|How do balloon pilots navigate around countries that forbid overflights? — LS, Ashland, OR
The speeds and directions of the winds vary considerably with altitude. For example, while surface winds near the sea blow toward shore on a hot summer day, high-altitude winds blow away from the shore at the same time, completing a huge circulation loop. Unlike a sailboat, which is at the mercy of the surface winds, a balloonist can adjust the balloon's altitude to search for winds heading in the desired direction. The balloonist makes these altitude adjustments by changing the balloon's weight and volume so that it sinks or rises.