Two peaks in net radiation are visible on the graph. Minimum values of net radiation correspond to the time of the year when the sun reaches its minimum height of only 66.5 degrees above the horizon at solar noon . Because of the consistent nature of net radiation, mean monthly air temperature only varies by 2 degrees Celsius over the entire year. Net radiation at Bulawayo has a single peak and trough over the one year period graphed. Monthly temperature variations follow the monthly change in net radiation.
Net radiation represents energy available to do work.
When received at the Earth's surface much of this energy is used to create sensible heat . However, monthly temperature variations do not mirror the changes in net radiation exactly. Peak monthly temperatures occur about two months after the net radiation maximum. This lag is probably caused by the delayed movement of stored heat energy in the ground into the atmosphere. Minimum monthly temperatures do coincide with the lowest values of net radiation which occur during the winter solstice .