The rate of heating and cooling of the surface of the earth is the main factor determining the temperature of the air. The air is transparent to almost all solar radiation, which therefore has only indirect effect on air temperature. The humidity of the air does not directly affect the heat load operating on the body, but it determines the evaporative capacity of the air. This in turn determines the cooling efficiency of a humans sweating. In extremely hot conditions the humidity level determines the limits of comfort by restricting total evaporation of sweat.
Solar radiation has two effects on the human body, one thermal the other biological.
The Thermal effect of solar radiation determines the sweat rate of a person, it depends on the body's posture with respect to the sun, clothing, surface reflectivity of surroundings and wind velocity. The Biological effects come about due to the ultra-violet content of the solar spectrum causing tanning and sunburn of white skin. Tanning results from the accumulation of melanin pigment in the upper skin layers. The total amount of rain, hail , snow or dew, measured in rain gauges and expressed in mm per month. This factor is not recorded but is here to indicate the confusion that exists between wind speed at a location and the internal air movement.