2013 Volume 69 Issue 3 Pages 191-200
We investigated the temporal and spatial variability of nighttime temperatures in a complex of small valleys in the western Kanto Plain, Saitama Prefecture, Japan, by conducting horizontal and vertical temperature measurements throughout one winter season. The magnitude of nocturnal cooling in the valley was greater in March than during the mid-winter period. The horizontal distribution of mean nighttime temperatures and nocturnal cooling under clear and calm conditions indicated that temperatures in the middle or lower areas of the valleys tended to be lower than those in the upper areas even though the elevation differences were small. Vertical profiles of air temperature measured by a kytoon system on clear nights revealed the development of a temperature inversion above the valley floor at night; the top of the inversion exceeded the height of the ridge adjacent to the valley. Under these conditions, down-valley flows of cold air were a significant phenomenon below the inversion layer. Our results suggest that local nocturnal drainage flow below the temperature inversion could contribute to nocturnal cooling in these valleys.