On the center to limb variation of the separation of the Mg ii,H2 and K2 emission peaks

From observations of the center to limb variation of the emission peaks of the Mgii, H and K lines the optical thickness of the emitting layer for a simplified geometrical model has been calculated to be 300. The source function was approximated by a second order polynomial. The turbulent velocities of the emitting layer are found to be 6.8 km/sec, in agreement with other observations.     

Highn emission and absorption lines of the sun (II)

Considering the electronic pressure broadening of highn solar recombination lines, an upper wavelength limit of the observable region of possible lines is derived. The reason that no lines have been observed is discussed.     

Detection of the historical Askja ad 1875 and modern Icelandic cryptotephras in varved lake sediments – results from a first systematic search in northern Poland

Volcanic ash can disperse thousands of kilometres from the source volcano and provide valuable chronostratigraphic markers for palaeoclimate studies. We present new cryptotephra findings of historical and modern Icelandic eruptions in annually laminated lacustrine sediment records from several sites within a 570 km SW–NE transect across northern Poland. Sediments from the two lakes Wąsoskie and Szurpiły contain glass shards originating from the Plinian Askja ad 1875 eruption and showing bimodal, rhyolitic and dacitic affinities. A further cryptotephra finding in Lake Lubińskie suggests a potential origin from the Hekla ad 1845 eruption. These new findings extend the tephra dispersal map towards the south-east and provide valuable isochrons for the synchronisation of palaeoclimate proxy data at the termination of the Little Ice Age in central eastern Europe. Very low glass concentrations of modern cryptotephra in Lake Wąsoskie were potentially correlated with the Eyjafjallajökull ad 2010 eruption. Further findings in the uppermost sediments of lakes Szurpiły and Żabińskie in north-eastern Poland tentatively suggest other sources from either the Hekla and/or Kamchatkan volcanoes.     

A statistical analysis of climate variability and ecosystem response in the German Bight

We compiled homogeneous long-term time series comprising 39 variables representing the German Bight and for the period 1975–2004. A diverse set of variables was selected to cover multiple trophic levels and different environmental forcing thus to examine long-term changes in this coastal region. Previous studies have hypothesised the presence of regime shifts in observations extending over the entire North Sea. Focusing on a smaller spatial scale, and closer to the coast, we investigated the major modes of variability in the compiled time series using principal component analysis. The results obtained confirm a previously identified regime shift in the North Sea in 1987/1988 and suggest that the German Bight is dominantly characterised by long-term modes of variability. In the German Bight, the shift of 1987/1988 is driven primarily by temperature, Gulf Stream index, frost days and Secchi depth. Changes in some of the ecosystem variables (plankton and fish) appear to be related to changes in these driving variables. In particular, we documented strong positive correlations between the long-term trend showed by the first principal component and herring, Noctiluca scintillans, and, to a lesser extent, Pleurobrachia pileus. Two gadoids, namely cod and saithe, showed negative correlations with the observed long-term mode of variability. Changes in the sum of five small calanoid copepods were, however, less marked. Phosphate and ammonium exhibited a decreasing trend over the last 30 years. Diatoms and Calanus helgolandicus did not show evidence of changes in concert to this trend. Specific analyses of the data divided into three different subsets (biological, climatic and chemical) characterise the climate of the German Bight as highly dynamic also on short timescales (a few years) as compared to much smoother biological and chemical components. The dynamic regime of the German Bight taken together with a low correlation between the major mode of variability and phytoplankton and zooplankton data suggests that the lower trophic levels of this ecosystem are remarkably resilient.     

MAIC-2, a latitudinal model for the Martian surface temperature, atmospheric water transport and surface glaciation

The Mars Atmosphere-Ice Coupler MAIC-2 is a simple, latitudinal model, which consists of a set of parameterisations for the surface temperature, the atmospheric water transport and the surface mass balance (condensation minus evaporation) of water ice. It is driven directly by the orbital parameters obliquity, eccentricity and solar longitude (L_s) of perihelion. Surface temperature is described by the Local Insolation Temperature (LIT) scheme, which uses a daily and latitude-dependent radiation balance. The evaporation rate of water is calculated by an expression for free convection, driven by density differences between water vapor and ambient air, the condensation rate follows from the assumption that any water vapour which exceeds the local saturation pressure condenses instantly, and atmospheric transport of water vapour is approximated by instantaneous mixing. Glacial flow of ice deposits is neglected. Simulations with constant orbital parameters show that low obliquities favour deposition of ice in high latitudes and vice versa. A transient scenario driven by a computed history of orbital parameters over the last 10 million years produces essentially monotonically growing polar ice deposits during the most recent 4 million years, and a very good agreement with the observed present-day polar layered deposits. The thick polar deposits sometimes continue in thin ice deposits which extend far into the mid latitudes, which confirms the idea of “ice ages” at high obliquity.     

Influence of ice rheology and dust content on the dynamics of the north-polar cap of Mars

The evolution and dynamics of the north-polar cap (residual-ice-cap/layered-deposits complex) of Mars is simulated with a thermomechanical ice-sheet model. We consider a scenario with ice-free initial conditions at 5 Ma before present due to the large obliquities which prevailed prior to this time. The north-polar cap is then built up to its present shape, driven by a parameterized climate forcing (surface temperature, surface mass balance) based on the obliquity and eccentricity history. The effects of different ice rheologies and different dust contents are investigated. It is found that the build-up scenarios require an accumulation rate of approximately 0.15-0.2 mm a⁻¹ at present. The topography evolution is essentially independent of the ice dynamics due to the slow ice flow. Owing to the uncertainties associated with the ice rheology and the dust content, flow velocities can only be predicted within a range of two orders of magnitude. Likely present values are of the order of 0.1-1 mm a⁻¹, and a strong variation over the climatic cycles is found. For all cases, computed basal temperatures are far below pressure melting.