Temperature Patterns in Space and Time

By examining a few sets of observations of temperature, we have noticed some patterns of variation in temperature, in both time and space:

1. From meteograms (which show weather conditions at one place at a series of times):
   
   
   1. Systematic variation in temperature over the course of a day
      1. generalized conceptual model: the daily temperature cycle
         • lowest temperatures near sunrise
         • temperature then rises to their highest values in mid afternoon (plus or minus an hour or two)
         • temperatures then generally decrease until near sunrise again
           
           
2. From global plots of temperature in the lower atmosphere:
   
   
   1. Global spatial pattern in temperature (that is, patterns in space—that is, from place to place)
      
      
      1. warmest in the tropics, decreases with increasing latitude (farther from the equator), coldest in polar regions
      2. the variation from lower to higher latitudes is relatively rapid across a relatively narrow zone in the midlatitudes
         1. this feature noteworthy enough to be given its own name: the polar front
         2. the polar front is not oriented straight east-to-west, but has "wobbles" in it
            • the wobbles define alternating "tongues" of relatively warmer and colder air
            • the warm tongues "protrude" from lower latitudes (where it is warm) toward higher latitudes
            • the cold tongues "protrude" from higher latitudes (where it is cold) toward lower latitudes
              
              
   2. Global temporal patterns in temperature (that is, patterns in time)
      
      
      1. Global temperature pattern varies with time of year
         1. the Northern Hemisphere is generally colder in February and warmer in August
         2. opposite is true in Southern Hemisphere
         3. in both hemispheres, the polar front shifts northward by August and back southward by February
            
            
      2. At midlatitudes, the temperature pattern shows systematic variations over several days
         1. the alternating "tongues" of relatively colder and warmer air outlined by the polar front (that is, wobbles in the polar front) shift eastward over periods of days both hemispheres
         2. as the alternating tongues pass over any particular place, that place experiences variations in temperature over periods of days
   
   

What accounts for these spatial and temporal patterns of temperature?

• Anonymous survey: Why does it cool off at night? (Part of the daily temperature cycle.)
  • Most responses: The sun goes down or is absent at night.
  • More generally, perhaps variations in temperature over the course of the day might have something to do with variations in solar radiation over the course of the day?
    
    
• Might some or all of the other temperature variations in space and time listed in Section II above also have something to do with variations in solar radiation, too?
  
  
• To find out:
  • Define, describe, or otherwise express solar radiation so that it can be quantified (so we can talk about variations in it):
    • Solar radiative intensity (or solar radiative flux): the rate at which solar radiative energy strikes a unit of surface area
  • Now ask, how does solar radiative intensity vary from time to time or place to place (and why)?
    • The "how does it vary" question, we'll begin exploring soon by looking at observations of solar radiation intensity
    • The "why does it vary" question we began to address with the flashlight-on-paper model (a physical model) of solar radiation striking the earth
      • We discovered reasons (mechanisms for) why the intensity of light from a flashlight striking a surface might vary:
        • We varied the angle between the light from the flashlight and the surface on which the the light shines. When that angle decreases, the light spreads out over the paper and becomes less concentrated, or less intense—a unit of area on the surface receives a smaller share of the (constant) total. That is, the intensity of the light decreases.
        • When the light source (the flashlight) moves away from the surface (while keeping the angle between the light and the surface the same), the light shining on the surface also spreads out and becomes less concentrated. That is, again the intensity of the light decreases.
      • Are there others that you can think of? At least one:
        • When the batteries in the flashlight begin to fade, so does the light source. For the same angle and distance, reducing the strength of the source of light reduces the intensity of light striking the surface.
        • Anything else?
  • To apply lessons learned from the physical model represented by the flashlight to the sun shining on the earth, we need to understand the following ideas:
    • Some geometric ideas, directions, etc.:
      • angle, down, zenith, perpendicular, normal, horizontal, horizon, zenith angle, sun angle (see Lab #2, Part I for some definitions)
      • solar radiation reaching at any part of the earth arrives basically parallel to solar radiation reaching any other part of the earth
        • because the distance between earth and sun is large compared to the size of either the earth or sun, only a tiny sliver of all of the solar radiation emitted by the sun reaches the earth, and all of the solar radiation in that sliver is travelling in virtually the same direction (parallel)
    • Consider what happens to solar radiation striking surfaces with various orientations at different locations at different times of the year
  • Then ask, do these variations correlate with variations in temperature that we observe?
    • We'll begin exploring that in lab soon.
  • Even if they do correlate (no guarantee!), we won't be done—there's still the question of why they might correlate. Does one physically cause the other, and if so, how?