Study Finds Taylor Hypothesis Limitations in Forest Clearcut Flows
Researchers tested Taylor's hypothesis (TH) against a more general elliptic model in a highly turbulent forest clearcut environment, finding that TH fails under buoyant, high-turbulence conditions. Using distributed temperature sensing (DTS) and eddy covariance (EC) datasets, they showed that space-time correlation functions of temperature fluctuations follow elliptic curves rather than the straight lines TH predicts. The findings have implications for how micrometeorological tower measurements are interpreted in heterogeneous landscapes.
Taylor's hypothesis is a widely used tool in micrometeorology that converts temporal flow measurements into spatial information, relying on the assumption of 'frozen turbulence' — that eddies do not evolve significantly as they are advected past a sensor. This study tested TH against the elliptic model, a more general framework that accounts for curvature in space-time correlation functions, using data collected at 3.1 m above a forest clearing during buoyant atmospheric conditions. When mean wind was parallel to a nearby forest edge, DTS-derived space-time correlations of temperature fluctuations were elliptic rather than linear, indicating TH's frozen turbulence assumption was violated. The researchers attribute this breakdown to random sweeping events driven by large-scale eddies, with the sweeping velocity scale correlating with the turbulence kinetic energy of the clearcut flow — consistent with the random sweeping hypothesis. Both temporal DTS and EC temperature measurements were found to be affected by these sweeping events, suggesting that standard TH-based scaling introduces errors in such heterogeneous, high-turbulence environments. The results underscore the need to apply the elliptic model, rather than TH, when analyzing flows in complex terrain such as forest clearcuts.
What's missing
The dataset is limited to a single clearcut site and one measurement height (3.1 m) under buoyant conditions; generalizability to other forest edge geometries, stability regimes, or measurement heights remains untested. The authors do not quantify the magnitude of errors introduced by applying TH versus the elliptic model in practical micrometeorological applications.
What different sources said
- arXiv physicsCenter
Limitations of Taylor hypothesis in a forest clearcut flow
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