Jet streams are wind streams that reach great speeds in narrow zones at a high altitude. They occur where atmospheric pressure gradients are strong. Along a jet stream, the air moves in pulses along broadly curving tracks. The greatest wind speeds occur in the center of the jet stream, with velocities decreasing away from it. …
The idea of lateral movement of continents or continental drift was put forward in 1912 by Alfred Wegener in a book ‘The Origin of Continents and Oceans’. The continental drift theory of Wegener ‘grew out of the need for explaining the major variations of climate in the past’. According to A. Wegener, The climatic changes which have occurred on the …
The rigid lithospheric slabs are called plates. The study of the whole mechanism of evolution, nature and motions of plates, deformation within plates and interactions of plate margins with each other is collectively called as plate tectonics. Plate tectonic theory, a significant scientific advancement of the decade 1960’s is based on two major scientific concepts e.g. (1) the continental …
Strong, turbulent winds blowing over barren surfaces can lift great quantities of fine dust into the air, forming a dense, high cloud called a dust storm. In semiarid grasslands, dust storms are generated where ground surfaces have been stripped of protective vegetation cover by cultivation or grazing. Strong winds cause soil particles and coarse sand …
Concept of underpopulation is just the opposite of overpopulation. Underpopulation occurs when the population of an area is too small for full utilization of its resources. The condition of under-population may also appear when the resources of an area can support a larger than the existing population without lowering the standard of living or without creating any type …
An urban heat island is an urban area or metropolitan area that is significantly warmer than its surrounding rural areas due to human activities. The temperature difference is usually larger at night than during the day, and is most apparent when winds are weak. Air temperatures in the central region of a city are typically …
The optimum population is an economic concept which denotes a balanced population-resource relationship in an area. According to Preston Cloud, optimum population is the one that lies within limits, large enough to realize the potentialities of human creativity to achieve a life of high quality for all the inhabitants indefinitely, but not so large as to threaten dilution …
The British economist and demographer Thomas Robert Malthus undoubtedly was the first scholar two propound a population theory based on scientific and natural law. His book on the principles of population growth was published in 1798. Malthus traveled various West European countries and collected many important data in support of his population theory. Thus, the Malthus theory of Population was …
Demographic Transition Theory in its original form was propounded by Warren Thompson and Frank Wallace Notestein. The theory postulates of a special pattern of demographic transformation high fertility and high mortality to low fertility and low mortality, when society progresses from a dominantly rural, agrarian and illiterate society to a predominantly urban, industrial and literate society. These changes occur …
More than 80% population of the world lies in developing countries. The list of developing countries is very long. It includes all the countries of Asia (except only Japan), Africa, Latin America and some countries of Southern Europe. The level of economic, social and technological development in these countries is, however, low and very low …