A Conceptual View on Inertial Oscillations and Nocturnal Low-Level Jets

Abstract

In the present work Blackadar’s concept of nocturnal inertial oscillations is extended. Blackadar’s concept describes frictionless inertial oscillations above the nocturnal inversion layer. The current work includes frictional effects within the nocturnal boundary layer. It is shown that the nocturnal wind speed profile describes an oscillation around the nocturnal equilibrium wind vector, rather than around the geostrophic wind vector (as in the Blackadar case). By using this perspective, continuous time-dependent wind profiles are predicted. As such, information on both the height and the magnitude of the nocturnal low-level jet is available as a function of time. Preliminary analysis shows that the proposed extension performs well in comparison with observations when a simple Ekman model is used to represent the equilibrium state in combination with a realistic initial velocity profile. In addition to jet dynamics, backward inertial oscillations are predicted at lower levels close to the surface, which also appear to be present in observations. The backward oscillation forms an important mechanism behind weakening low-level winds during the afternoon transition. Both observational and theoretical modeling studies are needed to explore this phenomenon further.

Impacts of the low-level jet's negative wind shear on the wind turbine

“…Blackadar (1957) was the first who explained the formation of the jets as the result of the inertial oscillation of the Earth. The periodicity of the inertial oscillation was later calculated by Stensrud (1996) and Van de Wiel et al (2010). Additionally, other theories of LLJ's formation have also been proposed.…”

“…Bonner (1968) confirmed the finding but maintained that the inertial oscillation was still the predominant mechanism and refined the conceptual model of the oscillations. Another theory was later proposed, when Uccellini (1980) observed that strong jets in the upper layers of the atmosphere can induce slower jets within the atmospheric boundary layer.…”

Low-Level Jets in the Moscow Region in Summer and Winter Observed with a Sodar Network

“…Baas et al 2009;Van de Wiel et al 2010;Shapiro and Fedorovich 2010). It is not yet clear, however, if the inertial oscillations are significant for the LLJ appearance in the longlived temperature inversions over snow-covered surfaces, when diurnal changes in the ABL thermal stratification are small.…”

A Study of the Stable Boundary Layer Based on a Single-Column K-Theory Model

“…1a, and in addition to the 9-h profiles (black lines), the profiles obtained after 18-h of simulation are also shown in the figure (blue lines). The difference between the 9-h and the 18-h profiles is associated with inertial effects (e.g., Blackadar 1957; Van de Wiel et al 2010). The effects are noticeable in the upper part of the boundary layer, from about 100 to 200 m. They vanish above the boundary layer, as a result of the adopted initial condition, which forces the wind to become geostrophic above the boundary layer.…”