Showing papers on "Atmospheric wave published in 1981"

Turbulence and stress owing to gravity wave and tidal breakdown

Abstract: It has been suggested (Lindzen, 1967, 1968a, b; Lindzen and Blake, 1971; Hodges, 1969) that turbulence in the upper mesosphere arises from the unstable breakdown of tides and gravity waves. Crudely speaking, it was expected that sufficient turbulence would be generated to prevent the growth of wave amplitude with height (roughly as (basic pressure)−1/2). This work has been extended to allow for the generation of turbulence by smaller amplitude waves, the effects of mean winds on the waves, and the effects of the waves on the mean momentum budget. The effects of mean winds, while of relatively small importance for tides, are crucial for internal gravity waves originating in the troposphere. Winds in the troposphere and stratosphere sharply limit the phase speeds of waves capable of reaching the upper mesosphere. In addition, the existence of critical levels in the mesosphere significantly limits the ability of gravity waves to generate turbulence, while the breakdown of gravity waves contributes to the development of critical levels. The results of the present study suggest that at middle latitudes in winter, eddy coefficients may peak at relatively low altitudes (50 km) and at higher altitudes in summer and during sudden warmings (70–80 km), and decrease with height rather sharply above these levels. Rocket observations are used to estimate momentum deposition by gravity waves. Accelerations of about 100 m/s/day are suggested. Such accelerations are entirely capable of producing the warm winter and cold summer mesopauses.

Array measurements of atmospheric pressure fluctuations above surface gravity waves

Abstract: A joint experiment to study microscale fluctuations of atmospheric pressure above surface gravity waves was conducted in the Bight of Abaco, Bahamas, during November and December 1974. Field hardware included a three-dimensional array of six wave sensors and seven air-pressure sensors, one of which was mounted on a wave follower. The primary objectives of the study were to resolve differences in previous field measurements by Dobson (1971), Elliott (1972b) and Snyder (1974), and to estimate the vertical profile of wave-induced pressure and the corresponding input of energy and momentum to the wave field.Analysis of a pre-experiment intercalibration of instruments and of 30 h of field data partially removes the discrepancy between the previous measurements of the wave-induced component of the pressure and gives a consistent picture of the profile of this pressure over a limited range of dimensionless height and wind speed. Over this range the pressure decays approximately exponentially without change of phase; the decay is slightly less steep than predicted by potential theory. The corresponding momentum transfer is positive for wind speeds exceeding the phase speed. Extrapolation of present results to higher frequencies suggests that the total transfer is a significant fraction of the wind stress (0·1 to 1·0, depending on dimensionless fetch).Analysis of the turbulent component of the atmospheric pressure shows that the ‘intrinsic’ downwind coherence scale is typically an order-of-magnitude greater than the crosswind scale, consistent with a ‘frozen’ turbulence hypothesis. These and earlier data of Priestley (1965) and Elliott (1972c) suggest a horizontally isotropic ‘intrinsic’ turbulent pressure spectrum which decays as k−ν where k is the (horizontal) wave-number and ν is typically −2 to −3; estimates of this spectrum are computed for the present data. The implications of these findings for Phillips’ (1957) theory of wave growth are examined.

Lidar observation of gravity and tidal waves in the stratosphere and mesosphere

Abstract: Lidar measurements of atmospheric density and temperature in the altitude range 30-to 80 km have been performed during the last 2 years from the Observatory of Haute-Provence (latitude 44°N, longitude, 6°E). The potential of this technique for studying the middle atmospheric structure is presented and preliminary results on wave propagation are discussed. It is shown that wave-like structures are observed systematically in this height range. Fourier analysis indicates that most of the energy is transported by waves of vertical wavelengths on the order of 8 to 15 km. The amplitude of the density variations is shown to follow a ρ−l/2 law up to 70 km. The characteristics of the observed density waves suggest that they are caused by a superposition of internal gravity waves propagating upward from the troposphere and a diurnal tide component in the range 30–50 km. Such waves are able to induce quite significant perturbations in atmospheric density and therefore temperature on an hourly basis. The Lidar technique is able to monitor those variations for the first time from a ground station operating continuously.

Cloud motions on Venus - Global structure and organization

Abstract: Results on cloud motions on Venus obtained over a period of 3.5 days from Mariner 10 television images are presented. The implied atmosphere flow is almost zonal everywhere on the visible disk, and is in the same retrograde sense as the solid planet. Objective analysis of motions suggests the presence of jet cores (-130 m/s) and organized atmospheric waves. The longitudinal mean meridional profile of the zonal component of motion of the ultraviolet features shows presence of a midlatitude jet stream (-110 m/s). The mean zonal component is -97 m/s at the equator. The mean meridional motion at most latitudes is directed toward the pole in either hemisphere and is at least an order of magnitude smaller so that the flow is nearly zonal. A tentative conclusion from the limited coverage available from Mariner 10 is that at the level of ultraviolet features mean meridional circulation is the dominant mode of poleward angular momentum transfer as opposed to the eddy circulation.

Internal gravity waves in the solar atmosphere. I - Adiabatic waves in the chromosphere

Abstract: The properties of adiabatic and linear internal gravity waves propagating in a solar wind model are discussed, using nonlinearity criteria unique to gravity waves to estimate wave-breaking heights. The results are used to deduce information on the possible role of gravity waves in the chromospheric energy balance. Maximum vertical velocity amplitudes for gravity waves are estimated to be on the order of 2 km/sec or less, and maximum horizontal velocity amplitudes are less than 6 km/sec, with temperature perturbations as large as 1000-2000 K. It is also estimated that gravity waves with an incident energy flux of one million ergs/sq cm-sec can propagate upward to a maximum height of 900-1000 km above the visible surface before nonlinearities lead to wave breaking, while those with an energy flux of 100,000 ergs/sq cm-sec can reach maximum heights of 1400-1600 km.

Umbral oscillations as resonant modes of magneto-atmospheric waves. [in sunspots]

Abstract: Umbral oscillations in sunspots are identified as a resonant response of the umbral atmosphere to forcing by oscillatory convection in the subphotosphere. The full, linearized equations for magneto-atmospheric waves are solved numerically for a detailed model of the umbral atmosphere, for both forced and free oscillations. Resonant ‘fast’ modes are found, the lowest mode having a period of 153 s, typical of umbral oscillations. A comparison is made with a similar analysis by Uchida and Sakurai (1975), who calculated resonant modes using an approximate (‘quasi-Alfvén’) form of the wave equations. Whereas both analyses give an appropriate value for the period of oscillation, several new features of the motion follow from the full equations. The resonant modes are due to upward reflection in the subphotosphere (due to increasing sound speed) and downward reflection in the photosphere and low chromosphere (due to increasing Alfvén speed); downward reflection at the chromosphere-corona transition is unimportant for these modes.

Umbral oscillations as resonant modes of magneto-atmospheric waves

Abstract: Umbral oscillations in sunspots are identified as a resonant response of the umbral atmosphere to forcing by oscillatory convection in the subphotosphere. The full, linearized equations for magnetoatmospheric waves are solved numerically for a detailed model of the umbral atmosphere, for both forced and free oscillations. Resonant 'fast' modes are found, the lowest mode having a period of 153 s, typical of umbral oscillations. A comparison is made with a similar analysis by Uchida and Sakurai (1975), who calculated resonant modes using an approximate ('quasi-Alfven') form of the wave equations. Whereas both analyses give an appropriate value for the period of oscillation, several new features of the motion follow from the full equations. The resonant modes are due to upward reflection in the subphotosphere (due to increasing sound speed) and downward reflection in the photosphere and low chromosphere (due to increasing Alfven speed); downward reflection at the chromosphere-corona transition is unimportant for these modes.

Planetary waves and solar activity in the stratosphere between 50 and 10 mbar

Abstract: The effects of solar activity on the geopotential height and temperature fields of the 50-, 30- and 10-mbar surface, resolved into zonal harmonic components, were investigated. This was done by means of cross-spectral analysis between the 10.7-cm radiation of the sun and planetary waves up to zonal wave number 3. Frequent significant responses of various harmonic components in a broad range of oscillation frequencies give evidence that solar activity plays a significant role for the dynamics of the middle and lower stratosphere. Oscillations of the amplitudes of the zonal harmonics that are coherent with solar activity fluctuations were extracted from the spectra and recomposed into coherent (planetary) waves. Three waves with periods of 25 days (near to the sun's rotation period), 13.6 days (first harmonic of solar rotation), and 15.1 days (corresponding to the well known 15- to 16-day wave in the atmosphere) are examined in detail. They show the properties of free planetary modes (13.6 and 15.1 days) and possibly of internal waves (25 days) at higher latitudes. Vacillation cycles of the mean atmospheric state (including stationary waves) seem to be important for the generation of the studied wave phenomena.

Atmospheric oscillations after the May 18, 1980 eruption of Mount St. Helens

Abstract: Air waves corresponding both to direct (A1) and antipodean (A2) travel paths were clearly recorded on a sensitive microbarograph at Berkeley after the violent eruption of Mount St. Helens on May 18, 1980 (see Figure 1). These unusual complementary recordings throw light on the acoustic energy released as compared with Krakatoa [Strachey, 1888], atmospheric oscillations and their attenuation, and the directive properties of the phreatic blast. The principal explosive eruptions followed closely on an earthquake, Richter magnitude 4.9, origin time 1532 GMT, centered near the volcano. Atmospheric waves and associated magnetic perturbations [Fougere and Tsacoyeanes, 1980] from these eruptions were recorded by microbarographs, seismographs, and magnetometers around the world. In particular, Ritsema [1980] has published records of the A1 atmospheric wave train and the A2 wave (called B1 by him) recorded at De Bilt, Holland. The A2 waves at De Bilt, however, are barely visible on the paper record.

Waves at 200 mb during GATE

Abstract: A 200 mb data set obtained during the GATE experiment of the 1974 summer for the period 15 June-23 September and covering the global tropics 25°S to 45°N has been analyzed to determine the presence of certain wave modes in the tropical troposphere. The wavenumber-frequency method of analysis was used and the flow separated into eastward and westward moving waves. Results show what could be identified as Kelvin, Rossby and mixed Rossby- gravity waves. The period of the Kelvin wave was longer than that normally reported for similar waves in the stratosphere.

Theoretical and lidar studies of the density response of the mesospheric sodium layer to gravity wave perturbations

Abstract: The density response of atmospheric layers to gravity waves is developed in two forms, an exact solution and a perturbation series solution. The degree of nonlinearity in the layer density response is described by the series solution whereas the exact solution gives insight into the nature of the responses. Density perturbation in an atmospheric layer are shown to be substantially greater than the atmospheric density perturbation associated with the propagation of a gravity wave. Because of the density gradients present in atmospheric layers, interesting effects were observed such as a phase reversal in the linear layer response which occurs near the layer peak. Once the layer response is understood, the sodium layer can be used as a tracer of atmospheric wave motions. A two dimensional digital signal processing technique was developed. Both spatial and temporal filtering are utilized to enhance the resolution by decreasing shot noise by more han 10 dB. Many of the features associated with a layer density response to gravity waves were observed in high resolution density profiles of the mesospheric sodium layer. These include nonlinearities as well as the phase reversal in the linear layer response.

The Lagrangian-mean motions forced by steady, dissipating equatorial waves. I

Abstract: Waves are treated with a normal mode structure in order to determine the steady mean motion of the atmosphere that can be induced by dissipating equatorial waves. A model is developed which comprises a continuously stratified atmosphere at rest on the equatorial beta-plane. It is assumed that waves are excited by the corrugated bottom and are in a steady state, that dissipation is due to Newtonian cooling and Rayleigh friction, steadiness in wave magnitude is up to the second order, the waves have a long wave length, wave induced mean flows do not affect the waves, mean flows are steady, and dissipation mechanisms for the mean flows are the same as for the waves. Disturbance equations are formulated, along with Eulerian- and Lagrangian-mean flows, and the nonexistence of cross equatorial mean flows is demonstrated. Kelvin waves are shown to possess a Lagrangian-mean meridional circulation which is the same as the Eulerian-mean circulation. In the Boussinesq limit, however, neither the Eulerian- nor the Lagrangian-mean meridional circulations are caused by Kelvin waves. Further examination is made of Rossby-gravity waves and n = 1 westward propagating inertio-gravity waves.

Envelope soliton solution for finite amplitude equatorial waves

Abstract: Using shallow water equations on an equatorial beta plane, the nonlinear dynamics of the equatorial waves is investigated. A general mathematical procedure to study the nonlinear dynamics of these waves is developed using the asymptotic method of multiple scales. On faster temporal and spatial scales the equations describe the equatorial wavesviz, the Rossby waves, Rossby gravity waves, the inertia gravity waves and the Kelvin waves. Assuming that the amplitude of these waves are functions of slower time and space scales, it is shown that the evolution of the amplitude of these waves is governed by the nonlinear Schrodinger equation. It is then shown that for the dispersive waves like Rossby waves and Rossby-gravity waves, the envelope of the amplitude of the waves has a ‘soliton’ structure.

The Secondary Flow near a Baroclinic Planetary Wave Critical Line

Abstract: A critical line (CL) is the surface where the phase speed of a wave in a fluid is equal to the speed of the background flow. The considered investigation is concerned with one aspect of the simplest model of a CL in which the CL is assumed to totally absorb energy from steady, stationary, planetary waves. The aspect of interest is the secondary mean circulation near a CL in a baroclinic atmosphere. The motivation for this study is the observation of the nearly vertical CL by O'Neill and Taylor (1979) which appeared during the sudden warming of 1976/77. Even though the treatment of the CL is highly idealized in the investigation, there is evidence which indicates a very large rate of change in the zonally averaged temperature along a CL may occur. The Lagrangian-mean properties of an idealized baroclinic CL are also examined. It is found that the Lagrangian jets may provide an important transport process for exchange of stratospheric and tropospheric air.

Theoretical and Lidar Studies of the Density Response of the Mesospheric Sodium Layer to Gravity Wave Perturbations

Abstract: The density response of atmospheric layers to gravity waves is developed in two forms, an exact solution and a perturbation series solution The degree of nonlinearity in the layer density response is described by the series solution whereas the exact solution gives insight into the nature of the responses Density perturbation in an atmospheric layer are shown to be substantially greater than the atmospheric density perturbation associated with the propagation of a gravity wave Because of the density gradients present in atmospheric layers, interesting effects were observed such as a phase reversal in the linear layer response which occurs near the layer peak Once the layer response is understood, the sodium layer can be used as a tracer of atmospheric wave motions A two dimensional digital signal processing technique was developed Both spatial and temporal filtering are utilized to enhance the resolution by decreasing shot noise by more han 10 dB Many of the features associated with a layer density response to gravity waves were observed in high resolution density profiles of the mesospheric sodium layer These include nonlinearities as well as the phase reversal in the linear layer response

Atmospheric and Water Waves and Companion Seismic Phenomena

Abstract: Elastic waves, traveling in the solid body of the earth, sometimes convert part of their energy to other waves that propagate in the water or in the air. The opposite also happens. Large explosions in the atmosphere or in the ocean produce waves that travel through the solid earth. For example, a volcanic eruption in the ocean will simultaneously generate air, sea, and earth waves. Submarine earthquakes generate gravity sea waves (tsunamis) that carry the destructive powers of the source to distant shores, thousands of kilometers away. Also, seismic waves from major earthquakes are known to cause huge waves (seiches) in lakes and canals several thousand kilometers away. We therefore cannot fully explore the nature of earthquake waves without having some knowledge about wave phenomena in fluids.

The Negative Group Velocity of Subsonic Atmospheric Waves

Abstract: The double splitting of the spectrum of the subsonic waves due to the action of the wind is discussed. Such double-splitting is accompanied by the origin of a negative group velocity, characterizing some new branches of the wave spectrum. The wind action extends the possibilities of resonant non-linear three wave interaction between the subsonic waves.