Time–space variations of temperature in the nocturnal boundary layer

Abstract

This study examines nocturnal temperature changes on time‐scales of 5–60 min over gentle terrain. Such temperature variations are often important after the early evening period of rapid cooling and can lead to large temporary warming or enhanced cooling. The time–space structure of temperature changes is examined statistically with a network of flux stations over gentle topography. Large temperature changes are often associated with coherent propagating modes and associated temporary reduction or elimination of the valley cold pool, local drainage flows, and lee turbulence. The largest variations of temperature with time occur for intermediate wind speeds. Low wind speeds correspond to greater spatial variability of temperature but less time dependence. Two nondimensional ratios are developed to represent the relative importance of temporal and spatial variability.