% Introduction

The \ac{IPCC} report, 2007 has caused a big interest regarding global climate change in the media, politics and society. Great effort has been undertaken and is still on going to understand the mechanism of climate change and the anthropogenic impact on it \cite{baeumer2007feb}.

One approach for a better understanding of the anthropogenic effects on climate could be the analysis of the 7-day-periodicities in meteorological data. Since there is no natural long-term 7-day-cycle known, one can consider the weekly anomalies in meteorological data-sets as human made. A few studies have focused on this topic (section \vref{sec:researchhasbeendone}).

One objective of this master thesis is to check if there are similar weekly periodicities in Switzerland  as \citet{baeumer2007feb} found in Germany. Therefore, precipitation, temperature and daily sunshine duration data from several measurement stations are analysed.

Questions to be answered are the following: are there any differences between stations north or south of the Alps? How do these weekly pe\-ri\-od\-ic\-i\-ties---if there are any at all---change over time? Is the signal amplitude getting stronger with increasing industrial activity and pollution? Or are these weekly differences  just coincidence?

Another focus is given on the weekly regime of \ac{PM}. \citet{baeumer2007feb} showed that the influence has to be at least on a mesoscale-$\alpha$ (phenomenon with a range of 200--2,000\,km across), due to the fact that at mountain stations the weekly periodicity was also found. They suppose that the connection between a microscale to a mesoscale phenomena has to be an indirect aerosol effect.

\section{Research that has been done on weekly cycles}\label{sec:researchhasbeendone}
The research on weekly cycles is not a new issue. Already in the late twenties of the last century \citet{ashworth1929} analysed the precipitation data from England between 1890 and 1920. He detected that there was 13\% less rainfall on Sundays than on the average of all days. It was believed that the weekend reduction of smoke and hot gases from English factories was responsible for the decrease in precipitation. Referring to this, \citet{ashworth1933} wrote in his Nature article: ``In a factory town Sunday is a day of reduced smoke pollution and concurrently Sunday is, in the long run, the day of least rainfall of any day of the week.''

In the 1960s, various authors debated whether Tuesdays, Thursdays, or Saturdays, if any day of the week, were the wettest in London, England \cite{schultz2007}. But no consensus was reached, in part owing to the different observing stations, time periods, and methodologies employed by these authors, as well as the lack of statistical testing \cite{schultz2007}.

Later studies on this topic were not less contradictory. The only agreement between the different groups seemed to be a weekly cycle in air pollutants (e.\,g. \PM{10} or ozone).

\begin{itemize}
\item \citet{dettwiller1968} found that the precipitation on weekdays was significantly higher than on weekends in five French cities. 30 years later \citet{baeumer2007feb} found the contrary in Germany.

\item \citet{simmonds1986} found a weekly cycle in Melbourne, Australia, where the precipitation on weekdays was significantly higher than on weekends.

\item \citet{gordon1994} showed through an analysis of satellite microwave sounding data (from the years 1979--1992) a significant but very small weekly temperature cycle for the northern hemisphere.

\item \citet{simmonds1997} found weekly cycles in temperature and precipitation in Melbourne for the period 1960--1994. They attributed these to local heat emissions.

\item \citet{broennimann1997} detected weekend-weekday differences in the near-surface ozone concentration depending on the meteorological conditions in Switzerland.

\item \citet{cerveny1998} identified weekly cycles of precipitation and tropical cyclone maximum wind speed over the North-West Atlantic region and explained this with the help of an air pollution index that also showed a weekly cycle. Furthermore they detected that the difference of day and night wind speed in tropical cyclones reveals a weekly periodicity.

\item \citet{beaney2002} found weekend-weekday differences of ozone and temperature in Toronto. As they did not find these difference in the data of a remote station they concluded that it has to be a local phenomenon. 

\item \citet{marr2002} detected weekend-weekday differences of ozone, VOCs and NOx (in 1980--1999) at several stations in California.

\item \citet{cerveny2002} identified a weekly cycle of CO$_2$ at Mauna Loa, Hawaii. However at the South Pole they did not find a 7-day cycle.

\item \citet{delene2002} and \citeauthor{jin2005} found weekly periodicities of aerosol optical properties at different locations in North-America.

\item \citet{beirle2003} analysed satellite data and found significant weekly cycles of tropospheric NO$_2$ over many industrialised regions.

\item \citet{forster2003} detected a weekend effect in the daily temperature range in different regions.

\item \citet{tsai2005} found differences of the visibility and the \PM{10} concentration between weekdays and weekends in Taiwan.

\item \citet{shutters2006} reported weekly cycles of various chemical variables and of wind speed in Phoenix, Arizona.

\item \citet{gong2006} found increasing weekly cycles in various meteorological parameters (e.\,g. temperature and precipitation) in China.

\item \citet{baeumer2007feb} showed that climatological variables in Germany have an unexpected weekly distinction. They chose data from 1991 to 2005 from the \ac{DWD}
\end{itemize}

In contrast, other studies found no statistically significant signal between weekday and weekend precipitation. For example:
\begin{itemize}
 \item\citet{cehak1982} in Vienna, Austria
 \item \citet{horsley1995} in five Midwestern US cities \item \citet{delisi2001} along the Northeast Corridor
 \item \citet{wilby2000} at 92 stations in the United Kingdom
\end{itemize}

\citet{schultz2007} state that there is no significant weekly precipitation cycle at all: ``Daily precipitation records for 219 surface observing stations in the United States for the 42-year period 1951--1992 are investigated for weekly cycles in precipitation. Results indicate that neither the occurrence nor amount of precipitation significantly depends upon the day of the week.''
They confirm the result of \citet{delisi2001} who did not find a significant weekly precipitation cycle along the Northeast Corridor.
They even question the results of a study with the satellite derived precipitation estimates by \citet{cerveny1998} due to ``the potential problems in estimating precipitation from \ac{MSU} data \cite{spencer1993}, as well as questionable causal links between their data sets''.

This thesis is organised as follows: Chapter \ref{chap:theory} focuses on a few hypothesised theories, that try to explain how a weekly cycle could come into being. Chapter \ref{chap:methods} focuses on the methods applied hereinafter. In Chapter \ref{chap:results} the results will be presented and discussed in Chapter \ref{chap:discussion}. Chapter \ref{chap:conclusion_outlook} is reserved for a short conclusion and an outlook.