The Koorin nocturnal low-level jet

Abstract

It has been long known by Australian meteorologists that a nocturnal jet is a frequent feature of the low-level wind profile at Daly Waters in the Northern Territory of Australia. The Koorin Expedition during the southern winter of 1974 obtained data on wind and temperature profiles in the boundary layer which form an ideal base for the study of this phenomenon. In this paper, a simple mode1 of the jet is described and the results of the model are compared with observations. The mode1 is essentially a development of the pioneering work of Blackadar, who proposed that a low-level jet could develop as an inertia1 oscillation. The observations do show some of the features of the model.

Analytical description of a nocturnal low‐level jet

“…This latter value is typical of many low-level jets, but is much less than the several hundred per cent values reported for the strongest cases (e.g. Hoecker, 1963;Bonner, 1968;Brook, 1985). Although these results are in qualitatively good agreement with some observations, one should be cautioned that some of the good agreement might be fortuitous.…”

“…A descent of the wind maximum during the first half of the night is prominent in some numerical simulations of nocturnal jets over flat terrain without an imposed thermal wind, for example, the one-dimensional planetary boundary layer simulations of Delage (1974, Fig. 5), Brook (1985, Fig. 3) and Beyrich and Klose (1988, Figs.…”

“…Thorpe and Guymer (1977), Beyrich and Klose (1988), and Singh et al (1993) further modified the one-dimensional Blackadar theory of the nocturnal low-level jet by considering a variety of stress parametrizations, though with various structural or dynamical features treated as vertically discontinuous, slab-like or layered. Wippermann (1973), Delage (1974), Brook (1985), and Davies (2000) extended the Blackadar conceptual model by incorporating vertically continuous (apart from numerical discretization) turbulent stress parametrizations in their one-dimensional planetary boundary layer models. Recent advances in computer technology are making large-eddy simulation (LES) of the Blackadar jet scenario increasingly feasible, with some simulations extending over the daytime dry convective regime, the evening transition period, and the nocturnal period during which the jet develops.…”

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

“…Bonner 1968;Garratt 1982;Brook 1985;Kraus et al 1985;Parish et al 1988;Lettau 1990;Sjostedt et al 1990;Beyrich 1994;Mitchell et al 1995;Whiteman et al 1997;Banta et al 2002;Song et al 2005;Baas et al 2009;Karipot et al 2009), however, up to now there is no commonly accepted criterion for identifying the LLJ, since such flows can be of different origins (such as breezes, mountain-valley circulation, synoptic baroclinity, atmospheric fronts etc.) and behave differently.…”

“…Most of the reported observations of LLJs were carried out over the US Great Plains (Parish et al 1988;Whiteman et al 1997;Karipot et al 2009), over the Australian plains (Garratt 1985;Brook 1985), and in northern Europe (Kraus et al 1985;van Ulden and Wieringa 1996;Baas et al 2009). …”