Abstract
Conditional sampling is used to locate coherent structures in a large data set obtained from flights by an instrumented light aircraft in convective boundary layers over Eyre Peninsula, South Australia. The high resolution and excellent spatial coverage of the data enable a detailed study of the internal structure of surface-layer plumes and mixed-layer thermals. A compositing technique is used to construct averaged traverses through coherent structures located within aircraft data runs of different altitudes and directions. Groups of composites are combined to form horizontal and vertical cross-sections which describe the internal flow patterns and the distribution of physical variables associated with “typical” coherent structures and their environment. In addition to the well-known along-wind features of surface-layer plumes, a strong, consistent inflow/entrainment pattern is evident in the lateral direction. Air from the horizontal plane channels around the sides and then in behind the microfront present at the upstream edge. Forces set up by the driving instability in the along-wind and vertical directions are counter-balanced by organised flow in the across-wind direction. It is found that mixed-layer thermal towers have a relatively simple form, consisting primarily of large columns of warm, upward-moving turbulent air, which may occasionally be in a state of slow rotation. An analysis of possible geometrical distortions within the results is performed, leading to a comparison ofδw/δz estimated from the horizontal velocity convergence field inside plumes/thermals, with that computed from the slope of partitionedw profiles.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Antonia, R. A. and Chambers, A. J.: 1978, ‘Note on the Temperature Ramp Structure in the Marine Surface Layer’,Boundary-Layer Meteorol. 15, 347–355.
Antonia, R. A., Chambers, A. J., Friehe, C. A., and Van Atta, C. W.: 1979, ‘Temperature Ramps in the ASL’,J. Atmos. Sci. 36, 99–108.
Deardorff, J. W.: 1970, ‘Convective Velocity and Temperature Scales for the Unstable PBL and for Rayleigh Convection’,J. Atmos. Sci. 27, 1211–1213.
Driedonks, A. G. M. and Tennekes, H.: 1984, ‘Entrainment Effects in the Well-Mixed Atmospheric Boundary Layer’,Boundary-Layer Meteorol. 30, 75–105.
Frisch, A. S., Chadwick, R. B., Moninger, W. R., and Young, J. M.: 1976, ‘Observations of Boundary-Layer Convection Cells Measured by Dual-Doppler Radar and Echosonde, and by Microbarograph Array’,Boundary-Layer Meteorol. 10, 55–68.
Greenhut, G. K. and Khalsa, S. J. S.: 1982, ‘Updraft and Downdraft Events in the ABL Over the Equatorial Pacific Ocean’,J. Atmos. Sci. 39, 1803–1818.
Greenhut, G. K. and Khalsa, S. J. S.: 1987, ‘Convective Elements in the Marine Atmospheric Boundary Layer. Part 1: Conditional Sampling Statistics. Part 2: Entrainment at the Capping Inversion’,J. Climate and Appl. Meteorol. 26, 813–836.
Hacker, J. M. and Schwerdtfeger, P.: 1988, ‘The FIAMS Research Aircraft System Description, 2nd Edition’, Flinders Institute for Atmospheric and Marine Sciences; Flinders University of South Australia.
Kaimal, J. C.: 1974, ‘Translation Speed of Convective Plumes in the ASL’,Quart J. R. Meteorol. Soc. 100, 46–52.
Kaimat, J. C. and Businger, J. A.: 1970, ‘Case Studies of a Convective Plume and a Dust Devil’,J. Appl. Meteorol. 9, 612–620.
Khalsa, S. J. S. and Greenhut, G. K.: 1985, ‘Conditional Sampling of Updrafts and Downdrafts in the Marine ABL’,J. Atmos. Sci. 42, 2550–2562.
Lenschow, D. H. and Stephens, P. L.: 1980, ‘The Role of Thermals in the Convective Boundary Layer’,Boundary-Layer Meteorol. 19, 509–532.
Nicholls, S. and Readings, C. J.: 1981, ‘Spectral Characteristics of Surface Layer Turbulence Over the Sea’,Quart. J. Meteorol. Soc. 107, 591–614.
Roadcap, J. R. and Rao, G. V.: 1986, ‘Features of Thermals in Stable Wake and Neutral Stratifications in the Disturbed Monsoon Boundary Layer’,Boundary-Layer Meteorol. 36, 133–148.
Schmidt, H. and Schumann, U.: 1989, ‘Coherent Structure of the Convective Boundary Layer Derived from Large-Eddy Simulations’,J. Fluid Mech. 200, 511–562.
Schols, J. L. J.: 1984, ‘The Detection and Measurement of Turbulent Structures in the Atmospheric Surface Layer’,Boundary-Layer Meteorol. 29, 39–58.
Schols, J. L. J., Jansen, A. E., and Krom, J. G.: 1985, ‘Characteristics of Turbulent Structures in the Unstable ASL’,Boundary-Layer Meteorol. 33, 173–196.
Schols, J. L. J. and Wartena, L.: 1986, ‘A Dynamical Description of Turbulent Structures in the Near Neutral ASL: The Role of Static Pressure Fluctuations’,Boundary-Layer Meteorol. 34, 1–15.
Schwerdtfeger, P.: 1985, ‘Climate [of Eyre Peninsula]. Chapter 6 of “Natural History of Eyre Peninsula”’,Royal Soc. S.A. 1985, 89–100.
Telford, J. W.: 1986, ‘Comment on “Large-Scale Eddies in the Unstably Stratified Atmospheric Surface Layer”, by Wilczak and Businger (1984)’,J. Atmos. Sci. 43, 499–500.
Warner, J. and Telford, J. W.: 1963, ‘Some Patterns of Convection in the Lower Atmosphere’,J. Atmos. Sci. 20, 313–318.
Wilczak, J. M. and Businger, J. A.: 1984, ‘Large Scale Eddies in the Unstably Stratified Atmospheric Surface Layer. Part 1 (Wilczak): Velocity and Temperature Structure. Part 2 (Wilczak and Businger): Turbulent Pressure Fluctuations and the Budgets of Heat Flux, Stress and T.K.E.’,J. Atmos. Sci. 41, 3537–3567.
Wilczak, J. M. and Tillman, J. E.: 1980, ‘The Three-Dimensional Structure of Convection in the Atmospheric Surface Layer’,J. Atmos. Sci. 37, 2424–2443.
Williams, A. G.: 1991, ‘Internal Structure and Interactions of Coherent Eddies in the Lower Convective Boundary Layer’, Ph.D. Thesis, Flinders University of South Australia.
Young, G. S.: 1988, ‘Turbulence Structure of the Convective Boundary Layer’,J. Atmos. Sci. 45, 719–735.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Williams, A.G., Hacker, J.M. The composite shape and structure of coherent eddies in the convective boundary layer. Boundary-Layer Meteorol 61, 213–245 (1992). https://doi.org/10.1007/BF02042933
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF02042933