Prior Knowledge Required or Recommended:
- Become acquainted with global temperature patterns in the lower atmosphere (but well above the earth's surface), including
- significant features of the global pattern that are independent of land and ocean distributions
- aspects of the temperature pattern that vary over periods from days to a week
- aspects of the pattern that vary over the course of the year
- Definition and meaning of latitude. Ability to identify latitude lines on a global map.
- Definition and location of low latitudes, midlatitudes, and high latitudes.
Global Temperature Patterns in the Lower Atmosphere:
level over periods of several days.
Select a period of 5 days early February of this year, with an interval
between images of 6 hours. Click on the "Build Animation" button
and wait until the individual images in the animation load. (Once the animation
starts, you can stop and restart it , speed it up and slow it down, and stop
it and step through the images one at a time, using the appropriate control
- Identify and describe what you think are the three most clearly identifiable spatial features of the global temperature pattern.
How does each of these features change (if it changes) over the period
of several days shown?
- It is warmer at low latitudes (lots of red) and colder at high latitudes (lots of blue)
- Much of the transition from warm low latitudes to cold high latitudes occurs across a relatively narrow zone in (mostly) the middle latitudes, in both hemispheres.
- This feature is noteworthy enough to merit a name: the polar front
- It is defined as a relatively narrow zone across which the temperature varies rapidly from the warm side to the cold side, located (mostly) in the middle latitudes
- (More generally, a front is defined as a relatively narrow zone across which there is a rapid transition in temperature.)
- The polar front is not oriented straight east-to-west. Rather, it has a waves or "wobbles" in its position.
- Each "wobble" is visible because it is outlined by the polar front on the temperature map. Each wobble or wave can be thought of as a "tongue" of relatively warm (red) or relatively cold (blue) air, "protruding" toward the poles ("poleward") or toward the equator ("equatorward"). These warm and cold "tongues" of air alternate with each other.
6 hours, this time in early August within the last year. Click on the "Build
Animation" button again.
- The warm low latitudes and cold high latitudes don't change much, except in detail.
- However, the alternating "tongues" of warm and cold air tend to migrate eastward over a period of days, in both hemispheres
- As a result, some midlatitude locations tend to experience significant changes in temperature over a period of several days, first warmer (as a warm tongue passes by), then colder (as a cold tongue passes by)
- Low and high latitudes don't tend to experience such relatively large changes in temperature over periods of several days. The midlatitudes looks like where much of the interesting meteorological action is occuring!
What differences do you see between the February and August animations?
- The low latitudes remain generally warm, while the high latitudes remain cold. However, from August to February, the Northern Hemisphere high latitudes become noticeably colder while the Southern Hemisphere high latitudes become somewhat warmer. From February to August, the Southern Hemisphere high latitudes become somewhat colder while the Northern Hemisphere high latitudes become noticeably warmer.
- From August to February, the polar front shifts noticeably southward in both hemispheres, while from February to August it migrates back northward, in both hemispheres.
- In summer in the Northern Hemisphere, the tongues of warm and cold air outlined by the polar front shift far enough north that they miss much of North America and parts of Europe and Asia, especially the southern parts, so at that time of year there are fewer of the significant temperature changes over several days than during fall, winter, and spring.
Notes: An altitude of 10,000 ft. (about 3 km) above sea level is in the lower part of the troposphere (which is 36,000 ft. deep on the average) but is relatively far above the
earth's surface in most places. As a result, temperatures at this altitude tend not to be affected
directly by day to night variations in temperature at the earth's surface. It also does not exhibit the strong variations
in temperature with elevation that are typical of surface temperatures. However,
10,000 ft. is still low enough in the troposphere to represent the part of the
broad, global temperature pattern near the earth's surface associated with longer
term (e.g., a day to a year) temperature variations associated mainly with (1)
differences in heating due to variation in sun angle with latitude, and (2) transport
of heat by air motions.
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