Have you played a Frogger type of video game? Logs, lily pads, or rafts glide back and forth across the screen. To advance, you jump to each at just the right moment. That’s sort of what a glider does. A glider rides an air current that is rising. When that air current begins to sink, the glider must catch a ride on another rising air current. A glider stays aloft for long periods of time without an engine or propeller. By experience and instruments, pilots “see” the rivers of air they can use to gain altitude.

Those air currents exist because of high and low air pressure. The Sun warms the Earth. The Earth warms the air. Warm air always rises. It presses against cool air above. That leaves less pressure below.

If you are in a room that is getting crowded, where do you go? You go to a less crowded room. You might even rush to get there. Crowded cool air rushes into the less crowded area below. That is wind, a stream of rushing air.

But wind runs into obstacles. Mountains and valleys are in the way. Wind has to push up and over them. Wind also runs into other wind. Air currents colliding change their flow. They can also push up or rush below each other.

Glider pilots take advantage of changes in nearby air currents. But in a bigger picture, Earth has air currents that flow the same way most of the time. They begin at the equator (Earth’s middle line) and form six major wind belts. There are three belts in each hemisphere. In the Northern Hemisphere, these wind currents are called the polar easterlies, the westerlies, and the northeasterly trade winds. The winds in the Southern Hemisphere have the same names, but the wind currents flow in the opposite direction: the southeasterly trade winds, the westerlies, and the polar easterlies.