Degree-days

oil production platform, which is located approxi-

sible meteorological and oceanographic variables with

mately 14 km east of the North Foreland. Both dates

the onset of ice in Cook Inlet for the 1970s decade.

varied by as much as two months over those years. The

They analyzed factors such as FDDs, winds, precipi-

mean dates are November 25 and April 7, respectively,

tation amount, river discharge data, and coastal cur-

and the standard deviation for both is 1718 days.

rent inflow based on sea surface and air temperatures.

Degree-days

A "degree-day" is a means of describing the magnitude and duration of time that the mean daily

air temperature differs from any specified temperature. In terms of sea ice formation, it is measured

in either freezing degree-days (FDDs) that grow ice or thawing degree-days (TDDs) that melt ice.

Every degree of temperature that the mean daily temperature departs from a given base value is

one degree-day. For example, if we specify a base value of 0C and the mean air temperature for a

day is 10C, then 10 Celsius FDDs have accumulated over the course of that day. Conversely a

mean daily air temperature of +10C would equal a 10-TDD accumulation. One Celsius degree-day

equals 1.8 Fahrenheit degree-days. The number of FDDs and TDDs are summed separately and

continuously over the entire winter season (from October 1 to April 30). The base value for the

melting or growth of ice is arbitrary but is often chosen to best fit empirical data for the region of

interest. The ice thickness models employed in Section 3.3 base the total thickness of ice grown or

melted on the accumulated number of degree-days at monthly intervals during the winter.

14