Currents
Input variables: Oceanographic
Currents are a second oceanographic feature that
Waves
we assumed have an effect on speed of transit.
We assumed that wind-induced waves would
Summary currents in the Arctic seas are composed
have an effect on navigation and that the larger
of tidal, permanent, and wind-induced currents.
the wave, the greater its influence. While storm
In simulating NSR passage, we did not take into
waves can be dangerous for a small ship, they also
account tidal currents, which are semidiurnal and
make navigation difficult for large ships. Waves in
primarily reversing in nature. We assumed instead
the Arctic seas are principally affected by wind
that their cumulative influence on transit naviga-
and ice conditions. Higher winds create larger
tion is essentially zero.
waves, while greater sea-ice concentration reduces
The summary current algorithm employed in
wave magnitude.* Maximum wave heights are
the model thus considers only permanent and
generally observed in autumn.
wind-induced currents. Permanent ocean currents
We constructed probabilities of wind wave
are related to general circulation of the Arctic Ocean
height based on available information on wind
and the general thermohaline structure of the re-
speed probability and maximum waves in April,
gion under consideration. In general, these cur-
June, August, and October (The Soviet Arctic 1970,
rents remain quite constant with regard to both
Wind and Waves in Oceans and Seas 1974,
speed and direction throughout the year. Due to
Proshutinsky et al. 1994). In retrospect, we now
our assumption that the permanent currents are
realize that wave heights were used incorrectly in
invariant, the MC algorithm is not needed to se-
the model. Our wave heights were derived directly
lect values. The permanent currents for each data
from the wind speed data in the following way. At
node were obtained from Treshnikov (1985),
every point of interest, we assumed that a 15 m/
Proshutinsky (1993), Proshutinsky et al. (1994), and
s wind produces waves of 01 m in height, winds
RSMOT (in prep.). These data, shown in Table B.8,
of 510 m/s generate wave heights of 12 m, winds
are read into the model from the PCURRNT.DAT
of 1015 m/s generate wave heights of 23 m,
file by subroutine ADDCCUR.
winds of 1520 m/s produce wave heights of 35
Wind-induced currents, near the sea surface, are
m, and winds of 2025 m/s lead to wave heights
generally in the direction of the wind and equal to
of 57 m. As such, these data were not indepen-
2.53.0% of the wind's speed (Zubov 1945). Using
dent PDFs, but they are treated in the model as if
this algorithm, the model calculates a wind-in-
they were. We should have simply assigned the
duced current based on the wind speed and direc-
appropriate wave height after selecting the wind
tion probabilities obtained from the WINDS**.DAT
speed instead of randomly selecting the wave
files discussed earlier. Wind-induced current is
height. This mistake resulted from a miscommu-
calculated in subroutine ADDWCUR by multiply-
nication between the study participants and has
ing wind speed by a factor of 0.025. The wind
been corrected in case the model is used in the
speed values used are those derived using sub-
future. As will be made clearer in the Sensitivity
routine WINDS as described above. The magni-
Analyses section, the resulting error in wave height
tude of the wind-induced current is assumed to be
has a negligible effect on the total time and cost
independent of ice conditions. Under ice-free con-
conclusions arrived at in this study.
ditions, the wind is assumed to induce a current
In the model, wave-height PDFs are read from
that moves parallel to the wind direction in the
WAVE**.DAT files (Table B.9) using subroutine
mixed surface layer of the open ocean. For ice-
GETDAT. Waves are evaluated at each data point
covered seas, the wind is assumed to push the
and every 8 hours according to the MC algorithm
pack in the direction the wind is blowing.
using subroutine WAVES.
Input variables: Ice conditions
Sea ice greatly affects navigation in the Arctic
Ocean, but its presence is highly variable in terms
of both space and time. Certain regions and key
straits have a very high probability for the pres-
ence of difficult ice during the summer season,
* More specifically, wave height is a function of wind
requiring icebreaker escort. These heavy ice accu-
speed, duration of the wind, fetch (the distance along
mulations, sometimes covering hundreds of square
open water over which the wind blows), and sea depth.
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