For the period of 1984-1995, the average ice sea- 

 son began on March 9 and closed on August 15. 

 LAKI data was available for analysis from March 

 15 to July 30. Before 1980, data was presented 

 without this regularity. For that period, the limit 

 setting icebergs were drifted using the operational 

 drift model for several days to estimate the ice- 

 berg limits on the 1 5th or 30th, provided the dura- 

 tion of drift was less than 7-9 days. This drift esti- 

 mate was made with calm winds, and iceberg de- 

 terioration was not considered. A summary of the 

 available data is given in Table 1 . In most cases 

 the missing data simply reflects that in a given year 

 the season began after the mean start date, or 

 ended before the mean stop date. In a few cases, 

 however, the bulletin did not show data for the given 

 date. 



For each case, the LAKI was re-drawn us- 

 ing current policy. The LAKI is drawn as a convex 

 polygon enclosing the iceberg region, and is off- 

 set from the extreme icebergs using an error circle 

 of 30 nm. Since IIP policy is to connect the limit- 

 setting icebergs with rhumb lines, the LAKI some- 

 times encloses areas were icebergs are absent. 

 This policy enables IIP to broadcast an alphanu- 

 meric product, and gives the simplest shape de- 

 fining the iceberg danger region. It also provides 

 the mariner with a convenient method of receiving 

 the report. Limits, by definition, include all the ice 

 of which IIP has knowledge. Therefore the ex- 

 treme limits can be set by a single iceberg which 

 is far separated from others. 



Following this analysis the LAKI were digi- 

 tized. Each one degree latitude/longitude square 

 was considered to be inside the limits if over half 

 of the area was within the LAKI, and a value of 1 

 was assigned to these blocks. Those blocks out- 

 side the limits were assigned a value of zero. The 

 mean value for each block was then computed. 

 This method provides the probability that a given 

 square was within the LAKI on the given date for 

 the analysis period. 



The Climatological LAKI 



The annual progression of the climatologi- 

 cal limits reflects the dominant features of the oce- 

 anic circulation within the IIP operations area (Fig- 

 ures 1-11). Icebergs are carried south by the La- 

 brador Current. Icebergs close to Newfoundland 

 move slowly southward on the inshore branch of 

 the Labrador Current, while the faster moving, off- 

 shore branch (30-40 cm/s) carries the icebergs 

 southward along the eastern edge of the Grand 

 Banks. 



The traditional height of the IIP season is 

 often viewed to be mid-April. This is probably due 

 to the sinking of the RMS TITANIC on April 15, 

 1912 at 41-54N, 50-1 4W. It is notable that the 

 position of the disaster is outside the 25th percen- 

 tile limit, but within the extreme limit of this mod- 

 ern period. This climatology shows that the most 

 extensive limits occur in May (Figures 6 and 11). 

 Both median and extreme limits reach their maxi- 

 mum on May 30. The median limit is 40 nm south 

 of the Tail of the Grand Bank (42-20N), and the 

 limits have been as far south as 38-30N (1990). 

 To the east, the median limit includes Flemish Cap 

 (a bank near 47N, 45W) throughout the year. Ice- 

 bergs which are not carried south by the offshore 

 branch of the Labrador current tend to drift east- 

 ward, passing to the north of Flemish Cap. By 

 late July, the limits have retreated near 45N with 

 warming sea surface temperatures. 



Early in the ice season, the extreme limits 

 are about 120 nm south of the median limit, and 

 are located about 60 nm south of the Tail of the 

 Grand Banks. In 1983, an unusual number of ice- 

 bergs were carried south by the inshore branch of 

 the Labrador Current, extending the extreme lim- 

 its to 41 N, 54W on 15 March. In May, the extreme 

 limits are up to 200 nm south of the median limit, 

 and this inter-annual variability extends through 

 the end of the ice season. The minimum iceberg 

 limit remains north of 47-30N, and west of 50W, 

 except for July when the minimum limit moves 

 eastward to 47W by month's end. 



60 



