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GS Paper: GS1-15.Geographical features and their location- Changes in critical geographical features (including water-bodies and ice-caps) and in flora and fauna and the effects of such changes.

  • [pib] International Monsoons Project Office (IMPO)

    Union Minister of Science & Technology has launched the International Monsoons Project Office (IMPO).

    International Monsoons Project Office (IMPO)

    • IMPO will be hosted at the Indian Institute of Tropical Meteorology (IITM), Pune, an institution under the Ministry of Earth Sciences, Govt of India, initially for five years.
    • Setting up the IMPO reiterates the importance of monsoons for the national economy.
    • It would encompass activities and connections related to international monsoon research that would be identified and fostered under the leadership of the World Climate Research Programme.
    • Both the World Climate Research Programme and World Weather Research Programme are international programmes coordinated by the United Nations World Meteorological Organisation (WMO).

    Significance of IMPO

    • Setting up the IMPO in India would mean expanding an integrated scientific approach to solve the seasonal variability of monsoons, enhancing the prediction skill of monsoons and cyclones.
    • It would promote knowledge sharing and capacity building in areas of monsoon research crucial for agriculture, water resources and disaster management, hydropower and climate-sensitive socio-economic sectors.
    • It is a step towards making India a global hub for monsoon research and coordination in a seamless manner for addressing common and region-specific aspects of the monsoons around the world.

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    Back2Basics:

    Various terms related to Indian Monsoon

  • Places in news: Erra Matti Dibbalu

    Citizens join hands to preserve the geological marvel of Erra Matti Dibbalu in Visakhapatnam.

    What is Erra Matti Dibbalu?

    • Located between Visakhapatnam and Bheemunipatnam, the Erra Matti Dibbalu are rare red sand dunes that are a reminder of the million years of geological processes.
    • Its towering red sand dunes with patches of greenery is like a meandering maze.
    • The width of the dunes, which runs for five kilometres along the coast, varies from 200 metres to two kilometres.
    • It is listed among the 34 notified National Geological Heritage Monument Sites of India by the Geological Survey of India.

    (Don’t they resemble to Ravines of Chambal?)

    Its formation

    • Studies indicate that the area was tectonically active between 2.5 million years and 11,000 years ago.
    • The sediments are mainly derived from the Khondalite rocks from the hinterland of the Eastern Ghats.
    • Geologically these red sand dune sediments particularly hold significance.
    • They are the result of the combined effect of numerous factors including global climatic changes, sea-level variations, monsoonal variability and as a result serves as valuable paleo-environment indicators.

     

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  • What is Bomb Cyclone?

    Major cities such as New York and Boston in US are witnessing a “Bomb Cyclone” characterized by the explosive power of rapid drops in atmospheric pressure.

    What is Bomb Cyclone?

    • A bomb cyclone is a large, intense mid-latitude storm that has low pressure at its center, weather fronts and an array of associated weather, from blizzards to severe thunderstorms to heavy precipitation.
    • It becomes a bomb when its central pressure decreases very quickly—by at least 24 millibars in 24 hours.
    • When a cyclone “bombs,” or undergoes bombogenesis, this tells us that it has access to the optimal ingredients for strengthening, such as high amounts of heat, moisture and rising air.

    Why is it called a bomb?

    • Most cyclones don’t intensify rapidly in this way.
    • Bomb cyclones put forecasters on high alert, because they can produce significant harmful impacts.

    Its etymology

    • The word “bombogenesis” is a combination of cyclogenesis, which describes the formation of a cyclone or storm, and bomb, which is, well, pretty self-explanatory.
    • This can happen when a cold air mass collides with a warm air mass, such as air over warm ocean waters.
    • The formation of this rapidly strengthening weather system is a process called bombogenesis, which creates what is known as a bomb cyclone.

    How does it occur?

    • Over the warmer ocean, heat and moisture are abundant.
    • But as cool continental air moves overhead and creates a large difference in temperature, the lower atmosphere becomes unstable and buoyant.
    • Air rises, cools and condenses, forming clouds and precipitation.

    Where does it occur the most?

    • The US coast is one of the regions where bombogenesis is most common.
    • That’s because storms in the mid-latitudes – a temperate zone north of the tropics that includes the entire continental US – draw their energy from large temperature contrasts.
    • Along the US East Coast during winter, there’s a naturally potent thermal contrast between the cool land and the warm Gulf Stream current.

     

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  • What is the Pacific ‘Ring of Fire’?

    The Hunga Tonga-Hunga Ha’apai volcano which massively erupted lies along the Pacific ‘Ring of fire’, and is just over 60 kilometers from the island nation of Tonga.

    What is the Pacific ‘Ring of Fire’?

    • The Pacific ‘Ring of Fire’ or Pacific rim, or the Circum-Pacific Belt, is an area along the Pacific Ocean that is characterized by active volcanoes and frequent earthquakes.
    • Volcanic arcs and oceanic trenches partly encircling the Pacific Basin form the so-called Ring of Fire.
    • It is home to about 75 per cent of the world’s volcanoes – more than 450 volcanoes.
    • Also, about 90 per cent of the world’s earthquakes occur here.

    Its spread

    • Its length is over 40,000 kilometres and traces from New Zealand clockwise in an almost circular arc covering Tonga, Kermadec Islands, Indonesia.
    • It is moving up to the Philippines, Japan, and stretching eastward to the Aleutian Islands, then southward along the western coast of North America and South America.

    Seismic activity of the region

    • The area is along several tectonic plates including the Pacific plate, Philippine Plate, Juan de Fuca plate, Cocos plate, Nazca plate, and North American plate.
    • The movement of these plates or tectonic activity makes the area witness abundant earthquakes and tsunamis every year.
    • Along much of the Ring, tectonic plates move towards each other creating subduction zones.
    • One plate gets pushed down or is subducted by the other plate.
    • This is a very slow process – a movement of just one or two inches per year.
    • As this subduction happens, rocks melt, become magma and move to Earth’s surface and cause volcanic activity.

    What has happened in recent eruption in Tonga?

    • In the case of Tonga, the Pacific Plate was pushed down below the Indo-Australian Plate and Tonga plate, causing the molten rock to rise above and form the chain of volcanoes.
    • Subduction zones are also where most of the violent earthquakes on the planet occur.
    • The December 26, 2004 earthquake occurred along the subduction zone where the Indian Plate was subducted beneath the Burma plate.

     

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  • Undersea Volcanic Eruption in Hunga Islands, Tonga

    A distant undersea volcano has erupted in spectacular fashion near the Pacific nation of Tonga sending large tsunami waves reaching the shore.

    Hunga Volcano

    • The Hunga-Tonga-Hunga-Ha’apai volcano has erupted regularly over the past few decades.
    • It consists of two small uninhabited islands, Hunga-Ha’apai and Hunga-Tonga, poking about 100m above sea level 65km north of Tonga’s capital Nuku’alofa.
    • But hiding below the waves is a massive volcano, around 1800m high and 20 kilometres wide.
    • During events in 2009 and 2014/15 hot jets of magma and steam exploded through the waves. But these eruptions were small, dwarfed in scale by the January 2022 events.
    • Researchers suggest this is one of the massive explosions the volcano is capable of producing roughly every thousand years.

    Impact of the eruption

    • The ash plume is already about 20km high.
    • Most remarkably, it spread out almost concentrically over a distance of about 130km from the volcano, creating a plume with a 260km diameter, before it was distorted by the wind.
    • The eruption also produced a tsunami throughout Tonga and neighbouring Fiji and Samoa.
    • Shock waves traversed many thousands of kilometres, were seen from space, and recorded in New Zealand some 2000km away.
    • All these signs suggest the large Hunga caldera has awoken.

    Why is it so explosive even after being underwater?

    Answer: Fuel-coolant interaction

    • If magma rises into sea water slowly, even at temperatures of about 1200 degrees Celsius, a thin film of steam forms between the magma and water.
    • This provides a layer of insulation to allow the outer surface of the magma to cool.
    • But this process doesn’t work when magma is blasted out of the ground full of volcanic gas.
    • When magma enters the water rapidly, any steam layers are quickly disrupted, bringing hot magma in direct contact with cold water.
    • Volcano researchers call this ‘fuel-coolant interaction’ and it is akin to weapons-grade chemical explosions.

    A chain reaction

    • Extremely violent blasts tear the magma apart.
    • A chain reaction begins, with new magma fragments exposing fresh hot interior surfaces to water, and the explosions repeat, ultimately jetting out volcanic particles and causing blasts with supersonic speeds.

    How has it emerged out to be so big?

    • The caldera is a crater-like depression around 5km across.
    • Small eruptions (such as in 2009 and 2014/15) occur mainly at the edge of the caldera, but very big ones come from the caldera itself.
    • These big eruptions are so large the top of the erupting magma collapses inward, deepening the caldera.
    • Looking at the chemistry of past eruptions, we now think the small eruptions represent the magma system slowly recharging itself to prepare for a big event.

    What next?

    • This latest eruption has stepped up the scale in terms of violence.
    • Researchers are still in the middle of this major eruptive sequence and many aspects remain unclear, partly because the island is currently obscured by ash clouds.

     

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  • India’s first open Rock Museum in Hyderabad

    The Ministry of Science & Technology has inaugurated India’s first open rock museum displaying different types of rocks gathered from different States of ages ranging from 3.3 billion years to around 55 million years.

    Rock System in India

    Based on this complex and varied geological history, the Geological Survey of India has classified rock systems of the country into 4 major divisions:

    1. Archaean Rock System
    2. Dravidian Rock System
    3. Purana Rock System
    4. Aryan Rock System

    [I] Archaean Rock System:

    The Archaean group of rocks consists of two systems-(a) Achaean granites and gneisses, and (b) Dharwarian sedimentary:

    Archaean Gneisses and Schists (pre-2500 million years)

    • The Archean System contains the first formed rocks of the earth.
    • The rocks are primarily gneisses and granites, having no marks of fossils.
    • They often underlie the strata formed subsequently and the system is generally known as the basement complex or fundamental gneisses.
    • The Archaean rocks cover two-thirds of peninsular India. They also occur in the roots of the mountain peaks all along the Greater Himalayas, trans-Himalayan ranges of Zaskar, Ladakh and Karakoram.

    Dharwar System (2500-1800 million years ago)

    • The weathering of the Archaean rocks yielded the earliest sediments and formed the oldest sedimentary strata, the Dharwar system.
    • These are found today in metamorphic forms and do not contain fossils.
    • These rocks occur in scattered patches in parts of Karnataka, Tamil Nadu, central and eastern parts of Chotanagpur plateau, Meghalaya plateau, Aravalis, Himalayan region etc

    Mineral contents:

    • They contain gneisses (which range from granite to gabbro) and schists (crystalline rocks such as mica, talc etc.).
    • These rocks have metallic and non-metallic minerals like copper, tin, graphite, lead, zinc, etc.

    [II] Dravidian Rock System:

    • This is also known as carboniferous rock system and formed during the Paleozoic era, i.e., from 600- 300 million years ago.
    • They are not much abundant in India.
    • They have plentiful fossils and beginning of coal formation can be seen in this period. The quality of carboniferous coal is high.
    • They are found in extra- Peninsular regions of the Himalayas and the Gangetic plains.

    Mineral content

    • This type of rock system comprises of limestones, shale and quartzite and Mount Everest is formed of upper Carboniferous limestones.
    • Most of the coal is not of the Carboniferous period, which is found in India.
    • The meaning of Carboniferous in geology is coal-bearing.

    [III] Purana Rock System:

    The Purana rock system has two divisions: Cuddapah system and Vindhyan system. The word ‘Purana’ was used in place of a Proterozoic era in India.

    Cuddapah Rock system:

    • They are observed in Cuddapah districts of Andhra Pradesh.
    • The non-fossiliferous clay, slates, sandstones and limestones were accumulated in the depression between two-fold mountains which is known as synclinal basins.
    • They also have a large accumulation of building purpose cement grade limestones and quartzites.
    • This type of rock contains ore of iron, cobalt, nickel, manganese etc.

    Vindhya Rock System:

    • This type of rock system is also ancient or old sedimentary rocks which are superimposed on the Archaean rock base and derived its name from Vindhya mountains.
    • The recognition of fossils is negligible, only traces of few animal and plant life were found.
    • This rock system has diamond-bearing regions from which Golconda and Panna diamond mined.

    [IV] Aryan Rock System

    The Aryan rock system in India has the following four subsystems:

    1. Gondwana rock system
    2. Jurassic Rock System
    3. Cretaceous system/ Deccan Trap
    4. Tertiary rock system

    (1) Gondwana Rock System:

    • These are found mainly in Raniganj, Jharia regions of Jharkhand, Damodar valley, Pench valley in Chhattisgarh and Madhya Pradesh.
    • They are called so after the name of Gondwana tribe (indigenous people especially residing in Telangana and Andhra Pradesh region).
    • In this type of rock system, you found metallic minerals like iron, manganese, uranium etc. other than coal.
    • They have low carbon content as it is much younger than Carboniferous coal. These rocks have nearly 98% of India’s coal reserve.

    (2) Jurassic Rock System

    • During the latter part of Jurrasic when sea level rises as compared to land and shoreline moves towards ground or land which result in a flood. In geology, this phenomenon is called marine transgression.
    • This gives rise to a thick series of shallow-water deposits kin Rajasthan and Kutch. Between the Guntur and Rajamundry, another transgression in the east coast of Peninsula.
    • In Kuchchh, coral limestone, shales and conglomerates are found.

    (3) Deccan traps

    • These are formed by the flow of magma over the solidified rock system in layers.
    • Deccan trap gets rise due to volcanic outburst over a major area of Peninsular India from the end of Cretaceous till the beginning of Eocene.
    • The meaning of trap is “stair” or “step” in Swedish and called due to deposition of the volcanic outburst which has a flat top and steep sides.
    • It is mainly found in parts of Kuchchh, Saurashtra, Maharashtra, the Malwa plateau and Northern Karnataka and presently cover near 5 lakh sq. Km.
    • Regur, which is black soil, is formed due to the weathering of these rocks for a long time.

    (4) Tertiary rock system

    • The formation of this type of rock system occurs from 60 to 7 million years ago.
    • It is the most noteworthy period in India’s geological history as the Himalayas were born and recent form came in this period.

    Also read:

    The Geological Structure of India

     

     

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  • Western Disturbances to bring rain in New Delhi

    Under the influence of two consecutive western disturbances, New Delhi is in for a wet spell.

    Western Disturbances

    • A western disturbance is an extratropical storm originating in the Mediterranean region that brings sudden winter rain to the northwestern parts of the Indian subcontinent.
    • It is a non-monsoonal precipitation pattern driven by the westerlies.
    • The moisture in these storms usually originates over the Mediterranean Sea, the Caspian Sea and the Black Sea.
    • Extratropical storms are global phenomena with moisture usually carried in the upper atmosphere, unlike their tropical counterparts where the moisture is carried in the lower atmosphere.
    • In the case of the Indian subcontinent, moisture is sometimes shed as rain when the storm system encounters the Himalayas.
    • Western disturbances are more frequent and strong in the winter season.

    Impact: Winter Rainfall and Extreme Cold

    • Western disturbances, specifically the ones in winter, bring moderate to heavy rain in low-lying areas and heavy snow to mountainous areas of the Indian Subcontinent.
    • They are the cause of most winter and pre-monsoon season rainfall across northwest India.
    • An average of four to five western disturbances forms during the winter season.

    Its significance

    • Precipitation during the winter season has great importance in agriculture, particularly for the rabi crops.
    • Wheat among them is one of the most important crops, which helps to meet India’s food security.

    Try this PYQ:

    Q. Consider the following statements:

    1. The winds which blow between 30°N and 60°S latitudes throughout the year are known as westerlies.
    2. The moist air masses that cause winter rains in the North-Western region of India are part of westerlies.

    Which of the statements given above is/are correct?

    (a) Only 1

    (b) Only 2

    (c) Both 1 and 2

    (d) Neither 1 nor 2

     

     

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  • Earth’s first landmass emerged in Singhbhum: Study

    A new study has challenged the widely accepted view that the continents rose from the oceans about 2.5 billion years ago.

    About Singhbhum

    • Singhbhum district of Jharkhand is part of the Chhota Nagpur Division.
    • It is one of the leading producers of copper in India.

    First landmass to emerge

    • The study suggests that the earliest continental landmass to emerge may have been Jharkhand’s Singhbhum region.
    • Scientists have found sandstones in Singhbhum with geological signatures of ancient river channels, tidal plains and beaches over 3.2 billion years old.
    • They somewhat represent the earliest crust exposed to air.

    Studying the sandstones

    • The research studies a sedimentary rock, called granite. They tried to find their age and in which conditions they have formed.
    • They found the age by analysing the uranium and lead contents of tiny minerals.
    • These rocks are 3.1 billion years old, and were formed in ancient rivers, beaches, and shallow seas.
    • All these water bodies could have only existed if there was continental land.
    • Thus, they inferred that the Singhbhum region was above the ocean before 3.1 billion years ago.

    How did they analyse?

    • The researchers studied the granites that form the continental crust of Singhbhum region.
    • These granites are 3.5 to 3.1 billion years old and formed through extensive volcanism that happened about 35-45 km deep inside the Earth.
    • This process continued on-and-off for hundreds of millions of years until all the magma solidified to form a thick continental crust in the area.
    • Due to the thickness and less density, the continental crust emerged above surrounding oceanic crust owing to buoyancy.

    Back2Basics: Emergence of Landmass

    • In the beginning, more than 4.6-billion years ago, the world was a ball of burning gas, spinning through space.
    • It took hundreds of millions of years for the first land masses to emerge.
    • About 250-million years ago, long, long after the Earth had formed, all the continents of the time had joined together to form a super-continent called Pangaea.
    • This super-continent broke up about 200-million years ago to form two giant continents, Gondwana and Laurasia.
    • Gondwana comprised what is now Africa, South America, Australia, Antarctica and India.
    • The Indian sub-continent lay off the east coast of Africa, before it broke off and moved north rapidly.

    Isostacy

    • Huge plates of crustal and upper mantle material (lithosphere) “float” on more dense, plastically flowing rocks of the asthenosphere.
    • The “depth” to which a plate, or block of crust, sinks is a function of its weight and varies as the weight changes.
    • This equilibrium, or balance, between blocks of crust and the underlying mantle is called isostasy.
    • The taller a block of crust is, the deeper it penetrates into the mantle because of its greater mass and weight. Isostasy occurs when each block settles into an equilibrium with the underlying mantle.
    • Blocks of crust that are separated by faults will “settle” at different elevations according to their relative mass.

     

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  • Sixth Mass Extinction?

    A paper published recently has come up with a new reason behind the first mass extinction, also known as the Late Ordovician mass extinction.

    Species Extinction

    • Extinction is a part of life, and animals and plants disappear all the time. About 98% of all the organisms that have ever existed on our planet are now extinct.
    • When a species goes extinct, its role in the ecosystem is usually filled by new species, or other existing ones.

    What is Mass Extinction?

    • Earth’s ‘normal’ extinction rate is often thought to be somewhere between 0.1 and 1 species per 10,000 species per 100 years.
    • This is known as the background rate of extinction.
    • A mass extinction event is when species vanish much faster than they are replaced.
    • This is usually defined as about 75% of the world’s species being lost in a ‘short’ amount of geological time – less than 2.8 million years.

    How many mass extinctions have there been?

    Five great mass extinctions have changed the face of life on Earth. We know what caused some of them, but others remain a mystery:

    [I] Ordovician-Silurian ME

    • It occurred 443 million years ago and wiped out approximately 85% of all species.
    • Scientists think it was caused by temperatures plummeting and huge glaciers forming, which caused sea levels to drop dramatically.
    • This was followed by a period of rapid warming. Many small marine creatures died out.

    [II] Devonian ME

    • It took place 374 million years ago and killed about three-quarters of the world’s species, most of which were marine invertebrates that lived at the bottom of the sea.
    • This was a period of many environmental changes, including global warming and cooling, a rise and fall of sea levels and a reduction in oxygen and carbon dioxide in the atmosphere.
    • We don’t know exactly what triggered the extinction event.

    [III] Permian ME

    • It happened 250 million years ago, was the largest and most devastating event of the five.
    • Also known as the Great Dying, it eradicated more than 95% of all species, including most of the vertebrates which had begun to evolve by this time.
    • Some scientists think Earth was hit by a large asteroid which filled the air with dust particles that blocked out the Sun and caused acid rain.
    • Others think there was a large volcanic explosion that increased carbon dioxide and made the oceans toxic.

    [IV] Triassic ME

    • It took place 200 million years ago, eliminating about 80% of Earth’s species, including many types of dinosaurs.
    • This was probably caused by colossal geological activity that increased carbon dioxide levels and global temperatures, as well as ocean acidification.

    [V] Cretaceous ME

    • It occurred 65 million years ago, killing 78% of all species, including the remaining non-avian dinosaurs.
    • This was most likely caused by an asteroid hitting the Earth in what is now Mexico, potentially compounded by ongoing flood volcanism in what is now India.

    What caused first ME?

    • The cooling climate likely changed the ocean circulation pattern.
    • This caused a disruption in the flow of oxygen-rich water from the shallow seas to deeper oceans, leading to a mass extinction of marine creatures.
    • Ordovician Sea has familiar groups like clams and snails and sponges.
    • Many other groups are now very reduced in diversity or entirely extinct like trilobites, brachiopods, and crinoids.

    The sixth mass extinction

    • We are currently experiencing a sixth mass extinction as the result of human-induced climate change.
    • There have been several theories behind each mass extinction and with advances in new technologies, researchers have been uncovering more intricate details about these events.

    Try this PYQ from CSP 2018

    The term “sixth mass extinction/sixth extinction” is often mentioned in the news in the context of the discussion of:

     

    (a) Widespread monoculture Practices agriculture and large-scale commercial farming with indiscriminate use of chemicals in many parts of the world that may result in the loss of good native ecosystems.

    (b) Fears of a possible collision of a meteorite with the Earth in the near future in the manner it happened 65million years ago that caused the mass extinction of many species including those of dinosaurs.

    (c) Large scale cultivation of genetically modified crops in many parts of the world and promoting their cultivation in other Parts of the world may cause the disappearance of good native crop plants and the loss of food biodiversity.

    (d) Mankind’s over-exploitation/misuse of natural resources, fragmentation/loss, natural habitats, destruction of ecosystems, pollution and global climate change.

     

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  • Various terms related to Indian Monsoon

    The monsoon is likely to begin withdrawing from the mainland from October 6, said the India Meteorological Department (IMD).

    Let us learn all terminologies related to Monsoon.

    What is Monsoon?

    • Indian monsoon, the most prominent of the world’s monsoon systems, which primarily affects India and its surrounding water bodies.
    • It blows from the northeast during cooler months and reverses direction to blow from the southwest during the warmest months of the year.

    Onset of Monsoon

    • This process brings large amounts of rainfall to the region during June and July.
    • As the high-sun season (that is, the Northern Hemisphere summer) moves northward during April, India becomes particularly prone to rapid heating because the highlands to the north protect it from any incursions of cold air.
    • There are three distinct areas of relative upper tropospheric warmth—namely, (1) above the southern Bay of Bengal, (2) above the Plateau of Tibet, and (3) across the trunks of the various peninsulas that are relatively dry during this time.
    • These three areas combine to form a vast heat-source region.
    • In contrast, a heat sink appears over the southern Indian Ocean as the relatively cloud-free air cools by emitting long-wavelength radiation.
    • Monsoon winds at the surface blow from heat sink to heat source.

    Peak period

    • The position of the easterly jet controls the location of monsoonal rains, which occur ahead and to the left of the strongest winds and also behind them and to the right.
    • The surface flow, however, is a strong, south-westerly, humid, and unstable wind that brings humidifies of more than 80 percent and heavy squally showers that are the “burst” of the monsoon.
    • The overall pattern of the advance follows a frontal alignment, but local episodes may differ considerably.

    Key areas

    • Most spectacular clouds and rain occur against the Western Ghats in India, where the early monsoonal airstream piles up against the steep slopes, then recedes, and piles up again to a greater height.
    • Each time it pushes thicker clouds upward until wind and clouds roll over the barrier and, after a few brief spells of absorption by the dry inland air, cascade toward the interior.
    • Various factors, especially topography, combine to make up a complex regional pattern.

    Break in Monsoon

    • During the south-west monsoon period after having rains for a few days, if rain fails to occur for one or more weeks, it is known as break in the monsoon.
    • These dry spells are quite common during the rainy season.
    • In northern India rains are likely to fail if the rain-bearing storms are not very frequent along the monsoon trough or the ITCZ over this region.
    • Over the west coast the dry spells are associated with days when winds blow parallel to the coast.

    Withdrawal of Monsoon

    • By August the intensity and duration of sunshine have decreased, temperatures begin to fall, and the surge of south-westerly air diminishes spasmodically almost to a standstill in the northwest.
    • In September, dry, cool, northerly air begins to circle the west side of the highlands and spread over north-western India.
    • The easterly jet weakens, and the upper tropospheric easterlies move much farther south.
    • Because the moist southwesterlies at lower levels are much weaker and variable, they are soon pushed back.
    • The rainfall becomes extremely variable over most of the region, but showers are still frequent in the south-eastern areas and over the Bay of Bengal.
    • By early October, variable winds are very frequent everywhere.

    Winter rains

    • At the end of the month, the entire Indian region is covered by northerly air and the winter monsoon takes shape.
    • The surface flow is deflected by the Coriolis force and becomes a north-easterly flow.
    • Tropical depressions and cyclones are important contributing factors.
    • Most of India thus begins a sunny, dry, and dusty season.
    • Conversely, the western slopes of the Karakoram Range and Himalayas are then reached by the midlatitude frontal depressions that come from the Atlantic and the Mediterranean.
    • The winter rains they receive, moderate as they are, place them clearly outside the monsoonal realm.

     

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