Tornadoes...:

Dangerous and destructive

The changing climatic conditions have had a drastic impact on the global weather patterns with many different countries experiencing extreme weather conditions today. Sri Lanka too has had to face such drastic weather conditions in the form of cyclones and severe storms over the past years but the intensity of such occurrences seems to have increased lately.

The inclement weather we have been experiencing recently in the form of heavy showers leading to severe flooding , strong winds akin to gales and cyclones and even tornadoes as was witnessed in Mirigama,Tangalle and Matara recently speaks volumes for the effects of global warming.

 Some of you may have seen or come to know through the print and electronic media about the funnel-like formation of the tornado over the sea in the Mirigama area which caused massive damage to property. Perhaps, it is the first time that you even saw or heard of a destructive weather condition such as this.

Fortunately, the tornado like formation which was spotted off the coast of Matara which hit the land eventually as a strong whirli wind was not as destructive as a typical tornado witnessed in many other parts of the globe. Since many of you may not be familiar with these destructive tornadoes we like to enlighten you about them today.

Would you believe that even though scientists have researched for about 140 years and intensively for around 60 years about tornadoes, there are still aspects of them which remain a mystery due to the fact that meteorology is a relatively young science and the study of tornadoes is newer still ? Scientists still do not know the exact mechanisms by which most tornadoes form, and occasional tornadoes still strike without a tornado warning being issued. Research programmes, including field projects such as the VORTEX projects (Verification of the Origins of Rotation in Tornadoes Experiment), deployment of TOTO (the Totable Tornado Observatory), Doppler On Wheels (DOW), and dozens of other programmes, hope to solve many questions that still plague meteorologists. Solar storms similar to tornadoes have been recorded, but it is unknown how closely related they are to their terrestrial counterparts.

So, what exactly are tornadoes and how do they form? A tornado is a violently rotating column of funnel-like storm of strong winds. It is formed when warm air goes up at a rapid phase while the cold air is at the Earth’s surface. When winds from two different directions collide they start to spin. The drafts in the air make the funnel cloud go in a vertical direction. The funnel cloud then reaches the bottom of a cumulonimbus cloud. It is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud.When the funnel finally reaches the ground it is known as a tornado. They are often referred to as twisters or cyclones. Generally, meteorologists use the word cyclone in a wider sense, to name any closed, low pressure circulation. Tornadoes come in many shapes and sizes. However, typically it is in the form of a visible condensation funnel, with the narrow end of it touching the Earth, and is often encircled by a cloud of debris and dust.

There are various types of tornadoes and they include the landspout, multiple vortex tornado, and waterspout. Waterspouts are characterized by a spiralling funnel-shaped wind current, connecting to a large cumulus or cumulonimbus cloud. They are generally classified as non-supercellular tornadoes that develop over bodies of water. Other tornado-like phenomena that exist in nature include the gustnado, dust devil, fire whirls, and steam devil. Tornadoes can have a wide range of colours too , depending on the environment in which they form. Those that form in dry environments can be nearly invisible, marked only by swirling debris at the base of the funnel. Condensation funnels that pick up little or no debris can be gray to white. While traveling over a body of water (as a waterspout), tornadoes can turn very white or even blue. Slow-moving funnels, which ingest a considerable amount of debris and dirt, are usually darker, taking on the colour of debris.

Tornadoes in the Great Plains can turn red because of the reddish tint of the soil, and tornadoes in mountainous areas can travel over snow-covered ground, turning white. Lighting conditions are a major factor in the appearance of a tornado. A tornado which is “back-lit” (viewed with the sun behind it) appears very dark. The same tornado, viewed with the sun at the observer’s back, may appear gray or brilliant white. Tornadoes which occur near the time of sunset can be of many different colours, appearing in hues of yellow, orange, and pink.Do you know that tornadoes have been observed on every continent except Antarctica? However, the vast majority of tornadoes in the world occur in the so-called “Tornado Alley” region of the United States.But they can occur nearly anywhere in North America. They also occasionally occur in south-central and eastern Asia, northern and east-central South America, Southern Africa, northwestern and southeast Europe, western and southeastern Australia, and New Zealand.

The United States has the most tornadoes of any country, nearly four times more than estimated in all of Europe, excluding waterspouts. This is mostly due to the unique geography of the continent. As a large portion of these tornadoes form in an area of the central United States known as Tornado Alley, the United States averages about 1,200 tornadoes per year.

The Netherlands has the highest average number of recorded tornadoes per area of any country (more than 20, or 0.0013 per sq mi (0.00048 per km2), annually), followed by the UK (around 33, or 0.00035 per sq mi (0.00013 per km2), per year),]but most are small and cause minor damage. In absolute number of events, ignoring area, the UK experiences more tornadoes than any other European country, excluding waterspouts.Most tornadoes have wind speeds less than 110 miles per hour (177 km/h), are about 250 feet (76 m) across, and travel a few miles (several kilometres) before dissipating.

The most extreme tornadoes can attain wind speeds of more than 300 miles per hour (483 km/h), stretch more than two miles (3.2 km) across, and stay on the ground for dozens of miles (more than 100 km).Wondering how scientists manage to detect them and also measure their strength? Tornadoes can be detected before or as they occur through the use of Pulse-Doppler radar by recognising patterns in velocity and reflectivity data, such as hook echoes, as well as by the efforts of storm spotters. When it comes to rating the strength of tornadoes there are several scales for it. The Fujita scale rates tornadoes by damage caused and has been replaced in some countries by the updated Enhanced Fujita Scale.

An F0 or EF0 tornado, the weakest category, damages trees, but not substantial structures. An F5 or EF5 tornado, the strongest category, rips buildings off their foundations and can deform large skyscrapers.

The similar TORRO scale ranges from a T0 for extremely weak tornadoes to T11 for the most powerful known tornadoes.] Doppler radar data, photogrammetry, and ground swirl patterns (cycloidal marks) may also be analysed to determine intensity and assign a rating.

Initially, the tornado has a good source of warm, moist inflow to power it, so it grows until it reaches the “mature stage”. This can last anywhere from a few minutes to more than an hour, and during that time a tornado often causes the most damage, and in rare cases can be more than one mile (1.6 km) across.

As the tornado’s air supply is choked , the vortex begins to weaken, and become thin and rope-like. This is the “dissipating stage”; often lasting no more than a few minutes, after which the tornado fizzles. During this stage the shape of the tornado becomes highly influenced by the winds of the parent storm, and can be blown into fantastic patterns.

Even though the tornado is dissipating, it is still capable of causing damage. The storm is contracting into a rope-like tube and, like the ice skater who pulls her arms in to spin faster, winds can increase at this point.

So, if another tornado occurs do not risk going out to look at it because we are not familiar with the phenomena and we do not know how dangerous it could be. Today, most developed countries have a network of weather radars, which remains the main method of detecting signatures probably associated with tornadoes. In the United States and a few other countries, Doppler weather radar stations are used. 

Types

* A multiple-vortex tornado is a type of tornado in which two or more columns of spinning air rotate around a common centre. 

* A waterspout is defined by the National Weather Service as a tornado over water. However, researchers typically distinguish “fair weather” waterspouts from tornadic waterspouts. Fair weather waterspouts are less severe but far more common, and are similar to dust devils and landspouts.

* A landspout, or dust-tube tornado, is a tornado not associated with a mesocyclone. The name stems from their characterisation as a “fair weather waterspout on land”. Waterspouts and landspouts share many defining characteristics, including relative weakness, short lifespan, and a small, smooth condensation funnel which often does not reach the surface. 

* A gustnado, or gust front tornado, is a small, vertical swirl associated with a gust front or downburst.

* A dust devil resembles a tornado in that it is a vertical swirling column of air. However, they form under clear skies and are no stronger than the weakest tornadoes. They form when a strong convective updraft is formed near the ground on a hot day. If there is enough low level wind shear, the column of hot, rising air can develop a small cyclonic motion that can be seen near the ground. They are not considered tornadoes because they form during fair weather and are not associated with any clouds. However, they can, on occasion, result in major damage in arid areas.

* Small-scale, tornado-like circulations can occur near any intense surface heat source. Those that occur near intense wildfires are called fire whirls. They are not considered tornadoes. Fire whirls usually are not as strong as tornadoes associated with thunderstorms. They can, however, produce significant damage.[

 *A steam devil is a rotating updraft that involves steam or smoke. Steam devils are very rare. They most often form from smoke issuing from a power plant smokestack. Hot springs and deserts may also be suitable locations for a steam devil to form. The phenomenon can occur over water, when cold arctic air passes over relatively warm water.

Some deadly tornadoes ...

* The most record-breaking tornado in recorded history was the Tri-State Tornado, which roared through parts of Missouri, Illinois, and Indiana on March 18, 1925. It was likely an F5, though tornadoes were not ranked on any scale in that era. It holds records for the longest path length (219 miles, 352 km), the longest duration (about 3.5 hours), and fastest forward speed for a significant tornado (73 mph, 117 km/h) anywhere on Earth. In addition, it is the deadliest single tornado in United States history (695 dead).

* The deadliest tornado in world history was the Daultipur-Salturia Tornado in Bangladesh on April 26, 1989, which killed approximately 1300 people. Bangladesh has had at least 19 tornadoes in its history kill more than 100 people, almost half of the total in the rest of the world.

*The most extensive tornado outbreak on record was the Super Outbreak, which affected a large area of the central United States and extreme southern Ontario in Canada on April 3 and 4, 1974. This outbreak, which saw 148 tornadoes develop in 18 hours, included six of F5 intensity and twenty-four that peaked at F4 strength. Sixteen tornadoes were on the ground at the same time during its peak. More than 300 people, possibly as many as 330, were killed by tornadoes during this outbreak.

Safety measures

Though tornadoes can strike in an instant, there are precautions and preventive measures that people can take to increase the chances of surviving a tornado.

Find a sturdy shelter. If no sturdy shelter is nearby, getting low in a ditch is the next best option.Highway overpasses are one of the worst places to take shelter during tornadoes, as the constricted space can be subject to increased wind speed and funnelling of debris underneath the overpass.

 The safest place is the side or corner of an underground room opposite the tornado’s direction of approach (usually the northeast corner), or the central-most room on the lowest floor. Taking shelter in a basement, under a staircase, or under a sturdy piece of furniture such as a workbench further increases chances of survival.Tornadoes have been known to cross major rivers, climb mountains,affect valleys, and have damaged several city centres. As a general rule, no area is “safe” from tornadoes, though some areas are more susceptible than others.

Facts and pix: Internet

[Fast facts]

* The word tornado is an altered form of the Spanish word tronada, which means “thunderstorm”. This in turn was taken from the Latin tonare, meaning “to thunder.”

* A tornado is also commonly referred to as a “twister”, and is also sometimes referred to by the old-fashioned colloquial term cyclone.

*A tornado is “a violently rotating column of air, in contact with the ground, either pendant from a cumuliform cloud or underneath a cumuliform cloud, and often (but not always) visible as a funnel cloud.

* Tornadoes often begin as funnel clouds with no associated strongwinds at the surface, and not all funnel clouds evolve into tornadoes.

 * Most tornadoes produce strong winds at the surface while the visible funnel is still above the ground, so it is difficult to discern the difference between a funnel cloud and a tornado from a distance.

* Tornadoes kill an average of 179 people per year in Bangladesh, the most in the world. Other areas of the world that have frequent tornadoes include South Africa, parts of Argentina, Paraguay, and southern Brazil, as well as portions of Europe, Australia and New Zealand, and far eastern Asia.

* Occasionally, a single storm will produce more than one tornado, either simultaneously or in succession. Multiple tornadoes produced by the same storm cell are referred to as a “tornado family”.

* Tornadoes in the dissipating stage can resemble narrow tubes or ropes, and often curl or twist into complex shapes.

* In the United States, tornadoes are around 500 feet (150 m) across on average and travel on the ground for 5 miles (8.0 km).

However, there is a wide range of tornado sizes. Weak tornadoes, or strong yet dissipating tornadoes, can be exceedingly narrow, sometimes only a few feet or couple metres across. One tornado was reported to have a damage path only 7 feet (2 m) long.

*Most tornadoes occur in the late afternoon, when the bright sun can penetrate even the thickest clouds. Night-time tornadoes are often illuminated by frequent lightning.

* Tornadoes normally rotate cyclonically (when viewed from above, this is counterclockwise in the northern hemisphere and clockwise in the southern). 

Approximately one per cent of tornadoes rotate in an anticyclonic direction in the northern hemisphere. 

* Since many tornadoes are audible only when very near, sound is not reliable warning of a tornado.

* Tornadoes often develop from a class of thunderstorms known as supercells.