluids.
• Conduction is the transfer of heat energy by
  contact (molecule to molecule)
• Radiation is the transfer of electromagnetic
  energy through space in the form of waves.

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Energy TransformationConservation of Energy

• A closed energy system is one in which no energy
  from outside the system can get in and no energy
  from inside can get out.
• Total amount of energy does not change.
• The total energy given off by an energy source is
  equal to the amount absorbed by an energy sink.

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Heat vs Temperature

• Heat is the total kinetic energy of the particles
  in a sample of matter.
• Temperature is a measure of the average kinetic
  energy of the particles in a sample of matter.

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Heat Terms

• One calorie is defined as the quantity of heat
  needed to raise one gram of water by one degree
  Celsius.
• Specific heat is the quantity of heat needed to
  raise one gram of a substance one degree Celsius.
• Latent heat is the term for energy added to a
  substance that does not raise the temperature of
  the substance. This is heat energy being used in
  a phase change.

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What Variables Affect the State of the Atmosphere?

• Temperature
• Humidity
• Atmospheric pressure
• Wind speed and direction
• Clouds and precipitation
• Note weather is greatly affected by water.

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Temperature Variations

• The weather machine of the Earth is driven by
  uneven heating of the Earths surface.
• Temperature is greatly affected by the intensity
  and duration of insolation.
• Insolation is incoming solar radiation.

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Factors Affecting Local Temperature

• Latitude
• Altitude
• Closeness to large bodies of water
• Amount of moisture in the air.

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What is Humidity?

• Humidity is the concept of the air holding water.
• Think of the air as a sponge with water in the
  holes between the molecules of air.

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What is Humidity?

• The amount of moisture in the air is constantly
  changing.
• The amount of water vapor the air can hold is
  called its capacity.
• When the air contains all the moisture it can
  hold, at a particular temperature, it is filled
  to capacity or saturated.

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What is Saturation?

• Saturation the point where the air contains the
  maximum amount of water vapor possible.

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What is Relative Humidity?

• Relative humidity is the measure of the amount of
  water vapor in the air at a particular
  temperature compared with the total amount of
  water vapor that the air can hold at that
  temperature.

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Calculating Relative Humidity

• Relative Humidity absolute humidity x
  100 capacity

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Relative Humidity (cont.)

• Warm air holds more water vapor because the water
  molecules are moving more rapidly and will not
  condense.
• Cold air holds less water vapor because the water
  molecules are moving less and are more likely to
  condense.

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Relative Humidity (cont.)

• When relative humidity 100 the air contains
  all the water vapor it can possibly hold and it
  said to be saturated.
• Relative humidity is measured with a sling
  psychrometer, a wet versus dry bulb instrument.

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What is Dew Point?

• Dew point the temperature at which the air is
  saturated and condensation takes place.

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Moisture and Air Pressure

• Air pressure, or atmospheric pressure is the
  weight of the air pushing down on a surface area.
• Air pressure is measured with a barometer.
• Low pressure greater moisture capacity.
• High pressure less moisture capacity.

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Altitude and Air Pressure

• As altitude increases air pressure decreases
  (less air above you).

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Moisture and Energy Input

• Evaporation is the process of changing liquid
  water into water vapor in the atmosphere.
• Transpiration is the process by which plants
  release water vapor into the atmosphere.
• Evapotranspiration refers to all the water vapor
  released into the atmosphere.
• Both processes require energy to change liquid
  water into water vapor. Evapotranspiration
  constitutes an energy input to the atmosphere
  (540 calories/gram of water).

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Factors Affecting the Rate of Evaporation

• Vapor pressure is the pressure exerted by only
  the water vapor in the air.
• More vapor pressure less evaporation
• Amount of energy available.
• More energy more evaporation
• Surface area of water.
• More surface more evaporation
• Amount of moisture in the air.
• More moisture less evaporation

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Dynamic Equilibrium

• Dynamic equilibrium occurs when the number of
  molecules changing from liquid to vapor equals
  the number changing from vapor to liquid.
• When the air is saturated, the amount of water
  vapor evaporating and the amount condensing are
  the same. This is called the saturation vapor
  pressure.
• Remember warm air holds more moisture so
  temperature affects saturation vapor pressure.

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