|
|
|
| Current Issue |
|
|
| Resources |
|
|
|
From the Gods of Chaos
| Article
# : |
17078 |
|
|
Section : |
NATURAL SCIENCE
|
| Issue
Date : |
8 / 1990 |
1,304 Words |
| Author
: |
Nancy C. Knight
Nancy C. Knight is a visiting scientist at the National Center
for Atmospheric Research (NCAR) in Boulder, Colorado. She has
spent a lifetime studying hail worldwide |
Hailstorms severe enough to damage crops and property and, in rare cases, to endanger lives occur in many parts of the world. In the Northern Hemisphere, they are most frequent over the high plains east of the Rocky Mountains in Canada and the United States. They often arise east of the Andes in South America; in the Po Valley and the northeastern corner of Italy; in southwestern France and northern Greece; in Serbia, Bohemia, Bulgaria; and in many of the southern republics of the Soviet Union, particularly Georgia, Moldavia, and Azerbaijan. They are also reported from India, Pakistan, and many provinces of China.
Severe storms likely to produce hail require unstable atmospheric conditions, which are created when a layer of cold, dry air lies above a layer of warm, moist air. These conditions often prevail in the late spring and early summer on the leeward side of mountain ranges. Hailstorms are frequent in the lee of the Rockies, where warm, moist surface air from the Gulf of Mexico meets cold, dry air moving eastward across the mountains. Similar conditions prevail to the lee of the Andes and the Caucasus. In many areas, storms producing hail that falls to the ground may not occur more than two or three times a year, although hail has been reported on as many as 200 days a year in Kericho and the Nandi Hills in northwestern Kenya.
Hailstorms are of great economic importance in many areas because of the value of the crops they destroy. It is ironic that those places subject to hail are often areas where abundant rain, sunshine, and warm temperatures produce such valuable crops as grapes, tobacco, tea, and citrus. These crops are vulnerable to damage from even small hailstones, which bruise their fruit or leaves. In fact, very large hailstones do less damage to crops than small ones since they are fewer in number and - because they often fall farther from the storm - are usually unaccompanied by wind. Strong winds may carry small stones with them, efficiently scything plants to the ground. Larger stones often fall straight down, doing less damage to crops although more to property.
A hailstone's size is primarily a function of the severity of the storm that produces it, in that the final size reflects the strength of the storm's updraft, a rising current of air. Hailstones grow by capturing and freezing water drops rising in the updraft, and as long as the speed of the updraft exceeds the speed at which the hailstones fall through it, the stones are held aloft and continue to grow. Secondary factors in hailstone size are the distance they must fall before hitting the ground and the temperature of the air through which
...
Read Full Article
Look for this article in Ask.com
|
|
