Urban climate and day of the week

Abstract

A brief survey is made of previous research on the day-of-week variation in a number of weather parameters, with special reference to rainfall amount. Further analysis suggests that the amplitude of the so-called “weekly rainfall cycle” in the London area is related to wind speed, sunshine duration and the magnitude of the urban heat-island. The present investigation on daily maximum and minimum air temperature in the London area, over the 20-yr period from April 1949 to March 1969, shows that there was a weekly cycle in the difference between the mean daily maximum temperature in central London and the surrounding rural area, in midsummer (May, June and July). The mean weekly amplitude of the difference in daily maximum temperature was approximately 0.5°C; the lowest mean difference of daily maximum temperature (London minus surroundings) occurred on Thursday and the highest on Sunday. The pattern is significant at the 0.1 per cent level. The weekly amplitude varied inversely as the wind speed. Although the weekly pattern of daily maximum temperature can be explained by the weekly pattern of air pollution, the results are generally consistent with the hypothesis that thermal convection can be an important cause of the differences between urban and rural rainfall regimes: also, results indicate that wind speed is an important factor in urban heatisland and rain-island phenomena.