As Different as Anabatic and Katabatic
Balloon pilots soon get on intimate terms with the wind. Most of us think of gusts and breezes, if at all, as having an unpredictable, capricious nature, but to a balloon pilot, they follow some rules of thumb. Once you become a balloon pilot, understanding these wind patterns will become almost second nature:
• Day, or anabatic, wind. Don’t sweat the Greek word. Anabatic simply means uphill, and anabatic winds are the wind currents that sometimes flow uphill when daytime sun heats a south-facing hillside or mountain slope that gets full sunshine. Because anabatic winds often flow in a different direction from higher-altitude winds, balloon pilots can use them to steer course, though with plenty of caution.
• Night, or katabatic, wind. Three guesses what this one means. That s right, katabatic winds are the downhill breezes that develop after sunset when the uphill anabatic winds lose energy. Katabatic winds can be deep and powerful, so pilots usually give those south-facing slopes a respectful margin.
By the Book
Ascending in a balloon is a matter of adding heat and buoyancy to the balloon by firing the propane burner, or by tapping into an anabatic wind. Descending is somewhat more passive, relying on gradual cooling of the air in the envelope or catching a ride on a descending wind. For a quick drop, the pilot can pull a cable in the gondola that vents hot air through the top of the envelope and guarantees that the balloon loses altitude quickly.
•Ridge waves. These can cause a bumpy ride, but they’re usually not hazardous. As their name implies, ridge waves are winds that are flowing perpendicular to a series of ridges; they can rise and descend in waves that resemble the gradual upward and downward pattern of sea swells.
•Valley wind. This is a fun wind pattern for most balloon pilots because it can allow them to turn on a dime, or on what passes for a dime in ballooning circles. Wind flowing in the deepest part of a valley tends to parallel the valley’s trough, and if the wind aloft is crossing the valley at a perpendicular angle, a descent into the valley wind can cause the balloon to turn sharply, a relatively spectacular maneuver in a sport where direction changes generally happen slowly.
There are other wind patterns, and the more experience a pilot has in ascending and descending, the more variations on the basic wind patterns he will add to his mental catalog.