ALBERT

Description: This study deals with observations and simulations of the evolution of coastal polynias focusing on the Ronne Polynia. We compare differences in polynia extent and ice drift patterns derived from satellite radar images and from simulations with the Finite Element Sea Ice Ocean Model, employing three atmospheric forcing data sets that differ in spatial and temporal resolution. Two polynia events are analyzed, one from austral summer and one from late fall 2008. The open water area in the polynia is of similar size in the satellite images and in the model simulations, but its temporal evolution differs depending on katabatic winds being resolved in the atmospheric forcing data sets. Modeled ice drift is slower than the observed and reveals greater turning angles relative to the wind direction in many cases. For the summer event, model results obtained with high-resolution forcing are closer to the drift field derived from radar imagery than those from coarse resolution forcing. For the late fall event, none of the forcing data yields outstanding results. Our study demonstrates that a dense (1–3 km) model grid and atmospheric forcing provided at high spatial resolution ( 〈 50 km) are critical to correctly simulate coastal polynias with a coupled sea-ice ocean model.

Description: The polynyas of the Laptev Sea are regions of particular interest due to the strong formation of Arctic sea-ice. In order to simulate the polynya dynamics and to quantify ice production, we apply the Finite Element Sea-Ice Ocean Model FESOM. In previous simulations FESOM has been forced with daily atmospheric NCEP (National Centers for Environmental Prediction) 1. For the periods 1 April to 9 May 2008 and 1 January to 8 February 2009 we examine the impact of different forcing data: daily and 6-hourly NCEP reanalyses 1 (1.875° × 1.875°), 6-hourly NCEP reanalyses 2 (1.875° × 1.875°), 6-hourly analyses from the GME (Global Model of the German Weather Service) (0.5° × 0.5°) and high-resolution hourly COSMO (Consortium for Small-Scale Modeling) data (5 km × 5 km). In all FESOM simulations, except for those with 6-hourly and daily NCEP 1 data, the openings and closings of polynyas are simulated in principle agreement with satellite products. Over the fast-ice area the wind fields of all atmospheric data are similar and close to in situ measurements. Over the polynya areas, however, there are strong differences between the forcing data with respect to air temperature and turbulent heat flux. These differences have a strong impact on sea-ice production rates. Depending on the forcing fields polynya ice production ranges from 1.4 km3 to 7.8 km3 during 1 April to 9 May 2011 and from 25.7 km3 to 66.2 km3 during 1 January to 8 February 2009. Therefore, atmospheric forcing data with high spatial and temporal resolution which account for the presence of the polynyas are needed to reduce the uncertainty in quantifying ice production in polynyas.