1. Oceanic climatic currents (mean seasonal speed and prevailing direction).
This description below is based on the original one from AARI (See Expl.doc).
The source tables referred to are included in the
\INSROP_GIS\Sourcedata\AARI-FNI 1996\OceanCurrents folder.
1.1. Initial data
The work uses data of direct measurements of current speed and direction in
the subsurface sea layer (5-10 m) at buoy moorings during the period 1956 to 1995
in the summer hydrological season (August-September) in the ice-free regions.
Processing included data of 107 buoy stations with duration of observations
from two weeks to one month in the five regions indicated in the contract which
have the largest data coverage, also including four buoy stations beyond these
regions. The time interval of observations was one hour.
1.2. General characteristics of tidal, permanent and wind-driven currents
The total observed current is composed of the tidal, wind and permanent
constituents. The non-periodic current (wind plus permanent) averaged over the period
from two weeks and more characterises mean current parameters for a season.
In the Arctic Seas the role of the tidal current in the total flow can be
significant. Thus for example, in the Kara Sea the contribution of the tidal
current to the total dispersion is 60-70% and the largest possible speed of the tidal
current in some regions (in the straits) reaches 130 cm/s (the probability of
occurrence is once in 18.6 years). In the other seas the influence of the tidal
currents is a little less. The largest possible speed of the tidal currents in
the open part of the Laptev Sea is from 10 to 40 cm/s, in the East-Siberian
from 10 to 20 cm/s and in the Chukchi Sea up to 40 cm/s.
The fraction of the wind constituent in the formation of the total current can
also be significant and, on the whole, decreases with distance from the shore
to the open sea from 50 to 25%. Structure of wind circulation depends on the
synoptic conditions.
1.3. Methods for data processing and analysis
At the first stage of data processing the tidal component was excluded from
the series of the measured parameters of the total currents using a method of
running averaging with a period of 25 hours. For each of the series the occurrence
frequency of the current direction by eight 45-degree ranges was calculated.
Then mean speed modules for the vectors referring to the modal ranges were
calculated. Finally, for further interpolation to the regular grid points the fields
of vectors of mean current speeds whose direction is within the modal range,
were prepared. The middle of the modal range was assumed to be the prevailing
current direction.
For presentation of data on currents the grids of squares constructed on a
uniform basis were employed. For the Chukchi, the East-Siberian and the Laptev
Seas in both cases a regular grid with a spacing of 100 km constructed at
reference meridian 130° was used. The beginning of the grid co-ordinates is in 700 km
from the North Pole along the X-axis and in 600 km along the Y-axis. In the Kara
Sea for presenting data on discontinuities in the ice cover, a grid with a
50-km spacing constructed at reference meridian 130° is used with the beginning of
co-ordinates in 350 km from the North Pole along the X-axis and in 2300 km
along the Y-axis. Data on currents in the Kara Sea are presented using a grid with
a 100 km spacing, like in the other seas. The grid squares have uniform
numbering. The numbers 1 to 53 refer to the Chukchi Sea, 54 to 134 - to the
East-Siberian, 135 to 200 to the Laptev Sea, 201 to 865 - to the Kara Sea.
In view of the non-uniform distribution of the initial data over the area, the
values of the current parameters for each of the regular grid points (the
centres of the squares) are obtained by means of one of the three methods.
In cases where in the vicinity of the point (as a rule, within one square)
there were three and more buoy stations, the orthogonal constituents of mean
seasonal currents were interpolated to the grid points using the weighted means
(points of type I). The values inverse to the distances from the measurement point
to the grid point were used as weights.
For those grid points in whose vicinity there were one or two stations, the
current characteristics based on one or on two averaged buoy stations,
respectively (points of type 2) were used.
In the event there were no data of measurements within the assumed maximum
interpolation range of 100 km, the prevailing directions and mean speeds of
currents were calculated from the climatic fields of water density (points of type 3).
1.4. A description of the data transferred
The co-ordinates of the grid points (centres of the squares) are presented in
the form of the ASCII file (tbl_01.txt), containing Table 1. The record of
Table 1 includes the following fields: No. of the square; latitude of the grid
point (degrees); longitude of the grid point (degrees).
Data on currents are presented in the form of the ASCII file (tbl_02.txt)
containing Table 2. The record of Table 2 includes the following fields: No. of
the square; type of the point; the prevailing current direction (degrees);
mean seasonal current speed (cm/s).
In total, Table 2 presents information on 43 points of type 1, 62 points of
type 2 and 26 points of type 3.
It should be noted that information on currents in Yugorsky Shar strait
(square No. 779) refers to the measurement point which is in the Center of the strait
with co-ordinates 69°.88 N, 60°.75 E and not to the centre of the square whose
co-ordinates are given in Table 1.
Path: <NSR_DATA>\oceanriv\currents
GeoDataset type: Shapefile with Point features.
Coordinate system: Latitude/longitude in decimal degrees
* AARI Ocean Currents
131 Points, 4 descriptive fields.
Fields: [<Name>] -- <Alias> (type of field)
[Point__] -- "Square #" (Numeric, no decimals)
No. of the analysis square
[Type_of_po] -- "Type of Point" (Numeric, no decimals)
Indicate how the current values were obtained
[Prevailing] -- "Prevailing current dir. (deg)" (Numeric, no decimals)
[Mean_seaso] -- "Mean seasonal current speed (cm/s)" (Numeric, no decimals)
AARI Ocean Currents