期刊
BOUNDARY-LAYER METEOROLOGY
卷 142, 期 2, 页码 177-192出版社
SPRINGER
DOI: 10.1007/s10546-011-9672-7
关键词
Cold-air pool; Distributed temperature sensing; Fibre optics; Spatial sampling; Stable boundary layer; Taylor's hypothesis; Turbulence
资金
- Army Research Office [W911NF-10-1-0361, W911NF-09-1-0271]
- National Science Foundation [AGS 0955444, 0529223, EAR 0930061]
- Swiss National Science Foundation [PBEZP2-127819]
- Swiss National Science Foundation (SNF) [PBEZP2-127819] Funding Source: Swiss National Science Foundation (SNF)
- Direct For Biological Sciences
- Emerging Frontiers [0529223] Funding Source: National Science Foundation
- Directorate For Geosciences
- Division Of Earth Sciences [0930061] Funding Source: National Science Foundation
- Div Atmospheric & Geospace Sciences
- Directorate For Geosciences [0955444] Funding Source: National Science Foundation
- Division Of Earth Sciences
- Directorate For Geosciences [1129003] Funding Source: National Science Foundation
We present a novel approach based on fibre-optic distributed temperature sensing (DTS) to measure the two-dimensional thermal structure of the surface layer at high resolution (0.25 m, a parts per thousand 0.5 Hz). Air temperature observations obtained from a vertically-oriented fibre-optics array of approximate dimensions 8 m x 8 m and sonic anemometer data from two levels were collected over a short grass field located in the flat bottom of a wide valley with moderate surface heterogeneity. The objectives of the study were to evaluate the potential of the DTS technique to study small-scale processes in the surface layer over a wide range of atmospheric stability, and to analyze the space-time dynamics of transient cold-air pools in the calm boundary layer. The time response and precision of the fibre-based temperatures were adequate to resolve individual sub-metre sized turbulent and non-turbulent structures, of time scales of seconds, in the convective, neutral, and stable surface layer. Meaningful sensible heat fluxes were computed using the eddy-covariance technique when combined with vertical wind observations. We present a framework that determines the optimal environmental conditions for applying the fibre-optics technique in the surface layer and identifies areas for potentially significant improvements of the DTS performance. The top of the transient cold-air pool was highly non-stationary indicating a superposition of perturbations of different time and length scales. Vertical eddy scales in the strongly stratified transient cold-air pool derived from the DTS data agreed well with the buoyancy length scale computed using the vertical velocity variance and the Brunt-Vaisala frequency, while scales for weak stratification disagreed. The high-resolution DTS technique opens a new window into spatially sampling geophysical fluid flows including turbulent energy exchange.
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