Boundary-Layer Meteorology

, Volume 67, Issue 4, pp 345–367 | Cite as

Observations of fluxes over heterogeneous surfaces

  • L. Mahrt
  • J. I. Macpherson
  • Ray Desjardins
Article
Accepted:

Abstract

This study analyzes data collected from repeated aircraft runs 30 m over alternating regions of irrigated and dry nonirrigated surfaces, each region on the order of 10 km across, during the California Ozone Deposition Experiment (CODE). After studying the scale dependence of the flow, the variables and their fluxes are decomposed into means for sublegs defined in terms of irrigated and nonirrigated regions and deviations from such subleg means. Since the repeated runs were flown over the same track, compositing the eight flight legs for each of the two days allows partial isolation of the influences of surface heterogeneity and transient mesoscale motions.

A variance analysis is carried out to quantify the relative importance of surface heterogeneity and transient mesoscale motions on the variability of the turbulence fluxes. The momentum and ozone fluxes are more influenced by transient mesoscale motions while fluxes of heat, moisture and carbon dioxide are more influenced by surface heterogeneity. The momentum field is also influenced by a quasi-stationary mesoscale front and larger scale velocity gradients.

For the present case, the mesoscale modulation of the turbulent flux is numerically more important than the direct mesoscale flux. This spatial modulation of the turbulent fluxes leads to extra Reynolds terms which act to reduce the area-averaged turbulent momentum flux and enhance the area-averaged turbulent heat flux.

Keywords

Heat Flux Momentum Flux Surface Heterogeneity Spatial Modulation Scale Dependence 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
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Copyright information

© Kluwer Academic Publishers 1994

Authors and Affiliations

  • L. Mahrt
    • 1
  • J. I. Macpherson
    • 2
  • Ray Desjardins
    • 3
  1. 1.Oceanic and Atmospheric SciencesOregon State UniversityCorvallisUSA
  2. 2.Flight Research LaboratoryNational Research CouncilOttawaCanada
  3. 3.Centre for Land and Biological Resource ResearchAgriculture CanadaOttawaCanada

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