Background Lessons for Journey North

Global Climates and Seasons
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What Scientists Think

  • Did you notice that one of the rainiest regions is closest to the equator (tropical zone)? Where did you notice drier regions?
  • Did you notice that an orange rain band moves north from South America (the equator) to Central America and Mexico during the summer? Then it moves south during the winter?
Here's Why
Click here for a Climate Zone Chart

Sunlight is strongest (most direct) near the equator (tropics). The heated air rises and as it does, it cools. Cool air can't hold as much water as warm air, so low pressure (L) forms, creating clouds and thunderstorms.
This tropical rain belt runs along the equator and spreads out to about the Tropic of Cancer (23.5 north latitude) and Tropic of Capricorn (23.5 south latitude). But by the time it reaches about 30 degrees north and south latitude, it's cool enough to sink back to the surface. This creates high pressure (H), which means drier conditions. Most of the world's deserts are at these latitudes!

Many of our long-distant migrants, such as hummingbirds and monarchs, winter in the tropics or subtropics.

This circulation continues, moving away from the equator through the force of global winds.* Those of us living in temperate zones (from 30 to 60 degrees north and south latitudes) have varied precipitation (rain, snow, or both) in each of our four seasons. The poles, in turn, are very dry.

* Winds are created by unequal heating of air masses above land and the oceans. These circulate air globally. Learn More About Global Wind Systems.

Try This!

  • Look at a globe or map and find your state or hometown. What is its latitude? Which of the climate zones on the above "globe" and on the Climate Zone Chart do you live in?
  • Do the same thing for the winter and breeding habitats of the migrating animal(s) you're studying. Describe the climates in these two habitats. What does it tell you about your animal's basic needs or ability to survive?

What Causes Wet and Dry Seasons?
In many tropical and subtropical regions, rainfall varies much more than temperature does. Also, because the earth tilts, the direct sun rays, and in turn, the tropical rain belt, shifts from the northern to the southern tropics. So these areas experience just two seasons: a wet season and a dry season.

  • October to March
    Wet season in the southern tropics/subtropics
    Dry season in the northern tropics/subtropics (e.g., monarch winter habitat)
  • April to September
    Dry season in the southern tropics/subtropics
    Wet season in the northern tropics/subtropics

(Right on the equator, there are two wet and two dry seasons as the rain belt passes over twice a year, once moving north and once moving south.)

Related Links

  • Also learn about global temperatures >>
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