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Subject: Geography

  • Why has the Northeast Monsoon remained deficient this year?

    Rainfall over the Southern peninsular region has been deficient so far due to prevailing La Nina conditions according to the India Meteorological Department (IMD).

    Try this PYQ:

    Q.La Nina is suspected to have caused recent floods in Australia. How is La Nina different from El Nino?

    1. La Nina is characterized by unusually cold ocean temperature in equatorial Indian Ocean whereas El Nino is characterized by unusually warm ocean temperature in the equatorial Pacific Ocean.
    2. El Nino has an adverse effect on south-west monsoon of India, but La Nina has no effect on monsoon climate.

    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

    What is the Northeast monsoon?

    • India receives rainfall during two seasons.
    • About 75 per cent of the country’s annual rainfall is received from the Southwest monsoon between June and September.
    • The Northeast monsoon, on the other hand, occurs from October to December and is a comparatively small-scale monsoon, which is confined to the Southern peninsula.
    • After the complete withdrawal of the Southwest monsoon from the country takes place by mid-October, the wind pattern rapidly changes from the south-westerly to the north-easterly direction.
    • Also called the winter monsoon, the rainfall associated with the Northeast monsoon is important for almost entire South India.

    Why it is important?

    • Tamil Nadu records about 48 per cent (447.4 mm) of its annual rainfall (943.7 mm) during these months, making it the key factor for undertaking agricultural activities and reservoir management in the state.
    • Some South Asian countries such as Maldives, Sri Lanka and Myanmar also record rainfall from October to December.

    Why there are distortions?

    • The majority of districts in Tamil Nadu remain highly rain-deficient up this time.
    • The period after the Southwest monsoon season, from October to December, is the peak time for cyclonic activity in the North Indian Ocean region — covering the Arabian Sea and the Bay of Bengal.
    • The winds associated with the formation of low-pressure systems, depressions, or cyclones influence this monsoon, and therefore, the rainfall.
    • Officials at IMD have linked it to the prevailing La Niña conditions in the Pacific Ocean.

    La Nina  link with the NE monsoon

    • While La Niña conditions enhance the rainfall associated with the Southwest monsoon, it has a negative impact on rainfall associated with the Northeast monsoon.
    • During La Niña years, the synoptic systems — low pressure or cyclones — formed in the Bay of Bengal remain significantly to the north of their normal position.
    • Besides, instead of moving westwards, these systems recurve. As they lie to the north of their normal position, not much rainfall occurs over southern regions like Tamil Nadu.

    Back2Basics: El Nino and La Nina

    • While El Niño (Spanish for ‘little boy’), the more common expression, is the abnormal surface warming observed along the eastern and central regions of the Pacific Ocean (the region between Peru and Papua New Guinea).
    • The La Niña (Spanish for ‘little girl’) is an abnormal cooling of these surface waters.
    • Together, the El Niño and La Niña phenomena are termed as El Niño Southern Oscillation (ENSO).
    • These are large-scale ocean phenomena which influence the global weather — winds, temperature and rainfall. They have the ability to trigger extreme weather events like droughts, floods, hot and cold conditions, globally.
    • Each cycle can last anywhere between 9 to 12 months, at times extendable to 18 months — and re-occur after every three to five years.
    • Meteorologists record the sea surface temperatures for four different regions, known as Niño regions, along this equatorial belt.
    • Depending on the temperatures, they forecast either as an El Niño, an ENSO neutral phase, or a La Niña.

  • Cyclone Nivar to make landfall in TN

    A developing cyclonic disturbance in the Bay of Bengal is expected to become a ‘severe cyclonic storm’ and make landfall in Tamil Nadu.

    Cyclone Nivar

    • The IMD has forecasted the development of a cyclone in the Southwest region of the Bay of Bengal, off Tamil Nadu coast.
    • It has said that it will strengthen into a cyclone. Once intensified, it would acquire its name ‘Nivar’, proposed by Iran.
    • After cyclone Gaja in 2018, this will be the second cyclone to cross Tamil Nadu in the last two years.

    Try this PYQ:

    In the South Atlantic and South-Eastern Pacific regions in tropical latitudes, cyclone does not originate. What is the reason?

    (a) Sea surface temperatures are low

    (b) Inter-Tropical Convergence Zone seldom occurs

    (c) Coriolis force is too weak

    (d) Absence of land in those regions

    Tropical Cyclone

    • A Tropical cyclone is an intense circular storm that originates over warm tropical oceans and is characterized by low atmospheric pressure, high winds, and heavy rain.
    • Cyclones are formed over slightly warm ocean waters. The temperature of the top layer of the sea, up to a depth of about 60 meters, need to be at least 28°C to support the formation of a cyclone.
    • This explains why the April-May and October-December periods are conducive for cyclones.
    • Then, the low level of air above the waters needs to have an ‘anticlockwise’ rotation (in the northern hemisphere; clockwise in the southern hemisphere).
    • During these periods, there is an ITCZ in the Bay of Bengal whose southern boundary experiences winds from west to east, while the northern boundary has winds flowing east to west.
    • Once formed, cyclones in this area usually move northwest. As it travels over the sea, the cyclone gathers more moist air from the warm sea which adds to its heft.

    Must read:

    [Burning Issue] Tropical Cyclones and India

  • Places in news: Mount Vesuvius

    The Italian Culture Ministry announced the discovery of well-preserved remains of two men, who perished during the volcanic eruption of Mount Vesuvius in 79 AD.

    Try this PYQ:

    Q.Consider the following statements:

    1. The Barren Island volcano is an active volcano located in the Indian Territory.
    2. Barren Island lies about 140 km east of Great Nicobar.
    3. The last time the Barren Island volcano erupted was in 1991 and it has remained inactive since then.

    Which of the statements given above is/are correct?

    (a) 1 only

    (b) 2 and 3 only

    (c) 3 only

    (d) 1 and 3 only

    Mount Vesuvius

    • Located in southern Italy near the coastal city of Naples, the 4,203-ft (1,281 metres) tall Vesuvius is the only active volcano in mainland Europe.
    • Vesuvius has been classified as a complex volcano (also called a compound volcano), one that consists of a complex of two or more vents.
    • It typically has explosive eruptions and pyroclastic flows –– defined as a high-density mix of hot lava blocks, pumice, ash and volcanic gas.
    • It has erupted more than 50 times and is considered among the most dangerous volcanoes in the world due to its proximity to Naples and surrounding towns.
    • Its last serious eruption, lasting two weeks, was in 1944 during World War II, which left 26 Italian civilians dead and around 12,000 displaced.

    The eruption of 79 AD

    • In 79 AD, the Roman Empire-era sister cities of Pompeii and Herculaneum were destroyed and buried during a catastrophic eruption of Vesuvius.
    • It was a catastrophic event that destroyed the ancient Roman city of Pompeii and killed around 16,000 people.
    • Pompeii, 8 km away from Vesuvius, served as a resort town on the Bay of Naples for Rome’s elite citizens, consisting of villas, cafes, marketplaces and a 20,000-seat arena.
    • In 63 AD, a major earthquake rattled the city, serving as a warning for the eruption to come. However, few residents bothered to abandon the region, known for its volatility.

  • Cyclonic storms during October

    October to December period is among the favourable months for the development of cyclones in the Bay of Bengal and the Arabian Sea. This year, however, October passed without witnessing a cyclonic storm.

    Must read: [Burning Issue] Tropical Cyclones and India

    https://www.civilsdaily.com/burning-issue-tropical-cyclones-and-india/

    When do cyclones form and hit Indian coasts?

    • About 80 cyclones are formed around the world annually, out of which five are formed in the Bay of Bengal and the Arabian Sea, together known as the North Indian Ocean.
    • India’s east and west coasts are prone to cyclones with the maximum associated hazards—rain, heavy winds and storm surge— faced by coastal districts of West Bengal, Odisha and Andhra Pradesh.
    • Cyclones in the North Indian Ocean are bi-modal in nature, that is, they occur during two seasons— April to June (pre-monsoon) and October to December (post-monsoon).
    • Of these, May and November remain the most conducive for the development of cyclones.

    When have cyclones skipped October, previously?

    • Cyclonic disturbances— either in the form of a well-marked low pressure, depression or a deep depression— are common in October.
    • Ocean disturbances enter the Bay of Bengal from the South China seaside and head towards the Indian coast.
    • IMD officials have attributed it to the weak La Nina conditions along the equatorial Pacific Ocean.
    • Cooler than normal sea surface temperatures over this region—termed as La Nina— has been prevailing since August this year.

    Madden Julian Oscillation (MJO)

    • Because Madden Julian Oscillation (MJO) was positioned in a favourable phase, the low-pressure systems intensified maximum up to a deep depression.
    • MJO is kind of an eastward-moving cyclic weather event along the tropics that influences rainfall, winds, sea surface temperatures and cloud cover. They have a 30 to 60-day cycle.
    • Most importantly, there was the high wind shear noted between the different atmospheric levels, last month.
    • The vertical wind shear— created due to significant wind speed difference observed between higher and lowers atmospheric levels— prevented the low-pressure systems and depression from strengthening into a cyclone.

  • Char-chaporis of Assam

    A proposed museum reflecting the “culture and heritage of the people living in char-chaporis” has stirred up a controversy in Assam.

    Do you know?

    Phumdis are a series of floating islands, exclusive to the Loktak Lake in Manipur. They cover a substantial part of the lake area and are heterogeneous masses of vegetation, soil and organic matter, in different stages of decay.

    What are char-chaporis?

    • A char is a floating island while chaporis are low-lying flood-prone riverbanks.
    • They are used interchangeably as they keep changing shapes — a char can become a chapori, or vice versa, depending on the push and pull of the Brahmaputra.
    • Prone to floods and erosion, these areas are marked by low development indices.
    • While Bengali-origin Muslims primarily occupy these islands, other communities such as Misings, Deoris, Kocharis, Nepalis also live here.
    • In the popular imagination, however, chars have become synonymous to the Bengali-speaking Muslims of dubious nationality.

    Who are the Miyas?

    • The ‘Miya’ community comprises descendants of Muslim migrants from East Bengal (now Bangladesh) to Assam.
    • They came to be referred to as ‘Miyas’, often in a derogatory manner.
    • The community migrated in several waves — starting with the British annexation of Assam in 1826, and continuing into Partition and the 1971 Bangladesh Liberation War.

  • What are Western Disturbances?

    With the approaching winter, minimum temperatures in the national capital have trended downward over the last due to the arrival of northwesterly winds called Western Disturbances.

    Try this PYQ:

    Q.Westerlies in the southern hemisphere is stronger and persistent than in northern hemisphere. Why?

    1. The southern hemisphere has less landmass as compared to the northern hemisphere.
    2. Coriolis force is higher in the southern hemisphere as compared to the northern hemisphere

    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

    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.

    Their significance

    • 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.
    • 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. An average of four to five western disturbances forms during the winter season.
    • The rainfall distribution and amount vary with every western disturbance.

    Also read: Polar Vortex 

  • Ladakh Fault in Indus Suture Zone (ISZ)

    A recent survey has found that a tectonic fault line that runs through Ladakh, all along the Indus river, is not inactive as was previously thought and is, in fact, moving northward.

    Tap here to read more about Himalayan orogeny:

    Indus Suture Zone (ISZ)

    • A suture zone is a linear belt of intense deformation, where distinct terranes, or tectonic units with different plate tectonic, metamorphic, and paleogeographic histories, join together.
    • The ISZ represents a belt of tectonic compression caused by the underthrusting of the Indian shield/ plate against the Tibetan mass.
    • It marks the boundary between the Indian and Eurasian plates.
    • The suture zone stretches from the North-Western Himalayan syntaxis bordering the Nanga Parbat to the East as far as the Namche Barwa Mountain.

    Its tectonic activity

    • The Karakoram Range and the Ladakh plateau lie to the north of ISZ and originally formed a part of the European plate.
    • The zone has been neo-tectonically active for the past 78,000-58,000 years.
    • While the frontal and central parts of the Himalayas — the Shivaliks, Himachal Pradesh, Uttarakhand, Jammu and Kashmir and Sikkim — are still known to be active and moving.
    • The fault line runs all along the Indus river, from China through India and Pakistan.
    • The study was conducted in Ladakh from the north of Ladakh’s capital, Leh, to the Tso Moriri lake, a distance of 213 kilometres.

    Why the Ladakh region is more vulnerable?

    • Fault lines weaken the rock formation in the region through which it runs, making the area vulnerable to excessive erosion and landslides.
    • What makes the Ladakh region vulnerable is that unlike other areas in the Himalayas and the rest of the country, there is very little vegetation here and very few trees that can root the soil down.
    • So, in the case of a flash flood or a cloud burst, this can have a widespread impact.

  • What is Global Warming Hiatus (GWH)?

    A new study on variability in the Mascarene High (MH) in the Southern Indian Ocean during global warming hiatus (GWH) has revealed that the region experienced significantly increased sea surface temperature (SST) during this period (1998-2016).

    Try this PYQ:

    Q.With reference to Ocean Mean Temperature (OMT), which of the following statements is/are correct? (CSP 2020)

    1. OMT is measured upto a depth of 26 degree Celsius isotherm which is 129 meters in the south-western Indian Ocean during January-March.
    2. OMT collected during January-March can be used in assessing whether the amount of rainfall in monsoon will be less or more than a certain long-term mean.

    Select the correct answer using the code given below:
    (a) 1 only
    (b) 2 only
    (c) Both 1 and 2
    (d) Neither 1 nor 2

    What is Global Warming Hiatus (GWH)?

    • A global warming hiatus is referred to a global warming pause, or a global warming slowdown, which is a period of relatively little change in globally averaged surface temperatures.
    • The hiatus, however, can result in an increase in the SST.

    What is Mascarene High (MH)?

    • The Mascarene High (MH) is a semi-permanent subtropical high-pressure zone in the South Indian Ocean.
    • It is also called the Indian Ocean subtropical high, which is a high-pressure area located between 20° to 35° South latitude and 40° to 90° East longitude.
    • It is a region from where the cross-equatorial winds blow to India.
    • It has been named after the Mascarene Islands, in the Indian Ocean east of Madagascar consisting of the islands belonging to Mauritius as well as the French Réunion Islands.
    • Apart from its large influence on African and Australian weather patterns, it also helps in driving the inter-hemispheric circulation between the Indian Ocean in the south and subcontinental landmass in the north.

    Role of MH

    • The warming in SST due to global warming has resulted in a decrease in the pressure gradient between the MH and the Indian landmass.
    • This in turn suppressed the intensity of low-level cross-equatorial winds over the western Indian Ocean affecting the onset of the monsoon over the Indian subcontinent and rainfall over East Asia.

  • Places in news: Kamchatka Peninsula

    An ‘ecological disaster’ of sorts is unfolding on a black volcanic beach of the Kamchatka Peninsula in the Russian Far East, according to a report.

    Note the features of the map and surrounding seas.

    About Kamchatka Peninsula

    • The Kamchatka Peninsula is a 1,250-kilometre-long peninsula in the Russian Far East.
    • The Pacific Ocean and the Sea of Okhotsk make up the peninsula’s eastern and western coastlines, respectively.
    • Immediately offshore along the Pacific coast of the peninsula runs the 10,500-metre-deep Kuril–Kamchatka Trench.
    • The Kamchatka Peninsula, the Commander Islands, and Karaginsky Island constitute the Kamchatka Krai of the Russian Federation.
    • The vast majority of the 322,079 inhabitants are ethnic Russians, although about 13,000 are Koryaks (2014).
    • The Kamchatka peninsula contains the volcanoes of Kamchatka, a UNESCO World Heritage Site.

    Why in news?

    • Then, sea animals begin to die in large numbers, their bodies littering the beach.
    • These included octopuses, seals, sea urchins, stars, crabs and fish.
    • Examination of the seawater by the administration has shown that levels of phenols and oil compounds have spiked.

  • Location in news: English Channel

    Hundreds of migrants have taken advantage of the warm weather and calm seas in the English Channel to reach the UK in a flurry of small boat crossings.

    Try this PYQ:

    Q.Which one of the following pairs of islands is separated from each other by the ‘Ten Degree Channel’?

    (a) Andaman and Nicobar

    (b) Nicobar and Sumatra

    (c) Maldives and Lakshadweep

    (d) Sumatra and Java

    English Channel

    • The English Channel is an arm of the Atlantic Ocean that separates southern England from northern France.
    • It links to the southern part of the North Sea by the Strait of Dover at its northeastern end.
    • It is the busiest shipping area in the world.
    • It is about 560 km long and varies in width from 240 km at its widest to 34 km in the Strait of Dover.
    • It is the smallest of the shallow seas around the continental shelf of Europe.