Francis Todd, age 12, of Asbury Park, N.J., for his question:
WHAT EXACTLY IS A CYCLONE?
A cyclone is a low pressure area in the atmosphere in which winds spiral inward. Sometimes a cyclone may cover an area that is half as large as the entire United States.
A tornado is a special, intense kind of cyclone. A tornado is usually only about 300 yards across.
All cyclones have two characteristics: the atmospheric pressure is lowest at the center and the winds spiral in toward the center.
In the Northern Hemisphere, the winds of a cyclone blow counterclockwise. In the Southern Hemisphere, they blow inward in a clockwise direction.
Cyclones move at speeds that will vary from 240 miles a day to 1,200 miles a day.
Some parts of the world have so many cyclones that their average atmospheric pressure is below that of the rest of the world. In the Aleutian low in the North Pacific Ocean, for example, the pressure is low most of the winter. Such a region may be called a semi-permanent low pressure center or a center of action.
Storms usually occur with cyclones. The falling atmospheric pressure usually is a fairly good indication that bad weather is coming.
But some cyclones do not bring bad weather because the kind of air also has much to do with the weather. If a cyclone forms in dry air, for example, there may not be any clouds.
A tropical cyclone is a severe kind of cyclone that occurs over warm ocean waters in the tropics. The cyclones are called hurricanes if they form in the West Indies, and typhoons if they form in the Pacific Ocean.
Hurricanes and typhoons may bring winds up to 180 miles an hour, terrific rains, violent thunder and lots of lightning.
A cyclonic storm often develops at a low pressure center.
Cyclones may be either warm core or cold core types.
Warm core cyclones are warmer at the center than near the edgers. They are fairly shallow and become weaker in the upper atmosphere. They often occur over specially warm land areas, such as the desert of the southwestern United States.
Cold core cyclones are coldest near the center and warmer near the edges. These cyclones may be very deep and are more intense several thousand feet in the air than they are at the surface of the earth.
A tornado is a rotating funnel cloud that extends downward from a mass of dark clouds. Some funnels do not reach the earth but others may strike the surface of the earth, withdraw into the dark clouds above and then dip down and strike the earth again.
In the United States, most funnel clouds of tornadoes tend to travel toward the northeast. Most last less than an hour and travel a distance of about 20 miles at a speed of 10 to 25 miles per hour.