Storm
Storms are one
of the destructive natural disasters. These are very many different types of
storms, ranging from minor to totally destructive. A storm is any disturbed
state of the atmosphere that affects Earth`s surface. Some types of Storms can
be described as extreme, severe or unique. They include thunderstorms,
mesoscale storms with their associated exceptional hailstorms and derechos,
tropical and extra-tropical storms and dust storms.
Storm Scale
The scale of weather systems varies greatly. Synoptic-scale or broad-scale weather occurs over wide areas (600 to 1500 miles/ 1000 to 2500 km) on time scales exceeding 12 hours. Meso-scale systems, ranging from around 50 miles (80km) to several hundred miles, are medium-size storms that range from squall lines and complexes of major thunderstorms to the very destructive tropical cyclones, known as hurricanes and typhoons in the northern hemisphere and cyclones in the Indian Ocean and Australia. Small-scale storms include localized thunderstorms. Extra-tropical cyclones are the largest of all and occur in the middle to high latitudes, sometimes spanning 1200 miles (2000 km). These synoptic-scale events which form over land or water in all seasons are usually characterized by a cold front that extends toward the equator for hundreds of miles. Extra-tropical cyclones come in two types. The first begins with a clash of warm and cold air and results in typical winter storms. The second forms when a tropical cyclone (hurricane, typhoon) leaves the tropics. Cooler air comes from the Polar Regions and clashes with the warmer mass of usually moist air to form a front commonly associated with destructive winds, flooding rains, hail and snow. Some of the “Great Storms” of Britain and Europe, such as the Great Storm of 1987, had their origins in Atlantic hurricanes that left the tropics. Subtropical storms usually form out of extra tropical storms but are unusual in having a warm core like a tropical cyclone. They also develop cyclones. As such they are considered hybrid storms.
Thunderstorms
Thunderstorms can be relatively small-scale events that vary from short-lived single cells to destructive super-cells. A thunderstorm, or electrical storm, is usually made up of one or more convective clouds with electrical discharge (lightning) that is heard as thunder.
There are three main types of thunderstorms:-
1. Single-cell,
2. Multi-cell, and
3. Super-cell.
A thunderstorm is said to be severe when it produces either hail with a diameter of 8/10 inch (2cm) or more when it hits the ground.
Lightning
Lightning causes an estimated 2500 fatalities a year worldwide. It is caused by a difference in electrical charge between the top and the bottom of a thunderhead. Why the bottom of the cloud becomes negatively charged is not fully understand, but it is probably related to the rapidly rising moist air. Lightning is discharged within the cloud or from the cloud to the ground when the charge overcomes the electrical resistance of the atmosphere. The lightning bolt superheats the surrounding air to temperature of around 50,000°F (27,800°C), hotter than the surface of the Sun, which is around 9,000°F (5000°C). The violet expansion of the surrounding air causes the sound of thunder. A single lightning flash, which is often no more than 1 inch (25mm) wide, carries an electric current as high as 3,00,000 amps, rather higher than domestic electrical wiring, which carries 10 to 20 amps. Well over 10,000 volts per yard or meter at ground level is sometimes reached during a storm.
Tornado
A Tornado is a tall, rapidly rotating column of air between 16 and 3,300 feet (5-1000m) in diameter that reaches the ground. It always starts with a funnel cloud, which usually hangs from the bass of a cumulonimbus or large cumulus cloud. It is the most destructive of all atmospheric phenomena on a local scale and is accompanied by a loud roar.
Dust and Sand Storms
A dust storm is caused by strong winds sweeping dust through air over extensive distances. The same winds can also carry sand, although the sand, being larger and heavier than, rarely rises above 50 feet (15m) and is mostly confined to the lowest 10 feet (3m). Major sand-dust Storms occur when prolonged drought or overgrazing causes the unprotected soil surface to dry out. Sand particles range in size from around 2 to 4 hundredths of an inch (0.6 – 1mm). Dust particles are smaller, in the nanometre to micrometer range.
