Abstract
ABSTRACTIn this study, the recently found lead–lag relationship between Eurasian snow cover increase in October and wintertime precipitation totals on the Iberian Peninsula is re‐visited and generalized to a broad range of atmospheric variables on the synoptic and local scale. To this aim, a robust (resistant to outliers) method for calculating the index value for Eurasian snow cover increase in October is proposed. This ‘Robust Snow Advance Index’ (RSAI) is positively correlated with the wintertime (DJF) frequency of cyclonic and westerly flow circulation types over the Iberian Peninsula, while the corresponding relationship with anticyclonic and easterly flow types is negative. For both cases, an explained variance of approximately 60% indicates a strong and highly significant statistical link on the synoptic scale.Consistent with these findings, it is then shown that the lead–lag relationship equally holds for the DJF‐mean conditions of (1) precipitation amount, (2) diurnal temperature range, (3) sun hours, (4) cloud cover and (5) wind speed on the local scale. To assess if these target variables can be skillfully hindcast, simple linear regression is applied as a statistical forecasting method, using the October RSAI as the only predictor variable. One‐year out cross‐validation yields locally significant hindcast correlations of up to approximately 0.8, obtaining field significance for any of the five target variables mentioned above. The validity for a wide range of atmospheric variables and the consistency of the local‐ and synoptic‐scale results affirm the question posed in the title.
Highlights
Wintertime precipitation totals on the Iberian Peninsula were recently found to be statistically related to Eurasian snow cover increase during the previous October (Brands et al 2012)
A possible dynamical pathway for this formerly unknown lead-lag relationship has been identified by observational and idealized generalized circulation model studies, linking Eurasian snow cover in fall to the Northern Hemisphere extratropical circulation during the following winter (Cohen and Entekhabi 1999; Saito et al 2001; Gong et al 2003; Cohen et al 2007; Fletcher et al 2007, 2009; Smith et al 2011; Mote and Kutney 2012), the latter commonly described by the Arctic Oscillation (Kutzbach 1970; Thompson and Wallace 1998)
‘Robust Snow Advance Index’ is shown to be significantly associated with the DJF circulation characteristics over the Iberian Peninsula, which in turn control the concurrent mean conditions of 1) precipitation amount, 2) diurnal temperature range, 3) sun hours, 4) cloud cover and 5) wind speed on the local/station scale
Summary
Wintertime precipitation totals on the Iberian Peninsula were recently found to be statistically related to Eurasian snow cover increase during the previous October (Brands et al 2012). This study is dedicated to the regional manifestation of this hemispheric-wide teleconnection for the December-to-January (DJF) mean climate on the Iberian Peninsula. To this aim, a robust method for calculating the index value of October Eurasian Snow cover increase (Cohen and Jones 2011) is proposed. A robust method for calculating the index value of October Eurasian Snow cover increase (Cohen and Jones 2011) is proposed This ‘Robust Snow Advance Index’ is shown to be significantly associated with the DJF circulation characteristics over the Iberian Peninsula, which in turn control the concurrent mean conditions of 1) precipitation amount, 2) diurnal temperature range, 3) sun hours, 4) cloud cover and 5) wind speed on the local/station scale. By linking large-scale predictability to local scale predictability for a wide range of atmospheric variables, this study strengthens the hypothesis that Eurasian snow cover increase is a meaningful statistical predictor for the wintertime-mean climate conditions on the Iberian Peninsula
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