STORY
OF CYCLONES
Nikunja Bihari Sahu
Generally, October has been the month
of major atmospheric disturbances over the Bay of Bengal. This is the month when ravaging cyclones used
to form in the far seas and race miles across the waters with awesome speed to
unfold on the eastern Indian coast. While the Phailin struck Orissa on October
12, 2013, exactly a year later the Hudhud pounded the coastal districts of
Andhra Pradesh. This was followed by Titli that battered both the Odisha and Andhra
coast recently with heavy rain and gale winds. All these cyclones left behind a
trail of destruction by flattening thousands of mud and thatched houses and tearing
down road and communication links. But people are still unaware of the impacts
of the cyclone as evident from their reluctance to leave their ancestral homes
for relocation to safer places. Hence, an
understanding of cyclones is essential.
Origin
and Development
Given the vast devastation as
described above, the huge strength of the Cyclone can be easily understood. The
secret to its enormous prowess lies on a very basic property of Water. Water,
unlike all other liquids, has a high Latent Heat of Vaporization which is
essentially the heat released when Water in gaseous state changes its form to
liquid state as a result of Condensation. This value for Water is 2.5 x 106
J/kg in contrast to other liquids like Ammonia: 1.2 x 106 J/kg,
Propane: 4.2 x 105 J/kg, Ether: 3.9 x 105 J/kg, Carbon
Tetrachloride: 2.2 x 105
J/kg.
A Cyclone has its humble beginning as
a small twister over the far tropical seas as the sunrays heat up water surface
producing copious mass of warm and moist air. Sometimes, the moist air mass
lays stationary as a huge cloud over the sea surface without dispersing away.
This mass is highly unstable in nature that eventually becomes the cradle for
the Cyclone. Further heating causes streams of air rising up within the moist
air cloud creating a low pressure region. Surrounding mass of moist air rushes
towards the region that curves around due to the Earth’s spin. On reaching the
Low pressure centre, the mass of moist air rises upward and expands suddenly at
the higher atmosphere eventually getting cooled. The cooling triggers
condensation of millions of water vapours present in the moist air releasing a
large quantity of heat to the surrounding due to the high Latent heat of Water.
The heat that was released evaporates more amount of moist air from the sea
surface that further feeds and fuels the cyclic process and keeps it raging for
weeks. Under favourable conditions, the situation rapidly intensifies into a
sequence of events such as Depression, Deep Depression, Cyclonic storm and
Severe and Very Severe Cyclonic Storms with wind speeds reaching as high as 300
km/h.
Although the common name for such typical storms is Hurricanes, these
are named differently in different local regions such as Typhoons in the
Pacific and Cyclones in the Bay of Bengal. The word Cyclone is actually a Greek
word that means coil of a Snake which was first used by a British meteorologist
to refer to small depressions created over the Bay of Bengal.
Eventually,
the storm of the far seas heads towards the land and appears as killer winds for
the coastal population. But on reaching the land, it quickly subsides as no
moist air is available to keep its cyclic process going. Before that, it had wrecked
widespread damage to life and property.
Damage
and Destruction
Of the 23 cyclones in the last 300 years that
have each resulted in loss of more than 10,000 lives, 20 have been formed over
the Bay of Bengal and affected India. Almost 75% of the cyclones that have
killed more than 5,000 people during this time have been originated in this
region. This, despite the fact that only 7% of the World’s cyclones in a year
are generated in this part of the globe and also the fact that cyclones in the
Bay of Bengal and the Arabian Sea are of moderate intensity as compared to the
hurricanes raged in the Western Atlantic and Typhoons in the Western Pacific
regions. The Super cyclone of October
29, 1999 killed around 10,000 people in Odisha. One reason for the heavy
casualty in the past is that the Indian coastline is densely populated.
Weather Forecasting Has Come of Age
But
the situation has been drastically changed over the years owing to very
accurate weather forecasting as evident from the lesser death tolls of Phailin
(38), Hudhud (nearly 100) and Titli (62). Weather forecasting today has come of
age and the science has developed considerably enabling very accurate and reliable
prediction of cyclones facilitating relief and rescue operations. With the advent of the Space Age, it has now become
possible to directly see the cyclone with satellites and monitor its progress
in real time by satellite imagery allowing an early warning to be issued for
befitting response from the Govt. and the people. This can be appreciated from
the fact that while an early warning for the Super
cyclone of 1999 could be generated only 2 days earlier , the same for Phailin
was issued 4 days beforehand allowing sufficient time for the Govt. to mobilize its resources to carry out one of the biggest evacuation drives in Indian history .
Preparedness is Safety
Like many other natural calamities, a
Cyclone cannot be prevented with the present day technology. But timely warning
of the impending disaster with accurate meteorological inputs can bolster the
preparedness of the people to lessen the scale of devastation. The prime responsibility of the Govt. in the post
Cyclonic period is to restore power, road and communication links. As the cyclone abruptly releases vast amount of water on land collected
from the seas in its huge mass of moist air (often half the size of India), a
flash flood situation in the aftermath
of the cyclone is very likely and the Govt. must be prepared to face that. Finally,
we must go by the weather reports meticulously to keep ourselves prepared for
ensuring individual and collective safety.
Education Officer
Dhenkanal Science Centre
(National Council of Science Museums
Ministry of Culture, Govt. of India)
(Near
Rajbati)
Dhenkanal-759001
Phone: 8018708858
ODISHA
Further
Reading :
1.
Conquest
of Phailin by Nikunja Bihari Sahu (Science Horizon: Feb, 2014 issue).
2.
Hunt
of the Hudhud by Nikunja Bihari Sahu (Science Horizon: June, 2015 issue).
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