Fig. 3-CO, p. 54

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Fig. 3-CO, p. 54
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SEASONAL and DAILY TEMPERATURES

• REASONS for the SEASONS
• We are a space object obeying the Laws of
  Gravity, orbiting the sun in 365.2422 days.
• Our orbit is elliptical having an eccentricity of
  0.017. (Zero is a perfect circle)
• The earth is inclined to the plane of its orbit
  by 23 1/2 degrees.

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Fig. 3-1, p. 56
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Fig. 3-2a, p. 56
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Fig. 3-2b, p. 56
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Fig. 3-3, p. 57
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Fig. 3-4, p. 58
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Fig. 3-5, p. 58
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Fig. 3-6, p. 58
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Fig. 3-7, p. 59
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Table 3-1, p. 60
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When does a Season Begin?

• Season Astronomically Meteorologically
• Spring March 20 March 1
• Summer June 21 June 1
• Autumn Sept. 22 Sept 1
• Winter Dec. 21 Dec 1
• Latitudes Tropic of Cancer 23.5o
• Tropic of Capricorn - 23.5o
• Arctic Circle 66.5 o Anarctic Circle -66.5o.

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Fig. 3-8, p. 61
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Fig. 1, p. 62
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Hemispheric Seasonal Variations

• The sun is located at one focus of an ellipse, so
  one half of the earths orbit is longer than the
  other.
• Northern Hemisphere --Summer is a week longer
  than Winter. Reversed in the SH.
• Earth is closer to the sun (3 Million Miles) in
  NH so winters are slightly warmer. More water
  around SH moderates their winters.

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Fig. 3-9, p. 62
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Local Seasonal Variations

• South sides of hills -- more sunlight
• Vinyards , Solar Collectors
• Clear sky regions -- drier less vegetation
• Southside-Large windows for winter sun
• North sides of hills --less sunlight
• Ski Lodges, Summer porches and patios
• Northside--Bedrooms for better sleeping

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Fig. 3-10, p. 63
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Solar Collector Angle Settings

• Location of collector is south facing roof
• Angle of collector should be an average for the
  winter sun maximum altitude.
• Boone Latitude is 36.2o So lowest max is on Dec
  21st. 36.2 23.5 59.7o or 30.3o
• The highest max is on March 20th. So the value is
  36.2 - 0 36.2o or 53.8o The average is (53.8
  30.3)/2 42o . In general the
  angle is Latitude 6o .

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Fig. 2, p. 64
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Daily Temperature Variations

• The earth spins one revolution on its rotational
  axis in 24 hours. This is not quite 24 hours and
  so a second is added when needed on either Jan
  1st or July 1st. Last century about 54 seconds
  were added. This amounts to the day lengthening
  by 1.5 ms/century.
• The lengthening is caused by tidal friction
  mostly by the Moon and lesser by the Sun.

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Cause of Temperature Variation

• Daytime Warming -- lack of wind causes large
  temperature variation.
• Nightime Cooling -- radiation cooling
• radiation inversions, thermal belts. Wind
  effects.
• Crop Protection -- orchard heaters, wind
  machines, sprinkling water.

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Fig. 3-11, p. 65
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Fig. 3-12, p. 65
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Fig. 3-13, p. 65
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Table 1, p. 66
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Fig. 3, p. 66
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Radiation Inversion

• At night the ground loses temperature quickly by
  radiation, this causes a radiation temperature
  inversion.
• The inversion is more pronounced on a dry clear
  calm night.

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Fig. 3-14, p. 67
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Fig. 3-15, p. 67
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Thermal Belt

• Oin mid-latitudes on dry cold clear nights a
  valley between high hills or mountains will have
  cold air slowly falling into basins or valleys.
  Thus the nearby hillsides will be warmer and are
  less likely to be below freezing. Thus orchards
  planted in this region about 100-300 meters above
  are less likely to freeze. Above this height
  there will be freezing temperatures.

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Fig. 3-16, p. 68
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Table 2, p. 69
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Fig. 3-17, p. 70
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Fig. 3-18, p. 70
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Fig. 3-19, p. 70
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The Controls of Temperature

• Latitude -- determines the intensity of solar
  radiation and the length of daylight hours
• Land and water distribution -- large amounts of
  land with its low specific heat leads to colder
  regions in winter and hotter regions in the
  summer. Water with its high specific heat
  moderates the temperature.

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The Controls of Temperature

• Ocean currents -- warm currents transports energy
  poleward, cold currents transport cold water
  equatorward.
• Elevation -- the lapse rate cools these regions.
  

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Fig. 3-20, p. 72
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Fig. 3-21, p. 72
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Air Temperature Data

• The greatest daily (diurnal) variation in
  temperatures is at the ground level.
• The largest range of variation is in the deserts.
  Less vapor and more radiation.
• Less change in very humid climates.
• Cities have urban heat island effect. Lot of
  asphalt which absorbs more radiation. More energy
  used all day and evening.

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Fig. 3-22, p. 73
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Fig. 3-23, p. 74
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Fig. 3-24, p. 74
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NORMAL CLIMATE VALUES

• Normal values of all climate parameters are based
  on a 30 year running average. This average is
  changed every decade.
• The present normal values are based on the years
  1971-2000.
• Normals are prepared for local cooperative
  weather stations, airports, state, and national
  averages.

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NORMAL CLIMATE VALUES

• Normal climate values are found for
• Temperatures avg,high,low and extremes.
• Annual Heating and Cooling Degree Days,
• Rainfall
• Snowfall
• Freeze Data
• Growing Degree Units

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Fig. 4, p. 75
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HEATING AND COOLING DEGREE DAYS

• Heating degree days is a quantity which
  approximates how much energy must be added to a
  structure each day to raise the temperature to a
  base level (usually 65oF).
• Mathematically this is
• HDD (65 - (Tmax Tmin)/2)x 1 day.
• Annual values are summed for 365 days
• HDD S (65 - (Tmax Tmin)/2).

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HEATING AND COOLING DEGREE DAYS

• Cooling degree days is a quantity which
  approximates how much energy must be removed from
  a structure each day to lower the temperature to
  a base level (usually 65oF). Mathematically
• CDD ((Tmax Tmin)/2) 65)x 1 day.
• Annual values are summed for 365 days
• CDD S ((Tmax Tmin)/2) 65)

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Fig. 3-25, p. 76
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Fig. 3-26, p. 76
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Growing Degree Days

• This is the number of Heating degree days for a
  plant to reach maturity from its emergence from
  the soil. The base temperature for that plant may
  be different.
• GDD SUM (( Tmax Tmin )/ 2 ) - Tbase
• Plants Base Temperature
  Turnips, Cabbage Peas 40 F
• Peppers 65 F
  

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Table 3-2, p. 76
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Air Temperature and Human Comfort

• ON CALM DAYS
• The human body looses heat primarily by
  radiation. It is replentished by absorbing
  radiation from the environment, the sun and by
  converting food into heat. (Metabolism)
• ON WINDY DAYS
• The body can lose a significant amount of heat by
  conduction and convection.

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Air Temperature and Human Comfort

• Sensible Temperature -- the temperature our body
  feels when the air is calm.
• A layer of warm air surrounds the body and allows
  us to perceive a temperature that is higher than
  the actual temperature.
• The temperature the body perceives when the wind
  is blowing is the WIND-CHILL INDEX.

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WIND-CHILL INDEX

• The wind-chill scale was revised in 2001 and
  gives the effective temperature the face would
  feel when a particular value of wind is blowing.
• For example If the wind is blowing at
• 15 mph when the temperature is 25 oF. The
  wind-chill temperature is 13 oF.
• 13 oF is the temperature the face would perceive
  if it was calm.

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Table 3-3, p. 77
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Table 3-4, p. 78
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HUMAN DISCOMFORT

• If an uncontrolled amount of heat is lost from
  the body such that the body is unable to
  replentish that heat than the body can
  experience
• Frostbite - freezing of the skin and extremities.
• Hypothermia - rapid physical and mental collapse
  accompanying by the lowering of the core body
  temperature.

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Fig. 5, p. 79
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Measuring Air Temperature

• The following instruments are used by Cooperative
  Observers in wooden shelters.
• These are louvered shelters painted white and
  instruments are located about 5 1/2 feet above
  the ground. They contain
• Liquid in Glass Thermometer
• Maximum Thermometer
• Minimum Thermometer

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Fig. 3-27, p. 80
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Fig. 3-28, p. 80
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Fig. 3-29, p. 80
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ASOS

• The wooden shelters are being replaced with
  Automated Surface Observation System. These are
  located at airports and at critical locations
  where the weather needs to be measured.
• Shown are precip, wind, max, min, and air
  temperature, visibility and humidity. They
  contain data loggers which use computers to
  record all data at regular intervals.

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Fig. 3-30, p. 81