Annual cycle refers to the set of changes or events that uniformly, or consistently, take place at the same time of year.
In biology, the annual cycle for plants and animals details behaviorial and chemical changes that take place as the seasons advance.
In religion, the annual cycle refers to the various celebrations or memorials that occur in the same sequence from year to year. For example, Christianity has two annual cycles, the temporal cycle that tracks the events in the life of Christ, and the sanctoral cycle which tracks the various saint's days. Some Christian churches only observe the temporal cycle.
In climatology, an annual cycle is the part of a measured quantity's fluctuation that is attributed to Earth's changing position in orbit over the course of the year. Such quantities might be influenced directly (e.g. incoming solar radiation at a point at the surface) or indirectly (e.g. stratospheric westerlies and easterlies over the winter and summer hemispheres, respectively) by orbital position.
Mathematically, the climatological annual cycle is commonly estimated from observational data or model output by taking the average of all Januaries, all Februaries, and so forth. If the observational record is long enough and conditions are stationary (i.e. there is no significant long-term trend), a meaningful annual cycle will result that can be used to calculate an anomaly time series.
Famous quotes containing the words cycle and/or annual:
“Only mediocrities progress. An artist revolves in a cycle of masterpieces, the first of which is no less perfect than the last.”
—Oscar Wilde (1854–1900)
“...there was the annual Fourth of July picketing at Independence Hall in Philadelphia. ...I thought it was ridiculous to have to go there in a skirt. But I did it anyway because it was something that might possibly have an effect. I remember walking around in my little white blouse and skirt and tourists standing there eating their ice cream cones and watching us like the zoo had opened.”
—Martha Shelley, U.S. author and social activist. As quoted in Making History, part 3, by Eric Marcus (1992)