M22 Understanding and Predicting High-impact Weather and Climate Extremes

IAMAS (Meteorology)

28-Jun-2015, 15:00 - 16:30

Abstract content:

Variability of the relation of the North Atlantic Oscillation and European winter windstorms during the last millennium

Winter windstorms are the most loss-relevant natural hazard for the European region. This study investigates winter windstorms using a comprehensive Earth System Model (ESM) with variable radiative forcing (e.g. solar irradiance, volcanoes, CO2) simulating the last millennium. This model run covers a broad range of natural variability. An objective methodology for the identification and tracking of windstorms is applied. Variability of storm activity is investigated in terms of its relation to the North Atlantic Oscillation (NAO). Results are compared with 20th century reanalysis (20CR).

Both, the ESM simulation and 20CR show maximum track density of winter windstorms over the North Atlantic. These storms are propagating towards Central and Northern Europe. The position of the windstorm track density is strongly correlated with the phase of the NAO. A positive NAO phase is related to higher storm frequencies, both in the North Atlantic and Europe, north of 45┬░N and lower frequencies south of it. The overall pattern of this correlation is stable during the last millennium, whereas its intensity varies between 0.6 and 0.75 and the exact positions of the maxima are ranging between Central Europe and the Eastern North Atlantic. The temporal variability of the NAO pattern is analysed, by means of the first EOF of the 500hPa geopotential height, for sub-periods of different length. Especially the southern centre of action, associated with the Azores High, shows variability in its position. This finding is discussed in relation to the variable position and intensity of the correlation between the NAO and winter windstorms.

U. Ulbrich1, J. Grieger1, M. Schuster1, I. Kuhnel2.
1Freie Universit├Ąt Berlin, Insitute for Meteorology, Berlin, Germany.
2EQECAT, CoreLogic, Paris, France.


NAO     Europe     millennium     variability     center of action     hazard     winter     windstorms