Analysis Of Sub-mesoscale Coherent Structures Influenced On Turbulence In Stable Boundary Layer

Recent observations show non-turbulent non-stationary movements in the stable boundary layer,with scales from principal turbulent eddy to minimal mesoscale motions,leading to complex nonlinear interactions with turbulence.However,these interactions still have not been fully understood to date.For this reason,this thesis analyzes turbulence and coherent structures of temperature and velocity field in the nocturnal stable boundary layer,by long period observations on two types of the underlayer(bare land and maize field)of arid and semi-arid areas,by developing a novel mathematical method on revealing coherent structures,and by reducing turbulent kinetic energy equations to deduction expression of Richardson number.Then this thesis inspects the isotropic characteristics of turbulence in the two kinds of the stable boundary layer distinguished by the critical Richardson number,with the discussion about changes in physical quantities before and after the pivotal point of the isotropic characteristics.Moreover,this thesis analyzes the linearity stability condition on the bifurcation diagram about the normalized friction velocity and the normalized heat flux of the coherent structures above the canopy underlayer.By theoretical discussions on the variation rate of turbulence kinetic energy before and after the critical point of the‘Hokey Stick Transition’,this thesis reveals the details of the sub-mesoscale coherent structures changed by the existence of the canopy underlayer.The long-range correlation of sub-mesoscale coherent structures and turbulence is acquired.The genialized multifractal intermittency model adapted to the turbulence in the stable boundary layer is evolved.And last,the damping of turbulence autocorrelation influenced by coherent structures above the canopy underlayer is explained.The creative results are as follows: 1)The Koopman operator is given by defining the observational operator Ri on the turbulent state space.And the dynamical analysis of the Koopman subspace reveals the primary mode of coherent structures in the nocturnal stable boundary layer.2)The critical invariance on normalized Reynolds stress tensor is discovered.And the physical graph is described,which is that the influence of boundary layer characteristics on turbulent non-isotropic evolution is driven by ‘the horizontal shear enhancement coupling downward vertical temperature flux enhancement’.3)The Algorithm of the ‘Coupled Levenberg-Marquardt Method with Stage Initial Value’ is developed to calculate the three-staged zero displacement height and aerodynamic roughness length of the two-layer observation on the maize field.The inconsistency of canopy influence on momentum flux and heat flux is detected.And the necessary condition of the linearity stability on the bifurcation diagram about the normalized friction velocity and the normalized heat flux is discussed.4)The explanation of the ‘J-shape’ HOST curve is given by theoretical analysis combined with observation.The formation of the ‘J-shape’ is due to the cumulative effect of the horizontal shear term changing with the negative slope of the average horizontal kinetic energy.5)The generalized multifractal intermittency model based onα-stable distribution adapted to stable boundary layer turbulence is developed.And based on this model,the stage of long-range autocorrelation about sub-mesoscale coherent structures changed with the velocity time interval is revealed.6)The model in the transition relationship between average horizontal kinetic energy and normalized Reynolds stress tensor is classified.And based on the essential difference in the response of vertical velocity variance to friction velocity before and after the coupling,the damping of turbulence autocorrelation influenced by coherent structures above the canopy underlayer is demonstrated.