A study of intermittent turbulence with cases-99 tower measurments

Characteristics of intermittent turbulence events in the stably stratified nocturnal boundary layer are investigated with data collected in the CASES-99 tower array of 300-m radius. The array consists of a central 60-m tower with eddy covariance measurements at eight levels and six satellite towers with eddy covariance measurements at 5 m. A significant increase in the magnitude of vertical wind velocity (σ) and spectral information are used to define the onset of an intermittent turbulence event. Normally, only a subset of 5 m-levels in the tower network experience an intermittent turbulence event concurrent with one at the 5 m-level on the main tower. This behaviour reveals the small horizontal extent of most events. Intermittent turbulence events at the main tower 5-m level are normally confined to a layer much thinner than the 60-m tower height. The turbulent kinetic energy budget is evaluated for intermittent turbulence events observed at the 5-m level on the main tower. Generally, the onset of an intermittent turbulence event is not closely related to the reduction of the gradient Richardson number below 0.25, the critical Richardson number of turbulence generation for linear instability. Possible explanations including the influence of advected turbulence patches are discussed.

[1]  Dean Vickers,et al.  Contrasting vertical structures of nocturnal boundary layers , 2002 .

[2]  Larry Mahrt,et al.  Simple formulation of turbulent mixing in the stable free atmosphere and nocturnal boundary layer , 1992 .

[3]  R. Narasimha,et al.  Turbulent bursts in the atmosphere , 1990 .

[4]  J. Howell,et al.  Surface-Layer Fluxes in Stable Conditions , 1999 .

[5]  Andrew J. Majda,et al.  Elementary stratified flows with instability at large Richardson number , 1998, Journal of Fluid Mechanics.

[6]  Turker Ince,et al.  Intermittent Turbulence Associated with a Density Current Passage in the Stable Boundary Layer , 2002 .

[7]  Christopher W. Fairall,et al.  Similarity Relationships in the Marine Atmospheric Surface Layer for Terms in the TKE and Scalar Variance Budgets , 1998 .

[8]  C. Nappo.  An introduction to atmospheric gravity waves , 2002 .

[9]  K. Kunkel,et al.  Intermittent turbulence in measurements of the temperature structure parameter under very stable conditions , 1982 .

[10]  P. Drazin.  On the instability of an internal gravity wave , 1977, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[11]  Jerrold E. Marsden,et al.  Richardson number criterion for the nonlinear stability of three-dimensional stratified flow , 1984 .

[12]  Douglas K. Lilly,et al.  Stratified Turbulence and the Mesoscale Variability of the Atmosphere , 1983 .

[13]  Larry Mahrt,et al.  Intermittent of Atmospheric Turbulence , 1989 .

[14]  R. Coulter,et al.  A case study of turbulence in the stable nocturnal boundary layer , 1990 .

[15]  Joan Cuxart,et al.  CASES-99: a comprehensive investigation of the stable nocturnal boundary layer , 2002 .

[16]  J. C. Doran,et al.  Spatial and Temporal Occurrences of Intermittent Turbulence During CASES-99 , 2002 .

[17]  Larry Mahrt,et al.  Multiresolution Flux Decomposition , 1997 .

[18]  Dean Vickers,et al.  The Cospectral Gap and Turbulent Flux Calculations , 2003 .

[19]  J. D. Woods,et al.  On Richardson's Number as a Criterion for Laminar-Turbulent-Laminar Transition in the Ocean and Atmosphere , 1969 .

[20]  J. Kondo,et al.  Heat and Momentum Transfers under Strong Stability in the Atmospheric Surface Layer , 1978 .

[21]  W. Blumen.  An observational study of instability and turbulence in nighttime drainage winds , 1984 .

[22]  J. H. Richter,et al.  The Birth of “CAT” and Microscale Turbulence , 1970 .

[23]  J. Finnigan,et al.  The interaction between an internal gravity wave and the planetary boundary layer. Part II: Effect of the wave on the turbulence structure , 2007 .

[24]  S. A. Thorpe,et al.  Turbulence in stably stratified fluids: A review of laboratory experiments , 1973 .

[25]  M. Parlange,et al.  Conditional sampling, bursting, and the intermittent structure of sensible heat flux , 1994 .

[26]  H. A. Panofsky,et al.  The Critical Richardson Number and Its Implications for Forecast Problems , 1964 .

[27]  C. Nappo.  Sporadic breakdowns of stability in the PBL over simple and complex terrain , 1991 .

[28]  J. Finnigan.  Kinetic Energy Transfer between Internal Gravity Waves and Turbulence , 1988 .

[29]  Ron F. Blackwelder,et al.  On the wall structure of the turbulent boundary layer , 1976, Journal of Fluid Mechanics.

[30]  L. Mahrt.  Vertical Structure and Turbulence in the Very Stable Boundary Layer , 1985 .

[31]  S. Larsen,et al.  Small scale drainage front , 1982 .