ALBERT

Description: Spatial and temporal characteristics of the Storfjorden polynya, which forms regularly in the proximity of the islands Spitsbergen, Barentsøya and Edgeøya in the Svalbard archipelago under the influence of strong north-easterly winds, have been investigated using thermal infrared satellite and airborne imagery. Thin ice thicknesses were calculated from MODIS ice surface temperatures, combined with ECMWF ERA-Interim reanalysis atmospheric data in an energy balance model for the winters of 2002/2003 to 2013/2014 (Nov.-Mar.). Based on calculated thin ice thicknesses, associated quantities like polynya area and total ice production were derived. Calculated values underline the importance of this relatively small coastal polynya system considering its contribution to the cold halocline layer through salt release during ice formation processes. Airborne thermal infrared scanner data were collected during the field campaign LEAST (Lead and ABL study in the Transpolar System) in March 2014 using the POLAR 5 aircraft (Basler BT-67). Spatia l distributions of the ice surface temperature were acquired with a swath-width of approximately 2 km and a spatial resolution of 2.7 m at nadir for an area of roughly 16x18 km². In addition, in-situ meteorological measurements were performed (including turbulent flux measurements at low levels). This aircraft–based dataset is used for an improvement of remote sensing methods, the verification of the MODIS-derived quantities and investigations of sub-grid effects on the scale of a satellite pixel. A case study is presented for 16th March 2014 in the Storfjorden polynya area.

Description: Mesoscale model simulations were conducted for the Weddell Sea region for the autumn and winter periods of 2008 using a high-resolution, limited-area, non-hydrostatic atmospheric model. A sea ice–ocean model was run with enhanced horizontal resolution and high-resolution forcing data of the atmospheric model. Daily passive thermal and microwave satellite data was used to derive the polynya area in the Weddell Sea region. The focus of the study is on the formation of polynyas in the coastal region of Coats Land, which is strongly affected by katabatic flows. The polynya areas deduced from two independent remote sensing methods and data sources show good agreement, while the results of the sea ice simulation show some weaknesses. Linkages between the pressure gradient force composed of a katabatic and a synoptic component, offshore wind regimes and polynya area are identified. It is shown that the downslope surface offshore wind component of Coats Land is the main forcing factor for polynya dynamics, which is mainly steered by the offshore pressure gradient force, where the katabatic force is the dominant term. We find that the synoptic pressure gradient is opposed to the katabatic force during major katabatic wind events.