Abstract
Abstract. The Baltic Sea is a seasonally ice-covered marginal sea in northern Europe with intense wintertime ship traffic and a sensitive ecosystem. Understanding and modeling the evolution of the sea-ice pack is important for climate effect studies and forecasting purposes. Here we present and evaluate the sea-ice component of a new NEMO–LIM3.6-based ocean–sea-ice setup for the North Sea and Baltic Sea region (NEMO-Nordic). The setup includes a new depth-based fast-ice parametrization for the Baltic Sea. The evaluation focuses on long-term statistics, from a 45-year long hindcast, although short-term daily performance is also briefly evaluated. We show that NEMO-Nordic is well suited for simulating the mean sea-ice extent, concentration, and thickness as compared to the best available observational data set. The variability of the annual maximum Baltic Sea ice extent is well in line with the observations, but the 1961–2006 trend is underestimated. Capturing the correct ice thickness distribution is more challenging. Based on the simulated ice thickness distribution we estimate the undeformed and deformed ice thickness and concentration in the Baltic Sea, which compares reasonably well with observations.
Highlights
The Baltic Sea is seasonally ice covered and in the northern part the sea-ice season can last for up to 7 months
We aim at evaluating the biases of some of the forcing parameters that impact the ice cover: the 2 m air temperature, snow thickness, and sea surface temperature
We have presented the ice component of a new NEMO– LIM3.6-based configuration of the Baltic Sea
Summary
The Baltic Sea is seasonally ice covered and in the northern part the sea-ice season can last for up to 7 months. The maximum total sea-ice extent is usually reached in late February and between mid-February and mid-March the ice covers on average 45 % of the total Baltic Sea area. Interannual fluctuations around this mean are very large and during severe winters the entire Baltic Sea can be completely ice covered (Leppäranta and Myrberg, 2009; Vihma and Haapala, 2009). With 15 % of the world’s cargo transportation, the Baltic Sea is one of the heaviest trafficked seas in the world (HELCOM, 2009). This usually requires some assistance by ice-breakers and traffic restrictions based on the ship’s ice class are imposed by the ice-breaking authorities (HELCOM, 2004)
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