Geography Insolation and Temperature - 3 (in Hindi)

Lesson 3 of 5 • 22 upvotes • 10:18mins

R K Shukla

UPSC/ MPPSC SPECIAL GEOGRAPHY LECTURE 1 (PART 3) Heating & cooling of the atmosphere The sun is the ultimate source of atmospheric heat and energy. There are different ways of heating and cooling of the atmosphere. They are: Terrestrial Radiation Conduction Convection Advection Terrestrial radiation Before discussing terrestrial radiation, the following facts about radiation are worth noting. i) All objects whether hot or cold emit radiant energy continuously. ii) Hotter objects emit more energy per unit area than colder objects. iii) The temperature of an object determines the wavelength of radiation. Temperature and wavelength are inversely proportional. Hotter the object, shorter is the length of the wave. So, when the earth’s surface after being heated up by the insolation (in the form of short waves), it becomes a radiating body. The earth’s surface starts to radiate energy to the atmosphere in the form of long waves This is what we call as terrestrial radiation This energy heats up the atmosphere from bottom to top.The long-wave radiation is absorbed by the atmospheric gases particularly by carbon dioxide and other greenhouse gases. Thus, the atmosphere is indirectly heated by the terrestrial radiation. The atmosphere, in turn, radiates and transmits heat to space. Finally, the amount of heat received from the sun is returned to space, thereby maintaining a constant temperature at the earth’s surface and in the atmosphere. conduction Conduction is the process of heat transfer from a warmer object to a cooler object when they come in contact with each other. The flow of heat energy continues till the temperature of both the objects become equal or the contact is broken. The conduction in the atmosphere occurs at the zone of contact between the atmosphere and the earth’s surface. Conduction is important in heating the lower layers of the atmosphere. convection Transfer of heat by the movement of a mass or substance from one place to another, generally vertical, is called convection. The air of the lower layers of the atmosphere gets heated either by the earth’s radiation or by conduction. The heating of the air leads to its expansion. Its density decreases and it moves upwards. The continuous ascent of heated air creates a vacuum in the lower layers of the atmosphere. As a consequence, cooler air comes down to fill the vacuum, leading to convection. The cyclic movement associated with the convectional process in the atmosphere transfer heat from the lower layer to the upper layer and heats up the atmosphere. The convection transfer of energy is confined only to the troposphere. . Advection The transfer of heat through horizontal movement of air (wind) is called advection. Winds carry the temperature of one place to another. The temperature of a place will rise if it lies in the path of winds coming from warmer regions. The temperature will fall if the place lies in the path of the winds blowing from cold regions. Horizontal movement of the air is relatively more important than the vertical movement. In the middle latitudes, most of diurnal (day and night) variations in daily weather are caused by advection alone. In tropical regions particularly in northern India during the summer season, local winds called ‘Loo’ is the outcome of advection process.