ABSTRACT
The primary properties that characterize an air mass have been said to be its temperature and humidity, and the distribution of the elements vertically within the air mass. The earth receives heat from the sun by day, but loses that heat by radiation at night; the temperature changes thus brought about at the earth’s surface are communicated to the lower layers of the air, thus affecting the lapse rate. The migration of air masses from their source must result eventually in their meeting and interference, and this will occur in regions of low pressure which, by their very nature, must be regions of convergence. The tongue of warm air, generally of tropical origin, thrusts deeper northwards towards the developing centre of low pressure; it is known as the ‘warm sector’, and its advancing edge is known as the ‘warm front’.
