Chaos and "bursting' in the planetary boundary layer

Abstract

A theoretical study of the intermittent breakdowns of the planetary boundary layer (PBL) has been carried out using a one-dimensional, "flat' terrain, PBL model of the type originally developed by A.K. Blackadar. The turbulent burst effects predominate in the lowest tens of meters of the PBL where an alternation between successive regimes of laminar and turbulent flow drive either rapid cooling or rapid heating, respectively, of the near-surface air temperature under certain conditions. This rather discontinuous change of the air temperature occurs with variable amplitudes at irregular intervals depending critically on the specified surface aerodynamic roughness length, the prevailing geostrophic wind, the magnitude of the radiation cooling with respect to the soil and its thermal properties, etc. For an aerodynamic roughness length of 1 m, collapse was found to occur within only a very narrow range of geostrophic winds (between 1.5 and 3 m s-1, with a maximum response in the air temperature changes occurring at about 2 m s-1). -from Author