Reproduction of the large-scale state of water and sea ice in the Arctic Ocean from 1948 to 2002: Part II. The state of ice and snow cover |
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| Authors: | N G Yakovlev |
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| Institution: | 1.Institute of Numerical Mathematics,Russian Academy of Sciences,Moscow,Russia |
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| Abstract: | This paper presents the results of reconstructing the state of ice and snow covers on the Arctic Ocean from 1948 to 2002 obtained
with a couplod model of ocean circulation and sea-ice evolution. The area of the North Atlantic and Arctic Ocean north of
65° N, excluding Hudson Bay, is considered. The monthly mean ice areas and extents are analyzed. The trends of these areas
are calculated separately for the periods of 1970–1979, 1979–1990, and 1990–2002. A systematic slight underestimation by the
model is observed for the ice extent. This error is estimated to fit the error of 100 km in determining the position of the
ice edge (i.e., close to the model resolution). In summer the model fails to reproduce many observed polynias: by observational
data, the ice concentration in the central part of the Arctic Ocean constitutes around 0.8, while the model yields around
0.99. The average trend for the area of ice propagation in 1960–2002 is 13931 km2/year (or approximately 2% per decade); the trend of the ice area is 17643 km2/year (or approximately 3% per decade). This is almost three times lower than satellite data. The calculated data for ice
thickness in the late winter varies from 3.5 to 4.8 m, with a clear indication of periods of thick ice (the 1960s–1970s) and
relatively thin ice (the 1980s); 1995 is the starting point for quick ice-area reduction. The maximum ice accumulation is
in 1977 and 1988; here, the average trend is negative: −121 km3/year (or approximately 5.5% per decade). In 1996–2002, the average change in the ice thickness constituted +1.7 cm/year.
This speaks to the relatively fast disappearance of thin-ice fractions. This model also slightly underestimates the snow mass
with a trend of −2.5 km3/year (almost 0.35 mm of snow per year or 0.1 mm of liquid water per year). An analysis of the monthly mean ice-drift velocity
indicates the good quality of the model. Data on the average drift velocity and the results of comparisons between the calculated
and satellite data for individual months are presented. A comparison with observational data from 1990–1996 in the Fram Strait
shows that the model yields 3.28 m for the average ice thickness against the observed value of approximately 3.26 m. For the
same period, the model yields a monthly mean transport of 291.29 km3 as compared to the observed value of 237.17 km3. A comparison between the measured and calculated drift velocities in the Fram Strait indicates that the model value is around
9.78 cm/s, which is comparable to the measured value of 10.2 cm/s. The existing problems with describing the ice redistribution
by thickness gradations are illustrated by comparing data on ice thickness in the Fram Strait. |
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