TRAC98: Detection of Coherent Structures in a Convective Boundary Layer using Airborne Measurements

The TRAC98 experimental campaign (Turbulence Radar Aircraft Cells) devoted to coherent structures analysis took place over the Beauce plain (France) during summer 1998. It allowed us to collect a large dataset of airborne measurements in addition to various ground measurements. This study aims at diagnosing the occurrence of coherent structures within the atmospheric boundary layer (ABL) through airborne measurements. The statistical analysis performed as a first step from turbulent parameters underlined the homogeneity of the ABL over the Beauce plain. However mixed-layer scaling failed at the top of the ABL, even when taking into account the entrainment rate. Coherent structures were detected through the analysis of ABL isotropy, using the opportunity of sampling with two perpendicular crossing planes, one of them being aligned with the wind. This approach allowed us to determine an organization scheme of the ABL for three of the five flights (ARAT30, MIV30 and MIV27). For the ARAT30 flight, the analysis was pursued by focusing on measurements of fluctuations in the inner flight legs. In this way, the low-level cloud cover has been investigated from the downward visible radiation (VISD). The results indicated an anisotropy of the horizontal cloud size. Secondly, the variations of some parameters were analysed through lagged correlation functions. This allowed us to infer relationships between the vertical velocity, VISD, mixing ratio and lifting condensation level. Length scales have also been extracted, and confirmed the ABL organization during the ARAT30 flight. Finally, the anisotropy observed in various flights has been investigated with respect to the underestimation of the latent heat fluxes revealed by the imbalance of the surface energy budget.

[1]  Donald H. Lenschow,et al.  The Temperature-Humidity Covariance Budget in the Convective Boundary Layer , 1978 .

[2]  A. Druilhet,et al.  Experimental Studies of the Turbulence Structure Parameters of the Convective Boundary Layer , 1983 .

[3]  P. Drobinski,et al.  Evidence of Organized Large Eddies by Ground-Based Doppler Lidar, Sonic Anemometer and Sodar , 1998 .

[4]  Donald H. Lenschow,et al.  Length Scales in the Convective Boundary Layer , 1986 .

[5]  J. Kaimal,et al.  Turbulence Structure in the Convective Boundary Layer , 1976 .

[6]  John C. Wyngaard,et al.  Local Free Convection, Similarity, and the Budgets of Shear Stress and Heat Flux , 1971 .

[7]  Donald H. Lenschow,et al.  Mean-Field and Second-Moment Budgets in a Baroclinic, Convective Boundary Layer , 1980 .

[8]  J. Deardorff,et al.  A Laboratory Model of the Unstable Planetary Boundary Layer , 1974 .

[9]  P. Duynkerke,et al.  Turbulence in the atmospheric boundary layer , 1996 .

[10]  Stephen Nicholls,et al.  The Fair Weather Boundary Layer in GATE: The Relationship of Subcloud Fluxes and Structure to the Distribution and Enhancement of Cumulus Clouds , 1980 .

[11]  C. Readings,et al.  Aircraft observations of the structure of the lower boundary layer over the sea , 1979 .

[12]  B. Carissimo,et al.  Turbulent Dissipation Rate In The Boundary Layer Via UHF Wind Profiler Doppler Spectral Width Measurements , 2002 .

[13]  Georges Scialom,et al.  A New Analysis for the Retrieval of Three-Dimensional Mesoscale Wind Fields from Multiple Doppler Radar , 1990 .

[14]  E. K. Webb,et al.  Correction of flux measurements for density effects due to heat and water vapour transfer , 1980 .

[15]  D. Lenschow,et al.  The Use of Pressure Fluctuations on the Nose of an Aircraft for Measuring Air Motion , 1983 .

[16]  D. Lenschow,et al.  The role of thermals in the convective boundary layer , 1980 .

[17]  John C. Wyngaard,et al.  Spectral analysis of large-eddy simulations of the convective boundary layer , 1988 .

[18]  J. Kuettner.  Cloud bands in the earth's atmosphere. Observations and theory , 1971 .

[19]  R. J. Doviak,et al.  Clear-Air Roll Vortices and Turbulent Motions as Detected with an Airborne Gust Probe and Dual-Doppler Radar , 1981 .

[20]  Y. Miura.  Aspect Ratios of Longitudinal Rolls and Convection Cells Observed during Cold Air Outbreaks , 1986 .

[21]  L. Eymard,et al.  Investigation of Clear Air Convective Structures in the PBL Using a Dual Doppler Radar and a Doppler Sodar , 1982 .

[22]  L. Mahrt,et al.  Heat Transport in the Atmospheric Boundary Layer. , 1984 .

[23]  B. Campistron,et al.  Spatial and Temporal Characteristics of Horizontal Rolls and Cells in the Atmospheric Boundary Layer Based on Radar and in Situ Observations , 1998 .

[24]  C. Coulman.  Boundary-layer evolution and nocturnal inversion dispersal—Part I , 1978 .

[25]  D. Lenschow,et al.  Errors in airborne flux measurements , 1994 .

[26]  D. Etling,et al.  Roll vortices in the planetary boundary layer: A review , 1993 .

[27]  Margaret A. LeMone,et al.  The Structure and Dynamics of Horizontal Roll Vortices in the Planetary Boundary Layer , 1973 .

[28]  P. Sullivan,et al.  A Comparison of Shear- and Buoyancy-Driven Planetary Boundary Layer Flows , 1994 .

[29]  P. Durand,et al.  The marine atmospheric boundary layer during semaphore. II: Turbulence profiles in the mixed layer , 1999 .

[30]  Errors in Eddy Correlation Turbulence Measurements from Aircraft: Application to HAPEX-MOBILHY , 1991 .

[31]  Tammy M. Weckwerth,et al.  Thermodynamic Variability within the Convective Boundary Layer Due to Horizontal Convective Rolls , 1996 .

[32]  Alan G. Barr,et al.  Comparison of regional surface fluxes from boundary-layer budgets and aircraft measurements above boreal forest , 1997 .

[33]  J. Deardorff.  Three-dimensional numerical study of the height and mean structure of a heated planetary boundary layer , 1974 .

[34]  A. Grant.  The Structure of Turbulence in the Near-neutral Atmospheric Boundary Layer , 1992 .

[35]  R. Stull.  An Introduction to Boundary Layer Meteorology , 1988 .

[36]  B. Campistron,et al.  Numerical Study Of The Impact Of Coherent Structures On Vertical Transfers In The Atmospheric Boundary Layer , 2000, Boundary-Layer Meteorology.

[37]  Pierre Durand,et al.  Turbulence structure of the boundary layer below marine clouds in the SOFIA experiment , 1995 .

[38]  A. Verhoef,et al.  Surface energy balance of shrub vegetation in the Sahel , 1995 .

[39]  Ernest M. Agee,et al.  An Aircraft Investigation of Mesoscale Convection over Lake Michigan during the 10 January 1984 Cold Air Outbreak , 1989 .

[40]  B. W. Atkinson,et al.  Mesoscale shallow convection in the atmosphere , 1996 .

[41]  Burghard Brümmer,et al.  Roll and cell convection in wintertime Arctic cold-air outbreaks. , 1999 .

[42]  S. Caughey,et al.  Some aspects of turbulence structure through the depth of the convective boundary layer , 1979 .

[43]  S. Chou,et al.  Heat fluxes and roll circulations over the western Gulf Stream during an intense cold-air outbreak , 1991 .

[44]  B. Campistron,et al.  Turbulence and Coherent Organizations in the Atmospheric Boundary Layer: A Radar-Aircraft Experimental Approach , 1998 .

[45]  Z. Sorbjan,et al.  Structure of the atmospheric boundary layer , 1989 .

[46]  M. Lemone,et al.  The Relationship of Trade Wind Cumulus Distribution to Subcloud Layer Fluxes and Structure , 1976 .

[47]  Structure, dynamics and energetics of boundary layer rolls from Kon Tur aircraft observations , 1985 .

[48]  P. Durand,et al.  The marine atmospheric boundary layer during semaphore. I: Mean vertical structure and non‐axisymmetry of turbulence , 1999 .

[49]  S. Khalsa,et al.  Convective Elements in the Marine Atmospheric Boundary Layer. Part I: Conditional Sampling Statistics , 1987 .

[50]  Donald H. Lenschow,et al.  Aircraft measurements in the boundary layer , 1986 .

[51]  Molecular dissipation of turbulent fluctuations in the convective mixed layer part I: Height variations of dissipation rates , 1983 .

[52]  M. Lemone.  Some Observations of Vertical Velocity Skewness in the Convective Planetary Boundary Layer , 1990 .

[53]  J. Deardorff,et al.  Three-dimensional numerical study of turbulence in an entraining mixed layer , 1974 .

[54]  John C. Wyngaard,et al.  Statistics of Conservative Scalars in the Convective Boundary Layer , 1984 .

[55]  E. Agee.  Observations from Space and Thermal Convection: A Historical Perspective. , 1984 .