Improvement and Sensitivity Analysis of Thermal Thin-Ice Thickness Retrievals

Considering the sea ice decline in the Arctic during the last decades, polynyas are of high research interest since these features are core areas of new ice formation. The determination of ice formation requires accurate retrieval of polynya area and thin-ice thickness (TIT) distribution within the polynya. We use an established energy balance model to derive TITs with MODIS ice surface temperatures $(T_{s})$ and NCEP/DOE Reanalysis II in the Laptev Sea for two winter seasons. Improvements of the algorithm mainly concern the implementation of an iterative approach to calculate the atmospheric flux components taking the atmospheric stratification into account. Furthermore, a sensitivity study is performed to analyze the errors of the ice thickness. The results are the following: 1) 2-m air temperatures $(T_{a})$ and $T_{s}$ have the highest impact on the retrieved ice thickness; 2) an overestimation of $T_{a}$ yields smaller ice thickness errors as an underestimation of $T_{a}$; 3) NCEP $T_{a}$ shows often a warm bias; and 4) the mean absolute error for ice thicknesses up to 20 cm is $pm$4.7 cm. Based on these results, we conclude that, despite the shortcomings of the NCEP data (coarse spatial resolution and no polynyas), this data set is appropriate in combination with MODIS $T_{s}$ for the retrieval of TITs up to 20 cm in the Laptev Sea region. The TIT algorithm can be applied to other polynya regions and to past and future time periods. Our TIT product is a valuable data set for verification of other model and remote sensing ice thickness data

Optimization of Enzymatic Gas-Phase Reactions by Increasing the Long-Term Stability of the Catalyst

Enzymatic gas-phase reactions are usually performed in continuous reactors, and thus very stable and active catalysts are required to perform such transformations on cost-effective levels. The present work is concerned with the reduction of gaseous acetophenone to enantiomerically pure (R)-1-phenylethanol catalyzed by solid alcohol dehydrogenase from Lactobacillus brevis (LBADH), immobilized onto glass beads. Initially, the catalyst preparation displayed a half-life of 1 day under reaction conditions at 40 °C and at a water activity of 0.5. It was shown that the observed decrease in activity is due to a degradation of the enzyme itself (LBADH) and not of the co-immobilized cofactor NADP. By the addition of sucrose to the cell extract before immobilization of the enzyme, the half-life of the catalyst preparation (at 40 °C) was increased 40 times. The stabilized catalyst preparation was employed in a continuous gas-phase reactor at different temperatures (25-60 °C). At 50 °C, a space-time yield of 107 g/L/d was achieved within the first 80 h of continuous reaction.

How Europe can deliver: Optimising the division of competences among the EU and its member states

This study aims to give guidance for a better-performing EU through an improved allocation of competences between the European Union and its member states. The study analyses eight specific policies from a wide range of fields with respect to their preferable assignment. The analysis applies a unified quantified approach and is precise in its definition of ‘counterfactuals’. These counterfactuals are understood as conceptual alternatives to the allocation of competences under the status quo. As such, they either relate to a new European competence (if the policy is currently a national responsibility) or a new national competence (if the policy is currently assigned to the EU). The comprehensive, quantification-based assessments indicate that it would be preferable to have responsibility for higher education and providing farmers with income support at the national level. Conversely, a shift of competences to the EU level would be advantageous when it comes to asylum policies, defence, corporate taxation, development aid and a (complementary) unemployment insurance scheme in the euro area. For one policy – railway freight transport – the findings are indeterminate. Overall, the study recommends a differentiated integration strategy comprising both new European policies and a roll-back of EU competences in other fields

Aircraft-based studies of katabatic winds and boundary layer structures over the NOW polynya near Greenland during summer

During June 2010, the aircraft based experiment IKAPOS was performed in northwestern Greenland. The main goals were studies of the summertime katabatic wind system and of the atmospheric boundary layer (ABL) over the North Water Polynya (NOW). Katabatic winds play a key role in exchange processes of energy and momentum between the atmosphere and the underlying surface over the ice sheet of Greenland. During summer, cooling of the boundary layer and hence the katabatic forcing is much less than during winter, but strong winds can occur during appropriate synoptic forcing. On the other hand, the NOW represents one of the largest polynyas of the Arctic, and the air-sea interaction over the NOW has important consequences for ocean processes, ice formation, gas exchange and biology. The present study is based on aicraft measurements in the ABL using the research aircraft POLAR 5 of Alfred-Wegner-Institute (AWI, Bremerhaven). In order to study the turbulence structure and 3D spatial structures of mean quantities POLAR 5 was instrumented with a turbulence measurement system collecting data on a nose boom sampling at a rate of 100 Hz, additional basic meteorological equipment, radiation and surface temperature sensors, laser altimeter, and photo and video cameras. For different synoptic situations four flights over the NOW and one flight each over the Humboldt and the Steenstrup Glaciers were performed. Over the glaciers, katabatic winds with up to 16 m/s wind speed were found. Over the NOW, a stable, but fully turbulent ABL was present during conditions of strong and relatively warm synoptically induced northerly winds. Strong surface inversions were found in the lowest 100 m – 200 m agl. As a consequence of channeling effects at Smith Sound a well-pronounced low-level jet with wind speed maxima of more than 20 m/s was detected. Thus wind-induced sea-ice export from the Nares Strait is considerably increased

Polar Low Workshop Summary

The 13th European Polar Low Workshop was organized by the European Polar Low Working Group (www.uni-trier.de/index.php?id=20308)and gathered scientists from nine countries focusing on polar mesocyclones in both hemispheres and other mesoscale weather phenomena such as katabatic winds, tip jets, boundary layer fronts, cold air outbreaks, and weather extremes in polar regions. Topics included experimental, climatological, theoretical, modeling, and remote sensing studies. The aim was to bring together scientists and forecasters to present their latest work and recent findings on these topics and to encourage discussions on improving forecasting and understanding of these phenomena

Airborne investigations of summertime katabatic winds and boundary layer structures over the NOW polynya near Greenland

The aircraft based experiment IKAPOS (Investigation of Katabatic winds and POlynyas during Summer) was performed in June 2010 over northwestern Greenland. The main goals were studies of the summertime katabatic wind system and of the atmospheric boundary layer (ABL) over the North Water Polynya (NOW). IKAPOS is mainly based on measurements using research aircraft POLAR 5 of Alfred-Wegner-Institute (AWI, Bremerhaven). In order to study the turbulence structure and 3D spatial structures of mean quantities, POLAR 5 was instrumented with a turbulence measurement system collecting data on a nose boom sampling at a rate of 100 Hz, additional basic meteorological equipment, radiation and surface temperature sensors, laser altimeter, and photo and video cameras. Katabatic winds play a key role in exchange processes of energy and momentum between the atmosphere and the underlying surface over the ice sheet of Greenland. During summer, cooling of the boundary layer and hence the katabatic forcing is much less than during winter, but strong winds can occur under appropriate synoptic forcing. On the other hand, the NOW represents one of the largest polynyas of the Arctic, and the air-sea interaction over the NOW has important consequences for ocean processes, ice formation, gas exchange and biology. For different synoptic situations four flights over the NOW and one flight each over the Humboldt and the Steenstrup Glaciers were performed. Over the glaciers, katabatic winds with up to 14 m/s wind speed were found. Over the NOW, a stable, but fully turbulent ABL was present during conditions of strong and relatively warm synoptically induced northerly winds. Strong surface inversions were found in the lowest 100 m – 200 m agl. As a consequence of channeling effects at Smith Sound a well-pronounced low-level jet with wind speed maxima of more than 20 m/s was detected. Thus wind-induced sea-ice export from the Nares Strait is considerably increased