Accueil > Actualités > Séminaires > Séminaire de Pablo Ortega au LOCEAN


Titre : A multi-proxy model-tested North Atlantic Oscillation reconstruction for the last millennium
Nom du conférencier : Pablo Ortega
Son affiliation : LOCEAN
Laboratoire organisateur : LOCEAN
Date et heure : 06-11-2014 11h00
Lieu : salle de réunion LOCEAN, tour 45/55, 4eme étage
Résumé :

The North Atlantic Oscillation (NAO) is the dominant mode of winter atmospheric circulation variability in the Northern Hemisphere, with large impacts on temperature, precipitation, storm tracks and therefore on strategic sectors such as insurance, renewable energy production, crop yields and water management. Recent developments of empirical and dynamical methods offer promising advances for seasonal NAO predictions. Assessing potential predictability at multi-annual time scales requires a documentation of past NAO low-frequency variability. A recent bi-proxy NAO reconstruction8 spanning the last millennium suggests that long-lasting positive NAO conditions were established during medieval times, explaining the particularly warm conditions over Europe. Here, we present a new annually-resolved NAO reconstruction for the last millennium based on an initial selection of 59 proxy records distributed around the Atlantic Ocean and surrounding continents and built through an ensemble of multivariate regressions. This approach has been validated in perfect model analyses with eight climate simulations, showing better performance than the bi-proxy record. The new reconstruction shows no persistent positive values in the medieval period. A positive phase of the NAO appears almost systematically in the three years following 18 strong volcanic eruptions, offering an invaluable benchmark to better constrain the magnitude and timing of this response, and thus narrow the climate predictability associated to volcanoes.