Abstract
Abstract. Seasonal forecasts have improved during the last decades, mostly due to an increase in 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 are constantly evolving and changing. 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 (FTLEs) have been calculated from 1979 to 2008 to 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 with other climatic variables such 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.
Highlights
Seasonal forecast at mid-latitudes is still an open research field
A significant negative correlation was observed between the summer (JAS) Finite-time Lyapunov exponents (FTLEs) anomalies and winter (JFM) precipitation over the western Iberian Peninsula
Wind speed, sea level pressure (SLP) and geopotential anomalies during winter show the opposite relationship, as lows may reach the Iberian Peninsula, in agreement with the negative correlation observed between summer FTLE and winter (JFM) precipitation
Summary
Seasonal forecast at mid-latitudes is still an open research field. the importance of this scale is relevant for different sectors such as agriculture (Howden et al, 2007; Meza et al, 2008), health (Thomson et al, 2008), energy (García-Morales and Dubus, 2007), or the financial sector (Meza et al, 2008). Two of the most important patterns that influence European climate variability are the North Atlantic Oscillation (NAO) and El Niño–Southern Oscillation (ENSO) (Visbeck et al, 2003; Brönnimann, 2007). The indices of these large-scale climatic patterns are used as predictors for seasonal forecast over Europe (Lloyd-Hughes and Saunders, 2002). The relationship between NAO and ENSO and the European variability is nonstationary (Trigo et al, 2004); that is, the strength of the correlation between these two teleconnections and climate anomalies has changed over time These patterns, though dominant on a large scale, often fail to provide forecast skill in specific regions. Changes in mid-latitude circulation are often directly linked to the occurrence of regional temperature
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