1. Anthropogenic Aerosol – A Cause Of The Weekend Effect? A significant weekly cycle has been found in diurnal temperature range (DTR). A candidate for causing this 'weekend effect' is anthropogenic aerosol. Enhanced atmospheric aerosol loading during weekdays is likely to affect the radiation flux at the surface by direct forcing and indirect forcing by altering cloud properties on short time scales. If a weekly cycle can be found in cloud cover then it may be possible to quantitatively link anthropogenic aerosol loading and the observed DTR variations. This will help produce a reliable estimate of the radiative forcing due to the indirect aerosol effect - a major uncertainty when trying to predict future climate. It will also provide conclusive evidence that industrial emissions are contributing significantly to the current climatic changes. Motivation for Research

2. DTR difference between Saturday-Monday average and Wednesday-Friday average over the USA 1 (the ‘weekend effect’) 1 Forster PMD, Solomon S, Observations of a "weekend effect" in diurnal temperature range, PNAT 11225-11230 SEP 30 2003 Anthropogenic Aerosol – A Cause Of The Weekend Effect? Significant weekly cycles have been show to exist in diurnal temperature range (DTR), an important climatic indicator. As no natural phenomena has a stable 7 day cycle the cause of this is likely to be anthropogenic. Weekly cycles in aerosol loading may be directly and indirectly (via changes in cloud properties) forcing the climate. The ‘Weekend Effect’

3. Observed daily SO 2 levels from Manchester, UK averaged over 4 years. Values are displayed as a fraction of the mean Clear weekly cycles in aerosol precursor gases indicate that aerosol formation will have a similar trend too Further research involves analysing weekly variations in aerosol optical properties over the globe using AERONET station and satellite-bourne instrument data. Weekly Cycles in Aerosol Burden

4. Cloud cover difference between Saturday-Monday average and Wednesday-Friday average over the Pacific and USA. It is found that the difference between weekday and weekend cloudiness can vary by up to 3% 16 years of global cloud cover data from ISCCP (International Satellite Cloud Climatology Project) is being analysed for weekly signals. Statistical testing shows a high pattern significance, although the signal to noise ratio is low. Further work will involve making a direct comparison between weekly cycles in cloud cover and the ‘weekend effect’ reported in DTR. Weekly Cycles in Cloud Cover