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Abstract Nocturnal spatial variation of temperature, wind, and turbulence over microtopography is generally poorly understood. Low amplitude microtopography covers much of the Earth’s surface and, with very stable conditions, can produce significant spatial variations of temperature and turbulence. We examine such variations over gentle terrain that include two shallow gullies that feed into a small valley. The gullies are covered by a sub-network of seven flux stations that is embedded within a larger network that covers the valley. The measurements indicate that gullies of only 2–5-m depth and 100-m width can often lead to spatial variations of temperature of several kelvin or more. Such variations depend on ambient wind speed and direction and the near-surface stratification. We investigate the surprising importance of microscale lee turbulence occurring over the gentle microtopography with slopes of only 5%. Near-surface stratification unexpectedly tends to increase with surface elevation on the slopes. We examine the potential causes of this puzzling behaviour of the near-surface stratification.
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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.
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- Award ID(s):
- 1945587
- PAR ID:
- 10456268
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Quarterly Journal of the Royal Meteorological Society
- Volume:
- 146
- Issue:
- 731
- ISSN:
- 0035-9009
- Page Range / eLocation ID:
- p. 2756-2767
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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