Tornado
Weather
and climate affects human life in many ways. That is why the American Geography
Professor Ellsworth Huntington said,
‘Our life can develop only in the manner it is decided by the Sun, the Air and
the Water. The logo of the India Meteorological Department also express the
same. It has the following words in the logo ‘Adityaat jaayate vruShTi:’
The
weather events that affect the life and property of mankind can be divided in
to several groups on the basis of space and time. These scales of
Meteorological events are:
- Planetary waves scale systems – These
are very large scale events affecting a large area of the globe almost
through out the year. Examples: General Air circulation, ocean currents
etc
- Synoptic Scale events – These are
large scale weather events that can affect an area of about 1000 to 600
kms and for a period of several weeks to several months. Indian summer
monsoon is the best example for this type of weather event.
- Macro scale events – These are
medium scale weather events that can affect an area of 100 to 1000 kms and
for a period of several days to several weeks. The monsoon depressions and
the tropical cyclones that for in the Indian seas can be cited as examples
of this kind of events.
- Meso scale events – These are small
scale weather events extending from 10 kms to 100 kms and can exist for a
few hours. The Andhis, Kalabhaishaakis, the winter time fog are some
examples.
- Micro scale events – These are very
very small events. They affect a very small area and for a very small
period of time. Tornodoes and hailstorms can be cited as examples for this
type of events.
Some
weather phenomenon, what ever be its scale can create havac in the society.
Tornodo is one such event. Though it is a micro scale event, it can affect greatly
in the areas of its occurrence. It will be a very bad experience to the people
who have experienced it.
Names of Tornodo
(Etymology)
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". It most likely reached its present form through a combination of
the Spanish tronada and tornar ("to turn"); however, this
may be a folk etymology. A tornado is also commonly referred to
as a "twister", and is also sometimes referred to by the
old-fashioned colloquial term cyclone. The term "cyclone" is used
as a synonym for "tornado" in the often-aired 1939 film The Wizard of Oz. The term
"twister" is also used in that film, along with being the title of
the 1996 tornado-related film Twister.
In Hindi it is called as ‘Bavander’ and in North East
India it is called as ‘Hathisnoora’ meaning the ‘trunk of an elephant”.
Formation
A tornado is a violently rotating column of air that
is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. Tornadoes come in many
shapes and sizes. But they are typically
in the form of a visible condensation
funnel, whose narrow end touches the earth and is often encircled by a cloud of debris and dust.
Most tornadoes have wind speeds less than 177 kilometer per hour. They have a diameter of about 76 meter.
They travel several kilometers before dissipating. The most extreme tornadoes (often seen in America) can
attain wind speeds of more than 483 kilommeter per hour.
It
all starts from a dark thunder cloud known as Cumulonimbus (Cb) cloud. A funnel shaped portion extends
from the base of the Cumulonimbus cloud downwards. It does not extend vertically downwards, but
like an elephant’s tusk it swings up and down while comming downwards. Before
the funnel touch the ground we can observe the whirl near the ground. Dust,
leaves and paper bits from the ground will go up with whirl. The funnel cloud
will touch the ground with a roar. Once
touches the ground then unimaginable events will happen. Roofs, human beings,
animals, light vehicles like cars, heavy vehicles like buses and lorries will
be lifted from the ground and thrown away. The description of the eye witnesses
is only the mode of understanding the disasters due to a tornodo.
Places of occurrence
Tornadoes
have been observed on every continent except Antarctica. However, the vast
majority of tornadoes occur in the Tornado
Alley region of the United
States, although 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. Tornadoes can be detected before or as they occur through
the use of Pulse-Doppler radar by recognizing patterns in velocity
and reflectivity data, such as hook
echoes or debris balls, as well as through the
efforts of storm spotters.
The
research on tornodoes in India is very less. H.N. Gupta and S.K. Gosh of India
Meteorological Department in 1978 have listed 35 tornodoes that have occured
during 1876 to 1978. Among them 26 tornodoes have occurred during March, April
and May months. They have mostly occurred in north east India. But they have
also mentioned about a tornodo occurred in Kerala and another that have occurred
in Tamil Nadu. In 1967 S.R. Saha of IMD have listed tornodoes that have
occurred during 1838 to 1950.
Definition and Description(shape)
As
mentioned earlier tornodo is a micro-scale
phenomenon. It has diameter of 150 to 600 meters. The speed of its movement is
roughly 30 to 45 kilometers per hour. It can travel to a distance of about 20
kilometers after touchdown. As per the records the distance of travel can be
500 meters to 500 kilometers. While moving the damaes due
to the tornodo is due to its wind component. This wind can be from 70 to 200 kilometers per hour. Tornodoes are
classified by two different methods on the basis of the wind speed associated
with the tornodo. They are (1) Fujita-Pearson Scale (2) TORRO Scale.
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 similarTORRO 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 may also be analyzed to determine intensity and assign a rating.
Various types
of tornadoes include the landspout, multiple vortex tornado, and waterspout. Some spiraling columns of
air frequently develop in tropical areas close to the equator, and are less common at high latitudes. Other tornado-like phenomena that
exist in nature include the gustnado, dust devil, fire whirls, and steam devil. Cumulonimbus clouds often
exhibits downbursts. But these downbursts are frequently confused with
tornadoes, though their action is dissimilar.
The
origin of a tornodo is from the circulation around an axis inside a thunder
cloud or cumulonimbus cloud. Such a circulation inside these type of clouds
happen because of the turbulance (updarfts and downdrafts) inside the cloud. But once a circulation inside a cumulonimbus
cloud starts then it will increase the turbulance also. The wind raising upward
raises as an anticyclonic whirl which creates a low pressure area inside the
cloud. This low pressure will increase the speed of the whirl wind. This
continues as a cycle and becomes a reason for the formation of a funnel cloud.
The presence of instability in the atmosphere is avery important factor for the
formation and development of tornodos. Tornodo normally form from a Super Cell.
Thunder shower, hail storm, strong wind are some weather events occur with a
tornodo. Tornodos form as a single
tornodo or a family of tornodos and move in a straight line.
Detction of tornado
by RADAR
Stout
and Huff identified a tornodo cloud by the Hook form of RADAR echo present in
the radar screen. But mostly the hook form of echo occurs only when a tornodo
forms from cumulonimbus cloud, hence there will be not much time for giving
tornodo warnings. But Doppler Weather Radar are very useful tools to detect the
formation and movement of a tornodo.
Electrical and sound effects of a tornodo
Blue,
bright and strong lightening is seen along with tornodo. Ball lightening is
also seen sometimes. Due to continous lightening the funnel cloud portion is
seen in yellow colour. As the funnel
portion of the cloud touches the ground we hear a roar. Tornodo give a sound of
one million bees.
Tornodos in India
The
Scientists of India Meteorological Department have done research on the
following tornodos.
|
Sl.No.
|
Tornodo’s
|
IMD Scientists
who have done the research
|
|
|
|
Date
|
Place of
occurrence
|
|
|
01
|
19.04.1963
|
Coochbihar
district and Golpara district of Assam
|
J. Nandy, A.K.
Mukharji
|
|
02
|
13.05.1967
|
Kanpur,
Uttarpradesh
|
Ranjit Singh
|
|
03
|
21.03.1969
|
Dimond Harbour,
Kolkatta
|
A.K. Mukharji,
Battacharya
|
|
04
|
07.11.1969
|
Kollur lake,
Krishna district, Andhrapradesh
|
Ranjit Singh
|
|
05
|
10.03.1975
|
Ludhiana,
Panjab
|
G.S.
Balachandra, M.L. Balachandra
|
|
06
|
17.05.1976
|
Balasur
district, Odisha
|
Ranjit Singh
|
|
07
|
17.03.1978
|
New Delhi
|
H.N. Gupta,
S.K. Gosh
|
|
08
|
16.04.1978
|
Kionjar, Odisha
|
A.K. Gosh
|
|
09
|
18.04.1978
|
Nadia district,
West Bengal
|
Ranjit Singh
|
|
10
|
17.04.1981
|
Kionjar
district, Odisha
|
Ranjit Singh
|
|
11
|
06.04.1980
|
Raepalli,
Tenali taluks of Guntur district, Andhrapradesh
|
K.
Veeraraghavan, S.K. Subramanian, V. Venkateswaralu, N.S. Bhaskara Rao
|
|
12
|
07.02.1984
|
Chandrapadi
(near Tarangampadi) Nagapatnam district and adjoining Karaikal region
|
N.S.
Rajagopalan, S.A.H. Albeez and three others
|
|
13
|
19.10.1987
|
Chapra, Bihar
|
P. Prasad
|
Damages
Tornodo
sucks all small objects over which the tunnel cloud portion of the tornado
moves. Small bits of paper, dry leaves, wooden pieces, dusct particles, small
fishes et are sucked like a pump, carried away with the rotating air coloumn
and thrown away several kilometers away. Tornodo’s funnel cloud portion
contains more or less empty space (like an eye of a tropical cyclone) inside
and rotatinf air coloumn outside as a wall. The very small inner space has a
cloud and weather less region. The outer wall region wind whirls going upwards.
The updraft may have a speed of 100 to 120 meters per second. Hence when a
tornado passes over a building or a house, due huge pressure gradient they are
broken to pieces, lifted up by the rotating air, carried away by the moving
tornado and thrown away at different places.
Due to the pressue difference inside a tornado and its outside even the
lids of bottles are flown away. The fur of sheeps and wings of birds are also
plucked and thrown away.
There
are some unbelievable incidents due to tornodos. A tornado which occurred at
New Delhi on 17.03.1978 has lifted a passenger bus with 70 passengers and
dropped it in a canal 20 meters away with its front portion down in the canal.
This tornado lasted for only three minutes. But due to this 28 people died, 700
injured and property worth rupees 10 millon was damaged.
A
tornado which formed in America 0n 30.05.1879 is considered as the most intense
tornado. Records say that this tornado has removed a iron bridge of weight 108
ton from its holdings, rolled it into a ball and dumped it in a nearby 2 meter
deep river.
The
tornado which occurred in Kionjar district of Odisha on 16.04.1978 was
accompanied with severe hailstorm. A hail of cricket ball size hit a farmer and
broke his hip, another hail hit his ox and broke its neck. On 17.04.1981, a
tornado formed in the same district killed 35 people and thousands of cattle.
The Chapra tornado of Bihar on 19.10.1987 killed 20, injured 517 people and
damaged 2773 houses. In Chapre town a two storey building at Roopganj Mohalla
was lifted from ground and broken to pieces. A
tornado which occurred on 07.02.1984 in Nagapatnam district. It was
first seen at Boodhanoor village then moved to Sankaranpandal, Arasangudi and
Nallathur. A bullock-cart of weight 15 tons was lifted to height of 150 feet
and was thrown away at a distance of 800 feet. One person died in Bhoodanoor
village due to wall collapse. This was reported as news item in the Indian
Express as a news item titled as The
Fury from the Sky.
Multiple vortex
A multiple-vortex
tornado is a type of tornado in which two or more columns of spinning air
rotate around a common center. A multi-vortex structure can occur in almost any
circulation, but is very often observed in intense tornadoes. These vortices
often create small areas of heavier damage along the main tornado
path. This is a distinct phenomenon from a satellite tornado, which
is a smaller tornado which forms very near a large, strong tornado contained
within the same mesocyclone. The satellite tornado may appear to
"orbit" the larger tornado (hence the name), giving the appearance of
one, large multi-vortex tornado. However, a satellite tornado is a distinct
circulation, and is much smaller than the main funnel.
Waterspout
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. They form at the bases
of cumulus congestus clouds over tropical and subtropical waters.
They have relatively weak winds, smooth laminar walls, and typically
travel very slowly. They occur most commonly in the Florida Keys and
in the northern Adriatic Sea. In contrast, tornadic waterspouts are
stronger tornadoes over water. They form over water similarly to mesocyclonic
tornadoes, or are stronger tornadoes which cross over water. Since they form
from severe thunderstorms and can be far more intense, faster, and
longer-lived than fair weather waterspouts, they are more dangerous. In
official tornado statistics, waterspouts are generally not counted unless they
affect land, though some European weather agencies count waterspouts and tornadoes
together.
Landspout
A landspout, or dust-tube
tornado, is a tornado not associated with a mesocyclone. The name stems from
their characterization 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. Landspouts also create a distinctively
laminar cloud of dust when they make contact with the ground, due to their
differing mechanics from true mesoform tornadoes. Though usually weaker than
classic tornadoes, they can produce strong winds which could cause serious
damage.
Similar circulations
Gustnado
A gustnado, or gust front
tornado, is a small, vertical swirl associated with a gust
front or downburst. Because they are not connected with a cloud base,
there is some debate as to whether or not gustnadoes are tornadoes. They are
formed when fast moving cold, dry outflow air from a thunderstorm is
blown through a mass of stationary, warm, moist air near the outflow boundary,
resulting in a "rolling" effect (often exemplified through
a roll cloud). If low level wind shear is strong enough, the rotation
can be turned vertically or diagonally and make contact with the ground. The
result is a gustnado. They usually cause small areas of heavier rotational
wind damage among areas of straight-line wind damage.
Dust devil
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.
Fire whirls and steam
devils
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, except in the rare case where they connect to a
pyro-cumulus or other cumuliform cloud above. 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's
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.
Intensity and damage
|
Tornado
rating classifications[21][57]
|
|||||
|
F0
EF0 |
F1
EF1 |
F2
EF2 |
F3
EF3 |
F4
EF4 |
F5
EF5 |
|
Weak
|
Strong
|
Violent
|
|||
|
Significant
|
|||||
|
Intense
|
|||||
The Fujita scale and the Enhanced
Fujita Scale rate tornadoes by damage caused. The Enhanced Fujita (EF) Scale
was an update to the older Fujita scale, by expert elicitation, using
engineered wind estimates and better damage descriptions. The EF Scale was
designed so that a tornado rated on the Fujita scale would receive the same
numerical rating, and was implemented starting in the United States in 2007. An
EF0 tornado will probably damage trees but not substantial structures, whereas
an EF5 tornado can rip buildings off their foundations leaving them bare and
even deform large skyscrapers. The similar TORRO scale ranges from a T0
for extremely weak tornadoes to T11 for the most powerful known
tornadoes.Doppler weather radar data, photogrammetry, and ground
swirl patterns (cycloidal marks) may also be analyzed to determine
intensity and award a rating.
Tornadoes vary in intensity
regardless of shape, size, and location, though strong tornadoes are typically
larger than weak tornadoes. The association with track length and duration also
varies, although longer track tornadoes tend to be stronger. In the case
of violent tornadoes, only a small portion of the path is of violent intensity,
most of the higher intensity from sub-vortices.
In the United States, 80% of
tornadoes are EF0 and EF1 (T0 through
T3) tornadoes. The rate of occurrence drops off quickly with increasing
strength—less than 1% are violent tornadoes (EF4, T8 or stronger). Outside
Tornado Alley, and North America in general, violent tornadoes are extremely
rare. This is apparently mostly due to the lesser number of tornadoes overall,
as research shows that tornado intensity distributions are fairly similar
worldwide. A few significant tornadoes occur annually in Europe, Asia, southern
Africa, and southeastern South America, respectively.
picture 1 : sound generation in tornodo
picture 2 : rope tornodo
picture 5 : wedge tornodo
picture 6: dust devi
