Variability Variability One of the most important variable is the timing of the begining of the wet season. This onset date propogates across the Indian subcomtinent from the Bay of Bengal towards the interior bringing the intense rains. The reverse process, the monsoon retreat, marks the end of the wet season, and travels from the interior out towards the Bay of Bengal. The highest variability in rainfall is observed between the onset and retreat date of a given wet season. Within the wet monsoon period is a series of active and break periods which occur without any discernable pattern.
All climates have changes which occur on an annual cycle.
This is often a dominant period of variability as this is the time it takes for the earth to revolve once around the sun. This has a predictible period of 1 year. The regularity of the rotation of the earth each day leads to a predictible diurnal cycle in any weather pattern. Since differential heating is regulated by the position of the sun, there is a regular and predictible periodicity to this behavior. The regularity is due to the earths revolving around the sun in a predictible way to produce seasons.