The nocturnal jet

Thorpe, Alan; Guymer, T. H.

doi:10.1002/qj.49710343809

Cited by 156 publications

(47 citation statements)

References 12 publications

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“…At night, winds at higher levels usually tend to accelerate by an inertial oscillation as a result of flow decoupling (Blackadar 1957). Near the surface, winds weaken owing to a combination of inertial effects and turbulent stress divergence around sunset (Thorpe and Guymer 1977;Baas et al 2012). At intermediate heights (some decameters above the surface), a ''crossing level'' exists where the wind remains relatively constant in magnitude.…”

Section: Model Descriptionmentioning

confidence: 99%

Regime Transitions in Near-Surface Temperature Inversions: A Conceptual Model

Wiel

Vignon

Baas

et al. 2017

Journal of the Atmospheric Sciences

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A conceptual model is used in combination with observational analysis to understand regime transitions of near-surface temperature inversions at night as well as in Arctic conditions. The model combines a surface energy budget with a bulk parameterization for turbulent heat transport. Energy fluxes or feedbacks due to soil and radiative heat transfer are accounted for by a ''lumped parameter closure,'' which represents the ''coupling strength'' of the system.Observations from Cabauw, Netherlands, and Dome C, Antarctica, are analyzed. As expected, inversions are weak for strong winds, whereas large inversions are found under weak-wind conditions. However, a sharp transition is found between those regimes, as it occurs within a narrow wind range. This results in a typical S-shaped dependency. The conceptual model explains why this characteristic must be a robust feature. Differences between the Cabauw and Dome C cases are explained from differences in coupling strength (being weaker in the Antarctic). For comparison, a realistic column model is run. As findings are similar to the simple model and the observational analysis, it suggests generality of the results.Theoretical analysis reveals that, in the transition zone near the critical wind speed, the response time of the system to perturbations becomes large. As resilience to perturbations becomes weaker, it may explain why, within this wind regime, an increase of scatter is found. Finally, the so-called heat flux duality paradox is analyzed. It is explained why numerical simulations with prescribed surface fluxes show a dynamical response different from more realistic surface-coupled systems.

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Section: Model Descriptionmentioning

confidence: 99%

Regime Transitions in Near-Surface Temperature Inversions: A Conceptual Model

Wiel

Vignon

Baas

et al. 2017

Journal of the Atmospheric Sciences

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“…The low-level jet of the Great Plains region of the United States has been extensively studied by among others, Hoecker (1963Hoecker ( ,1965; Blackadar (1957);Wexler (1961) and Bonner (1968). Other mid-to-higher latitude nocturnal low-level jets have been detected in southeastern Australia (Clarke et al, 1971), southern England (Thorpe and Guymer, 1977), northwestern Germany (Kraus er al., 1985), the United States Gulf coast (Hsu, 1979), and the coastal regions of northeastern United States and the Canadian Maritimes (Dickerson and Neumann, 1982). In the tropical and subtropical regions of the world, however, only a few documented cases of lowlevel nocturnal jets or wind maxima are in existence.…”

Section: Introductionmentioning

confidence: 99%

Low-level nocturnal wind maximum over the central Amazon basin

Greco

Ulanski

Garstang³

et al. 1992

Boundary-Layer Meteorol

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A low-level nocturnal wind maximum is shown to exist over extensive and nearly undisturbed rainforest near the central Amazon city of Manaus. Analysis of meteorological data collected during the 1985 and 1987 Amazon Boundary Layer Experiments (ABLE 2A and 2B) indicates the presence of this nocturnal wind maximum during both the wet and dry seasons of the Central Amazon Basin. Daytime wind speeds which are characteristically 3-7 m s-' between 300 and 1000 m increase to lo-15 m s-l shortly after sunset. The wind speed maximum is reached in the early evening, with wind speeds remaining high until several hours after sunrise. The nocturnal wind maximum is closely linked to a strong low-level inversion formed by radiational cooling of the rainforest canopy. The night-time inversion extends up to 300 m with strong vertical shear of the horizontal wind below the inversion top and uniformly strong horizontal winds above the inversion top. Frictional decoupling of the air above the inversion from the rough forest below, however, is responsible for only part of the observed increase. Surface and low-level pressure gradients between the undisturbed forest and the large Amazon river system and the city of Manaus are shown to be responsible for much of the nocturnal wind increase. The pressure gradients are interpreted as a function of the thermal differences between undisturbed forest and the river/city. The importance of both the frictional decoupling and the horizontal pressure gradient suggest that the nocturnal wind maximum does not occur uniformly over all Amazonia. We suspect that stronger low-level winds are pervasive under clear skies and strong surface cooling and that, in many places (i.e., near rivers), local pressure gradients enhance the low-level nocturnal winds.

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“…More recently, Thorpe and Guymer (1977) and Beyrich and Klose (1988) have analysed vector-time hodographs showing an inertial spiral and compared these with simple models with good results. Using a barotropic model, Logsdon and Revelle (1987) have shown that the inertial oscillation mechanism is most effective at latitudes 22-23" where the length of night matches the inertial period.…”

Section: Mechanismssustainingthewinternocturnallowleveljetmentioning

confidence: 99%

Characteristics of the winter boundary layer over the African Plateau: 26 � S

Jury

Tosen

1989

Boundary-Layer Meteorol

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Characteristics of the winter boundary layer over the African Plateau (elevation 1600 m) in the vicinity of Johannesburg, 26" S, 29" E, are described in relation to air pollution potential by means of doppler sounder observations and background climatological data. Regional mean winds for the 800 hPa level show that the winter boundary layer is dominated by a cell of high pressure over the Limpopo River Valley to the northeast of Johannesburg. To the south of Johannesburg, westerly circumpolar flow is prevalent and encroaches onto the plateau during the passage of frontal perturbations. Doppler sounder wind and turbulence profiles, averaged for the months of August 1984 and June 1985, are presented to establish a boundary-layer climatology. Diurnally averaged doppler sounder profiles for both months revealed a very consistent convective/day -stable/night cycle in the very dry winter conditions. A sharp radiation inversion formed just after sunset up to the 150-200 m level and grew in depth to reach 300 m on average near sunrise. The inversion caused a reduction in frictional drag and the formation of nocturnal low level jet during westerly encroachment. A case study is evaluated to determine the detailed structure of the low level jet near Johannesburg. The thermal wind plays a role in the nocturnal acceleration; mechanisms for its development and maintenance are explored. Additional work is presented on the synoptic cycle and its influence on air pollution dispersion over the African Plateau.

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The nocturnal jet

Cited by 156 publications

References 12 publications

Regime Transitions in Near-Surface Temperature Inversions: A Conceptual Model

Regime Transitions in Near-Surface Temperature Inversions: A Conceptual Model

Low-level nocturnal wind maximum over the central Amazon basin

Characteristics of the winter boundary layer over the African Plateau: 26 � S

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