degree-hour

As used by U.S. Army Corps of Engineers, the departure (in °F) of the hourly temperature from a standard of 32°F, positive if above and negative if below.

Degree-hours may be accumulated (summed) over any period of time, depending upon the use to which they are applied.
Compare degree-day.

Any function of time f(t) is periodic with period t if f(t) = f(t + τ) for all times t, where τ is the smallest number for which this equality holds.