In recent years the existence of weekly periodicities in various meteorological variables and atmospheric pollutants has been investigated in numerous studies. Evidence of weekly cycles in anthropogenic pollution has been shown for different regions in Europe (e.g. Bäumer et al., 2008; Barmet et al., 2009; Stjern, 2011), North America (e.g. Cerveny and Balling, 1998; Murphy et al., 2008) and Asia (e.g. Gong et al., 2007). Concerning different meteorological variables several investigations point to the presence of weekly periodicities in surface air temperature (e.g. Forster and Solomon, 2003; Bäumer and Vogel, 2007; Gong et al., 2007; Laux and Kunstmann, 2008; Sanchez-Lorenzo et al., 2008), precipitation (e.g. Cerveny and Balling, 1998; Bäumer and Vogel, 2007; Gong et al., 2007; Bell et al., 2008), wind speed (e.g. Cerveny and Balling, 1998) or cloudiness (e.g. Bäumer and Vogel, 2007; Sanchez-Lorenzo et al., 2008), just to name a few of the analysed variables. However, it has to be mentioned that the detected periodicities vary distinctly concerning their phase and amplitude among different regions, time periods and variables (e.g. Laux and Kunstmann, 2008). Moreover, serious doubts concerning the applied methods and the results achieved in some of these studies have been repeatedly raised (e.g. Hendricks Franssen, 2008; Hendricks Franssen et al., 2009). Also in contradiction to the above mentioned studies a number of studies did not find any proof for statistical significant weekly cycles in different meteorological variables in varying regions of the world (e.g. DeLisi et al., 2001; Schultz et al., 2007; Barmet et al., 2009; Stjern, 2011).
Given the absence of any known natural phenomena that may cause the weekly weather cycles several anthropogenic factors have been proposed as potential causes for the observed periodicities in meteorological parameters. In this context several authors (e.g. Cerveny and Balling, 1998; Bäumer and Vogel, 2007; Sanchez-Lorenzo et al., 2008) have supposed corresponding cycles in aerosol concentrations. Weekly cycles in greenhouse gases have been mentioned for example by Cerveny and Coakley (2002). Sanchez-Lorenzo et al. (2008) and Laux and Kunstmann (2008) found evidence for the relationship between weekly cycles in meteorological variables and corresponding periodicities in large-scale atmospheric circulation dynamics reflected by occurrence frequencies of objectively derived circulation types. These periodicities in large-scale circulation dynamics are supposed to be in turn triggered by air pollution effects in the lower troposphere (Laux and Kunstmann, 2009). Sanchez-Lorenzo et al. (2008) analysed occurrence frequencies of nine daily circulation types determined by an optimized cluster analysis (Philipp et al., 2007) for the period 1961–2003. A statistical significant weekly cycle turned out for one type during winter (December, January, February—DJF). However this finding has been brought into doubt by Hendricks Franssen et al. (2009). Laux and Kunstmann (2009) investigated weekly cycles in occurrence frequencies of objectively derived European circulation types according to Beck et al. (2007). By applying a robust bootstrap method they detected significant weekly cycles in occurrence frequencies of 10 out of 18 circulation types for the period 1991–2005.
Thus, so far all findings on possible weekly cycles in large-scale circulation dynamics are based on the analyses of occurrence frequencies of only two different circulation classifications applied to different data sets, for different regions and different time periods. Against this background it appears appropriate to analyse weekly cycles in occurrence frequencies of circulation types using a more comprehensive data base of circulation classifications in order to avoid the over interpretation of single results that are maybe due to inconsistencies in individual classifications.
In this contribution the existence of weekly periodicities in occurrence frequencies of circulation types is analysed on the basis of 231 different daily circulation-type classifications that were applied to varying spatial domains for the period 1957–2002. The basic idea behind this comprehensive approach is that any essential and realistic signal of a weekly cycle in large-scale circulation dynamics should be reflected in occurrence frequencies of circulation types derived from varying classification methods.