<Month
The ice pressure tables were created by joining the tables for the southern
and northern route for each month, as prepared by INSROP Project I.4.2 as part of
INSROP Phase 2. These table records refer to points along the ship route
segments included in the Tbl_1 shapefile set, which is a part of the dataset
provided by INSROP Project I.4.2. These segments are an extract of the ship routes as
defined in INSROP Working paper no. 108 (1998), prepared by Work Package 1 (Box
B) as part of INSROP Phase 2.
Ice pressures in the ice cover
The mean multiyear values of different pressure intensity probabilities are
given for the 20-mile route segments selected within the framework of WP1 Project.
As initial data, the calculated mean monthly values of ice pressure intensity
for the period 1960-1985 were used. The calculation method is described in the
following:
Ice pressure belongs to the most dangerous phenomenon for ships. However, due
to difficulty of observations and measurements, its spatial distribution
characteristics were insufficiently investigated with ice pressure observations being
of occasional character. However, using the atmospheric pressure databases we
can calculate the wind fields in the near-water layer and based on the
empirical relations (Busuyev, Fedyakov, 1979), the probability of different intensity
of ice pressures can be assessed with sufficient statistical reliability in the
prescribed regions at the given time.
The wind fields at a 10 m height for four synoptic times were calculated on
the basis of the data set of surface atmospheric pressure above the Arctic Basin
at 1° x 1° grid points for 1960-1985. For this purpose, the calculation method
formally adopted in Russia was applied (Handbook..., 1994).
In addition to wind, for calculating the probability of different ice pressure
intensity the ice concentration data at 0.5° x 0.5° grid points and landfast
ice boundaries at 0.25° x 0.25° grid points for 1960-1985 were used.
The following assumptions were adopted for calculating the probability of
different pressure intensity:
- the ice cover has average hummock and ridge concentration for this 10-day
period;
- ice concentration is equal to 9-10 tenths;
- the relationship between the quantity of ice of different age categories is
within mean multiyear values.
For wind speeds derived from the air pressure fields, in each square the
statistical distributions were calculated from the following formulas:
P(B) = n1(x) / (deltaX * N) (1),
where n1(x) is the number of parameters possessing the indication
{(x - deltax/2) < (Vi)j < (x + deltax/2)} (2),
where x is the initial data grouping interval; V is the wind; i is the wind
speed index, j is the wind direction index by 45° sectors.
Data on the wind direction are subdivided into 3 types: "onshore", "offshore"
and "neutral". The wind type was established taking into account the location
of the landfast ice boundary and ice concentration by eight points surrounding
the calculation (central) point.
For calculation of the probability of different ice pressure intensity, the
formula of full probability for the incompatible event groups was used:
P = Sum_k [ P(Bk) * Sum_i[P(Bi) * P(Aik / Bik) ]] (3)
where: i is the wind speed range number and k is the wind type indicator, and
Sum_k is the sum from k = 1 to n, and Sum_i is the sum from i = 1 to n.
The conventional probability P(Aik / Bik) was obtained from shipborne
observation data.
The probabilistic estimates of ice pressure intensity were obtained for the
routes selected in WP1 for the 1960-1985 period.
Path: <NSR_DATA>\icesnow\i_4_2
Table type: DText table.
* Ice pressure - <month>
282 records, 7 descriptive fields.
Fields: [<Name>] -- <Alias> (type of field)
[No] -- "No" (Numeric, no decimals)
[Freq_0_1] -- "0-1 point" (Numeric, 1 decimal)
Frequency of occurrence (%) of 0-1 point pressure intensity
[Freq_1] -- "1 point" (Numeric, 1 decimal)
Frequency of occurrence (%) of 1 point pressure intensity
[Freq_1_2] -- "1-2 point" (Numeric, 1 decimal)
Frequency of occurrence (%) of 1-2 point pressure intensity
[Freq_2] -- "2 point" (Numeric, 1 decimal)
Frequency of occurrence (%) of 2 point pressure intensity
[Freq_2_3] -- "2-3 point" (Numeric, 1 decimal)
Frequency of occurrence (%) of 2-3 point pressure intensity
[Freq_3] -- "3 point" (Numeric, 1 decimal)
Frequency of occurrence (%) of 3 point pressure intensity
Ice pressure - <Month>