2018 Volume 96 Issue 2 Pages 147-160
The climatological features of surface air temperature variations on time scales of a few minutes to 1 h were examined using 1 min data spanning a 4-year period from 917 automated stations in Japan. The temperature time series was spectrally analyzed after the application of a Gaussian high-pass filter, and the variances with periods of 64 min or less were statistically analyzed as sub-hourly temperature variations. The result obtained shows that daytime temperature variation is observed throughout the country with relatively small regional differences. The amplitudes of daytime temperature variations were larger during spring and summer than during autumn and winter and were larger under high temperature and sunny weather than under low temperature, no sunshine, and precipitation. A cross-spectral analysis of temperature and wind speed reveals that temperature peaks tend to coincide with or lag behind wind speed minima. The variation is likely to correspond to the convective motion in the mixing layer. On the other hand, the intensity of nighttime temperature variation showed a large amount of scatter among stations, with exceptionally large variations during winter at some stations in northern and eastern Japan. Nighttime temperature variation tends to be in phase with wind speed variation, with longer periods than daytime temperature variation and with more intensity under low temperature and low wind speed than under high temperature, high wind speed, and precipitation. Stations with large winter nighttime temperature variations tend to be located on a col or a slope, where the surface inversion layer is likely to be easily disturbed by any kind of atmospheric motion.
