The Structure of a Fair Weather Boundary Layer Based on the Results of Several Measurement Strategies

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  • 1 University of Virginia, Department of Environmental Sciences, Charlottesville, VA 22903
  • | 2 Max-Planck-Institut fur Meteorologie, Hamburg, Federal Republic of Germany
  • | 3 National Center for Atmospheric Research, Boulder, CO 80307
  • | 4 Meteorological Research Flight, Royal Aircraft Establishment, Farnborough, U.K.
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Abstract

A fair weather boundary layer (BL) with light winds and scattered cumulus to 1100 m is examined in the GATE C-scale triangle using data from tethered balloons, surface measurements from the booms of the ships, structure sondes and gust probe aircraft. The original goal was a comparison of the instrumentation in an expected uniform field of wind, temperature and humidity. It became rapidly obvious that nonuniformities existed not only at the turbulence scales (a few meters to 1 km) but also on scales 10 km and larger. Thus the goal evolved into 1) combining the observations to present a coherent picture of the day, 2) putting the results of various observational techniques in perspective and 3) examining the nonuniformity.

Different aspects of the day are revealed by the different observational techniques. The Dallas tethered balloon reveals a noticeable modification of the BL nearly coincident with a change in convective activity. In spite of nonuniformity, and the interception of convective events similar to that at the Dallas, the flux profiles from aircraft show that the BL behaves in a similar way to those reported previously near “horizontally homogeneous” conditions. Moisture and energy budgets performed for this day show the expected convergence of sensible and latent heat in the boundary layer but in a shallower layer than expected.

Abstract

A fair weather boundary layer (BL) with light winds and scattered cumulus to 1100 m is examined in the GATE C-scale triangle using data from tethered balloons, surface measurements from the booms of the ships, structure sondes and gust probe aircraft. The original goal was a comparison of the instrumentation in an expected uniform field of wind, temperature and humidity. It became rapidly obvious that nonuniformities existed not only at the turbulence scales (a few meters to 1 km) but also on scales 10 km and larger. Thus the goal evolved into 1) combining the observations to present a coherent picture of the day, 2) putting the results of various observational techniques in perspective and 3) examining the nonuniformity.

Different aspects of the day are revealed by the different observational techniques. The Dallas tethered balloon reveals a noticeable modification of the BL nearly coincident with a change in convective activity. In spite of nonuniformity, and the interception of convective events similar to that at the Dallas, the flux profiles from aircraft show that the BL behaves in a similar way to those reported previously near “horizontally homogeneous” conditions. Moisture and energy budgets performed for this day show the expected convergence of sensible and latent heat in the boundary layer but in a shallower layer than expected.

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