Observational evidence of an inertial wind structure in the stratosphere

Sidi, Claude; Barat, J.

doi:10.1029/jd091id01p01209

Cited by 26 publications

(8 citation statements)

References 15 publications

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“…As a potential interpretation of these observations, it has previously been suggested that similar layered structures found in the stratosphere were related to the dissipation of an internal gravity wave near a critical level (Sidi & Barat, 1986). The production of the layers observed above Iqaluit may be due to an orographic effect as sustained gravity waves produced via the hills to the northeast of Iqaluit, but further analysis (e.g., Froude number) is required.…”

Section: Discussionmentioning

confidence: 76%

Multi‐Instrument Observations of Prolonged Stratified Wind Layers at Iqaluit, Nunavut

Mariani

Dehghan

Gascon

et al. 2018

Geophysical Research Letters

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Data collected between October 2015 and May 2016 at Environment and Climate Change Canada's Iqaluit research site (64°N, 69°W) have revealed a high frequency (40% of all days for which observations were available) of stratified wind layer events that occur from near the surface up to about 7.2 km above sea level. These stratified wind layers are clearly visible as wind shifts (90 to 180°) with height in range‐height indicator scans from the Doppler lidar and Ka‐band radar and in wind direction profiles from the Doppler lidar and radiosonde. During these events, the vertical structure of the flow appears to be a stack of 4 to 10 layers ranging in vertical width from 0.1 to 4.4 km. The stratification events that were observed occurred predominantly (81%) during light precipitation and lasted up to 27.5 h. The integrated measurement platforms at Iqaluit permitted continuous observations of the evolution of stratification events in different meteorological conditions.

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Section: Discussionmentioning

confidence: 76%

Multi‐Instrument Observations of Prolonged Stratified Wind Layers at Iqaluit, Nunavut

Mariani

Dehghan

Gascon

et al. 2018

Geophysical Research Letters

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“…Therefore these oscillations tend to persist, as is observed in the atmosphere and the ocean (Sidi & Barat 1986;Maas & van Haren 1987) and in the experiments of Hallworth et al (2001). These two types of motion are studied here both computationally and theoretically.…”

Section: Introductionmentioning

confidence: 94%

Effects of rotation and sloping terrain on the fronts of density currents

et al. 2005

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The initial stage of the adjustment of a gravity current to the effects of rotation with angular velocity f/2 is analysed using a short time analysis where Coriolis forces are initiated in an inviscid von Kármán-Benjamin gravity current front at t F = 0. It is shown how, on a time-scale of order 1/f , as a result of ageostrophic dynamics, the slope and front speed U F are much reduced from their initial values, while the transverse anticyclonic velocity parallel to the front increases from zero to O(NH 0 ), where N = √ g /H 0 is the buoyancy frequency, and g = g ρ/ρ 0 is the reduced acceleration due to gravity. Here ρ 0 is the density and ρ and H 0 are the density difference and initial height of the current. Extending the steady-state theory to account for the effect of the slope σ on the bottom boundary shows that, without rotation, U F has a maximum value for σ = π/6, while with rotation, U F tends to zero on any slope. For the asymptotic stage when f t F 1, the theory of unsteady waves on the current is reviewed using nonlinear shallow-water equations and the van der Pol averaging method. Their motions naturally split into a 'balanced' component satisfying the Margules geostrophic relation and an equally large 'unbalanced' component, in which there is horizontal divergence and ageostrophic vorticity. The latter is responsible for nonlinear oscillations in the current on a time scale f −1 , which have been observed in the atmosphere and field experiments. Their magnitude is mainly determined by the initial potential energy in relation to that of the current and is proportional to the ratio √ Bu = L R /R 0 , where L R = NH 0 /f is the Rossby deformation radius and R 0 is the initial radius. The effect of slope friction also prevents the formation of a steady front. From the analysis it is concluded that a weak mean radial flow must be driven by the ageostrophic oscillations, preventing the mean front speed U F from halting sharply at f t F ∼ 1. Depending on the initial value of L R /R 0 , physical arguments show that U F decreases slowly in proportion to (f t F ) −1/2 , i.e. U F /U F 0 = F (f t F , Bu). Thus the front only tends to the geostrophic asymptotic state of zero radial velocity very slowly (i.e. as f t F → ∞) for finite values of L R /R 0 . However, as L R /R 0 → 0, it reaches this state when f t F ∼ 1. This analysis of the overall nonlinear behaviour of the gravity current is consistent with two two-dimensional non-hydrostatic (Navier-Stokes) and axisymmetric hydrostatic (shallow-water) Eulerian numerical simulations of the varying form of the rotating gravity current. When the effect of surface friction is considered, it is found that the mean movement of the front is significantly slowed. Furthermore, the oscillations with angular frequency f and the slow growth of the radius, when f t F > 1, are consistent with recent experiments.

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“…convective and frontal activity, and wind shear will be having their energy mostly confined to periods less than about 4 hours and the energy of the long-period gravity waves will be mostly occurring near the inertial period [e.g., Fritts and Luo, 1992]o Unlike the short-period gravity waves only limited observational studies of IGWs have been carried out, especially in the tropical region. Some of the earlier studies of IGWs were done using balloon data [e.g.. Thomson, 1978: Cadet and Teitelbaum, 1979: Sidi and Barat, 1986] and rocket data [e.g.. Hirota andNiki, 1985: Hamilton, 1991 Thomas et al, 1992Thomas et al, , 1999.…”

Section: Paper Number 1999gl011216mentioning

confidence: 99%