reinforce this area of the ship. The storm finally abated as the Eisenhower reached the coast of Norway.

THUNDERSTORMS, LIGHTNING, WATER SPOUTS

Weather conditions are key to understanding how extreme waves on the surface of the ocean form and propagate. The next several pages summarize some of the principal types of weather likely to be encountered at sea.

Thunderstorms occur when there are strong upward currents of warm air with considerable water vapor. The air rises to an altitude of a few miles to as much as 12 miles, forming the distinctive cumulonimbus cloud rising to an “anvil” top. The anvil appearance is caused by the high-velocity winds in the upper atmosphere blowing the tops away from the updraft. The rising air reaches an altitude at which the temperature is well below freezing, causing small particles of ice to form. In the center of this turbulent region of swirling air and abrupt temperature, electrons are stripped from some atoms and are swept to other parts of the cloud, leaving some portions negatively charged and other parts positively charged. When the potential difference has built to a high enough value to break down the resistance of the air, a lightning flash occurs. Thunder is the sound of lightning; the rapid passage through the air of the lightning flash’s huge electrical current heats air to a high temperature and creates a shock wave we know as thunder.

Waterspouts are caused by a strong updraft over a large body of water. They are more likely to occur in tropical latitudes where the water temperature is at least 27 degrees Celsius (80 degrees Fahrenheit) than in higher latitudes. Lower atmospheric pressure within the center of the rotating column of air sucks water from the surface of the sea and also condenses water vapor in the swirling air. A waterspout is similar to a tornado but occurs over water and can be as high as 1,500 feet and last as long as half an hour. Waterspouts occur occasionally in the Pacific near Southern California as well. One or two per year are observed here, usually close to land. While they can be damaging to small craft, it is usually possible to avoid them. However, in December 1969, a waterspout struck the Huntington Beach, California, pier, destroying the head of the pier, injuring 17 people, and killing three.7



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