At the Earth's surface quantities of insolation and net radiation undergo daily cycles of change because the planet rotates on its polar axis once every 24 hours.
Insolation is usually the main positive component making up net radiation.
Variations in net radiation are primarily responsible for the particular patterns of rising and falling air temperature over a 24 hour period. Hourly variations in insolation received for a location at 45 degrees North latitude over a 24 hour period. In the above graph, shortwave radiation received from the sun is measured in Watts . For all dates, peak reception occurs at solar noon when the sun attains its greatest height above the horizon. Hourly variations in net radiation for a location at 45 degrees North latitude over a 24 hour period.