Wednesday, May 29, 2013

Day and Night (Earth's rotation)

When the earth rotates on its axis, only one portion of the earth's surface comes into the rays of the the sun and experiences daylight. The other portion which is away from the sun's rays will be in darkness. As the earth rotates from west to east, every part of the earth's surface will be brought under the sun at some time or other. A part of the earth's surface that emerges from darkness into the sun's rays experiences sunrise. Later, when it is gradually obscured from the sun's beams it experiences sunset. The sun is, in fact, stationary and it is earth which rotates. The illusion is exactly the same as when we travel in a fast-moving train. The trees and houses around us appear to move and we feel that the train is stationary.

Monday, May 27, 2013

Evidence of the Earth's Sphericity

There are many ways to prove that the earth is spherical. The following are some of them. 1. CIRCUMNAVIGATION OF THE EARTH. The first voyage around the world by Ferdinand Magellan and his crew, from 1519 to 1522, proved beyond doubt that the earth is spherical. No traveller going roumd the world by land or sea has eve encountered an abrupt edge, over which he would fall. Modern air routes and ocean navigation are based on the assumption that the earth is round. 2. THE CIRCULAR HORIZON. The distant horizon viewed from the deck of a ship at sea, or from a cliff on land is always and everywhere circular in shape. This circular horizon widens with increasing altitude and could only be seen on a spherical body. 3. SHIP'S VISIBILITY. When a ship appears over the distant horizon, the top of the mast is seen first before the hull. In the same way, when it leaves habour, its disappearance over the curved surface is equally gradual. If the earth were flat, the entire ship would be seen or obscured all at once. 4. SUNRISE AND SUNSET. The sun rises and sets at different times in different places. As the earth rotates from west to east, places in the east see the sun earlier than those in the west. If the earth were flat, the whole world would have sunrise and sunset at the same time. But we know this is not so. 5. THE LUNAR ECLIPSE. The shadow cast by the earth on the moon during a lunar eclipse is always circular. It takes the outline of an arc of a circle. Only a sphere can cast such a circular shadow. 6. PLANETARY BODIES ARE SPHERICAL. All observations from telescopes reveal that the planetary bodies, the sun, moon, satellites and stars have circular outlines from whichever angle you see them. They are strictly spheres. Earth, by analogy, cannot be the only exception. 7. DRIVING POLES ON LEVEL GROUND ON A CURVED EARTH. Engineers when driving poles of equal length at regular intervals on the ground have found they do not give a perfect horizontal level. The centre pole normally projects slightly above the poles at either end because of the curvature of the earth. Surveyors and field engineers therefore have to make certain corrections for this inevitable curvature, i.e. 12.6 cm to 1 km. 8. SPACE PHOTOGRAPHS. Pictures taken from high altitudes by rockets and satellites show clearly the curved edge of the earth. This is perhaps the most convincing and the most up-to-date proof of the earth's sphericity.

Sunday, May 26, 2013

The Shape of the Earth

In the olden days, sailors feared to venture far into the distant ocean because they thought that when they reached the edge of the earth, they would slip down and perish in the bottomless ocean. This is, of course, not true. From years of accumulated knowledge, experience and observations in different parts of the world, we know that the earth is round. Its spherical shape is an established fact, proved and accepted by all. There has been so much research done on earth science that its various dimensions have been accurately found. It has an equatorial circumference of 40,084 km and its polar circumference is less by 133 km. Its equatorial diameter is 12,761 km and its polar diameter is shorter by 42 km. This simply shows that the earth is not a perfect sphere. It is a little flattened at both ends like an orange. It can, in fact, be called a geoid ('earth-shaped'). The spherical shape of the earth is also masked by the intervening highlands and oceans on its surface.

The Solar System

The solar system comprises the sun and its nine planets which are believed to have been developed from the condensation of gases and other lesser bodies. All the planets revolve round the sun in elliptical orbits. Like the earth, they shine only by the reflected light of the sun. The sun has a surface temperature of 6000'C and increases to 20 million'C in the interior. All over its surface are fiery gases that leap up in whirls of glowing flames like a volcano in eruption. In size, the sun is almost unimaginable. It is about 300,000 times as big as the earth! Amongst the nine planets, MERCURY is the smallest and closest to the sun, only 57,900,000 km away. It thus completes its orbit in a much shorter space of time than does earth. A year in Mercury is only 88 days. VENUS, twice the distance away from the sun, is the next closest planet. It is often considered as "Earth's twin" because of their close proximity in size, mass (weight) and density. But no other planet is in any way comparable to EARTH which has life and all the living things we see around us. Like many other planets, the earth has a natural satellite, the moon, 384,629 km away, that revolves eastward around the Earth once in every 27 days. The fourth planet from the sun is MARS which has dark patches on its surface and is believed by most professional astronomers to be the next planet after Earth to have the possibility of some plant life. Much attention has been focused on Mars to explore the possibilities of extending man's influence to it. Next comes JUPITER, the largest planet in the solar system. Its surface is made up of many gases like hydrogen, helium and methane. It is distinguished from other planets by its circular light and dark bands, and the twelve satellites that circle round it. As it is more than 780 million km from the sun, its surface is very cold, probably about - 128'C. Another unique planet is SATURN which has three rings and nine satellites around it. In size, it is the second largest after Jupiter. It is so far from the sun that it takes 29 and half years to complete its orbit. The seventh planet, URANUS, was not known to astronomers until the late eighteenth century when it was first seen as a faint bluish-green disc through a very powerful telescope. It is another giant planet, 50 times larger than earth and 15 times as heavy. Unlike other planets, Uranus orbits around the sun in a clockwise direction from east to west with five satellites revolving round it. The two outermost planets in the solar system, Neptune and Pluto, are just visible with telescopes. Their discoveries were the result of mathematical calculations on their irregular gravitational effects on neighbouring planetary bodies. NEPTUNE closely resembles Uranus, except that it has only two known satellites and is probably much colder. Pluto is smaller than earth. As the orbits of the planets are not circular but elliptical, the distance of Pluto from the sun during perihelion (i.e. when it is closest to the sun) is 4451 million km, and at aphelion (i.e. when it is farthest from the sun) is 7348 million km. A year in PLUTO is no less than 247 years on earth! Due to their very recent discovery and their extreme remoteness from the earth, very little is so far known about these last two planets.

Exploring the Universe

On a bright night when you look up at the sky, it seems to be studded with stars. Little do you realize that each of the stars is far bigger than the earth on which we live. Some of the larger ones have been estimated to be many millions of times the size of the earth. The stars are not scattered regularly in space; they occur in clusters, better described as galaxies or nebulas. Each galaxy may contain as many as 100,000 million stars. The stars appear small to us even through a telescope because they are so far away. The light from the nearest star traveling at the speed of light (i.e. 299,400 kilometres/186,000 miles per second) takes something like four years to reach us. A ray of light from the sun takes about eight minutes to reach the earth. Light takes only a second to reach us from the moon. In recent years much interest has been shown and vast expenditure has been made, particularly by the United States and the Soviet Union, in exploring outer space. Many problems have had to be overcome. For example, the problem of meeting man's basic needs of oxygen, water and food; temperature control and the problem of weightlessness, while he is in outer space. A number of technological advances have been made in the course of these space programmes, particularly in the fields of radio and television communications. On 4 October 1957 the Soviet Union successfully launched the first artificial satellite (Sputnik I). This was followed by a series of unmanned spacecraft that sent back to earth television pictures of the surface features of the heavenly bodies, and coded information by radio. In April 1961 the Soviet Union successfully placed the first man, Yuri Gagarin, in orbit round the earth. Since then there have been many manned flights into outer space, culminating in the first landing on the moon by American astronauts in a rocket called Apollo 11 in July 1969. The importance of space exploration to man in general, and to geographers and other earth scientists in particular, is immense. Much has been learnt about space temperature, the magnetic fields of the sun and the earth, the amount and kinds of radiation, the shape and extent of the earth's upper atmosphere. We have learnt much about the surface of the moon and about human adaptability to its environment.

Wednesday, May 22, 2013

ANIMAL LIFE OF THE SAVANNA

The savanna, particularly in Africa, is the home of wild animals. It is known as the 'big game country' and thousands of animals are trapped or killed each year by people from all over the world. Some of the animals are tracked down for their skins, horns, tusks, bones or hair, others are captured alive and sent out of Africa as zoo animals, laboratory specimens or pets. There is such a wealth of animal life in Africa that many of the animal films are actually taken in the savanna. There are, in fact, two main groups of animals in the savanna, the herbivorous animals and the carnivorous animals. The herbivorous animals are often very alert and move swiftly from place to place in search of green pastures. The leaf and grass eating animals include the zebra, antelope, giraffe, deer, gazelle, elephant and okapi. The carnivorous animals like the tiger, lion, leopard, hyena, panther, jaguar, jackal, lynx and puma have powerful jaws and teeth for attacking other animals.

Tropical Upper Atmosphere 'Fingerprint' of Global Warming

The pulse of the QBO has weakened substantially at some altitudes over the last six decades, according to a new study by scientists at theInternational Pacific Research Center, University of Hawaii atManoa, and the Japan Agency for Marine-Earth Science and Technology. The decline in thestrength of the QBO is consistent with computer model projections of how the upper atmosphere responds to global warming induced by increased greenhouse gas concentrations. The study appears in the May 23, 2013, online issue of Nature . "This is the first demonstration of a systematiclong-term trend in the observed QBO record," says co-author Kevin Hamilton and Director of the IPRC. "We see a similar trend in computer models of the global atmosphere when they simulate the last century using the historical changes of greenhouse gases. So this change in upper atmospheric behavior can be considered part of the "fingerprint" of theexpected global warming signal in the climate system." The global atmospheric circulation is characterized byair slowly rising in the tropics into the upper atmosphere and sinking at higher latitudes. While this circulationis so slow that a blob of air may take decades to travel tothe upper atmosphere, it impacts the chemical composition of the global atmosphere because many chemical properties are very different in the lower and upper atmosphere layers. Although computer models used to project climate changes from increasing greenhouse gas concentrations consistently simulate an increasing upwardairflow in the tropics with global warming, this flow cannot be directly observed. "We demonstrated that the mean upward-air motion suppresses the strength of the QBO winds in the models and thus interpret our observed weakened QBO trend as confirmation that the mean upward velocity in the tropics has indeed been increasing," notes Hamilton. Hamilton provides an exampleof why the upward airflow is so significant: "The manufacture of ozone-destroying chemicals such as the freon compounds used in the past in spray cans and in refrigerators has been largely banned for over 20 years. These chemicals, however, remain in the atmosphere for many decades. They are slowly flushed out of the lower atmosphere into the upper atmosphere where they are destroyed. Stronger mean upward airflow transports these chemicals more quickly into the upper atmosphere, and the ozone layer will recover more quickly to its natural state before the introduction of man-made freon compounds."

GPS data could improve tsunami early warnings

The researchers say that GPS technology could provide vital extra minutes before a tsunami strikes Scientists say they have found a way to provide faster and more accurate early warning systems for tsunamis. A German team says GPS satellite-based positioning could
offer detailed information about the events within minutes of an earthquake occurring. They believe the technology could have improved alerts issued when the devastating tsunami hit Japan in 2011. The study is published in Natural Hazards and Earth Systems Sciences . When an underwater earthquake happens, with the power to generate a tsunami, every second counts. The shifting tectonic platescan generate giant walls ofwater that can travel towards land in minutes, giving little time to put evacuation plans into action. Precise measurements Existing early warning systems use seismological data, measuring the wavesof energy that are generated as the earth moves and shakes. You can predict thetsunami and see how high a wave could be expected, with some accuracy Dr Andreas Hoechner, GFZ German Research Centre for Geosciences But in the vital first stagesof an earthquake, this is not always reliable. Now a team from the GFZ German Research Centre for Geosciences says that satellite navigation technology could help. GPS sensors placed around the coastlines of vulnerable countries could make highly precise measurements of how underwater tremors shift the ground. Lead researcher Dr Andreas Hoechner explained: "In case of a subduction earthquake, one plate slips under another plate. "It is measured in terms of relative displacement. Thisdeformation is mostly above the source, but the coastal area is also deformed and this can be picked up by GPS." He said that this information could be used to reconstruct the source of the earthquake and calculate its magnitude. "Then you can then predictthe tsunami and see how high a wave could be expected, with some accuracy." This process would take a matter of minutes, which would allow alerts to be issued extremely quickly. Disseminate warnings In the case of the 2011 tsunami that killed 16,000 people in Japan, the technology could have made a significant difference. Although the Japan Meteorological Agency issued a warning three minutes after the earthquake hit, it underestimated the scale of the event. It suggested that the quake was 7.9 magnitude; it was actually 30 times more powerful. By looking at data collectedby GPS stations in Japan - which at the time were not used to measure earthquakes - the researchers calculated that this would have provided an accurate estimate of the magnitude within three minutes. A number of countries are now installing GPS networks, including Chile and the US. But Dr Hoechner said that as well as having accuratealert systems, well thought-out evacuation plans were also essential. He said: "One point is to have the technology to realise what the earthquake is and where tsunami will be. But it is at least as important is to disseminate the warning. "You have to have the infrastructure to transmit this information to the population, and the population has to be readyto know what to do."

Oklahoma tornado: Mayor of Moore pushes for shelter law

Glenn Lewis said he would propose an ordinance requiring a reinforced shelter to be built in everynew home. Volunteers are now engaged in a recovery mission - delivering supplies and helping people find accommodation. The White House says thatPresident Barack Obama will travel to Moore on Sunday. The Oklahoma medical examiner's office said 23 of the 24 victims had now been identified and that 10of them were children. Disaster centres Mr Lewis said he would propose the ordinance in the next few days and wasconfident it would pass thesix-member city council. The houses are broken (and the cars, and the school, and the street signs), but the people are not. The law would require a storm shelter or safe roomin all single- and multi-family homes and could be in place in a few months. "We'll try to get it passed as soon as I can," Mr Lewis told CNN. An underground safe roomcan cost several thousanddollars. More than 100 schools in Oklahoma had been provided with state-funded safe rooms. But Plaza Towers Elementary - where sevenof the children killed in the tornado died - and one other school hit by the storm, Briarwood Elementary, did not. The tornado ripped the roof off Plaza Towers Elementary and knocked down walls as students and teachers cowered in hallways and bathrooms. The tornado, which the National Weather Service (NWS) listed as an EF-5 - the most powerful type on the Fujita scale - destroyed entire blocks of Moore, an Oklahoma City suburb of 56,000 people. The twister packed winds of at least 200mph (320km/h). Mr Lewis said he did not expect the death toll of 24 to rise. Some 237 people were known to have been injured. US media reaction "One day at a time" is the headline in the Oklahoman online, over a banner aerial picture of the rubble ofdevastated homes. When Moore gets hit"we kick back" it quotes defiant residents as saying asthey pick up the pieces. Oklahoma City's Journal Record shows Governor Mary Fallin flying in a helicopter over the devastation in Moore to illustrate its report that the state legislature proposed providing $45m (£30m)from the Rainy Day Fund for relief efforts. Local news channel KFOR-TV reports theheart-rending story ofa single father who searched all night for his daughter only to find she had been killed at Plaza Towers Elementary School. Further afield, the New York Times carries a front-page picture gallery showingresidents reacting to the destruction. It goeson to describe the minutes before the tornado struck in PlazaTowers - a teacher huddling pupils into theshelter of a bathroom as the sirens wailed. In an opinion piece, USA Today suggeststhat, while forecasts and sirens undoubtedly saved many lives, more reinforced shelters should be built. Oklahoma tornado:Zoomable image On Wednesday, the Oklahoma medical examiner's office said that all the children who died had now been identified - they ranged in age from four months to nine years. Medical examiner's spokesman Amy Elliott saidofficials were still trying to contact the relatives of eight of the victims. Hundreds of volunteer workers and federal officials have fanned out across the suburb to deliver food and other supplies to residents whose homes had been swept away. Disaster centres have been set up and help given to people to assess what they have lost and what their immediate needsare. Jerry Lojka, a spokesman for the Oklahoma emergency services, told Reuters news agency on Wednesday that search-and-rescue dog teams would continue their work"to be sure nothing is overlooked", but he added: "There's going to be more of a transition to recovery." Craig Fugate, of the Federal Emergency Management Agency (Fema), told MSNBC: "Right now it's about getting people a place to stay thathave lost their homes. So we're going to start going neighbourhood to neighbourhood and talking to people and seeing what they're going to need." Homeland Security Secretary Janet Napolitanohas arrived in Moore to monitor the assistance being provided to first responders. At a press conference she urged people in need to register with Fema so that they could get assistance. Ms Napolitano said Fema would be in Moore long after the television cameras had left. Residents are to be allowed back to what remains of their homes from 15:00 local time (21:00GMT) on Wednesday. One resident, Curtis Carver, was waiting for the go-ahead to return. He told Agence France-Presse: "It was my home, my kids' home. Now it's gone. There's nothing left. It's a pile of sticks... and they're keeping me away." Tornado's cost The NWS said the twister'spath was 17 miles (27km) long and 1.3 miles wide andit battered Moore for about45 minutes on Monday afternoon. Residents were given 16 minutes' warning before the tornado touched down - officials said such advisories were usually issued eight to 10 minutes ahead of a twister. Oklahoma insurance assessors have put the estimate of the damage caused at more than $2bn (£1.31bn).

Monday, May 20, 2013

TROPICAL MONSOON NATURAL VEGETATION

The natural vegetation of tropical monsoon lands depends on the amount of summer rainfall. The monsoon lands with three distinct seasons, cold, hot and rainy, exert great influence on the appearance of the vegetation. Trees have to be fairly tolerant of local physical and climatic conditions to survive. They grow rapidly in the rainy season, shed their leaves during the hot dry season and remain comparatively inactive in the cool season. Trees are normally deciduous since they shed their leaves during hot dry season tn withstand excessive transpiration. The overall vegetation varies from dense tropical evergreen vegetation to thorny scrubland, due to differences in precipitation in different parts of the monsoon lands. Where the rainfall is heavy, e.g. Southern Burma, peninsular India, northern Australia and coastal regions with a tropical marine climate, the resultant vegetation is forest. The forests are more open and less luxuriant than the equatorial forest with far fewer species. The less dense forest allows more sunlight to reach the ground, resulting in denser undergrowth. Bamboo thickets which predominate in regions of intermediate rainfall often grow to great heights.

THE TROPICAL MARINE CLIMATE

This type of climate is exprience along the eastern coasts of tropical lands, receiving steady rainfall from the Trade Winds all the time. The rainfall is both orographic, where the moist trades meet upland masses as in eastern Brazil, and convectional, due to intense heating during the day and in summer. Its tendency is towards a summer maximum as in monsoon lands, but without any distinct dry period. There is no month without any rainfall. The range of temperature is typical of the tropical latitudes with a maximum of 28 'C (82 'F) in January and a minimum of 21 'C (70 'F) in July - a range of 6.6 'C (12 'F) for the year. Due to the steady influence of the trades, the Tropical Marine Climate is more favourable for habitation, but it is prone to severe tropical cyclones, hurricanes or typhoons.

THE RETREATING MONSOON

THE RETREATING MONSOON The amount and frequency of rain decreases towards the end of the rainy season. It retreats gradually southwards after mid-September until it leaves the continent altogether. The Punjab plains which receive the South-West Monsoon earliest are the first to see the withdrawal of the monsoon. The skies are clear again and the cool, dry season returns in October, with the outblowing North-East Monsoon. The role of monsoons in India is vital in its economy. A late monsoon or one that ends far too early will condemn large stretches of agricultural land to drought. There will be widespread famine from crop failure and thousands will perish. When there is too much water from the rainy monsoons, severe floods occur, destroying both crops and lives and disrupting communications. In no part of the world has the climate affected Man's way of life so profoundly as in the monsoon lands.