News: Will the El Nino factor impact the monsoon?
Source: The Hindu
El Nino is synonymous with the Pacific Ocean that covers as much as one-third of the planet.
El Nino is a phenomenon in the equatorial Pacific, in which sea-surface temperatures rise over a threshold of +0.5 degree Celsius (and cools by the same margin during alter ego La Nina). These are averaged over five, three-month sessions on a trot across a stretch of water designated as the Nino 3.4 region (see graphic) to arrive at the Oceanic Nino Index (ONI). There are a few other acronyms which one comes across while tracking El Nino. For instance, the Southern Oscillation Index, or SOI, that gives an indication of the development and intensity of El Nino or La Nina.1
The SOI is calculated on the basis of the atmospheric pressure differences between Tahiti (South Pacific Ocean) and Darwin (Australia), separated by 8,569 km. Sustained positive SOI values are indicative of La Nina conditions while negative values suggest El Nino conditions. Another acronym is the ENSO (El Nino Southern Oscillation) which refers to the oscillation between the El Nino and the La Nina. ENSO shifts irregularly back and forth between El Nino and La Niña every two to seven years.
Each phase triggers predictable disruptions of temperature, precipitation, and winds disrupting large-scale air movements in the tropics, triggering a cascade of global side effects. Under ‘normal’ conditions, though, the west tropical Pacific is warmer than its eastern basin. The warmer area of the ocean is also a source for convection and is associated with cloudiness and rainfall. During El Nino years, the warmth shifts to Central and East Tropical Pacific (Nino 3.4 region), and along with it, cloudiness and rainfall.
El Nino was observed as far back as in the late 1800s when South American fishermen noticed the warming up of coastal waters around Christmas. They referred to it as “El Nino” (Spanish for the boy child), since it appeared around Christmas.
Sir Gilbert Walker, a British mathematician, discovered the Southern Oscillation (SO), or large-scale changes in sea level pressure across Indonesia and the tropical Pacific. However, he did not recognise that it was linked to changes in the Pacific Ocean or El Nino. It wasn’t until the late 1960s that Norwegian-American meteorologist Jacob Bjerknes and others realised that the changes in the ocean and the atmosphere were connected. This was how the coinage ‘ENSO’ came into existence.
El Nino has been found to impact almost half the world triggering droughts in Australia, India, southern Africa and floods in Peru, Ecuador, the United States, the Gulf of Mexico, and the Colorado River basin. If Sir Gilbert found in the 1920s that many global climate variations, including monsoon rains in India, were correlated with the SO, the credit of linking it with El Nino as part of ENSO involving both the ocean and atmosphere, goes to Bjerknes. But it took until the 1980s or later for ‘La Nina’ or even the ‘neutral phase’ (neither El Nino or La Nina) to gain currency.
India has not had a particularly productive monsoon since 2014 (save a tolerable 2017), with weak El Nino events unfolding on either side of the strong 2015-16 El Nino, a trend forecast to continue into this year. This comes on the back of a deficient post-monsoon season last year. After all, the south-west monsoon (June-September) accounts for over 70% of the country’s annual rainfall and irrigates over half of the crop land. The rain-fed kharif crops are heavily dependent on the monsoon and the quantity of rainfall determines agricultural production. Agriculture accounts for around 15% of the GDP and normal rains rejuvenate the farm sector and help the government deal with rural stress. Normal rains can boost sentiments, raise farm production, perk up rural demand, and tame inflation to some extent.
El Nino Southern Oscillation [ENSO]
The formation of an El Niño [Circulation of Water] is linked with Pacific Ocean circulation pattern known as the southern oscillation [circulation of atmospheric pressure.
Southern Oscillation, in oceanography and climatology, is a coherent inter-annual fluctuation of atmospheric pressure over the tropical Indo-Pacific region.
El Nino and Southern Oscillation coincide most of the times hence their combination is called ENSO – El Nino Southern Oscillation.
Only El Nino == [Warm water in Eastern Pacific + Cold water in Western Pacific].
Only SO == [Low Pressure over Eastern Pacific + High Pressure over Western Pacific]
ENSO = [Warm water in Eastern Pacific + Low Pressure over Eastern Pacific] + [Cold water in Western Pacific + High Pressure over Western Pacific].
SCIENCE & TECHNOLOGY
Source: The Hindu
A black hole can’t be seen. As a cosmic gobbler of all matter on its periphery, these sinkholes have gravitational fields so powerful that even light cannot escape them, rendering its contents invisible. Because the concept of black holes (the cemeteries of spent stars above a certain mass and massive cosmic objects) followed from Einstein’s theories of general relativity, scientists have had intricate mathematical descriptions and speculation of how they look, how many of them exist, how they behave, where they might be located and their relationship to the universe.
Recently astronomers shared an image, now christened on Indian Twitter as a ‘giant meduvada in the sky,’ from the black hole at Messier 87 or M87. It was a blurred, yellowish orange frame surrounding a black centre. While this wasn’t vastly different from how astronomers and artists have visualised black holes for decades, it’s still great to see reality correspond to imagination. The black hole measures 40 billion km across — three million times the size of the earth — and is 55 million light years from earth.
Since the 1970s, astronomers have known that there are ‘super massive’ black holes (about a billion times heavier than the sun) in the Milky Way or galaxies close to it. While black holes themselves are invisible, the region around them — the luminous frenzy of charged particles from matter in their vicinity — is, in theory, ‘visible’. The bigger a black hole, the greater the odds of it having a massive event horizon — the fiery periphery of a black hole — and the better our chances of observing wisps of radiation from it. After the discovery of a super massive black hole in M87 (a ‘neighbouring’ galaxy about 55 million light years away) and one in our Milky Way, astronomers formed a network of ultra-sensitive telescopes — called the Event Horizon Telescope — to dedicatedly train their sights towards trying to capture some radiation from them and hopefully, snap a real picture from the black hole’s periphery.
The astronomers used a technique known as interferometry, which combines radiation from eight telescopes from around the world in a way that it appears as one single telescope capture. What this virtual telescope would capture were traces — electromagnetic radiation — from jets of particles spewed from the event horizons of the black hole. This faint radiation, in the form of mostly radio waves, would have travelled trillions of kilometres and for the telescope to observe them would be the equivalent of trying to snap a picture of an ant from the moon.
The Laser Interferometer Gravitational-Wave Observatory (LIGO) was designed to open the field of gravitational-wave astrophysics through the direct detection of gravitational waves predicted by Einstein’s General Theory of Relativity. LIGO’s multi-kilometer-scale gravitational wave detectors use laser interferometry to measure the minute ripples in space-time caused by passing gravitational waves from cataclysmic cosmic events such as colliding neutron stars or black holes, or by supernovae. LIGO consists of two widely-separated interferometers within the United States—one in Hanford, Washington and the other in Livingston, Louisiana—operated in unison to detect gravitational waves.
Comprising the world's largest precision optical instruments and the world's second-largest vacuum systems, LIGO is a marvel of engineering and human ingenuity.