A Multi-decadal Mediumresolution Wind, Wave and Storm Surge Hindcast Suitable for Coastal Applications. This Volume

Abstract A multi-decadal medium-resolution met-ocean hindcast for the North Sea and parts of the Northeast Atlantic is presented. The hindcast is based on a dynamical downscaling of the global NCEP/NCAR weather re-analyses using some simple data assimilation techniques. It is shown that the reconstructed wind, wave and storm surge climate agree reasonably with available in-situ observations. Analysis of the wind, wave and storm surge climate based on hindcast data reveals that they have undergone considerable variations from year to year and on longer time scales. An increase in storm activity from the beginning of the hindcast period has levelled off later and was replaced by a downward trend over the northeast North Atlantic. This behaviour closely corresponds to that based on the analysis of proxies for storm activity. Changes in extreme wave and storm surge conditions show a similar pattern over much of the North Sea area

A comparison of two identification and tracking methods for polar lows

In this study, we compare two different cyclone-tracking algorithms to detect North Atlantic polar lows, which are very intense mesoscale cyclones. Both approaches include spatial filtering, detection, tracking and constraints specific to polar lows. The first method uses digital bandpass-filtered mean sea level pressure (MSLP) fieldsin the spatial range of 200�600 km and is especially designed for polar lows. The second method also uses a bandpass filter but is based on the discrete cosine transforms (DCT) and can be applied to MSLP and vorticity fields. The latter was originally designed for cyclones in general and has been adapted to polar lows for this study. Both algorithms are applied to the same regional climate model output fields from October 1993 to September 1995 produced from dynamical downscaling of the NCEP/NCAR reanalysis data. Comparisons between these two methods show that different filters lead to different numbers and locations of tracks. The DCT is more precise in scale separation than the digital filter and the results of this study suggest that it is more suited for the bandpass filtering of MSLP fields. The detection and tracking parts also influence the numbers of tracks although less critically. After a selection process that applies criteria to identify tracks of potential polar lows, differences between both methods are still visible though the major systems are identified in both

Stürme über dem Nordatlantik und Nordeuropa

Stürme über dem Nordatlantik und Nordeuropa: Die Küsten Nordeuropas liegen im Bereich der vom Nordatlantik ostwärts ziehenden Tiefdruckgebiete und sind deshalb besonders anfällig für Stürme und die von ihnen verursachten Schäden. Diese betreffen sowohl die Küstenanwohner als auch ihren Besitz, ihre Häuser, die Forst- und Agrarwirtschaft sowie die Schifffahrt und die Offshore-Industrie. Extratropische Stürme über dem Nordatlantik können zudem zu extremen Wetterereignissen wie Sturmfluten, hohen Wellen und Überflutungen durch Starkniederschläge führen. Deshalb ist es wichtig, das vergangene Sturmklima zu untersuchen. Um zuverlässige Statistiken der Anzahl und Stärke der Stürme der Vergangenheit abzuleiten werden lange und homogene, kontinuierliche meteorologische Zeitreihen benötigt. Die Auswertung solcher Statistiken zeigt, dass in den letzten 50-60 Jahren die Sturmtätigkeit über dem Nordatlantik zugenommen hat. Betrachtet man allerdings längere Zeiträume von hundert und mehr Jahren wird deutlich, dass es sich dabei vor allem um dekadische Variabilität handelt und kein Langzeittrend erkennbar ist. Aus diesen Erkenntnissen, sowie aus Szenariorechnungen mit Klimamodellen, können Aussagen zu voraussichtlichen zukünftigen Sturmentwicklungen abgeleitet werden Storms over the North Atlantic and Northern Europe: The coasts of Northern Europe are located in a region which is affected by the North Atlantic eastwards moving low pressure areas and they are therefore vulnerable to storms and according damages. These affect coastal residents and their property such as houses, forestry and agriculture, or shipping and offshore industry. In addition, extratropical storms over the North Atlantic may lead to extreme weather related events such as storm surges, high waves and flooding due to high precipitation amounts. It is therefore of great importance to analyze past storm climate. To derive reliable statistics of past storm frequency and intensity changes, long homogeneous and continuous meteorological time series are necessary. The analysis of these statistics shows an increase in storm activity over the North Atlantic during the past 50-60 years. But when longer periods of 100 and more years are examined, decadal variability predominates and no long-term trend can be detected. From these findings, and from scenario simulations with climate models, possible future storm developments can be derive

The Concept of Large-Scale Conditioning of Climate Model Simulations of Atmospheric Coastal Dynamics: Current State and Perspectives

We review the state of dynamical downscaling with scale-constrained regional and global models. The methodology, in particular spectral nudging, has become a routine and well-researched tool for hindcasting climatologies of sub-synoptic atmospheric disturbances in coastal regions. At present, the spectrum of applications is expanding to other phenomena, but also to ocean dynamics and to extended forecasting. Additionally, new diagnostic challenges are appearing such as spatial characteristics of small-scale phenomena such as Low Level Jets