Temperature

Science 123		Spring 2026
	Temperature Controls

Cycles in the Earth's orbit
- Milankovitch Cycles (Wikipedia)
  - eccentricity - ellipticity of the orbit
    - varies from nearly circular to elliptical: 7% elongation
    - different frequencies in the cycle - the major component of has period of 413,000 years,
      several lesser components have a combined average periodicity of 100,000 years
    - elliptical orbit means the earth-sun distance is not constant during a revolution
      - minimum distance (perihelion) occurs (currently) January 3
      - maximum distance (aphelion) occurs (currently) July 4
      - dates change on a periodic timescale of roughly 20,000 years
    - earth-sun distance largely determines the angular speed of the earth
      - shorter the distance, the greater the speed
      - each of the four seasons corresponds to 90 degrees of the total 360 degree rotation
      - result : the seasons have different lengths
        
        northern hemisphere season length (days)
        
        winter 89.00
        
        spring 92.75
        
        summer 93.65
        
        fall 89.85
  - obliquity - axis of rotation tilt
    - tilt varies from a minimum of 22.1 degrees to a maximum of 24.5 degrees
    - approximate period of 41,000 years to complete a cycle
  - precession - wobble of the tilt
    - change in the direction of the Earth's axis of rotation relative to the fixed stars
    - period of roughly 26,000 years
    - due to the tidal forces exerted by the sun and the moon on the solid Earth,
      associated with the fact that the Earth is not a perfect sphere but has an equatorial bulge
  - orbital inclination - change in the Earth's orbital plane angle
    - The angle of inclination of the Earth's orbit must be measured relative to another plane.
      One such plane is that defined by the Sun's equator. With that reference plane, the Earth's
      angle of inclination is approximately 7.2 degrees.
    - The inclination of Earth's orbit drifts up and down relative to its present orbit with a cycle having a period of about 70,000 years.
  - With all of these cycles, the amount of radiation energy does not change, but the distribution on the surface of the earth does
  - The response (the effect) to these cycles (climate variation) is greater than the cause.
    Researchers believe these cycle work in conjunction with "internal" climate fluctuations (El Nino, for example), perhaps causing "positive" feedback that amplifies the effect
- orbit of the Earth around the sun
  - 365.25 day cycle
  - seasons due to the tilt of the Earth
  - Decorah annual insolation curve
- rotation of the Earth on its axis
  - 24 hour cycle
  - temperature and radiation incoming versus outgoing

Temperature Controls - seasonal or yearly averages
- latitude
  "climate" is the Greek word for "latitude"
- land/sea distribution - heat capacity (specific heat) differences
  compare northern and southern hemisphere temperature contours
  - average surface temperature for January
  - average surface temperature for July
- ocean currents
  British Isles and Scandinavia - the Gulf Stream
- altitude

Temperature Controls - daily high and low
- cloud cover
- wind speed (mixing)
- water vapor
- temperature advection

northern hemisphere season	length (days)
winter	89.00
spring	92.75
summer	93.65
fall	89.85