On the asymmetry of the urban daily air temperature cycle

The asymmetry phenomenon in daily temperature cycle refers to the smaller and decreasing diurnal temperature range, which resulted from much faster rise of the daily minimum temperature than that of the maximum temperature. The asymmetry is known to have occurred in greater magnitude in cities than rural sites. Spatially, the diurnal temperature range is much smaller in urban areas than in the surrounding rural areas. Temporally, the urban diurnal temperature range decreases much faster than that in the rural areas. Here, we demonstrate a new approach in understanding the spatial and temporal asymmetries in the urban daily air temperature cycle. Both asymmetries can be explained by a simple combination of a reduction in amplitudes with a rise in mean temperature, which are governed by difference factors. Our study provides new insights that increase our understanding of the mechanisms of urban warming.