7.4 Modelling intermittent turbulence bursts in the stable boundary layer

Thursday, 5 August 2010: 11:15 AM
Torrey's Peak I&II (Keystone Resort)
Felipe D. Costa, Universidade Federal do Pampa, Alegrete, Brazil; and O. C. Acevedo and G. A. Degrazia

The classical scheme proposed by Blackadar for the surface-atmosphere interaction is applied for the nocturnal boundary-layer. Prognostic equations for wind components, air and ground temperature are solved, based on first-order turbulence closure and the surface energy budget. Differently than in previous studies, no stability function relating turbulence intensity to thermal stratification is imposed. Rather, the turbulent kinetic energy equation is solved, based on appropriate parameterizations of its terms. Model integration for different numbers of sublayers yields previously found results, such as large turbulence intensity and connection between the surface and higher levels when strong enough winds are imposed at the boundary layer top or when clouds prevent the surface radiative cooling. When these conditions are not met, however, the model leads to an intermittent behavior of the surface layer variables. Turbulence bursts occur in a manner similar to commonly observed, causing large temperature variations. The bursts are nonperiodic and are shown to be chaotic under the proper conditions, which are analyzed in detail. Chaos and intermittency are favored under specific ranges of both the mechanical and radiative forcing. The temporal and vertical structure of the intermittent events is analyzed in terms of their TKE budget.
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