| Summary: | We evaluated the effects of sea ice concentration (SIC) on marine cold air outbreaks (MCAO) in the Barents Sea (BS) based on satellite observations and numerical modeling data. MCAOs were determined through MCAO-index calculated as a difference in vertical potential temperature between the surface and 800-hPa level. For the present climate, we used ERA-Interim reanalysis to calculate the MCAO-index and satellite microwave observations to estimate SIC. We also analyzed results of four sensitivity experiments with the atmospheric general circulation model ECHAM6 with different boundary conditions, i.e., with low and high SIC and low and high sea surface temperature (SST). We found a prominent decrease of the MCAO-index over BS in 1979–2018 that indicates the overall weakening of the MCAO intensity, e.g., a statistically significant decrease was revealed for frequency of both moderate and strong MCAOsin winter (down to -5%/decade). Because of SIC decrease during the 1979–2018 period, we found a positive correlation between SIC and the MCAO-index over BS during winter season. For the same season and area, model experiments, however, showed that higher values of the MCAO-index were associated with lower SIC, which implied their negative correlation. In particular, in the south of BS, values of the MCAO-index were up to 30% higher in the low-SIC experiments compared to the high-SIC experiments. The revealed opposite MCAO-SIC relationship in observations and model simulations is likely associated with the lack of changes of greenhouse gases concentration in model experiments.
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