Appendix E 



Season Severity by Three Variable Index: LAKI Area, 

 Length of Season, Iceberg Population below 48 °N 



Cadet 1/c Victoria Futch 

 Donald L. Murphy 



Introduction 



When International Ice Patrol (IIP) began to measure season severity, the main method was to count the 

 number of icebergs crossing south of 48°N during the season. It is not clear why 48 N was chosen, but it 

 is likely it was viewed as the latitude below which icebergs were considered a menace to the transatlantic 

 mariners. The first time Ice Patrol took an interest in season severity measurements was in 1926 with the 

 publication of Edward H. "Iceberg" Smith's. "Summary of Iceberg Records in the North- West North 

 Atlantic." In this publication. Iceberg Smith compiled actual iceberg counts of those crossing 48°N from 

 1 880-1926. After this, the number of icebergs crossing 48°N became a standard statistic in HP's annual 

 bulletins. Over the years, this statistic has become the standard indicator of iceberg season severity. 



However, the interpretation of the season severity measure has varied over the years. For example. 

 Alfultis ( 1987) defined four iceberg-population severity classes starting at 300 icebergs or fewer for a light 

 year and over 900 icebergs for an extreme year. Trivers (1994) modified the interpretation and defined a 

 light year as one with 300 or fewer icebergs but defined an extreme year as 600 or more icebergs. 



For the mariner, the number of icebergs present in the shipping lanes is not the only factor that indicates 

 the severity of an iceberg season. The area enclosed by IIP"s Limit of All Known Ice (LAKI). which 

 defines the iceberg danger area, and the length of the iceberg season (LOS) are also very important factors 

 to the mariners. If the iceberg population is widely distributed and persists over a long span of time, the 

 mariner may also view the season as severe, even though there might not be an extraordinary number of 

 icebergs south of 48°N. Each of the three factors costs the mariner money when they are forced to delay 

 or divert due to ice. In an effort to create a more accurate description of season severity, a new index has 

 been created using three variables: the area south of 48'N enclosed by LAKI. iceberg population south of 

 48°N and LOS. 



Methods 



The LAKI. LOS. and number of icebergs passing south of 48°N were taken from IIP's annual bulletins 

 from 1975-2001. As part of Ice Patrol's routine operations. LAKI is determined twice a day. every day 

 during the entire ice season. It is a line that encompasses all known icebergs in the northwestern Atlantic 

 Ocean, thus defining the iceberg danger area. A typical LAKI originates near the coast of Newfoundland, 

 proceeds southeastward over the Grand Banks, and then northward to 52'N. where the Canadian Ice 

 Service takes over the responsibility for defining the iceberg danger area. 



The bulletins from 1981 to 2001 contain LAKI plots for the 15* and 30* (or last) day of each month. 

 Before 1981. the LAKI plots were not consistently published on any particular day. but there were enough 

 plots to produce a twice-a-month record. Data from 1975-1980 were taken from the day as close to the 

 15 or 30' of the month as possible. Exact dates are nominal, and the slight difference between dates in 

 some months does not affect the results of the calculations. In the annual bulletins before 1975 the LAKI 

 information was not as regular as the more recent bulletins and could not be used. 



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