Storm

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.

Thunderstorm

Thunderstorm

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 (lightening) that is heard as thunder. Cumulus and cumulonimbus are convective clouds form when strong warmer air currents more upward (as updrafts), carrying moisture high into colder layers of the atmosphere. Their bases can range in height from 1000 to 10000 feet (300- 3000 m) and the cloud “tower” can rise as high as 59000 feet (18000m). These thunderheads are often indicators of unstable air.

Nearly 2000 thunderstorms producing some 100 lightening flashes per second are occurring worldwide at any one time, most frequently in rain forested areas. In temperature regions either side of the equator they are more common in spring and summer.

 

There are three main types of Thunderstorms:

1. Single-cell thunderstorm,

2. Multi-cell thunderstorm, and

3. Super-cell thunderstorm.

 

 

Single-Cell Thunderstorm

A single cell thunderstorm forms when the wind speed and direction of the updraft (the wind shear) have relatively little effect, so the storm remains poorly organized and short – lived. The downdraft of the cool air, which brings some rain, cuts off the storm growth cycle, so the storm are typically for no more than an hour.

 

Multi-Cell Thunderstorm

Multi cell thunderstorm form when the wind shear is of sufficient strength and persistence to increase the storm`s growth cycle, giving it a more organized structure and a longer lifetime. They are made up of several cells one after another, leading 30 to 40 minutes each. Severe multi cell storms might have several cells operating at any one time. Squall lines form sometimes through convective updrafts from an orderly line up of multi cell that can have gust fronts. Associated with squall lines are heavy rain and hail and damaging winds, particularly the derechos of North America. The term “derecho”, from the Spanish word for “direct” is used to describe straight – line winds, in comparison to the turning or rotating winds of a tornado. Derechos are very widespread, occurring over areas hundreds of miles long and more than 100 miles (160 km) across.

 

Super-Cell Thunderstorm

Super cells, although rare, are the most severe of all thunderstorms and are responsible for a remarkably high percentage of severe weather events, especially tornadoes, extremely large hail, and derechos. A super cell is caused by a persistent rotating updraft or meso cyclone. It can form from a multi cell storm when there is sufficient directional wind shear to skew the updraft and so allow the cool downdraft to flow free of it. As a result, the main updraft can strengthen and start rotating. Super cell fronts can take the form of a line of cumulus clouds that usually step up toward the tallest clouds near the main storm or that produce gust fronts that form from the winds associated with downdrafts. Super cell storms can last several hours and spawn tornadoes, create wall clouds and drop very large hail (in rare cases up to 4 inches/ 10 cm across). The meso cyclone, the storm scale region of rotation, usually measures around 2 to 6 miles (3 – 10 km) in diameter.

 

Thunderstorm severity

A thunderstorm is said to be severe when it produces either hail with a diameter of 8/10 inch (2 cm) or more when it hits the ground, wind gusts at the ground of 56 miles per hour heavy rain with possible flash flooding. The size of a hailstone depends on the strength of the updraft. The smallest hailstone requires an up-draft of at least 22 mph (36 km/h), those of golf ball size (1 ¾ inch / 44 mm diameter) require updrafts of around 55 mph (88 km/h) and the larger, and softball size hail needs updrafts of over 100 mph (160 km/h)

 

In the United States, when weather warnings are issued, familiar objects are used for comparison:-

1. Pea: 6mm

2. Marble or Mothball: 13mm

3. Penny or Dime: 19mm

4. Nickel: 22mm

5. Quarter: 25mm

6. Half Dollar: 32mm

7. Walnut or Ping-pong ball: 38mm

8. Golf ball: 44mm

9. Hen`s egg: 51mm

10. Tennis ball: 64mm

11. Baseball: 70mm

12. Tea cup: 76mm

13. Grape fruit: 102mm

14. Soft ball: 114mm.

 

Precautions during Thunderstorm

1. Listen to weather updates for warnings about the severity of the storm and whether hail is forecast.

2. If possible, remain indoors and keep away from windows, they can be shattered by large hail.

3. In the case of hail, close any window covers to reduce the risk of broken glass.

4. Avoid contact with telephones and other electrical appliances (unplug them), metal pipes, and electrical wires- lightening can and does travel along these.

5. If you are in your car, shelter in it with the windows up and unplug any chargers.

6. If hail is forecast, park your vehicle in a garage or under shelter. Hail damage can be costly.

7. If no shelter is nearby, stay away from trees, poles and metal objects such as fences, sports equipment or bikes. Away from open ground, but if it is unavoidable, then try to minimize body contact with the ground by crouching with your arms together. Stay away from bodies of water, like lakes or the ocean, which can conduct the electricity.

Sand And Dust Storm

Sand and Dust Storm

Parts of the world experience sand and dust storms, the Sahara Desert are an obvious example. But changing climate, increasing cultivation and overgrazing are increasing the incidence of sand and dust storms worldwide. Many cities, notably Beijing, China are regularly blanketed by choking dust that reduces visibility, clogs machinery, contaminates food and even kills.

There are five ingredients essential to the development of sand and dust storms:-

1. A source of fine dust or sand particles that can be lifted and transported,

2. Winds of sufficient force and velocity in a direction that will raise and carry the particles,

3. Weather conditions that can form convection cells of sufficient energy to develop the winds,

4. Landform features that help concentrate the force of the wind, and

5. Exposed soil surfaces susceptible to wind erosion, such as in deserts and over-cropped and disturbed semi-arid lands.

Characteristics of Dust Storms

A dust storm usually arises suddenly in the form of an advancing dust wall that may be many miles long and a thousand yards (1 km) or so deep. Ahead of the dust wall the air is very hot and the wind is light.

The US weather watches classify dust storms according to visibility:-

1. If blowing dust reduces visibility to between 5/8 and 5/16 mile (1.0 and 0.5 km), a dust storm is reported.

2. If the visibility is reduced to below 5/16 mile (500 m), it is reported as severe.

Dust storm winds can also be associated with thunderstorm outflows and gust fronts. Vertical downdrafts of chilled air during thunderstorms may locally strike the ground with velocities of 25 to 50 miles per hour (40 – 80 km/h). Under such conditions, fine particles may also be swept upward hundreds or thousands of feet into the air. The average height of a dust storm is 3,000 to 6,000 feet (900 – 1800m) and stronger storms have dust to 8,000 – 10,000 feet (2400- 3000 m). Haze and dust from extreme storms have been documented as high as 35,000 to 40,000 feet (10,700 – 12,200 m). While these are often shorter, lived than wind-forced dust storms, they can be quite intense, with an impressive leading edge, called a dust wall. Dust storms on Mars can reach 130,000 feet (40 km) high.

North Africa is a source of dust that is transported to Southern Europe, and the Sahara region is the main global source of wind- blown dust. About 10 million tons of dust particles can be transported and brought to Britain from the Sahara Desert during a Single dust storm. Arid and semi-arid regions around the Arabian Sea are other significant sources of dust. India, Pakistan, Iran and the Arabian Peninsula Contribute to Arabian Sea dust deposition and dust from China contributes to sediment in the Pacific Ocean. Storms regularly occur in the arid and semi-arid regions of the Earth, particularly in subtropical latitudes. Sand and dust storms are natural events that have occurred throughout Earth`s history. The geological record shows that changes in the growth and decline of desert sand surfaces over time are characterized by evidence of sand and dust storms, making the storms useful indicators of climate during past eras.

In recent times the action of humans has greatly increased the desert sand surface area through poor land management, which has destabilized the desert margins. Such actions include overgrazing vegetation beyond its carrying capacity, gathering firewood for fuel and clearing to plant crops. Corresponding to these areas of accelerated desertification is an increase in the severity and frequency of the many major sand- dust storms throughout several regions of the world. As in past geological eras, they could be considered indicators of current climate change.

 

Precautions to take during a Sand and Dust Storm:-

1. During threatening weather, listen for dust storm warnings on radio or television.

2. Dust can cause respiratory failure, so stay indoors with windows and doors closed.

3. If you are driving pull over as far as possible when you see dust blowing across or approaching a roadway, stop and drivers might try to follow you and run into you.

4. If there is nowhere you can pull over, then proceed at a safe speed, turn on your lights and sound your horn occasionally. Use the painted centre line to help guide you look for a safe place to pull off the roadway. Never stop on the road.