Mean ground cover or NDVI plotted against solar radiation, measured ca. 60 km northwest of the experiment site, as a relative indicator of the diurnal variation in daylight. (a) Event 1 and (b) Event 2. Each symbol corresponds to the mean value for a particular hourly measurement. The actual hourly measurement time is indicated by the number inside each symbol. The size of the symbol is scaled according to the hourly measurement time.