Transient Gravity Wave-Critical Layer Interaction. Part I: Convective Adjustment and the Mean Zonal Acceleration

Abstract. 11-years long K Doppler lidar observations of temperature profiles in the mesosphere and lower thermosphere (MLT) between 85 and 100 km, conducted at the Arecibo Observatory, Puerto Rico (18.35° N, 66.75° W), are used to estimate seasonal variations of the mean temperature, the squared Brunt-Väisälä frequency, and the gravity wave potential energy in a composite year. The following unique features are obtained: (1) The mean temperature structure shows similar characteristics as a prior report based on a smaller dataset: (2) The profiles of the squared Brunt-Väisälä frequency usually reach the maxima at or just below the temperature inversion layer when that layer is present. The first complete range-resolved climatology of potential energy of temperature fluctuations in the tropical MLT exhibits an altitude dependent combination of annual oscillation (AO) and semiannual oscillation (SAO). Between 88 to 96 km altitude, the amplitudes of AO and SAO are comparable, and their phases are almost the same and quite close to day of year (DOY) 100. Below 88 km, the SAO amplitude is significantly larger than AO and the AO phase shifts to DOY 200 and after. At 97 to 98 km altitude, the amplitudes of AO and SAO reach their minima, and both phases shift significantly. Above that, the AO amplitude becomes greater. The annual mean potential energy profile reaches the minimum at 91 to 92 km altitude. The altitude-dependent SAO of the potential energy is found to be highly correlated with the satellite observed mean zonal winds reported in the literature.

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The Reflection of a Stationary Gravity Wave by a Viscous Boundary Layer

Journal of the Atmospheric Sciences ◽

10.1175/jas4020.1 ◽

2007 ◽

Vol 64 (9) ◽

pp. 3363-3371 ◽

Cited By ~ 11

Author(s):

François Lott

Keyword(s):

Boundary Layer ◽

Gravity Wave ◽

Richardson Number ◽

Critical Level ◽

Inviscid Limit ◽

Mean Flow ◽

Viscous Boundary Layer ◽

Lee Waves ◽

The Mean ◽

Viscous Boundary

Abstract The backward reflection of a stationary gravity wave (GW) propagating toward the ground is examined in the linear viscous case and for large Reynolds numbers (Re). In this case, the stationary GW presents a critical level at the ground because the mean wind is null there. When the mean flow Richardson number at the surface (J) is below 0.25, the GW reflection by the viscous boundary layer is total in the inviscid limit Re → ∞. The GW is a little absorbed when Re is finite, and the reflection decreases when both the dissipation and J increase. When J > 0.25, the GW is absorbed for all values of the Reynolds number, with a general tendency for the GW reflection to decrease when J increases. As a large ground reflection favors the downstream development of a trapped lee wave, the fact that it decreases when J increases explains why the more unstable boundary layers favor the onset of mountain lee waves. It is also shown that the GW reflection when J > 0.25 is substantially larger than that predicted by the conventional inviscid critical level theory and larger than that predicted when the dissipations are represented by Rayleigh friction and Newtonian cooling. The fact that the GW reflection depends strongly on the Richardson number indicates that there is some correspondence between the dynamics of trapped lee waves and the dynamics of Kelvin–Helmholtz instabilities. Accordingly, and in one classical example, it is shown that some among the neutral modes for Kelvin–Helmholtz instabilities that exist in an unbounded flow when J < 0.25 can also be stationary trapped-wave solutions when there is a ground and in the inviscid limit Re → ∞. When Re is finite, these solutions are affected by the dissipation in the boundary layer and decay in the downstream direction. Interestingly, their decay rate increases when both the dissipation and J increase, as does the GW absorption by the viscous boundary layer.

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Gravity waves observed from the Equatorial Wave Studies (EWS) campaign during 1999 and 2000 and their role in the generation of stratospheric semiannual oscillations

Annales Geophysicae ◽

10.5194/angeo-24-2481-2006 ◽

2006 ◽

Vol 24 (10) ◽

pp. 2481-2491 ◽

Cited By ~ 10

Author(s):

V. Deepa ◽

G. Ramkumar ◽

B. V. Krishna Murthy

Keyword(s):

Gravity Wave ◽

Gravity Waves ◽

Propagation Characteristics ◽

Mean Flow ◽

Vertical Wavelength ◽

Flow Acceleration ◽

Equatorial Wave ◽

The Mean ◽

Phase Propagation ◽

Rayleigh Lidar

Abstract. The altitude profiles of temperature fluctuations in the stratosphere and mesosphere observed with the Rayleigh Lidar at Gadanki (13.5° N, 79.2° E) on 30 nights during January to March 1999 and 21 nights during February to April 2000 were analysed to bring out the temporal and vertical propagation characteristics of gravity wave perturbations. The gravity wave perturbations showed periodicities in the 0.5–3-h range and attained large amplitudes (4–5 K) in the mesosphere. The phase propagation characteristics of gravity waves with different periods showed upward wave propagation with a vertical wavelength of 5–7 km. The mean flow acceleration computed from the divergence of momentum flux of gravity waves is compared with that calculated from monthly values of zonal wind obtained from RH-200 rockets flights. Thus, the contribution of gravity waves towards the generation of Stratospheric Semi Annual Oscillation (SSAO) is estimated.

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Fully coupled resonant-triad interactions in a free shear layer

Journal of Fluid Mechanics ◽

10.1017/s0022112094003630 ◽

1994 ◽

Vol 278 ◽

pp. 101-121 ◽

Cited By ~ 18

Author(s):

R. Mallier ◽

S. A. Maslowe

Keyword(s):

Flow Direction ◽

Mixing Layer ◽

Adverse Pressure Gradient ◽

Critical Layer ◽

Free Shear Layer ◽

Mean Flow ◽

Weakly Nonlinear ◽

Initial Interaction ◽

The Mean ◽

Fully Coupled

We report the results of an investigation of the weakly nonlinear evolution of a triad of waves, each slightly amplified on a linear basis, that are superimposed on a tanh y mixing layer. The triad consists of a plane wave and a pair of oblique modes that act as a subharmonic of order 1/2. The oblique modes are inclined at approximately ±60°. to the mean flow direction and because the resonance conditions are satisfied exactly the analysis is entirely self-consistent as an asymptotic theory. The nonlinearity first occurs within the critical layer and the initial interaction is of the parametric resonance type. This produces faster than exponential growth of the oblique waves, behaviour observed recently in the experiments of Corke & Kusek (1993). The critical-layer dynamics lead subsequently to coupled integro-differential equations governing the amplitude evolution and, as first shown in related work by Goldstein & Lee (1992) on boundary layers in an adverse pressure gradient, these equations develop singularities in a finite time.

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Application of the IDEMIX Concept for Internal Gravity Waves in the Atmosphere

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0107.1 ◽

2020 ◽

Vol 77 (10) ◽

pp. 3601-3618

Author(s):

B. Quinn ◽

C. Eden ◽

D. Olbers

Keyword(s):

Energy Balance ◽

Wave Field ◽

Gravity Wave ◽

Gravity Waves ◽

Momentum Flux ◽

Middle Atmosphere ◽

Internal Gravity Waves ◽

Wave Drag ◽

Mean Flow ◽

The Mean

AbstractThe model Internal Wave Dissipation, Energy and Mixing (IDEMIX) presents a novel way of parameterizing internal gravity waves in the atmosphere. IDEMIX is based on the spectral energy balance of the wave field and has previously been successfully developed as a model for diapycnal diffusivity, induced by internal gravity wave breaking in oceans. Applied here for the first time to atmospheric gravity waves, integration of the energy balance equation for a continuous wave field of a given spectrum, results in prognostic equations for the energy density of eastward and westward gravity waves. It includes their interaction with the mean flow, allowing for an evolving and local description of momentum flux and gravity wave drag. A saturation mechanism maintains the wave field within convective stability limits, and a closure for critical-layer effects controls how much wave flux propagates from the troposphere into the middle atmosphere. Offline comparisons to a traditional parameterization reveal increases in the wave momentum flux in the middle atmosphere due to the mean-flow interaction, resulting in a greater gravity wave drag at lower altitudes. Preliminary validation against observational data show good agreement with momentum fluxes.

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