The interannual variability of thermal atmospheric conditions in the northeastern part of the Black Sea (1935-2007)

A scheme is proposed to estimate actual seasons within the limits of a closed annual cycle. The winter and summer modifications of actual seasons, or base periods, are determined according to the position of three-month intervals with extreme (within the annual cycle) average temperatures on the calendar scale of the year. The spring and autumn modifications of seasons are introduced as intervals between the base periods. This model takes into account the episodes when relatively cold or warm airflows influence the structure of the Black Sea waters more flexibly than the standard branch of the annual cycle into seasons can do. In this alternative model, the seasons acquire the properties that are not inherent in their calendar analogues.