Do North Sea storms increase?

The hooting of storm cyclones on the trail

FINO with storm damage © BSH
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Storms with gale-force winds over the North Sea are not uncommon. But every few years there is an unusually high accumulation of these storm cyclones. So also from the end of December 2006 to the end of January 2007, when several low-pressure areas crossed the North Sea area in rapid succession. Among them was the oracle depression KYRILL, which on January 18/19, 2007, according to preliminary estimates in Europe 49 fatalities and a total damage of 13 billion US dollars left behind. Experts from the German Weather Service are on the trail of the puzzle, whether this is normal "weather capers" or the effects of climate change.

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"An accumulation of very strong storms up to hurricane strength existed as early as 1990, from the end of January to the end of March, " explains Christiana Lefebvre from the German Weather Service in Hamburg. "At that time, winter storms such as DARIA, OTTILIE, VIVIAN and WIEBKE, which crossed the country at wind speeds comparable to those of KYRILL, caused great damage not only in Germany but also in much of Europe."

Isolated case or climate change?

But not only the year 1990 was extremely stormy, the following years were very windy. At the time, not only DWD scientists wondered if climate change was already recognizable. At the turn of the millennium, however, the wind volume initially dropped significantly. Supported by the temperature records from autumn 2006 to spring 2007, including the accumulation of extreme storm lows, this question arose again.

"The winter series of storm cyclones had already been preceded in October by the BRITTA orkantief, which had caused a long-lasting north-west to north-bound storm over the North Sea with gusts of up to 150 kilometers per hour and heavy waves", Lefebvre explains vividly the situation at that time. "This resulted in unusually high waves with a significant wave height of ten meters - not only in the deeper North Sea zones but also in the shallower waters of the southern North Sea." This had been proven by measurements and damage to the research platform "Fino1", which was around 50 Kilometers north of the island Borkum is anchored. display

look in the past

The wind conditions in January 2007 over the North Sea BSH

In order to be able to make statements about the change of the wind field over a longer period of time, the experts of the DWD resorted to the so-called geostrophic wind. This is based on reduced sea level air pressure values ​​and is thus independent of wind measurements that are usually not representative of a larger space, says Lefebvre. For their analysis, the scientists assembled the data from the daily air pressure values ​​from Emden, Hamburg and Sylt or Fan . In this way, they received the annual mean of the geostrophic wind over the German Bight in the period from 1879 to 2006.

It has been shown that between 1880 and 1925 quite similar mean wind speeds prevailed as in the `windy '1990s, Gudrun Rosenhagen of the DWD explains the result of the study. In our representative diagrams, the curve of the 10-year moving average suggests a 40-year oscillation. But this is neither explainable nor statistically resilient there is therefore no clear indication of climate change as the trigger for the summoning of storm cyclones over the North Sea.

(German Weather Service Seewetteramt Hamburg, 14.09.2007 - AHE)