[1] A simple approach to the smoothing of a potentially non-stationary time series is presented which provides an optimal choice among three alternative, readily motivated and easily implemented boundary constraints. This method is applied to the smoothing of the instrumental Northern Hemisphere (NH) annual mean and coldseason North Atlantic Oscillation (NAO) time series, yielding an objective ...

Carbon, water and energy exchanges between forests and the atmosphere depend upon seasonal dynamics of both temperature and precipitation, which are influenced by low frequency climate oscillations such as: El Niño-Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Arctic Oscillation (AO), Eastern Pacific Oscillation (EPO) and the Pacific-North American (PNA). This study investigate...

The relationship between winter (DJF) rainfall over Portugal and the variable large scale circulation is addressed. It is shown that the poles of the sea level pressure (SLP) field variability associated with rainfall variability are shifted about 15° northward with respect to those used in standard definitions of the North Atlantic Oscillation (NAO). It is suggested that the influence of NAO o...

Harp seals (Pagophilus groenlandicus) have evolved life history strategies to exploit seasonal sea ice as a breeding platform. As such, individuals are prepared to deal with fluctuations in the quantity and quality of ice in their breeding areas. It remains unclear, however, how shifts in climate may affect seal populations. The present study assesses the effects of climate change on harp seals...

The North Atlantic Oscillation (NAO) is one of the most prominent and recurrent patterns of atmospheric circulation variability. It dictates climate variability from the eastern seaboard of the United States to Siberia and from the Arctic to the subtropical Atlantic, especially during boreal winter, so variations in the NAO are important to society and for the environment. Understanding the pro...

The aim of this study is to assess the impact of the North Atlantic Oscillation (NAO) on both the winter precipitation and the temporal occurrence of different landslide types in Portugal. The analysis is applied to five sample areas located just north of Lisbon, the capital of Portugal. These sites are particularly relevant because actual dates of most of the recent landslide events are known ...

We use Normalized Difference Vegetation Index (NDVI) retrieved between 1982 and 2001 from the AVHRR instrument. The year-to-year variations of vegetation greenness in Europe were estimated and related the North Atlantic Oscillation NAO. Here, we intend to show the sequence of intermediate relevant physical mechanisms responsible for the changes induced in vegetation by the NAO. Therefore, upper...

Causal discovery seeks to recover cause–effect relationships from statistical data using graphical models. One goal of this paper is to provide an accessible introduction to causal discovery methods for climate scientists, with a focus on constraint-based structure learning. Second, in a detailed case study constraintbased structure learning is applied to derive hypotheses of causal relationshi...

The impact of El Niño–Southern Oscillation (ENSO) on the North Atlantic (NAO) has been controversially discussed for several decades, which exhibits prominent seasonality and nonstationarity. During early winter, there appears a positive ENSO-NAO relationship, while this relationship reverses its sign in late winter. Here, we show that subseasonal variation could be attributed to different mech...