> ## Content Index > Fetch the complete content index at: https://www.upscprep.com/llms.txt > Use this file to discover other available public pages before exploring further. # Previse 2025: Geography: Terms in News - URL: https://www.upscprep.com/previse-2024-geography-terms-in-news/ - Published: 2024-05-23T13:22:20.000Z - Updated: 2025-05-01T05:46:33.000Z - Description: GS1 | Geography - Author: UPSCprep.com - Tags: Previse 2025, Geography, UPSC Prelims, Current Affairs, #show-toc Understanding geographical concepts, from climate change and natural disasters to geopolitical conflicts and resource exploration, is essential for interpreting the news with a deeper lens. This section unpacks key geography terms making headlines, empowering you to grasp the spatial context of current events. ### **Pacific Decadal Oscillation** ![Pacific Decadal Oscillation  | UPSC](https://lh7-us.googleusercontent.com/FQUqU-J5K_Nw8pIfE3NSfqm9g76ArJLJpMAuwVffM3LpHLM1L6PGURJV9YIxnFIMx29N-3uNiBHFLLTbEGblztCYrO1ONvp8CecvSrx5OEYdSBf0zEy8o7OA6-7BTmIjfSOryZTPN4qVxw-yMwUiD68) ![Pacific Decadal Oscillation (PDO): Definition and Indices | Climate Data Guide UPSC](https://climatedataguide.ucar.edu/sites/default/files/styles/extra_large/public/2022-03/Deser-PDO1.png?itok=YPRrg4kv) - A phenomenon that **makes cyclones more frequent by combining global warming and the Pacific Decadal Oscillation (PDO)**. - Basically, it is a long-term ocean fluctuation in the Pacific Ocean. - Negative PDO, when encountered in the La Nina phase, creates suitable conditions for tropical cyclones. - PDO entered a cooler or negative phase in 2019. - The oscillation has two phases- - Cool or Negative Phase in which the Eastern Equatorial Pacific has lower than normal sea surface temperatures. - Warm or Positive phase in which the Western Pacific Ocean has higher than normal sea surface temperatures. --- ### **Blue Hole** ![Blue Hole Images – Browse 282,773 Stock Photos, Vectors, and Video | Adobe Stock](https://t4.ftcdn.net/jpg/05/31/30/09/360_F_531300948_uY0vbMOwDXOVfJtUCoJmGDj2XXFbAvRZ.jpg) ![Largest ever 'blue hole' uncovered 1.3k feet deep in the ocean and scientists still haven' | UPSC](https://lh7-us.googleusercontent.com/W4i72S9uWqkeN5zvx3Sdfm2nzj6POZXD3dDuyHkdbLl9yEyK3LAs1WCVdsvMBiwwG9-pYKvAVqIcZ-ME7gjBSLv432H8vCpD0Ou2lINM9qsY0ZeccdYb5K33Q6_JdjXinGdBlQF87FZ6WcwkxV1oW1w) ![In Graphic Detail: Taam ja' Blue Hole | UPSC](https://hakaimagazine.com/wp-content/uploads/chart-igd-blue-hole.jpg) - Blue Hole is a **massive underwater sinkhole** recently discovered off the coast of the Yucatan Peninsula in Mexico. - It is believed to have formed during the Ice Age when the sea level was 100–120 m lower than it is today. - It is a microbial biodiversity hotspot and gets its name due to indigo centres and light blue perimeters. - It is the deepest blue hole on Earth. --- ### **WISE Report** ![HI-WISE - Water, ice, society, and ecosystems in the Hindu Kush Himalaya | About ICIMOD | Members include Afghanistan, Bangladesh, Bhutan, China, India, Myanmar, Nepal, and Pakistan.](https://dics.co/uploads/2023/06/1687430446Fig4.1.jpg) ![Glaciers - ICIMOD | UPSC](https://www.icimod.org/wp-content/uploads/2019/12/glaciers_948X662.jpg) ![ICIMOD and HKH region upsc](https://dics.co/uploads/2024/02/1707387939Significance-of-the-HKH-region-ICIMOD-2019.png) - The **Water, Ice, Society, and Ecosystems (WISE)** report for the Hindu Kush Himalaya was released by the International Centre for Integrated Mountain Development (ICIMOD). - It reveals that glaciers disappeared 65% faster in the 2010s than in the last decade. - The accelerated glacier melt means that the ‘peak water’ stage (the supply of fresh snow water due to glacier melt is the highest ever) will reach around mid-century and decrease. - ICIMOD is an intergovernmental organization that focuses on climate and environmental risks, green economies, and sustainable action. - The members include **Afghanistan**, **Bangladesh**, **Bhutan**, **China**, **India**, **Myanmar**, **Nepal**, and **Pakistan**. --- ![Join UPSC Coaching | Crack IAS, IPS Exam](https://storage.ghost.io/c/92/07/9207d054-5e99-4b26-b8c8-424994497a07/content/images/2024/05/1.-UPSCprep-Banner-27.png) [Join Now](https://courses.upscprep.com/products?ref=upscprep.com) --- ### **Atlantification** ![ 'Atlantification' of the Arctic Ocean | UPSC](https://abhipedia.abhimanu.com/Uploads/image/Atlantification.jpg) ![ 'Atlantification' of the Arctic Ocean | UPSC](https://lh7-us.googleusercontent.com/kz1JTJxE9HQ0GfCVBu8s1Ahs5sz_J_CxK4MBI-Zs4kXrm02UZcqLevb0th_KzoMKyFRmh6wXr_XCJ4WApTE415EXQo59LqIgG0ffWC5LW2ff3DOCm8BW0Mu_VbCsxfTLkCY_nUro5R6kYsrgkEy3_o0) ![Physical manifestations and ecological implications of Arctic Atlantification | UPSC](https://media.springernature.com/lw685/springer-static/image/art%3A10.1038%2Fs43017-021-00228-x/MediaObjects/43017_2021_228_Fig3_HTML.png) - When **Arctic Ocean water becomes saltier and warmer**, it is known as Atlantification. - This occurs when warm water from the Atlantic Ocean is advected into the Arctic Ocean in increasing amounts. - The Barents Sea is a marginal water body in the Arctic Ocean that is starting to resemble the Atlantic Ocean. - The top of the Arctic Ocean is covered by sea ice, but below this layer, freshwater and a deeper layer of warmer, saltier water are delivered to the Arctic from the Atlantic Ocean. - The main driving force behind this occurrence is the process called Arctic Dipole. --- ### **Shelf Cloud** ![Shelf clouds are also known as Arcus clouds and were recently seen in Uttarakhand. | UPSC](https://lh7-us.googleusercontent.com/Ca2pw0suH61YL2cryrqit50-RI1vXmkoV-bl3STQ1_-Yxlkv-d2uYU_eOV2nJz1WkZs89UcOQnKiFAM4odhEGVAlkj2T5TnYACMrcTyOns7RwpqotNt2a9BG64xMc7iy2_w9bYWIuQUqxLNum7jbrgM) ![Shelf clouds are also known as Arcus clouds and were recently seen in Uttarakhand. | UPSC](https://lh7-us.googleusercontent.com/M36TDGu3OyYdR9ZfmFi4sn-xXbA3zwmRszf0SS23NAgn-oTWwTGhF16tdYZIlf0JsPA3Fn4o4ManNrN6tEYbL8CanFb-AcTz3zItTUg2jGq9QxKGhwVBce4IFqV_8eLfoZrZchz2-vIBgWXv3BZqoc0) - Shelf clouds, also known as **Arcus clouds**, were recently seen in Uttarakhand. - They are associated with powerful storm systems, commonly known as **wall clouds**, **rotation clouds** or **funnel clouds**. - The mechanism for their formation includes a cold downdraft from a cumulonimbus cloud reaching the ground and the rapid spreading of cold air along the ground, which pushes the warm, moist air upwards. - There are times when they are seen below the cumulonimbus clouds as dense and towering vertical clouds, causing intense rain. - Rising air condenses the water vapour into the patterns associated with shelf clouds. --- ### **Indian Ocean Geoid Low** ![The global geoid with Indian Ocean Geoid Low highlighted | UPSC](https://www.researchgate.net/publication/325417156/figure/fig1/AS:713121064828931@1547032719158/The-global-geoid-with-Indian-Ocean-Geoid-Low-highlighted-image-source.png) ![](https://lh7-us.googleusercontent.com/rPJmwGMzciVvxWvKZ8Z0fiEFjdvWtl7n3ZYy5lS2tlB2LVIy1AfvwKiujvTrMh1qPUwnvykXKFASNh5HUceXl6eN3l50t3oUkv8wAAekpq6QtOJi3PDNouMFGMzJNOwIkoxXDUvIOrdQx6BLLXaPHKc) - A geoid is a **‘gravity hole’** having anomalies on Earth's map, and the **Indian Ocean Geoid Low (IOGL)** is an approximately three million square kilometres-wide gravity hole in the Indian Ocean. - It is located just south of Sri Lanka because the Earth’s gravitational pull is weakest there. It is also the lowest geoid on Earth. - The sea level is also 100 meters lower than the global average sea level. - This is caused due to rising plumes of molten rock along the edges of Tethys Ocean bed. --- ### **Khazan Land** ![KHAZAN LAND | 'Khazans qualify as heritage ecosystem' | UPSC](https://www.heraldgoa.in/uploads/content_images/20210218.0045~haritage.png) ![KHAZAN LAND | 'Khazans qualify as heritage ecosystem' | UPSC](https://lh7-us.googleusercontent.com/mqhcDLTsPI6Dx_uDHRfNexp_p17Hoiulaag6c9Cc5ersOnCUUmfj1MTJHIFD20ikEEJPUpkWYQeIqsZUfwe_0Y8cWXBMfBQuoaxa9LjcZMhqFCJTqx7SBDKn_HdKyK1DiarCwHxjJHnvgF3QwV4DHdQ) - Khazan Land is a stretch of **low-lying, saline, water-logged coastal wetlands** of Goa influenced by tidal flows. - The estuarine agricultural system called Khazan farming is a carefully topo-hydro-engineered agro-aquaculture ecosystem based on the regulation of salinity and tides. - It has an important role in the ecosystem, serving as the main drainage system for floodwater. - It is reclaimed from mangrove forests through an intricate system of sluice gates, dykes and canals. - The **Salim Ali Bird Sanctuary** in the low-lying floodplains of Goa is an important example. --- ### **Aurora** ![Rare Aurora Phenomenon | Mount Saraswati in the Hanle Valley of Changthang | UPSC | Aurora](https://lh7-us.googleusercontent.com/ahxfLMBjZ8xOcH3JQh5Pt9GDpdTUVMc8y8zdbXvdkQnaCyelJwrncm9L-lUbKsj4K1cO_OfqnzWeMa-jEzH5bwvoLPrNdMxq12dqNKVBJewkxYDawlNSZnobd_yHnp9EWLiraC_ipLkP3qJQ-Mlhxbg) ![Mount Saraswati in the Hanle Valley of Changthang | UPSC | Aurora](https://scontent.fblr21-1.fna.fbcdn.net/v/t1.6435-9/51304244_692677421128905_6510863364934074368_n.jpg?_nc_cat=102&ccb=1-7&_nc_sid=5f2048&_nc_ohc=OqH86rsd8zAQ7kNvgElvg2q&_nc_ht=scontent.fblr21-1.fna&oh=00_AYBi07oBH55fEwSIKHbFfLxE7t9Jjn6uIFDhsVPNCMn4vQ&oe=667693CC) ![Hanle Observatory, Ladakh, India | UPSC | Solar Storm | geomagnetic storm | Aurora](https://pbs.twimg.com/media/GNTsJEjXEAALLjk?format=jpg&name=large) - It was documented at **Mount Saraswati** in the **Hanle Valley** of Changthang, Ladakh, by the Indian Astronomical Observatory. - They are usually visible near poles at any time of day but can be seen only at night with the naked eye. - Auroras are patterns of bright lights in the sky caused by the interaction of particles ejected by the Sun during coronal mass ejection with the magnetic field around the Earth. - The shape of Earth's magnetic field contributes to the creation of auroras, which are of two types- - **Northern lights (Aurora borealis)** in the Northern Hemisphere - **Southern lights (Aurora australis)** in the Southern Hemisphere --- ### **Omega Blocking** ![What is an Omega block? | UPSC](https://images.foxweather.com/static.foxweather.com/www.foxweather.com/content/uploads/2021/10/668/376/omega_high.png?ve=1&tl=1) ![An explanation of what a heat dome | Omega Block | UPSC](https://i.redd.it/jywxl2extt871.png) ![Gulfstream | Omega Blocking | UPSC](https://lh7-us.googleusercontent.com/cVnWnCOMxH2vNUPkdZZTuTjHLxRuVadAbHpsHK_KfeOTptWqV0cvZIehww1508TKVKtG_PpAteswyMIP5KlGe-nMUOm1FYWhri8D1tcTDzihj38Km0TGmFFypu64d5V5Hmcs2s0iNP0Swb78kZZOAvE) - After the recent floods in the Mediterranean region, a low-pressure system shaped like an Omega Block formed over the Netherlands. - They are also linked to heatwaves when a high-pressure pattern blocks and diverts the jet stream due to which a mass of hot air flows up from northern Africa and the Iberian peninsula. - When two low-pressure systems are cut off from the main flow of the jet stream and a high-pressure system is sandwiched between them, the structure resembles Ω. - This event is linked to other extreme events such as heatwaves in France & Germany, Pakistan floods, etc. ## Sign up for UPSCprep.com Simplify your UPSC journey Subscribe Email sent! 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