Tuesday, October 27, 2009

PHENOMENA OF OUTER ATMOSPHERE

PHENOMENA OF OUTER ATMOSPHERE
Certain physical phenomena of the outer atmospheric
region are of importance in the broad framework physical geography. Of particular interest is the devel ment of radio communication on a global scale in a la known as the ionosphere, located in the altitude rang~ 80 to 400 kIn (i.e., identical with the lower thermosphere.)

It is so called because the incoming solar radiation ionises the gases within it, forming ionised layers. These layers reflect radio signals and other electromagnetic waves back to the earth. Most of this reflection of long-wave radio.
.waves takes place in the lower part of ionosphere which bears the name of Kenelly-Heaviside layer. The process of ionisation, being based on solar radiation, takes place on the sunlight-side of the earth.

OZONE LAYER A zone within the atmosphere between 20 and 80 km, extending from upper stratosphere into the mesosphere, called the ozone layer, is of vital importance to all living forms on earth. The ozone layer is a region of concentration of the form of oxygen molecule called ozone (°3)' It results from the splitting of oxygen (°2) molecules by the ultraviolet radiation from the sun to form atomic oxygen (0), which then combines with other oxygen (°2) molecules to give ozone (°3)' The ozone layer serves as a shield preventing most of the potentially damaging ultraviolet radiation of the sun from reaching the tropo­pause and earth's surface. If the ultraviolet rays were to reach the earth in full intensity, all exposed bacteria would be destroyed and animal tissue severely burnt.

VAN ALLEN RADIATION BELTS
A region of intense radioactivity. within the magnetosphere was reported to be existing by the satellites. The mngnetospherf? is the area surrounding the earth extending to about 60,000 km on the side facing the sun and more on the opposite side. It was discovered that two ring-shaped belts of radiation, one lying within the other, existed and were named Van Allen Radiation belts after the physicist who first described them. The inner belt lies about 2600 km from earth's surface, while the outer lies at about 13,000 to 19,000 km from it. These belts represent concentrations of highly charged particles, protons and electrons from the sun, trapped within lines of force of the earth's external magnetic field­the magnetopause.

AURORA The aurorae are produced by the charged particles from the sun captured by earth's magnetic field at heights of about 100 km. It is a luminous phenomenon seen in the sky at night in high latitudes. It may be visible as arcs of light or as coloured curtains, streamers and rays. Aurorae occur most frequently during the intense periods of the ll-year sunspot cycle. In the northern hemisphere, they are called aurora borealis (or northern lights); in the southern hemisphere, as aurora australis (or southern lights). Areas experiencing aurorae most frequentfy Ii!'! about 20° from geomagnetic poles; the belt to the north of Norway, south of Iceland and Greenland, over north Canada and across northern Russia is the area of aurorae in northern hemisphere.

MAGNETIC STORMS
These are world-wide temporary disturbances of the earth's magnetic field that appear to be associated with the occurrence of solar flares and sunspots. The aurora is also usually visible and extensive during such a storm but whether this is a cause or an effect is not yet fully understood. The main effects are the disruption of radio and telegraph communications and magnetic surveys.

COSMIC PARTICLES These are elementary particles­protons-travelling through space at speeds approaching that of light. Most are nuclei of hydrogen atoms, others are helium and a few of other heavier atomic nuclei. Also called the cosmic rays, their penetrating power is enormous and they can reach earth's surface.

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