Seasonal predictability of the winter precipitation over Iberian Peninsula and its relationship with finite-time Lyapunov exponents

Seasonal forecasts have improved during the last decades, mostly due to an increase of understanding of the coupled ocean-atmosphere dynamics, and the development of models able to predict the atmosphere variability. Correlations between different teleconnection patterns and severe weather in different parts of the world have also evolved during the last years. This paper evaluates the connection between winter precipitation over the Iberian Peninsula and the large-scale tropospheric mixing over the eastern Atlantic ocean. Finite-time Lyapunov exponents (FTLE) have been calculated from 1979 to 2008 to 5 evaluate this mixing. Our study suggests that significant negative correlations exist between summer FTLE anomalies and winter precipitation over Portugal and Spain. To understand the mechanisms behind this correlation, summer anomalies of the FTLE have also been correlated to other circulation and temperature patterns as the sea surface temperature (SST), the sea level pressure (SLP) or the geopotential. The East Atlantic (EA) teleconnection index correlates with the summer FTLE anomalies confirming their role as a seasonal predictor for winter precipitation over the Iberian Peninsula. 10