IASbaba’s Session 14
Rapid Revision Series
for
!
PRELIMS 2021
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TOPICS TO REVISE
131. Tropical Cyclones and conditions for their formation "
132. Temperate cyclones and how they are different from Tropical Cyclones
133. Factors that have led to the increased frequency of Tropical Cyclones #
134. Naming of Tropical Cyclones "
135. Reasons for deficient rainfall during N-E Monsoon "
#
136. Artificial Rain
137. Western Disturbances
138. BoBBLE Experiment-Indian Monsoon $
139. Karman Line $
140. Heliosphere, Helio-sheath and Heliopause "
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Topic 131: Tropical Cyclones
(%
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Cyclones in 2020 and 2021 Key points:
"
Amphan Bay of Bengal West Bengal, Odisha, 1. Cyclone is an intense low pressure
)
Bangladesh, Sri Lanka, area with organised convection, and
(May 16-21, 2020) Bhutan "
winds at low levels, circulating +,
" Nisarga Arabian Sea Maharashtra, Goa
"
either anti-clockwise or clockwise
"
(June 1-4, 2020)
-
Nivar Bay of Bengal "
Sri Lanka, Andhra Pradesh,
(Nov 23-27, 2020) Tamil Nadu, Puducherry 2. Tropical cyclones are violent storms
"
Burevi Bay of Bengal Sri Lanka, Tamil Nadu, that originate over oceans in
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(Nov 30-Dec 5, 2020) Kerala tropical areas#
"
Tauktae Arabian Sea Delhi, Kerala, Lakshadweep,
(May 14-19, 2021) Maldives, Haryana, Sindh, 3. They are known as Cyclones in the
Sri Lanka, West India Indian Ocean, Hurricanes in the
-
Yaas Bay of Bengal
.
Andaman and Nicobar Atlantic, Typhoons# in the Western
(May 23-28, 2021) Islands, Bangladesh, East Pacific and South China Sea, and
India, Nepal, Uttar Pradesh
Willy-willies in#the Western
Australia.
"
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Topic 131: Tropical Cyclones
Conditions for formation of Tropical cyclones or
hurricanes
1. A source of warm, moist air derived from tropical oceans with
sea surface temperature normally near to or in excess of 27 °C
2. Winds near the ocean surface blowing from different
-
directions converging and causing air to rise and storm clouds
to form
#"0
/
"
3. Winds which do not vary greatly with height – known as low
wind shear. This allows the storm clouds to rise vertically to
high levels
4. Presence of Coriolis force, provides energy to rotate or curve
in anti-clockwise (in the northern hemisphere) or clockwise
(in the southern hemisphere)
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Topic 131: Tropical Cyclones
Six regions that are more vulnerable to tropical cyclones
"
1. Tropical North Atlantic (Gulf of Mexico, West Indies and
12.&
Caribbean Sea)
56 #
(
34&
2. Eastern part of the tropical north pacific (Western coast
"
of Mexico and Central America)
"
!
3. Western part of tropical north pacific (The Philippines,
the China Sea and areas around Japan) "
4. Bay of Bengal and Arabian Sea
5. Western South Pacific Ocean (regions of Samoa, Fiji
7
Island and the east and north coast of Australia)
6. The south coast of Indian Ocean (coastal regions of
Madagascar)
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Topic 132: 8
Temperate cyclones
Tropical Cyclone Temperate cyclone
Formed in the lower latitudes – Confined to 10-30º N and S of equator. " Formed in the higher latitudes – 35 to 65 degrees N and S of equator. "
"
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"
Originates via formation of central low-pressure zone surrounded by high pressure Originate via merger of cold and warm fronts.
zones. 19:.;4<
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They are more intense and destructive. Not so intense and destructive.
Due to the action of Coriolis force, they move from east to west. They move from west to east.
They affect a smaller area. They affect a wider area, mostly two to three continents.
Tropical Cyclone forms only on seas with temperature more than 26-27degree C and Temperate cyclones can be formed on both land and sea.
"
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dissipate on reaching the land.
D
A tropical cyclone doesn’t last for more than 7 days as they travel lesser distances. A Temperate cyclone can last for a duration of 15 to 20 days.
#Absence of such eye.
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"
E
It is characterised by cyclonic eye.
Eye is calm and cloudless without precipitation. Due to absence of eye, precipitation occurs even in the centre of the
cyclone.
to about 12 km
"
F
The diameter of tropical cyclone varies from 150 to 500 km and vertically from surface The diameter of these cyclones may vary from 160 km to 3200 km.
" "
The isobar of tropical cyclones are circular in shape and pressure gradient is very steep. Temperate cyclones isobars are V-shaped and pressure gradient is gentle.
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" "
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The velocity of wind of tropical cyclone is greater – 100 to 220 kmph (during severe The velocity of wind of temperate cyclone is comparatively low – 40 to 60
"
" "
storms). kmph
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Travel about 300 to 400 miles a day. Travel at about 20 to 30 miles per hour.
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Rainfall/Precipitation – Heavy but does not last beyond a few hours. If the cyclone stays In a temperate cyclone, rainfall is slow and continues for many days,
at a place, the rainfall may continue for a few days.
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Topic 133: Factors % that have led to the increased
frequency of tropical cyclones
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Key points: Frequency of tropical cyclones have increased specifically in Arabian Sea
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E
1. Winter monsoon circulations play crucial role
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2. Interplay of global warming, climate variability and weather changes led to weakening of northeast
monsoon circulation
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3. Role of wind shear over Arabian Sea or the change in direction and speed of the winds from bottom to
the top of the atmosphere
4. Rise in global temperatures due to rise in manmade black carbon particles and sulphate emissions
have increased the intensity of these cyclones # "
5. Burning of fossil fuels, aerosols, greenhouse gases, volcanic activity, solar variability, and internal
6" temperature, making the conducive weather
"
climate variability also add degrees to sea surface
conditions for tropical cyclones.
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Topic 133: Factors that have led to the increased
frequency of tropical cyclones
1
Reason for coastal India to be susceptible –
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Bay of Bengal is more susceptible compared to Arabian Sea due to various factors like:
1. "
High temperature difference between land and sea.
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2. Coriolis force.
3. Topographic of eastern region: absence of mountains to block.
4. Remnants of Pacific Ocean hurricane.
5. Air circulation and trade winds from north east.
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6. Heat Island: Coastal regions are heavily industrialized.
"
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%
Topic 134: Naming of Tropical Cyclones
Key points:
1. The tradition of naming Cyclones started
with hurricanes in the Atlantic Ocean
"
)
)
2. In 2000 WMO/ESCAP (World " " "
#
Meteorological Organisation/United
Nations Economic and Social 7
Commission for Asia and the Pacific) was
formed #
3. Currently, there are 13 nations
altogether in WMO/ESCAP
.
"
4. Each of these nations provide their own
list of names and subsequent cyclones
will be named accordingly
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O
Topic 135: Reasons for deficient rainfall during N-E
Monsoon
8 Southwest monsoon
E
1 Northeast monsoon
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Occurs between June and Occurs during October to
-7 P
September "
December "
5 "
Commonly known as summer Commonly known as winter
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monsoon monsoon
Blows from sea to land Blows from land to sea
)
Brings most of the rainfall during
It is comparatively a small-scale
a year in the country (75%) monsoon
These winds cause country-wide These cause rainfall only in
rainfall. Coromandel coast including Tamil
Nadu when these strike at the
- - wetlands of the Eastern Ghats.
These blow from oceanic high These winds blow from land to
pressure areas towards the low sea as a result of reversal in the
pressure areas of land. direction of wind or start of
retreating monsoon season.
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Topic 135: Reasons for deficient rainfall during N-E
Monsoon
"
%
Key points:
Q
1. Unless the southwest monsoon withdraws completely, the northeast monsoon cannot commence.
(The withdrawal of the southwest monsoon had remained stagnant) #
=.
2. Prevailing La Niña conditions in the Pacific Ocean While La Niña conditions enhance the rainfall
"
associated with the Southwest monsoon, it has a negative impact on rainfall associated with the
"
"
Northeast monsoon.
-AAA
3. Position of the Inter Tropical Convective Zone (ITCZ)
poor rainfall during NE monsoon
ITCZ position to the North contributes to the
"
"
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F Rain
Topic 136: Artificial
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Key points:
32R:
1. Practice of artificially inducing or increasing
precipitation through clouds by adding external agents.
G"
2. External agents or foreign particles could be Dry Ice
(solid carbon dioxide), Silver Iodide, Salt powder etc.
3. During the times of drought and dryness, the
temperature is so high that the mass of air is unable to
reach the due point. Hence,#condensation fails to take
"
place thus leading to prolonged drought.
#
4. In order to hasten the condensation, the condensation
nuclei are infused into the air masses, thereby speeding
up the condensation and in turn precipitation.
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Topic 136: Artificial Rain
How is artificial rain produced?
"
The process includes three stages, the first is agitation, second is called building-up stage and the third
bombardment of chemicals.
Agitation This process involves using chemicals to stimulate the air mass upwind of the target
Stage area to rise and form rain clouds.
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These clouds are capable of absorbing water vapour from the air mass thus stimulating
the condensation process in the clouds.
Chemicals like - Calcium Oxide, compound of Urea and Ammonium Nitrate or Chloride
Calcium Carbonate – are used.
Building- The cloud mass is built up using chemicals like kitchen salt, ammonium nitrate, urea and
up stage occasionally calcium chloride.
Seeding Chemicals such as super cool agents like silver iodide and dry ice are used to reach the
most unbalanced status which eventually leads to the formulation of droplets and make
them fall as raindrops.
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A
Topic 137: Western Disturbances
S
T
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Key points:
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1. #
It is an extra-tropical storm which originates in the
Mediterranean region
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)
2.
the westerlies.
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It is a non-monsoonal precipitation pattern driven by
3. Moisture in these storms usually originates over
J the Mediterranean Sea, the Caspian Sea and the Black
"
Sea " "
4. Extra-tropical storms are a global phenomenon with
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moisture usually carried in the upper atmosphere
5. Western disturbances are more frequent and stronger
in winter season. (important for the development of
the Rabi crop)
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8
Topic 138: BoBBLE Experiment-Indian Monsoon
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#
Key points: *" >%
1. BoBBLE Bay of Bengal Boundary Layer Experiment
2. It is a joint India-UK project
3. Objectives
1. To create a blueprint for accurate prediction of monsoon, tropical cyclones and other weather
related forecasts
2. Understand the role of thermodynamic surface and mixed layer processes in the monsoon
3. Understand the role of large-scale ocean structure, ocean dynamics and ocean biogeochemistry
in the monsoon
"
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%
Topic 139: Karman Line O
Key points:
1. It is the altitude where space begins (internationally
Q
"
recognized boundary of space).
2. It commonly represents the border between the Earth's
atmosphere and outer space.
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U
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3. The line is named after Theodore von Kármán, a"
Hungarian American engineer and physicist, who was
active primarily in aeronautics and astronautics.
4. In theory, once this Karman Line is crossed, the
atmosphere becomes too thin to provide enough lift for
conventional aircraft to maintain flight.
5. At this altitude, a conventional plane would need to
reach orbital velocity or risk falling back to Earth.
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6" and Heliopause
Topic 140: Heliosphere, Helio-sheath " "
Key points:
Heliosphere The solar wind, emanating from the Sun, creates a bubble that
" extends far past the orbits of the planets. This bubble is the
heliosphere.
It is shaped like a long wind sock as it moves with the Sun through
interstellar space.
Helio-sheath The helio-sheath is the outer region of the heliosphere, just beyond
$ # the solar wind slows abruptly,
the termination shock, the point where
"
becoming denser and hotter.
# outward against the approaching
The solar wind piles up as it presses
wind in interstellar space.
#
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Heliopause The boundary between solar wind and interstellar wind is the
$
6"
heliopause, where the pressure of the two winds are in balance.
This balance in pressure causes the solar wind to turn back and flow
down the tail of the heliosphere.
"
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%THANK YOU
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