Table of contents
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 (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)
![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.
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Atlantification
!['Atlantification' of the Arctic Ocean | UPSC](https://abhipedia.abhimanu.com/Uploads/image/Atlantification.jpg)
![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, 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)
- 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 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
![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)
- 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)
- 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.