Introduction

• Sun is the primary source of heat
• Heating of the atmosphere is an indirect process
• The earth surface converts the absorbed insolation into heat, which in turn, heats the atmosphere by different process of heat transfer.
• Process like evaporation and condensation play a significant role in the transfer of heat.
• Ambient Temperature is the temperature of surrounding medium of a given location at a particular time.

Some terminologies

1. a) Diurnal Variation

• The rotation of earth on its axis produces alternating periods of day and night, resulting the daily variations in temperature.

• The temperature difference between maximum and minimum during the day is called Diurnal Range of temperature
• Daily variation decreases with increase in height above earth surface.
• Temperature Lag is the difference in the time between maximum solar radiation and maximum temperature.
• Temperature of atmospheric air decreases at an average rate of about 6.5˚C per 1000 m increase in altitude within the troposphere,
• Relatively constant (with altitude) in the lower part of the stratosphere.

b) Lapse rate:

• Generally, there is a steady decrease of temperature with increasing elevation (up to tropopause).
• The observed rate of vertical decrease in temperature (also called vertical temperature gradient) is called the environmental lapse rate.
• It is not a constant but varies with height, location and season. Normal lapse rate is 6.50C/km.

c) Temperature inversion

• Generally, temperature decreases with height but sometimes when the colder air lies below warmer air and closer to earth surface the normal lapse rate is reversed and this is called temperature inversion.

Temperature inversion near the ground surface may produce under following condition-long and clear winter night, clear sky, relatively dry air and snow-covered surface.