Appendix E 



UP Iceberg Limits Climatology (1975-1995) 



CDR Bruce E. Viekman and MST3 Kenneth D. Baumer 



Introduction 



International Ice Patrol (IIP) provides a 

 service which monitors the extent of the iceberg 

 danger in the vicinity of the Grand Banks of New- 

 foundland. This danger area is passed to inter- 

 ested shipping as a broadcast Limit of All Known 

 Ice (LAKI). In order to define this limit as accu- 

 rately as possible, IIP uses reports from various 

 sources. These include icebergs detected by IIP 

 and Canadian aircraft reconnaissance and reports 

 from passing vessels. The path of reported ice- 

 bergs since sighting is predicted using the mo- 

 mentum balance for each target (Mountain, 1 980), 

 and the deterioration of each iceberg is estimated 

 using wave and sea surface temperature analy- 

 ses from U. S. Navy models (Anderson, 1983). 

 IIP watchstanders attempt to correlate new 

 sightings with prior observations through the pro- 

 cess of resights (Viekman, 1993). The broadcast 

 LAKI therefore reflects all iceberg sightings en- 

 tered into the model, MP's knowledge of the oce- 

 anic circulation, and estimations of drift based on 

 other environmental products, and the cumulative 

 actions of IIP watchstanders. 



The iceberg limits vary considerably 

 through the ice season and between seasons. IIP 

 has historically tracked the number of icebergs 

 crossing 48 degrees North latitude, and this"count" 

 forms the principal measure of iceberg season 

 severity (Trivers, 1994; see Anderson, 1993 for a 

 comprehensive review of the methods used to de- 

 termine this statistic). This count has the advan- 

 tage of providing a single value for the season se- 

 verity, but suffers in other ways. It does not ad- 

 dress the area covered by the iceberg population, 

 which impacts the trackline deviation required for 

 mariners to stay clear of the danger zone. The 

 extent of the LAKI also drives aircraft requirements 

 for IIP reconnaissance. 



The goal of this work is to determine a cli- 

 matology for the IIP Limits of All Known Ice using 

 historical records. The variability of the LAKI will 

 be considered through the typical IIP ice season 

 using the 21 year period from 1 975 to 1 995, inclu- 

 sive. This period was selected for two reasons. 

 First, the LAKI for this period were calculated us- 

 ing a computerized vector drift (1974 to 1979) or 

 dynamical force balance model (1979 to 1995). 

 These models were used to track most iceberg 

 reports, even those far from the LAKI (Anderson, 

 1993). Secondly, LAKI from this period are reli- 

 ably presented in the IIP Annual Report. Before 

 1 974, the IIP Annual Report shows only the sighted 

 position of icebergs, and does not give the results 

 of the manual vector addition used to predict ice- 

 berg movement. 



Two prior studies have investigated iceberg 

 climatological limits. The Pilot Charts for the North 

 Atlantic Ocean (Defense Mapping Agency 1992) 

 show a 'mean maximum iceberg limit' on each 

 month's chart, along with unusual iceberg reports. 

 The source of this limit is not known, and publica- 

 tion of the North Atlantic Pilot Chart ceased in 

 1992. 



Mudry (1991) prepared a climatology 

 based on IIP sightings for the period of 1960 to 

 1982, the period where visual aircraft reconnais- 

 sance was used. While this data provided a com- 

 prehensive frequency of aircraft sightings, it did 

 not include the iceberg drift predictions by IIP A 

 climatology for sea ice distribution for the period 

 1962-1987 was completed by Cote (1989). 



Methods 



The Limits of All Known Ice (LAKI) as pub- 

 lished in the IIP Annual Report were used in this 

 study Since 1 980, iceberg density and limits were 

 published in the IIP Annual Report on the 15th 

 and 30th of each month during the ice season. 



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