The annual cyclical pattern in any atmospheric variable, whether temperature or trace gas concentration, caused by the seasons. Also called an annual cycle. The seasonal cycle or seasonal variability is one type of variability. Other types of variability include short-term (day-to-day or week-to-week), interannual (year-to-year), or long-term (decade-to-decade or longer). Thus, the amount of ozone in a particular location has a short-term variability, a seasonal variability, an interannual variability, and a long-term variability.