Hilland et al. (2025) Horizontal Anisotropy of Turbulent Fluctuations in Surface and Air Temperatures Over a Flat, Homogeneous Surface

⚠️ Warning: This summary was generated from the abstract only, as the full text was not available.

Identification

• Journal: Journal of Geophysical Research Atmospheres
• Year: 2025
• Date: 2025-12-19
• Authors: Rainer Hilland, Andreas Christen
• DOI: 10.1029/2025jd044685

Research Groups

Not specified in abstract.

Short Summary

This study investigates the longitudinal and lateral integral length scales of temperature fluctuations and their anisotropy across a range of atmospheric stabilities in a desert surface layer. It finds that turbulence anisotropy varies significantly with wind speed and stability, with surface length scales being larger than near-surface atmospheric ones and generally exceeding previously reported values.

Objective

• To investigate the spatial length scales of temperature fluctuations (longitudinal and lateral integral length scales) and their anisotropy in a desert surface layer with low roughness over a range of atmospheric stabilities, comparing them between the surface interface and the near-surface atmosphere.

Study Configuration

• Spatial Scale: Desert surface layer with low roughness, including both the surface interface and the near-surface atmosphere.
• Temporal Scale: Not explicitly defined, but covers a range of atmospheric stabilities, implying observations over varying conditions.

Methodology and Data

• Models used: Not applicable; direct measurement and construction of 2D spatial correlation fields were used to calculate length scales.
• Data sources:
  • Horizontally arrayed distributed fiber-optic temperature sensor (for 2D spatial correlation fields of air temperature fluctuations).
  • Time-sequential thermography (for length scales of temperature fluctuations at the surface interface).

Main Results

• The longitudinal integral length scale ($\Lambda_x$) generally increases with increasing boundary layer height, increasing wind speed, and decreasing instability.
• The lateral integral length scale ($\Lambda_y$) is found to be more constant for both surface temperature and air temperature fields.
• More isotropic turbulence is observed at low wind speeds and in more unstable atmospheric regimes.
• More anisotropic turbulence is observed in (near-)neutral atmospheric stabilities at higher wind speeds.
• Length scales at the surface are found to be larger than those in the near-surface atmosphere.
• Surface length scales are generally higher than values reported in the existing literature.

Contributions

• Provides a comprehensive investigation of spatial length scales of temperature fluctuations and their anisotropy across a wide range of atmospheric stabilities, addressing a gap in literature predominantly focused on neutral stability.
• Utilizes novel measurement techniques, including a horizontally arrayed distributed fiber-optic temperature sensor and time-sequential thermography, to construct 2D spatial correlation fields.
• Reveals significant variations in turbulence anisotropy with wind speed and atmospheric stability.
• Highlights the distinct characteristics of length scales at the surface interface compared to the near-surface atmosphere, and identifies that these surface scales are generally larger than previously reported values.

Funding

Not specified in abstract.

Citation

@article{Hilland2025Horizontal,
  author = {Hilland, Rainer and Christen, Andreas},
  title = {Horizontal Anisotropy of Turbulent Fluctuations in Surface and Air Temperatures Over a Flat, Homogeneous Surface},
  journal = {Journal of Geophysical Research Atmospheres},
  year = {2025},
  doi = {10.1029/2025jd044685},
  url = {https://doi.org/10.1029/2025jd044685}
}