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Subject: Geography

  • [pib] Northern Limit of Monsoon (NLM)

    The Northern Limit of Monsoon (NLM) continues to pass through Diu, Surat, Nandurbar, Bhopal, Nowgong, Hamirpur, Barabanki, Bareilly, Saharanpur, Ambala & Amritsar.

    Try this question from CS Mains 2017:

    Q.What characteristics can be assigned to monsoon climate that succeeds in feeding more than 50 percent of the won population residing in Monsoon Asia?

    What is the Northern Limit of Monsoon?

    • NLM, is the northernmost boundary of India up to which monsoon rains have advanced on any given day.
    • So, it is a way of tracking the progress of monsoon clouds as they move over India’s landmass.
    • The India Meteorological Department (IMD) adds that the monsoon “advances northwards, usually in surges, and covers the entire country around July 15″.

    What are the Eastern and Western Arms?

    • It is the mountains of southern India that split the south-western winds, giving the Indian monsoon its ‘two arms.
    • The western arm of the monsoon is deflected northwards, by the Western Ghats, to (Mumbai) and then on to Pakistan.
    • The eastern arm travels up through the Bay of Bengal to (Kolkata) and Assam and is deflected north-westwards by the Himalayas.

    Also refer this link:

    Explain the formation of Indian monsoons. Highlight the link between monsoons and India’s cropping pattern. (15 marks)

  • Anti-hail guns to mitigate hailstorms crop damage

    To help out horticulturists who face crop damage due to hailstorms, the Himachal Pradesh government will be testing the use of indigenously developed ‘anti-hail guns’.

    What are anti-hail guns?

    • An anti-hail gun is a machine that generates shock waves to disrupt the growth of hailstones in clouds, according to its makers.
    • It comprises a tall, fixed structure somewhat resembling an inverted tower, several metres high, with a long and narrow cone opening towards the sky.
    • The gun is “fired” by feeding an explosive mixture of acetylene gas and air into its lower chamber, which releases a shock wave (waves that travel faster than the speed of sound, such as those produced by supersonic aircraft).
    • These shock waves supposedly stop water droplets in clouds from turning into hailstones, so that they fall simply as raindrops.

    Answer this PYQ in the comment box:

    Q.During a thunderstorm, the thunder in the skies is produced by the

    1. meeting of cumulonimbus clouds in the sky
    2. lightning that separates the nimbus clouds
    3. violent upward movement of air and water particles

    Select the correct option using the codes given below:

    (a) 1 only

    (b) 2 and 3 only

    (c) 1 and 3 only

    (d) None of the above

    How do they ‘prevent’ a hailstorm?

    • It is this hail formation process that the shock waves from anti-hail guns try to disrupt in a radius of 500 meters, so that the water droplets fall down before they can be lifted by the updrafts.
    • The machine is repeatedly fired every few seconds during an approaching thunderstorm.
    • However, the effectiveness of anti-hail guns has remained a contentious issue.

    How do Hailstorms occur?

    • Hail is produced by cumulonimbus clouds, which are generally large and dark and may cause thunder and lightning.
    • In such clouds, winds can blow up the water droplets to heights where they freeze into ice.
    • The frozen droplets begin to fall but are soon pushed back up by the winds and more droplets freeze onto them, resulting in multiple layers of ice on the hailstones.
    • This fall and rise is repeated several times, till the hailstones become too heavy and fall down.

  • Monsoon onset over Kerala delayed: IMD

    • The monsoon’s arrival over Kerala has been delayed to June 3, according to an update by the India Meteorological Department (IMD).
    • Private weather forecast agency, Skymet, however, said that the monsoon had arrived.
    • This was because two of the three criteria — as defined by the IMD — had been met.
    • Currently, IMD’s own data indicated that except for the OLR, the other criteria were met. Thus, there is an element of subjectivity in arrival.

    What are those criterias defined by IMD?

    1. Rain-bearing westerlies being at a minimum depth and speed;
    2. At least 60% of the available 14 stations in Kerala and coastal Karnataka, reporting rainfall of 2.5 mm or more for two consecutive days after May 10;
    3. A certain degree of clouding, indicated by a parameter called ‘outgoing long wave radiation’ (OLR), being below 200 W/square meter.

    What is meant by ‘Outgoing Long Wave Radiation’ (OLR)?

    • Outgoing Long-wave Radiation (OLR) is electromagnetic radiation of wavelengths from 3–100 μm emitted from Earth and its atmosphere out to space in the form of thermal radiation.
    • It is also referred to as up-welling long-wave radiation and terrestrial long-wave flux, among others.
    • The flux of energy transported by outgoing long-wave radiation is measured in W/m.
    • In the Earth’s climate system, long-wave radiation involves processes of absorption, scattering, and emissions from atmospheric gases, aerosols, clouds and the surface.
    • Over 99% of outgoing long-wave radiation has wavelengths between 4 μm and 100 μm, in the thermal infrared part of the electromagnetic spectrum.

    Factors responsible for south-west monsoon formation:

    1. Intense heating of Tibetan plateau during summer months.
    2. Permanent high pressure cell in the South Indian Ocean (east to north-east of Madagascar in summer).

    Factors that influence the onset of south-west monsoons:

    1. Above points +
    2. Subtropical Jet Stream (STJ).
    3. Tropical Easterly Jet (African Easterly Jet).
    4. Inter Tropical Convergence Zone.

    Factors that influence the intensity of south-west monsoons:

    1. Strengths of Low pressure over Tibet and high pressure over southern Indian Ocean.
    2. Somali Jet (Findlater Jet).
    3. Somali Current (Findlater Current).
    4. Indian Ocean branch of Walker Cell.
    5. Indian Ocean Dipole.

    Factors responsible for north-east monsoon formation:

    1. Formation and strengthening of high pressure cells over Tibetan plateau and Siberian Plateau in winter.
    2. Westward migration and subsequent weakening of high pressure cell in the Southern Indian Ocean.
    3. Migration of ITCZ to the south of India.

  • What is a Supermoon?

    The Moon will have the nearest approach to Earth on May 26, and therefore will appear to be the closest and largest Full Moon or “supermoon” of 2021.

    Tap here to read more about Solar and Lunar Eclipses

    What is a Supermoon?

    • A supermoon occurs when the Moon’s orbit is closest to the Earth at the same time that the Moon is full.
    • As the Moon orbits the Earth, there is a point of time when the distance between the two is the least (called the perigee when the average distance is about 360,000 km from the Earth).
    • Also, there is a point of time when the distance is the most (called the apogee when the distance is about 405,000 km from the Earth).
    • Now, when a full moon appears at the point when the distance between the Earth and the Moon is the least, not only does it appear to be brighter but it is also larger than a regular full moon.
    • According to NASA, the term supermoon was coined by astrologer Richard Nolle in 1979.
    • In a typical year, there may be two to four full supermoons and two to four new supermoons in a row.

    What is happening today?

    • Two celestial events will take place at the same time.
    • One is the supermoon and the other is a total lunar eclipse, which is when the Moon and Sun are on opposite sides of the Earth.
    • Because of the total lunar eclipse, the moon will also appear to be red.
    • This is because the Earth will block some of the light from the Sun from reaching the moon.
    • The Earth’s atmosphere filters the light, it will soften “the edge of our planet’s shadow” “giving the Moon a deep, rosy glow.”

  • Eruption of Mount Nyiragongo

    Thousands have fled a volcanic eruption in the Democratic Republic of Congo from Mount Nyiragongo on the outskirts of Goma City.

    These were some volcanoes in news this year:

    Mount Vesuvius, Taal Volcano, La Soufriere

    Mount Nyiragongo

    • Mount Nyiragongo is an active stratovolcano with an elevation of 3,470 m (11,385 ft) in the Virunga Mountains associated with the Albertine Rift.
    • The main crater is about 2km wide and usually contains a lava lake.
    • The crater presently has two distinct cooled lava benches within the crater walls.
    • It is one of the 16 Decade Volcanoes.
    • Nyiragongo’s lava lake has at times been the most voluminous known lava lake in recent history. The depth of the lava lake varies considerably.
    • Nyiragongo and nearby Nyamuragira are together responsible for 40 percent of Africa’s historical volcanic eruptions.

    Answer this PYQ in the comment box:

    Q.Which of the following adds/add carbon dioxide to the carbon cycle on the planet Earth?

    1. Volcanic action
    2. Respiration
    3. Photosynthesis
    4. Decay of organic matter

    Select the correct answer using the code given below:

    (a) 1 and 3 only

    (b) 2 only

    (c) 1, 2 and 4 only

    (d) 1, 2, 3 and 4

    What are Decade Volcanoes?

    • The Decade Volcanoes are 16 volcanoes identified by the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI).
    • They are considered worthy of particular study in light of their history of large, destructive eruptions and proximity to densely populated areas.
    • They are named Decade Volcanoes because the project was initiated in the 1990s as part of the United Nations-sponsored International Decade for Natural Disaster Reduction.

  • Cyclone Tauktae

    Cyclone Tauktae (pronounced Tau-Te), classified as a very severe cyclonic storm (VSCS) and developed in the Arabian Sea, is wreaking havoc all across the Indian Coast.

    Don’t you think?

     In recent years, strong cyclones have been developing in the Arabian Sea more frequently than earlier.

    Cyclone Tauktae

    • Tauktae is a currently active and strengthening tropical cyclone threatening the state of Gujarat in India and impacting the states Karnataka, Goa and Maharashtra.
    • It is the fourth cyclone in consecutive years to have developed in the Arabian Sea, that too in the pre-monsoon period (April to June).
    • All these cyclones since 2018 have been categorised as either ‘Severe Cyclone’ or above.
    • Once Tauktae makes its landfall, three of these will have hit either the Gujarat or Maharashtra coast.
    • After Cyclone Mekanu in 2018, which struck Oman, Cyclone Vayu in 2019 struck Gujarat, followed by Cyclone Nisarga in 2020 that struck Maharashtra.

    What is aiding such rapid intensification?

    • Any tropical cyclone requires energy to stay alive.
    • This energy is typically obtained from the warm water and humid air over the tropical ocean.
    • Currently, seawater up to depths of 50 metres has been very warm, supplying ample energy to enable the intensification of Cyclone Tauktae.
    • The more the heat released through condensation of water vapour, the steeper the drop in pressure.
    • A low-pressure system undergoes multiple stages of intensification to form cyclones.

    Not a rare phenomenon

    • Typically, tropical cyclones in the North Indian Ocean region (the Bay of Bengal and the Arabian Sea) develop during the pre-monsoon and post-monsoon (October to December) periods.
    • May-June and October-November are known to produce cyclones of severe intensity that affect the Indian coasts.

    Is the Arabian Sea becoming cyclone-friendly?

    • Annually, five cyclones on average form in the Bay of Bengal and the Arabian Sea combined.
    • Of these, four developments in the Bay of Bengal, which is warmer than the Arabian Sea.
    • In the Arabian Sea, cyclones typically develop over the Lakshadweep area and largely traverse westwards, or away from India’s west coast.
    • However, in recent years, meteorologists have observed that the Arabian Sea, too, has been warming. This is a phenomenon associated with global warming.

    Back2Basics: Tropical Cyclone

    • A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure centre, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rains.
    • Depending on its location and strength, a tropical cyclone is referred to by different names, including hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, or simply cyclone.
    • A hurricane is a tropical cyclone that occurs in the Atlantic Ocean and the northeastern Pacific Ocean, and a typhoon occurs in the northwestern Pacific Ocean.
    • In the south Pacific or the Indian Ocean, comparable storms are referred to simply as “tropical cyclones” or “severe cyclonic storms”.

    Also read:

    [Burning Issue] Tropical Cyclones and India

  • Major seismic hazard along Assam faultline

    Location of epicentre

    • An earthquake of magnitude 6.4 on the Richter scale hit Assam around 8 am on Wednesday.
    • The primary earthquake had its epicentre at latitude 26.690 N and longitude 92.360 E, about 80 km northeast of Guwahati, and a focal depth of 17 km, the National Centre for Seismology (NCS) said.

    The faultline

    • The preliminary analysis shows that the events are located near to Kopili Fault closer to Himalayan Frontal Thrust (HFT).
    • The Kopili Fault is a 300-km northwest-southeast trending fault from the Bhutan Himalaya to the Burmese arc.
    • The fault is a fracture along which the blocks of crust on either side have moved relative to one another parallel to the fracture.
    • The area is seismically very active falling in the highest Seismic Hazard zone V associated with collisional tectonics where Indian plate sub-ducts beneath the Eurasian Plate the NCS report said.
    • HFT, also known as the Main Frontal Thrust (MFT), is a geological fault along the boundary of the Indian and Eurasian tectonic plates.

    Need for earthquake preparedness

    • The Northeast is located in the highest seismological zone, so we must have constant earthquake preparedness at all levels.
    • Continuous tectonic stress keeps building up particularly along the faultlines.
    • Today’s earthquake was an instance of accumulated stress release — probably, stress was constrained for a fairly long time at this epicentre, and hence the release was of relatively higher intensity.

  • La Soufriere volcanic eruption

    Sulphur dioxide (SO2) emissions from La Soufriere volcano eruption in the Caribbean have reached all the way to India.

    Why in news?

    • Its eruption has sparked fear of increased pollution levels in the northern parts of India and acid rain.
    • Volcanic plumes can cause aviation and air quality hazards.

    La Soufriere

    • It is an active stratovolcano on the Caribbean island of Saint Vincent in Saint Vincent and the Grenadines.
    • It is the highest peak in Saint Vincent and has had five recorded explosive eruptions since 1718.

    Impact of such eruptions

    • Volcanic emissions reaching the stratosphere can have a cooling effect on global temperatures.
    • The most significant climate impacts from volcanic injections into the stratosphere come from the conversion of sulphur dioxide to sulphuric acid, which condenses rapidly in the stratosphere to form fine sulphate aerosols.
    • The aerosols increase the reflection of radiation from the Sun back into space, cooling the Earth’s lower atmosphere or troposphere.

    Try this PYQ:

    Q.Which of the following adds/add carbon dioxide to the carbon cycle on the planet Earth?

    1. Volcanic action
    2. Respiration
    3. Photosynthesis
    4. Decay of organic matter

    Select the correct answer using the code given below:

    (a) 1 and 3 only

    (b) 2 only

    (c) 1, 2 and 4 only

    (d) 1, 2, 3 and 4

  • How Asian desert dust enhances Indian summer monsoon?

    A new study has revealed how dust coming from the deserts in West, Central and East Asia plays an important role in the Indian Summer Monsoon.

    Try this PYQ:

    With reference to ‘Indian Ocean Dipole (IOD)’, sometimes mentioned in the news while forecasting Indian monsoon, which of the following statements is/are correct?

    1. IOD phenomenon is characterized by a difference in sea surface temperature between tropical Western Indian Ocean and tropical Eastern Pacific Ocean.
    2. An IOD phenomenon can influence an El Nino’s impact on the monsoon.

    Select the correct Option using the code given below:

    (a) Only 1

    (b) Only 2

    (c) Both 1 and 2

    (d) Neither 1 nor 2

    Why study dust?

    • Many studies have shown that the dust emission scheme is extremely sensitive to climate change.
    • Understanding these mechanisms and effects of dust will help us understand our monsoon systems in the face of global climate change.

    Impact of dust on Indian Monsoon

    • Dust swarms from the desert when lifted by strong winds can absorb solar radiation and become hot.
    • This can cause heating of the atmosphere, change the air pressure, wind circulation patterns, influence moisture transport and increase precipitation and rainfall.
    • A strong monsoon can also transport air to West Asia and again pick up a lot of dust.
    • The researchers say this is a positive feedback loop.

    Role of the Iranian plateau

    • Not just the dust from the Middle East, the Iranian Plateau also influences the Indian Summer Monsoon.
    • The hot air over the Iranian Plateau can heat the atmosphere over the plateau, strengthen the circulation over the deserts of the Arabian Peninsula and increase dust emission from the Middle East.
    • The researchers also explain how the Indian Summer Monsoon has a reverse effect and can increase the winds in West Asia to produce yet more dust.

    Transported aerosols

    • Deserts across the globe play important roles in monsoons.
    • The dust aerosols from deserts in West China such as the Taklamakan desert and the Gobi Desert can be transported eastward to eastern China and can influence the East Asia summer monsoon.
    • And in the southwest United States, we have some small deserts that influence the North African monsoon.

    Anthropogenic contributions

    • Some studies have found that the anthropogenic aerosols emitted from the Indian subcontinent can decrease summer monsoon precipitation.
    • However, some others found that absorbing aerosols such as dust can strengthen the monsoon circulation.

    Minor components

    • Earlier it was believed that dust from deserts across the globe will have the same components.
    • But it was found that different deserts have different chemical compositions and this can influence the dust’s properties.
    • For example, dust from the Middle East has the more absorbing ability of solar radiation than dust from North Africa and this difference in absorbing ability might influence monsoon systems.

  • Indian monsoon 25 million years ago resembled present day Australia’s

    Using leaf fossils, researchers have found that the Indian monsoon 25 million years ago resembled present-day Australia’s.

    Try this PYQ:

    Q.Which one of the following is the appropriate reason for considering the Gondwana rocks as the most important rock systems of India?

    (a) More than 90% of limestone reserves of India are found in them

    (b) More than 90% of India’s coal reserves are found in them

    (c) More than 90% of fertile black cotton soils are spread over them

    (d) None of the reasons given above is appropriate in this context

    India’s drift

    • About 180 million years ago, India separated from the ancient supercontinent Gondwana and took a long northward journey of about 9,000 km to join Eurasia.
    • During this journey, the subcontinent moved from the southern hemisphere, crossed the Equator to reach its current position in the northern hemisphere.
    • Due to these changing latitudes, it experienced different climatic conditions, and a new study has now tried to map these climatic variations using leaf fossils.

    Clueless over the evolution of monsoon

    • The evolution of the monsoonal climate in India is still debatable and not fully understood.
    • Though recent data indicates that the monsoon system we experience now dates back to about 25 million years, it is still unclear how the climate was during its long voyage.

    Indian research

    • The researchers analysed the morphological characters of fossil leaves collected from Deccan Volcanic Province, East Garo Hills of Meghalaya, Gurha mine in Rajasthan and Makum Coalfield in Assam.
    • The four fossil assemblages were found to be from four different geological ages.
    • It has been observed from across the globe that plant leaf morphological characters such as apex, base and shape are ecologically tuned with the prevailing climatic conditions.
    • The research applied this model to characterize the past monsoon from fossil leaves.

    It’s finding

    • The results indicated that the fossil leaves from India were adapted to an Australian type of monsoon and not the current Indian monsoon system during its voyage.
    • The reconstructed temperature data show that the climate was warm (tropical to subtropical) at all the studied fossil sites with temperatures varying from 16.3–21.3 degrees C.
    • All the fossil sites experienced high rainfall, which varied from 191.6 cm to 232 cm.