북극해 해빙 분포 경년변동에 관한 수치실험

Abstract

We here simulate the sea ice distribution in the Arctic Sea during the period 1979-2011 using an ice-coupled Ocean General Circulation Model (OGCM) and investigate a characteristic feature of inter-annual variation of sea ice distribution using the Cyclo-Stationary Empirical Orthogonal Function(CSEOF). The model covers the Arctic Sea north 65°N with orthogonal curvilinear coordinates of 41-63 km (50 km on average) grid resolution. Twelve-hourly European Centre for Medium-range Weather Forecasts (ECMWF) data during the period 1979-2011 are used for atmospheric forcing. Heat and salt fluxes at the sea surface are computed with a bulk formula without any relaxation of sea surface temperature and salinity. Temperature, salinity, sea surface elevation and velocity data for open boundaries are obtained from Hybrid Coordinate Ocean Model (HYCOM) data.

Comparisons with observations of sea ice distribution reveal that modeled sea ice extent is underestimated by 6% in winter, while it is overestimated by 5% in summer. Consequently, the model seems to underestimate the amplitude of seasonal variation than observation. Nonetheless, the modeled inter-annual variations of sea ice extent agree well with observation. By evaluating model performance, we find that root-mean-square error of modeled sea ice extent is less than that of IPCC AR4.

The results of CSEOF analysis are as follow. Since 2001, The amplitude of seasonal variation of sea ice appears to continually have increased by a decline in multi-year ice in the Arctic that happened recently. We find pattern that variation in sea ice has opposite phase in Canadian Sea and Siberian Sea. The total extent of Arctic sea ice is largely decreased by the impact of reduction of Siberian sea ice more than by that of Canadian one. An out-of-phase variation between sea ice conditions in these regions is likely to be affected by the dynamics in the Arctics more than thermodynamics. In particular, the Arctic oscillation shows a high coherence with the out-of-phase variation in the 16-32 month, which leads it by 90°.