Diurnal cycle is any pattern that recurs every 24 hours as a result of one full rotation of the planet Earth around its axis. Earth's rotation causes surface temperature fluctuations throughout the day and night, as well as weather changes throughout the year. The diurnal variation or diurnal range of important elements at Earth's surface can be summarized as temperature maximum occurs after local noon and minimum near sunrise, relative humidity and fog are the reverse of temperature and wind generally increases and veers by day and decreases and backs. Diurnal variation of surface wind speed and direction together with the vertical motion associated with convection regulated by the diurnal variation in temperature seems to play the lead role in causing the diurnal variation in water vapour. The seasonal variation of the diurnal cycle of short-term IWV fluctuations is possibly related to the annual variation in solar heating of the Earth's surface. Surface heating leads to increased turbulence, convection, and upward water vapour flux during daytime. The earth's spin axis is tilted with respect to its orbital plane. This is what causes the seasons. When the earth's axis points towards the sun, it is summer for that hemisphere.

The earth's orbit around the sun leads to seasons because of the tilt of the Earth's axis and the changes in the distribution of sunlight across the Earth's surface during the year. Diurnal variation, on the other hand, refers to the fluctuations that happen during the day and the variations in the day-night cycle that are not regulated by intrinsic or endogenous mechanisms but rather by extraneous factors. Diurnal temperature variation is the variation between a high air temperature and a low temperature that occurs during the same day. When solar radiation falls on the soil surface, it heats the soil causing a difference of temperature between surface soil and sub-soil. At day time, heat flows from surface soil to sub-soil and vice-versa at night. he large differences in the values, diurnal and seasonal variation of the measured incoming solar radiation between the dry and wet seasons are attributed to the attenuation of the flux by aerosol particles in the dry season and increased cloudiness and humidity in the wet season. The dominant pattern of diurnal variability is a maximum in rainfall over land during the afternoon/evening in response to solar heating of the surface and a morning maximum over the oceans; however, there are important exceptions to this pattern over both land and ocean. Variations in meteorological parameters such as temperature and relative humidity over the course of a day which result from the rotation of the Earth about its axis and the resultant change in incoming and outgoing radiation.