Krueger, O., Feser, F., & Weisse, R. (2019): Northeast Atlantic Storm Activity and its Uncertainty from the late 19th to the 21st Century. J. Climate, doi:10.1175/JCLI-D-18-0505.1
Geostrophic wind speeds calculated from mean sea level pressure readings are used to derive time series of northeast Atlantic storminess. The technique of geostrophic wind speed triangles provides relatively homogeneous long-term storm activity data and is thus suited for statistical analyses. This study makes use of historical air pressure data available from the International Surface Pressure Databank (ISPD) complemented with data from the Danish and Norwegian Meteorological Institutes. For the first time the time series of northeast Atlantic storminess is extended until the most recent year available, i. e. 2016. A multi-decadal increasing trend in storm activity starting in the mid-1960s until the 1990s, whose high storminess levels are comparable to those found in the late 19th century, initiated debate whether this would already be a sign of climate change. This study confirms that long-term storminess levels have returned to average values in recent years and that the multidecadal increase is part of an extended interdecadal oscillation. In addition, new storm activity uncertainty estimates were developed and novel insights into the connection with the North Atlantic Oscillation (NAO) are provided.
Stanev, E.V., Jacob, B., & Pein, J. (2019): German Bight estuaries: An inter-comparison on the basis of numerical modeling. Continental Shelf Research, Volume 174, Pages 48-65, doi:10.1016/j.csr.2019.01.001
The Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM), which is an unstructured-grid model, was coupled with a 3D sediment model and established for the German Bight and its estuaries. The horizontal resolution of the model ranges from ~10 m in the estuaries to ~400 m in most of the open sea. Validation against tidal gauge data, fixed station data, and FerryBox data demonstrated that the model adequately simulated tidal dynamics in the entire area as well as the salinity fronts and estuarine turbidity maxima in the Ems, Weser and Elbe estuaries. Comparisons of model output with that of experiments with constant density allowed to estimate the role of density control, which appeared to be strongest in the landward reaches of salinity front. The increase of tidal range caused by density effects was most prominent in the Weser and Elbe estuaries, and relatively small in the Ems, where the runoff was also small. The magnitude of the density effect on the sea level oscillations was comparable to that of the M4 tide amplitude, demonstrating its importance in shaping the tidal asymmetry in the estuaries. Density effects not only reduced the dissipation of tidal energy; density stratification suppressed also the resuspension of sediment and contributed to a displacement of the position of the estuarine turbidity maximum upstream compared to the case of an homogeneous estuary. In the case of hyper-turbid Ems Estuary, density effects on stratification caused by high sediment concentrations resulted in a suppression of turbulence and further increase of concentration of suspended matter at the bottom. Although the three estuaries, which are only ~100 km apart, were driven by similar tidal and atmospheric forcings, they exhibited different extensions of both fronts and vertical stratification, mainly due to different river runoff conditions. At intra-tidal time scales, the dependencies between sea surface height and sea surface salinity varied considerably from estuary to estuary, and the largest flood asymmetry appeared in the Elbe Estuary. Wind acted as the dominant factor driving the longer-term estuarine variability; the correlation between zonal wind magnitude and sea surface height appeared to be very strong. The simulated suspended particulate matter dynamics and position of the estuarine turbidity maxima (ETM) were in agreement with observations. Secondary ETM appeared at different locations depending on the grain size, providing an illustration of sediment sorting.