Freak monsoon - cyclones -flood -drought –hurricane and ongoing efforts on climate change research
Monsoon is
traditionally defined as a seasonal reversing wind accompanied by
corresponding changes in precipitation, but is now used to describe
seasonal changes in atmospheric circulation and precipitation
associated with the asymmetric heating of land and sea. Usually, the term
monsoon is used to refer to the rainy phase of a seasonally changing
pattern, although technically there is also a dry phase. The term is sometimes
incorrectly used for locally heavy but short-term rains, although these
rains meet the dictionary definition of monsoon.
The
major monsoon systems of the world consist of the West African and Asia-Australian
monsoons. The inclusion of the North and South
American monsoons with incomplete wind reversal has been debated. The term
was first used in English in British India and neighboring countries
to refer to the big seasonal winds blowing from the Bay of
Bengal and Arabian Sea in the southwest bringing
heavy rainfall to the area.
Strengthening of the Asian
monsoon has been linked to the uplift of the Tibetan Plateau after the
collision of the Indian sub-continent and Asia around 50 million
years ago. Because of studies of records from the Arabian
Sea and that of the wind-blown dust in the Loess
Plateau of China, many geologists believe the monsoon first became
strong around 8 million years ago. More recently, studies of plant fossils in
China and new long-duration sediment records from the South
China Sea led to a timing of the monsoon beginning 15–20 million years ago
and linked to early Tibetan uplift. Testing of this hypothesis awaits deep
ocean sampling by the Integrated Ocean Drilling Program. The monsoon has
varied significantly in strength since this time, largely linked to global
climate change, especially the cycle of the Pleistocene ice
ages. A study of marine plankton suggested that the Indian Monsoon
strengthened around 5 million years ago. Then, during ice periods, the sea level
fell and the Indonesian Seaway closed. When this happened, cold
waters in the Pacific were impeded from flowing into the Indian Ocean. It is
believed that the resulting increase in sea surface temperatures in the Indian
Ocean increased the intensity of monsoons.
The Leeuwin
Current is a warm ocean current which flows southwards
near the western coast of Australia. It rounds Cape Leeuwin to
enter the waters south of Australia where its influence extends as far
as Tasmania. The West Australian Current and Southern Australian
Countercurrent, which are produced by the West Wind Drift on the
southern Indian Ocean and at Tasmania, respectively, flow in the opposite
direction, producing one of the most interesting oceanic current systems in the
world.
The weakening of the Leeuwin Current (LC)
would have an effect on the sea surface temperature (SST) field in
the Indian Ocean, as the Indonesian through flow generally warms the Indian
Ocean. Thus these five intervals could probably be those of considerable lowering
of SST in the Indian Ocean and would have influenced Indian monsoon intensity.
During the weak LC, there is the possibility of reduced intensity of the Indian
winter monsoon and strong summer monsoon, because of change in the Indian Ocean
dipole due to reduction in net heat input to the Indian Ocean through the
Indonesian through flow. Thus a better understanding of the possible links
between El Niño, Western Pacific Warm Pool, Indonesian Through flow,
wind pattern off western Australia, and ice volume expansion and contraction
can be obtained by studying the behaviour of the LC during Quaternary at close
stratigraphic intervals.
Strength of impact
The
impact of monsoon on the local weather is different from place to place. In
some places there is just a likelihood of having a little more or less rain. In
other places, quasi semi-deserts are turned into vivid green grasslands where
all sorts of plants and crops can flourish.
The
Indian Monsoon turns large parts of India from a kind of semi-desert into green
lands. In places like India it is crucial for farmers to have the right timing
for putting the seeds on the fields, as it is essential to use all the rain
that is available for growing crops.
Process
Monsoons are large-scale sea
breezes which occur when the temperature on land is significantly
warmer or cooler than the temperature of the ocean. These temperature
imbalances happen because oceans and land absorb heat in different ways. Over
oceans, the air temperature remains relatively stable for two reasons: water
has a relatively high heat capacity (3.9 to 4.2 J g−1 K−1), and
because both conduction and convection will equilibrate a
hot or cold surface with deeper water (up to 50 metres). In contrast, dirt,
sand, and rocks have lower heat capacities (0.19 to 0.35 J g−1K−1), and
they can only transmit heat into the earth by conduction and not by convection.
Therefore, bodies of water stay at a more even temperature, while land
temperature are more variable.
During warmer months sunlight heats the surfaces of
both land and oceans, but land temperatures rise more quickly. As the land's
surface becomes warmer, the air above it expands and an area of low
pressure develops. Meanwhile, the ocean remains at a lower temperature
than the land, and the air above it retains a higher pressure. This difference
in pressure causes sea breezes to blow from the ocean to the land,
bringing moist air inland. This moist air rises to a higher altitude over land
and then it flows back toward the ocean (thus completing the cycle). However,
when the air rises, and while it is still over the land, the air cools.
This decreases the air's ability to hold water, and this
causes precipitation over the land. This is why summer monsoons cause
so much rain over land.
In the colder months, the cycle is reversed. Then
the land cools faster than the oceans and the air over the land has higher
pressure than air over the ocean. This causes the air over the land to flow to
the ocean. When humid air rises over the ocean, it cools, and this causes precipitation
over the oceans. (The cool air then flows towards the land to complete the
cycle)
Most summer monsoons have a dominant westerly
component and a strong tendency to ascend and produce copious amounts of rain
(because of the condensation of water vapor in the rising air). The intensity
and duration, however, are not uniform from year to year. Winter monsoons, by
contrast, have a dominant easterly component and a strong tendency to diverge,
subside and cause drought.
Similar rainfall is caused when moist
ocean air is lifted upwards by mountains, surface
heating, convergence at the surface, divergence aloft, or from
storm-produced outflows at the surface. However the lifting occurs, the
air cools due to expansion in lower pressure, and this produces condensation.
Global
monsoon
Africa (West African and Southeast
African)
The monsoon of western Sub-Saharan
Africa is the result of the seasonal shifts of the Intertropical
Convergence Zone (ITCZ) and the great seasonal temperature and humidity differences
between the Sahara and the equatorial Atlantic Ocean. It
migrates northward from the equatorial Atlantic in February, reaches western
Africa on or near June 22, then moves back to the south by October. The
dry, northeasterly trade winds, and their more extreme form,
the harmattan, are interrupted by the northern shift in
the ITCZ and resultant southerly, rain-bearing winds during the
summer. The semiarid Sahel and Sudan depend upon this
pattern for most of their precipitation.
North America
The North
American monsoon (NAM)
occurs from late June or early July into September, originating over Mexico and
spreading into the southwest United States by mid-July. It affects Mexico along
the Sierra Madre Occidental as well as Arizona, New Mexico, Nevada, Utah,
Colorado, West Texas and California. It pushes as far west as
the Peninsular Ranges and Transverse
Ranges of Southern California, but rarely reaches the coastal strip
(a wall of desert thunderstorms only a half-hour's drive away is a common
summer sight from the sunny skies along the coast during the monsoon). The
North American monsoon is known to many as the Summer, Southwest,
Mexican or Arizona monsoon. It is also
sometimes called the Desert
monsoon as large parts of the affected area are
the Mojaveand Sonoran deserts. However, it is debatable whether
the North and South American weather patterns with
incomplete wind reversal should be counted as true monsoons.
Asia
The Asian monsoons may be classified into a few
sub-systems, such as the Indian Subcontinental Monsoon which affects the Indian
subcontinent and surrounding regions including Nepal, and the East Asian
Monsoon which affects southern China, Taiwan, Korea and
parts of Japan.
Southwest monsoon
The southwestern summer monsoons occur from July
through September. The Thar Desert and adjoining areas of the
northern and central Indian subcontinent heat up considerably during the hot
summers. This causes a low pressure area over the northern and central Indian
subcontinent. To fill this void, the moisture-laden winds from the Indian
Ocean rush into the subcontinent. These winds, rich in moisture, are drawn
towards the Himalayas. The Himalayas act like a high wall, blocking the
winds from passing into Central Asia, and forcing them to rise. As the
clouds rise their temperature drops and precipitation occurs. Some
areas of the subcontinent receive up to 10,000 mm (390 in) of rain
annually.
The southwest monsoon is generally expected to
begin around the beginning of June and fade away by the end of September. The
moisture-laden winds on reaching the southernmost point of the Indian
Peninsula, due to its topography, become divided into two parts: the Arabian Sea Branch and the Bay of Bengal Branch.
The Arabian
Sea Branch of the Southwest Monsoon first hits the Western
Ghats of the coastal state of Kerala, India, thus making this area
the first state in India to receive rain from the Southwest Monsoon. This
branch of the monsoon moves northwards along the Western Ghats (Konkan and Goa)
with precipitation on coastal areas, west of the Western Ghats. The eastern
areas of the Western Ghats do not receive much rain from this monsoon as the
wind does not cross the Western Ghats.
The Bay
of Bengal Branch of Southwest Monsoon flows over the Bay of Bengal heading
towards North-East India and Bengal, picking up more moisture
from the Bay of Bengal. The winds arrive at the Eastern
Himalayas with large amounts of rain. Mawsynram, situated on the
southern slopes of the Khasi Hills in Meghalaya, India, is one of the
wettest places on Earth. After the arrival at the Eastern Himalayas, the winds
turns towards the west, travelling over the Indo-Gangetic
Plain at a rate of roughly 1–2 weeks per state, pouring rain all
along its way. June 1 is regarded as the date of onset of the monsoon in India,
as indicated by the arrival of the monsoon in the southernmost state of Kerala.
The monsoon accounts for nearly 80% of the rainfall
in India. Indian agriculture (which accounts for 25% of the GDP and
employs 70% of the population) is heavily dependent on the rains, for growing
crops especially like cotton, rice, oilseeds and coarse
grains. A delay of a few days in the arrival of the monsoon can badly affect
the economy, as evidenced in the numerous droughts in India in the 1990s.
The monsoon is widely welcomed and appreciated by
city-dwellers as well, for it provides relief from the climax of summer heat in
June. However, the roads take a battering every year. Often houses and
streets are waterlogged and slums are flooded despite drainage
systems. A lack of city infrastructure coupled with changing climate patterns
causes severe economic loss including damage to property and loss of lives, as
evidenced in the 2005 flooding in Mumbai that brought the city to a standstill. Bangladesh and
certain regions of India like Assam and West Bengal, also
frequently experience heavy floods during this season. Recently,
areas in India that used to receive scanty rainfall throughout the year, like
the Thar Desert, have surprisingly ended up receiving floods due to the
prolonged monsoon season.
The influence of the Southwest Monsoon is felt as
far north as in China's Xinjiang. It is estimated that about 70% of all
precipitation in the central part of the Tian Shan Mountains falls during
the three summer months, when the region is under the monsoon influence; about
70% of that is directly of "cyclonic" (i.e., monsoon-driven) origin
(as opposed to "local convection")
Northeast monsoon
Around September, with the sun fast retreating
south, the northern land mass of the Indian subcontinent begins to cool off
rapidly. With this air pressure begins to build over northern India, the Indian
Ocean and its surrounding atmosphere still holds its heat. This causes cold
wind to sweep down from the Himalayas and Indo-Gangetic
Plain towards the vast spans of the Indian Ocean south of
the Deccan peninsula. This is known as the Northeast Monsoon or
Retreating Monsoon.
While travelling towards the Indian Ocean, the dry
cold wind picks up some moisture from the Bay of Bengal and pours it
over peninsular India and parts of Sri Lanka. Cities like Chennai,
which get less rain from the Southwest Monsoon, receive rain from this Monsoon.
About 50% to 60% of the rain received by the state of Tamil Nadu is
from the Northeast Monsoon. In Southern Asia, the northeastern
monsoons take place from October to December when the
surface high-pressure system is strongest. The jet
stream in this region splits into the southern subtropical jet and the
polar jet. The subtropical flow directs northeasterly winds to blow across
southern Asia, creating dry air streams which produce clear skies
over India. Meanwhile, a low pressure system known as a monsoon
trough develops over South-East Asia and Australasia and
winds are directed toward Australia.
East Asian Monsoon
The East Asian monsoon affects large parts
of Indo-China, Philippines, China, Taiwan, Korea and Japan.
It is characterised by a warm, rainy summer monsoon and a cold, dry winter
monsoon. The rain occurs in a concentrated belt that stretches east-west except
in East China where it is tilted east-northeast over Korea and Japan. The
seasonal rain is known as Meiyu in
China, Jangma in
Korea, and Bai-u in
Japan, with the latter two resembling frontal rain.
The onset of the summer monsoon is marked by a
period of premonsoonal rain over South China and Taiwan in early May. From May
through August, the summer monsoon shifts through a series of dry and rainy
phases as the rain belt moves northward, beginning over Indochina and
the South China Sea (May), to the Yangtze River Basin and
Japan (June) and finally to North China and Korea (July). When the
monsoon ends in August, the rain belt moves back to South China.
Australia
Also known as the Indo-Australian Monsoon.
The rainy season occurs from September to February and it is a major source of
energy for the Hadley circulation during boreal winter. The Maritime Continent Monsoonand
the Australian Monsoonmay
be considered to be the same system, the Indo-Australian Monsoon.
It is associated with the development of
the Siberian High and the movement of the heating maxima from
the Northern Hemisphere to the Southern Hemisphere.
North-easterly winds flow down Southeast Asia, are turned
north-westerly/westerly by Borneo topography towards Australia.
This forms a cyclonic circulation vortex over Borneo, which together with
descending cold surges of winter air from higher latitudes, cause significant
weather phenomena in the region. Examples are the formation of a rare
low-latitude tropical storm in 2001, Tropical Storm Vamei, and
the devastating flood of Jakarta in 2007.
The onset of the monsoon over the Maritime
Continent tends to follow the heating maxima down Vietnam and
the Malay Peninsula (September),
to Sumatra, Borneo and the Philippines (October),
to Java, Sulawesi (November), Irian Jaya and Northern
Australia (December, January). However, the monsoon is not a simple
response to heating but a more complex interaction of topography, wind and sea,
as demonstrated by its abrupt rather than gradual withdrawal from the region.
The Australian monsoon (the "Wet") occurs in the southern summer when
the monsoon trough develops over Northern Australia. Over three-quarters of
annual rainfall in Northern Australia falls during this time.
Europe
The European
Monsoon (more commonly known as the return of the westerlies) is the result of a resurgence of
westerly winds from the Atlantic, where they become loaded with wind and
rain. These westerly winds are a common phenomenon during the European
winter, but they ease as spring approaches in late March and through April and
May. The winds pick up again in June, which is why this phenomenon is also
referred to as "the return of the westerlies".
The rain usually arrives in two waves, at the
beginning of June and again in mid- to late June. The European monsoon is not a
monsoon in the traditional sense in that it doesn't meet all the requirements
to be classified as such. Instead the return of the westerlies is more regarded
as a conveyor belt that delivers a series of low pressure centres
to Western Europe where they create unsettled weather. These storms
generally feature significantly lower than average temperatures, fierce rain or
hail, thunder and strong winds.
The return of the westerlies affects Europe's Northern
Atlantic coastline, more precisely Ireland, Great Britain,
the Benelux countries, Western Germany, Northern France and
parts of Scandinavia.
Monsoon in India
The southwest summer monsoon, a four-month period
when massive convective thunderstorms dominate India's weather, is Earth's most
productive wet season. A product of southeast trade
winds originating from a high-pressure mass centred over the southern
Indian Ocean, the monsoonal torrents supply over 80% of India's annual
rainfall. Attracted by a low-pressure region centred over South Asia, the
mass spawns surface winds that ferry humid air into India from the
southwest. These inflows ultimately result from a northward shift of the
local jet stream, which itself results from rising summer temperatures
over Tibet and the Indian subcontinent. The void left by the jet
stream, which switches from a route just south of the Himalayas to one tracking
north of Tibet, then attracts warm, humid air. The main factor behind this
shift is the high summer temperature difference between Central Asia and the
Indian Ocean. This is accompanied by a seasonal excursion of the normally
equatorial intertropical convergence zone (ITCZ), a low-pressure belt
of highly unstable weather, northward towards India. This system
intensified to its present strength as a result of the Tibetan
Plateau's uplift, which accompanied
the Eocene–Oligocene transition event, a major episode of global
cooling and aridification which occurred 34–49 Ma.
The southwest monsoon arrives in two branches:
the Bay of Bengal branch and the Arabian Sea branch. The
latter extends towards a low-pressure area over the Thar Desert and is roughly
three times stronger than the Bay of Bengal branch. The monsoon typically
breaks over Indian territory by around 25 May, when it lashes the Andaman
and Nicobar Islands in the Bay of Bengal. It strikes the Indian mainland
around 1 June near the Malabar Coast of Kerala. By 9 June, it
reaches Mumbai; it appears over Delhi by 29 June. The Bay of Bengal branch,
which initially tracks the Coromandal Coast northeast from Cape
Comorin to Orissa, swerves to the northwest towards the Indo-Gangetic
Plain. The Arabian Sea branch moves northeast towards the Himalayas. By the
first week of July, the entire country experiences monsoon rain; on average,
South India receives more rainfall than North India. However, Northeast
India receives the most precipitation. Monsoon clouds begin retreating
from North India by the end of August; it withdraws from Mumbai by 5 October.
As India further cools during September, the southwest monsoon weakens. By the
end of November, it has left the country.
Monsoon rains impact the health of the Indian
economy; as Indian agriculture employs 600 million people and
comprises 20% of the national GDP, good monsoons correlate with a booming
economy. Weak or failed monsoons (droughts) result in widespread agricultural
losses and substantially hinder overall economic growth. Yet such rains reduce
temperatures and can replenish groundwater tables, rivers.
Post-monsoon
During the post-monsoon months of October to
December, a different monsoon cycle, the northeast (or "retreating")
monsoon, brings dry, cool, and dense air masses to large parts of India. It is
called autumn. Winds spill across the Himalayas and flow to the southwest
across the country, resulting in clear, sunny skies. Though the India
Meteorological Department(IMD) and other sources refers to this period as a
fourth ("post-monsoon") season other sources designate only three
seasons. Depending on location, this period lasts from October to
November, after the southwest monsoon has peaked. Less and less precipitation
falls, and vegetation begins to dry out. In most parts of India, this period
marks the transition from wet to dry seasonal conditions. Average daily maximum
temperatures range between 28 and 34 °C (82 and 93 °F).
The northeast monsoon, which begins in September,
lasts through the post-monsoon seasons, and only ends in March. It carries
winds that have already lost their moisture out to the ocean (opposite from the
summer monsoon). They cross India diagonally from northeast to southwest.
However, the large indentation made by the Bay of Bengal into India's eastern
coast means that the flows are humidified before reaching Cape Comorin and
rest of Tamil Nadu, meaning that the state, and also some parts of Kerala,
experience significant precipitation in the post-monsoon and winter periods.
However, parts of West Bengal, Orissa, Andhra
Pradesh, Karnataka and Mumbai also receive minor precipitation from
the north-east monsoon.
Disasters
Climate-related natural disasters
cause massive losses of Indian life and property. Droughts, flash floods,
cyclones, avalanches, landslides brought on by torrential rains, and snowstorms
pose the greatest threats. Other dangers include frequent summer dust storms,
which usually track from north to south; they cause extensive property damage
in North India and deposit large amounts of dust from arid regions. Hail
is also common in parts of India, causing severe damage to standing crops such
as rice and wheat.
Floods and landslides
In the Lower Himalaya, landslides are common. The
young age of the region's hills result in labile rock formations,
which are susceptible to slippages. Short duration high intensity rainfall
events typically trigger small scale landslides while long duration low
intensity rainfall periods tend to trigger large scale catastrophic landslides.
Rising population and development pressures, particularly from logging and
tourism, cause deforestation. The result, denuded hillsides, exacerbates the
severity of landslides, since tree cover impedes the downhill flow of
water. Parts of the Western Ghats also suffer from low-intensity
landslides. Avalanches occur in Jammu and Kashmir, Himachal Pradesh, Uttarakhand,
Sikkim and Arunachal Pradesh.
Floods are the most common natural disaster in
India. The heavy southwest monsoon rains cause the Brahmaputra and
other rivers to distend their banks, often flooding surrounding areas. Though
they provide rice paddy farmers with a largely dependable source of natural
irrigation and fertilisation, the floods can kill thousands and displace
millions. Excess, erratic, or untimely monsoon rainfall may also wash away or
otherwise ruin crops. Almost all of India is flood-prone, and extreme
precipitation events, such as flash floods and torrential rains, have become
increasingly common in central India over the past several decades, coinciding
with rising temperatures. Mean annual precipitation totals have remained steady
due to the declining frequency of weather systems that generate moderate
amounts of rain.
Cyclones
Tropical cyclones, which are severe storms spun off
from the Intertropical Convergence Zone, may affect thousands of Indians
living in coastal regions. Tropical cyclogenesis is particularly
common in the northern reaches of the Indian Ocean in and around the Bay of
Bengal. Cyclones bring with them heavy rains, storm surges, and winds that
often cut affected areas off from relief and supplies. In the North Indian Ocean
Basin, the cyclone season runs from April to December, with peak activity
between May and November. Each year, an average of eight storms with
sustained wind speeds greater than 63 km/h (39 mph) form; of these,
two strengthen into true tropical cyclones, which sustain gusts greater than
117 km/h (73 mph). On average, a major (Category 3 or higher)
cyclone develops every other year.
During summer, the Bay of Bengal is
subject to intense heating, giving rise to humid and unstable air masses that
morph into cyclones. The 1737 Calcutta cyclone, the 1970 Bhola
cyclone, and the 1991 Bangladesh cyclone rank among the most
powerful cyclones to strike India, devastating the coasts of eastern India and
neighbouring Bangladesh. Widespread death and property destruction are reported
every year in the exposed coastal states of West Bengal, Orissa, Andhra
Pradesh, and Tamil Nadu. India's western coast, bordering the more placid
Arabian Sea, experiences cyclones only rarely; these mainly strike Gujarat and,
less frequently, Kerala.
Cyclone 05B, a super cyclone that struck Orissa on
29 October 1999, was the deadliest in more than a quarter-century. With peak
winds of 160 miles per hour (257 km/h), it was the equivalent of
a Category 5 hurricane. Almost two million people were left homeless;
another 20 million people lives were disrupted by the cyclone. Officially,
9,803 people died from the storm; unofficial estimates place the death
toll at over 10,000.
Droughts
Indian agriculture is heavily dependent on the
monsoon as a source of water. In some parts of India, the failure of the
monsoons results in water shortages, resulting in below-average crop yields.
This is particularly true of major drought-prone regions such as southern and
eastern Maharashtra, northern Karnataka, Andhra Pradesh, Western Orissa,
Gujarat, and Rajasthan. In the past, droughts have periodically led
to major Indian famines. These include the Bengal famine of 1770, in
which up to one third of the population in affected areas died; the 1876–1877
famine, in which over five million people died; the 1899 famine, in which over
4.5 million died; and the Bengal famine of 1943, in which over five
million died from starvation and famine-related illnesses.
All such episodes of severe drought correlate
with El Niño-Southern Oscillation (ENSO) events. El Niño-related
droughts have also been implicated in periodic declines in Indian agricultural
output. Nevertheless, ENSO events that have coincided with abnormally high
sea surfaces temperatures in the Indian Ocean—in one instance during 1997 and
1998 by up to 3 °C (5 °F)—have resulted in increased oceanic
evaporation, resulting in unusually wet weather across India. Such anomalies
have occurred during a sustained warm spell that began in the 1990s. A
contrasting phenomenon is that, instead of the usual high pressure air mass
over the southern Indian Ocean, an ENSO-related oceanic low pressure
convergence centre forms; it then continually pulls dry air from Central Asia,
desiccating India during what should have been the humid summer monsoon season.
This reversed air flow causes India's droughts. The extent that an ENSO
event raises sea surface temperatures in the central Pacific Ocean
influences the extent of drought.
The only
difference between a hurricane, a cyclone, and a typhoon is
the location where the storm occurs. Hurricanes, cyclones, and typhoons
are all the same weather phenomenon; we just use different names for these
storms in different places. In the Atlantic and Northeast Pacific, the term
“hurricane” is used. The same type of disturbance in the Northwest Pacific is
called a “typhoon” and “cyclones” occur in the South Pacific and Indian Ocean.
Tropical
cyclone or cyclone. What’s the difference?
A tropical
cyclone is a generic term used by meteorologists to describe a rotating,
organized system of clouds and thunderstorms that originates over tropical or
subtropical waters and has closed, low-level circulation. Once a tropical
cyclone reaches maximum sustained winds of 74 miles per hour or
higher, it is then classified as a hurricane, typhoon,
or cyclone depending upon where the storm originates in the world.
Tropical
cyclones rotate counterclockwise in the Northern Hemisphere.
They
are classified as follows:
·
Tropical
Depression: A tropical cyclone with maximum sustained winds of 38 mph (33
knots) or less.
·
Tropical
Storm: A tropical cyclone with maximum sustained winds of 39 to 73 mph (34
to 63 knots).
·
Hurricane: A
tropical cyclone with maximum sustained winds of 74 mph (64 knots) or higher.
In the western North Pacific, hurricanes are called typhoons; similar storms in
the Indian Ocean and South Pacific Ocean are called cyclones.
·
Major
Hurricane: A tropical cyclone with maximum sustained winds of 111 mph (96
knots) or higher, corresponding to a Category 3, 4 or 5 on the Saffir-Simpson
Hurricane Wind Scale.
But tornadoes
are a different kettle of fish
Tornadoes are nature’s hardest weather
event to predict. They are essentially flukes of nature.
Unlike hurricanes, they form spontaneously, are short-lived, and traverse
a much smaller land mass by comparison.
Many atmospheric conditions need to
converge at the right time for tornadoes to form. They need hot, humid air near
the ground with a cool air mass above them. They also need strong wind velocity
at higher altitudes, known as wind shear, to get them spinning.
What is the
difference between tornadoes and hurricanes?
A tornado is a violently spiraling funnel cloud that
extends from the bottom of a thunderstorm to the ground. It is important
not to confuse a tornado with a hurricane or tropical cyclone because
tornadoes and hurricanes are very different phenomena. The only
similarity between them is that they both contain strong rotating winds that
can cause damage.
Location :Tornadoes
usually occur over land, while hurricanes almost always form over the ocean.
Size: The largest
tornado every observed was 4 km wide, but most tornadoes are about 0.8 km wide.
Hurricanes are much larger, ranging from about 160 km to 1600 km wide.
Life cycles: A tornado’s lifetime
is short, ranging from a few seconds to a few hours. A hurricane’s life cycle
can last from days to weeks.
Wind speeds: The strongest
tornadoes can have wind speeds over 483 kph, but even the strongest hurricanes
rarely produce wind speeds over 322 kph.
Why are
tropical storms and hurricanes named?
NOAA’s National Hurricane Center
does not control the naming of tropical storms. Instead, there is a strict
procedure established by the World Meteorological Organization. For Atlantic
hurricanes, there is a list of male and female names which are used on a
six-year rotation. The only time that there is a change is if a storm is so
deadly or costly that the future use of its name on a different storm would be
inappropriate. In the event that more than twenty-one named tropical cyclones
occur in a season, any additional storms will take names from the Greek
alphabet.
Research
in EPA
Researches
as per United states Environmental protection Agency are on the topics like air
quality and Climate Change, Ecosystems and Climate Change, Energy and Climate
Change, Human Health and Climate Change, Clean Cookstove Research, Black Carbon
Research, Wildfire Research, Integrated Climate and Land-Use Scenarios, Climate
and Health Assessment
Researches
carried out in India (MoEFCC)
Researches carried out in India by Ministry of Environment and Forest
and Climate Change are Carbon-cycle
Research, Centre for climate change research, Climate
services, Chrysosphere process and climate change, Crysosphere studies in Himalaya, Geo engineering –carbon sequestration, Impact
of sea level rise, Modelling of changing water cycle and climate, Reconstruction
of palaeoclimatic conditions, Short term climate prediction and variability, Studies on carbon and nitrogen biogeochemistry in coral system
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