57 research outputs found
On the nonlinear shaping mechanism for gravity wave spectrum in the atmosphere
The nonlinear mechanism of shaping of a high vertical wave number spectral tail in the field of a few discrete internal gravity waves in the atmosphere is studied in this paper. The effects of advection of fluid parcels by interacting gravity waves are taken strictly into account by calculating wave field in Lagrangian variables, and performing a variable transformation from Lagrangian to Eulerian frame. The vertical profiles and vertical wave number spectra of the Eulerian displacement field are obtained for both the case of resonant and non-resonant wave-wave interactions. The evolution of these spectra with growing parameter of nonlinearity of the internal wave field is studied and compared to that of a broad band spectrum of gravity waves with randomly independent amplitudes and phases. The calculated vertical wave number spectra of the vertical displacements or relative temperature fluctuations are found to be consistent with the observed spectra in the middle atmosphere
Observations of internal waves generated by an anticyclonic eddy: a case study in the ice edge region of the Greenland Sea
Internal waves in the ocean play an important role in turbulence generation due to wave-breaking processes and mixing of the ocean. Airborne radar images of internal waves and ocean eddies north of Svalbard suggested that ocean eddies could generate internal waves. Here, we test this hypothesis using data from a dedicated internal wave experiment in the Greenland Sea. Internal waves with dominant frequencies of 1â3 cycles per hour and amplitudes up to 15 m were observed using three thermistor chains suspended from a drifting array conveniently placed on the ice in a triangle with sides of several km. Analysis shows that internal waves propagated westwards with a speed of about 0.2 m/s and wavelength of 0.4â1.0âkm, away from an anticyclonic ocean eddy located just east of the array. This was consistent with the remote-sensing observations of internal waves whose surface signature was imaged by an airborne radar in the western part of this eddy, and with theories that eddies and vortexes can directly generate internal waves. This case study supports our hypothesis that ocean eddies can be the direct sources of internal waves reported here for the first time and not only enhancing the local internal wave field by draining energy from the eddies, as studied previously. The present challenge is to explore the role of eddies as a new source in generating internal waves in the global ocean
Detektion interner Schwerewellen in der stabilen Grenzschicht mittels akustischer Fernerkundung
Der Einfluss interner Schwerewellen (IGW) auf die untere AtmosphĂ€re bei stabiler Schichtung wurde mittels einer Kombination zweier akustischer Fernerkundungsmethoden untersucht. Im Juli 2015 wurde in Zvenigorod, Russland ein gemeinsames Experiment durchgefĂŒhrt, an welchem sowohl eine Arbeitsgruppe des Oboukhov Institute of Atmospherie Physics (OLAP) als auch des Leipziger Instituts fĂŒr Metrologie (LIM) teilnahmen. Bei der Feldkampagne wurde die sogenannte acoustic pulse sounding method des OLAPs und die aktustische Laufzeittomographie des LIM eingesetzt, SODAR und RASS Messungen kontrollierten dabei stĂ€ndig den Zustand der AtmosphĂ€re bezĂŒglich der Wind- und Temperaturprofile. Die internen Schwerewellen wurden anschlieĂend mittels Kreuzkorrelationsanalyse der Zeitserien der gemessenen akustischen Parameter (hier:Laufzeiten) detektiert. Die EmpfĂ€ngersysteme waren an verschiedenen Stellen im Messgebiet verteilt. Deswegen konnten zwei verschiedene Detektionsmethoden angewendet werden. Erstens die Detektion entlang gebrochener Schallstrahlen in der NĂ€he deren Umkehrpunkte zwischen 50m und 100m und zweitens die Detektion von nahezu horizontal verlaufenden Schallstrahlen welche Sender/EmpfĂ€nger-Paare verbinden. Somit konnten sowohl vertikale als auch horizontale Informationen ĂŒber den Zustand der AtmosphĂ€re wĂ€hrend des Experiments erfasst werden
A Hamiltonian Formulation for Long Internal Waves
A novel canonical Hamiltonian formalism is developed for long internal waves
in a rotating environment. This includes the effects of background vorticity
and shear on the waves. By restricting consideration to flows in hydrostatic
balance, superimposed on a horizontally uniform background of vertical shear
and vorticity, a particularly simple Hamiltonian structure arises, which can be
thought of as describing a nonlinearly coupled infinite collection of shallow
water systems. The kinetic equation describing the time evolution of the
spectral energy of internal waves is subsequently derived, and a stationary
Kolmogorov solution is found in the high frequency limit. This is surprisingly
close to the Garrett--Munk spectrum of oceanic internal waves
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Toward an improved representation of middle atmospheric dynamics thanks to the ARISE project
This paper reviews recent progress toward understanding the dynamics of the middle atmosphere in the framework of the Atmospheric Dynamics Research InfraStructure in Europe (ARISE) initiative. The middle atmosphere, integrating the stratosphere and mesosphere, is a crucial region which influences tropospheric weather and climate. Enhancing the understanding of middle atmosphere dynamics requires improved measurement of the propagation and breaking of planetary and gravity waves originating in the lowest levels of the atmosphere. Inter-comparison studies have shown large discrepancies between observations and models, especially during unresolved disturbances such as sudden stratospheric warmings for which model accuracy is poorer due to a lack of observational constraints. Correctly predicting the variability of the middle atmosphere can lead to improvements in tropospheric weather forecasts on timescales of weeks to season. The ARISE project integrates different station networks providing observations from ground to the lower thermosphere, including the infrasound system developed for the Comprehensive Nuclear-Test-Ban Treaty verification, the Lidar Network for the Detection of Atmospheric Composition Change, complementary meteor radars, wind radiometers, ionospheric sounders and satellites. This paper presents several examples which show how multi-instrument observations can provide a better description of the vertical dynamics structure of the middle atmosphere, especially during large disturbances such as gravity waves activity and stratospheric warming events. The paper then demonstrates the interest of ARISE data in data assimilation for weather forecasting and re-analyzes the determination of dynamics evolution with climate change and the monitoring of atmospheric extreme events which have an atmospheric signature, such as thunderstorms or volcanic eruptions
Three-dimensional spectrum of temperature fluctuations in stably stratified atmosphere
A phenomenological model is proposed for a 3-D spectrum of temperature
inhomogeneities generated by internal waves in the atmosphere. This model is
a development of the theory based on the assumption that a field of
Lagrangian displacements of fluid particles, induced by an ensemble of
internal waves with randomly independent amplitudes and phases, is
statistically stationary, homogeneous, axially symmetric in horizontal plane
and Gaussian. For consistency of this model with measured spectra of
temperature fluctuations in the stratosphere and mesosphere the additional
assumption was introduced in to the model about the anisotropy of
inhomogeneities to be dependent on their vertical sizes. The analytic
expressions for both the 3-D and 1-D spectra are obtained. A model vertical
wave number spectrum follows a −3 power law, whereas a horizontal spectrum
contains two regions with a −3 slope, and the intermediate region with the
slope between −1 and −3 depending on the rate of anisotropy decrease as a
function of increasing sizes of the inhomogeneities. In the range of a few
decades the model showed a good agreement with the results of measurements
of the spectra in the troposphere, stratosphere and mesosphere
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