FOG TALK

摘要

UNTIL YOU BECAME INVOLVED IN FLYING, YOU MAY NOT HAVE ever heard the term "dew point temperature," or "dew point" for short. But the more you fly, the more you'll realize the importance of this term. Think of the dew point as a kind of threshold for fog formation. When the air temperature drops to within 5 or so degrees Fahrenheit (or about 2 degrees Celsius) of the dew point, fog is likely. So, when you hear someone say that there's a close temperature-dew point "spread," you'll know what they mean. And when you hear that the temperature and dew point are "on top of each other," you'll know that the temperature and dew point are the same. At times like that, it's almost guaranteed that fog-or some form of precipitation-is present. Fog is basically a cloud on the ground, and it's one of the biggest adverse weather events you'll face as your flying career evolves. It can make surface visibilities low enough to prevent safe takeoffs and landings, and it can close even the largest, most well-equipped airports if visibilities go to zero. The National Weather Service defines fog in terms of yielding surface visibilities at or below 5/8 statute mile. Under visual flight rules (VFR)-the rules you'll fly under as a student pilot-you can't legally take off if the visibility drops to three statute miles or less.