| Term: | Freezing index |
| Definition: |
The cumulative number of degree-days below 0 degrees Celsius for a given time period. NSIDCCryosphere
A measure of the combined duration and magnitude of below freezing temperatures occurring during a specific freezing season and calculated by accumulating the number of degree-days below 0 degrees C and subtracting from that total the number of degree-days above 0 degrees C over the same period. WMOMeteoterm The cumulative number of degree-days below 0˚C for a given time period IPAPermafrost As used by the U. S. Army Corps of Engineers, the number of Fahrenheit degree-days (above and below 32F) between the highest and lowest points on the cumulative degree-days time curve for one freezing season. For a critical review of the topic see Sakari Tuhkanen (1980). "The freezing index is used as a measure of the combined duration and magnitude of below freezing temperatures occurring during any given freezing season. The index determined for air temperatures at 4.5 feet above the ground is commonly designated as the air freezing index, while that determined for temperatures immediately below a surface is known as the surface freezing-index." (Also called "coldness sun.") AMSglossary The cumulative number of degree-days below 0C for a given time period. Four main types of air freezing indices have been used: Approximate Freezing Index - calculated from the mean monthly air temperatures for a specific station without making corrections for positive degree-days (T > 0C) in spring and fall (Boyd, 1979); I_af = SUM (NT) where N = number of days per month for months with a mean monthly temperature below 0C during one complete year. T= mean monthly temperature. Total annual Freezing Index - calculated by adding all the negative mean daily air temperatures (C) for a specific station during a calendar year (Harris, 1981); I_af = SUM (T) where T = mean daily air temperatures (C) below 0C for one complete calendar year. _ Seasonal Freezing Index - calculated as the arithmetic sum of all the negative and positive mean daily air temperatures (C) for a specific station during the time period between the highest point in the fall and the lowest point the next spring on the cumulative degree-day time curve (Huschke, 1959); I_af = SUM (T) where T = mean daily air temperatures (C) during the time period between the highest temperature in the Fall and the lowest temperature in the Spring. _ Design Freezing Index - calculated by taking the average of the seasonal freezing indices for the three coldest winters in the most recent 30 years of record. If data for 30 years are not available, then the index is based on the coldest winter in the latest 10-year period of record (U.S. Army/Air Force, 1966). TrombottoGeocryology GCW |