Showing papers on "Atmospheric wave published in 1980"

Numerical Prediction and Dynamic Meteorology

Abstract: An advanced, updated, and self-contained treatment. Includes the fundamental system of equations governing large-scale atmospheric motions, coordinate systems, atmospheric wave motions, energetics, hyperbolic and elliptic equations, moisture modeling, solar and terrestrial radiation modeling, seasonal and climate prediction. Presupposes a knowledge of mathematics through calculus, some vector analysis, and introductory meteorology.

Non‐WKB Alfvén waves in the solar wind

Abstract: We treat, both analytically and numerically, small-amplitude, undamped, toroidal Alfven waves in a model of axisymmetric solar wind flow in which solar rotation is neglected. There is no restriction to WKB waves; the waves may have any frequency. By transforming in simple ways the equations governing the waves we are able to obtain exact formal solutions to the general time-dependent problem as well as to the Fourier-analyzed problem. We discuss the equations and their solutions in terms of coupled inward and outward propagating waves. One integral of the equations for the Fourier amplitudes is obtained; it relates the amplitudes of the ingoing and outgoing waves. The integral is a special case of a general law of conservation of wave action, which we show to hold for finite wavelengths. The statement of the conservation of wave action is shown to be analogous to the conservation of particle-antiparticle pairs in relativistic quantum theory. We obtain the condition required for WKB waves and show that it depends on the coupling of waves in a flowing medium. The solar wind problem is discussed in terms of the Fourier amplitudes. It is shown that there is a singularity in the equations, at the Alfven point, which determines physically acceptable solar wind solutions. A qualitative account of the amplitudes far from the sun is given based on an exact solution for a model with constant solar wind flow speed. A conservation equation for the wave energy is obtained, and the relations among the wave energy density, energy flux density, force, and acceleration are stated. Numerical solutions, based on realistic solar wind profiles, are given. We show that non-WKB waves with wave periods of about a day or two have somewhat greater wave energy densities, up to a factor of 2 or so, in the corona than do WKB waves with the same amplitude at 1 A.U. On the other hand, non-WKB waves of any wave period are no more effective in accelerating the plasma than are WKB waves; they are much less effective for wave periods of a day or more. We conclude that, for conditions actually existing in the corona, WKB estimates quite accurately account throughout the corona for the wave energy density, energy flux density, and wave acceleration of the plasma for Alfven waves with periods less than about 0.05, 1, and 0.01 day, respectively; the corresponding periods in the solar wind are about 1, 1, and 0.5 day.

Cloud morphology and motions from Pioneer Venus images

Abstract: The horizontal and vertical cloud structures, atmospheric waves, and wind velocities at the cloud top level were determined by the Pioneer Venus photopolarimeter images in the UV from January through March 1979. The images indicate long-term evolution of cloud characteristics, the atmospheric dynamics, and rapid small changes in cloud morphology. The clouds show a globally coordinated oscillation relative to latitude circles; retrograde zonal winds of 100 m/s near the equator are determined from the tracking of small-scale cloud properties, but two hemispheres show important variations. The zonal wind velocity in the southern hemisphere is reduced toward the poles at a rate similar to solid body rotation; the midlatitude jet stream noted by Mariner 10 is not observed.

Seasonal Differences in the Stationary Response of a Linearized Primitive Equation Model: Prospects for Long-Range Weather Forecasting?.

Abstract: A linear steady-state primitive equation model has been developed for the computation of stationary atmospheric waves that are forced by anomalies in surface conditions. The model has two levels in the vertical. In the zonal direction the variables are represented by Fourier series, while in the meridional direction a grid-point representation is used. The equations governing atmospheric motion are linearized around a zonally symmetric state which depends on latitude and height according to Oort (1980). We have studied the amplitude and phase relations of the model response as a function of latitude for a very simple beating, which is sinusoidal in the zonal direction, with zonal wavenumber m (m=1, 10) and constant in the meridional direction, using February mean conditions. The response of the model indicates that a heating in the tropics can have a substantial influence on the middle and high latitudes, provided that part of the heating is in the westerlies. We have compared the model response ...

Gravity Waves from Thunderstorms

Abstract: Gravity waves generated by severe thunderstorms in the eastern Ohio-Pennsylvania area were recorded by an array of microbarovariographs at Palisades, New York and by standard microbarographs across northeastern United States. The waves were associated with the cold mesohigh from the outflow of the thunderstorms. Along their path the waves apparently triggered new thunderstorms. The waves were observed to propagate with the velocity of the wind just below the tropopause. The long-distance propagation of the waves is explained by the presence of a dust associated with the critical level (steering level), in agreement with the derivations given by Lindzen and Tung (1976). The dust was directional and waves were absent to the west of the generating area. In the generating area wave-CISK might have been operating. Sharp vertical temperature gradients associated with the passage of the waves were observed by temperature sensors on a tower.

Wave Propagation and Transport in the Middle Atmosphere

Abstract: The paper reviews the dynamics of wave propagation and wave transport for vertically propagating, planetary scale waves in the middle atmosphere. Such waves are divided into two major classes: extratropical planetary waves and equatorial waves. The most significant extratropical modes are the quasi-stationary Rossby waves, while the most significant equatorial modes are the Kelvin wave and the mixed Rossby-gravity wave. Both types of waves are capable of generating mean flow changes through wave-mean flow interaction.

Turbulent phase shift of Rossby waves

Abstract: The properties of turbulent flows are strongly modified by the presence of dispersive waves the period of which can be less than the eddy-turnover time of turbulence for sufficiently large scales. ...

A case of persistent breaking of internal gravity waves in the atmospheric surface layer over the ocean

Abstract: Formation and breaking of internal gravity waves contributing to a very significant increase in turbulence in the atmospheric surface layer over the Atlantic Ocean off Long Island, New York are reported. Contrary to the bursts that are characteristically of short duration, this increase in turbulence lasted for more than one hour and was typical of what one would observe during unstable atmospheric conditions. However, mean temperature profiles indicated strong stable conditions.

Radar measurement of short-period atmospheric waves and related scattering properties at the altitude of 13–25 km over Jicamarca

Abstract: The sensitive Doppler radar (49.92 MHz) at Jicamarca (12.0°S, 76.9°W) is used to investigate short-period atmospheric waves at the altitudes of 13–25 km. The dominant short-period waves observed are largely buoyancy, or Brunt-Vaisala, oscillations, the periods of which are about 5 min in the lower stratosphere and about 11 min in the upper troposphere. The buoyancy oscillations are, on the average, convected with the mean horizontal wind. It is also confirmed that the partial reflection is relatively dominant in these altitudes compared with turbulent scatter. These features are not found around the tropopause, where a vertical shear of horizontal winds of the order of 5 m s−1 km−1 is observed.

Traveling planetary waves in the stratosphere

Abstract: This paper reviews the theory and observations of some traveling planetary waves in the stratosphere. Two categories of waves which appear prominently in the literature are discussed: westward propagating waves of periods in the range 3–7 days (the ‘5-day wave’) and in the range 10–20 days (the ‘16-day wave’). Although the observations seem to indicate that these waves are waves of the Rossby type (planetary waves), the evidence is less clear regarding (1) the question of whether these waves are forced internal waves or free (resonant) external waves, and (2) the identification of the observed waves with specific theoretical waves of the Rossby type. When recent observations are compared with theory, the evidence seems to favor the notion that the 5-day and 16-day waves of longitudinal wave number 1 may be identified, respectively, with the gravest and next gravest symmetric free Rossby modes. However, the observational evidence seems to be less clear regarding the nature of the 16-day wave than the 5-day wave.

Long Atmospheric Waves and the Polar-Plane Approximation to the Earth’s Spherical Geometry

Abstract: The spherical geometry of the earth is replaced by polar cylindrical geometry, with a plane tangential to the earth at the pole. The resulting frequency and structure of free motions in an isothermal, adiabatic atmosphere with a resting basic state is studied in both geometries. The solutions for ν (meridional wind) may be written as a single Bessel function if certain approximations are made. For positive equivalent depths, the geometrical approximation is best when the Lamb parameter ϵ≳ 10, so that Rossby waves are well modeled, while fast moving gravity waves are not well approximated. The impact of setting f to a constant value when undifferentiated, as in the usual midlatitude beta-plane approximation, is examined. It is found that the value of f is as important in determining how well the model behaves as are the geometrical and other approximations.

Three-dimensional lee waves

Abstract: Linear wave theory is used to find the stationary, trapped lee waves behind an isolated mountain. The lower atmosphere is approximated by a three-layer model with Brunt-Vaisala frequency and wind velocity constant in each layer. The Fourier-integrals are solved by a uniformly valid asymptotic expansion and also by numerical methods. The wave pattern is found to be strongly dependent on the atmospheric stratification. The way the waves change when the parameters describing the atmosphere and the shape of the mountain vary, is studied. Further, the results predicted by the theory are compared with waves observed on satellite photographs. It is found that the observed wave patterns are described well by the linear theory, and there is good agreement between observed and computed wavelengths.

On the propagation, reflexion, transmission and stability of atmospheric Rossby-gravity waves on a beta-plane in the presence of latitudinally sheared zonal flows

Abstract: The propagation properties of Rossby-gravity waves in an isothermal atmosphere on a beta-plane are investigated in the presence of a latitudinally sheared zonal now. The perturbation equation is found to possess seven regular singularities provided the fluid is non -Boussinesq, and only five for Boussinesq fluids. In slowly varying shear a local dispersion relation is derived and used to study the wave normal surfaces and ray trajectories. The cross sections of the wave normal surfaces in horizontal planes possess three critical latitudes occurring where the intrinsic frequency w takes the values 0, + N ,where N is the Brunt—Vaisalla frequency. The former is the usual Ross by wave critical latitude (R.w.c.l.) and the latter are essentially gravity wave critical latitudes (g.w.c.l.). Waves can propagate only on one side of a R.w.c.l. while propagation is possible on both sides of a g.w.c.l. provided the vertical wavenumber, m , there is real and non-zero. Also for real values of m and provided the atmosphere is non -Boussinesq the g.w.c.l. exhibits valve-like behaviour. Such valve behaviour is shown to be responsible for aiding high frequency waves (i.e. gravity waves) to penetrate jet-like wind streams and may facilitate the transfer of energy and momentum across latitudes. The full wave treatment shows that the system possesses a wave-invariant which has a simple physical interpretation only when m is real in which case it represents the conservation of the total northward wave energy flux. The invariant is used, together with the legitimate solutions near the critical latitudes, to study the influence of each of the critical latitudes on the intensity of the wave. It is found that the R.w.c.l. can be associated with energy absorption or emission, depending on certain specified conditions, but the g.w.c.l. is always associated with energy absorption although the amount of energy absorbed depends crucially on whether m is real or imaginary. The reflexion, transmission and stability of atmospheric waves by a finite shear, thickness L , are also studied, by using a full wave treatment in the presence of general flow profiles. For smoothly varying shear flows the use of the wave-invariant yields a relation between the reflexion and transmission coefficients. It is then deduced that in the absence of critical latitudes within the shear over-reflexion (i.e. the amplitude of the reflected wave exceeds that of the incident one) is possible only for real values of m in which case planetary waves incident on the shear are transmitted as gravity waves on the far side of the shear. Such over-reflecting regimes are, however, due to the presence of natural modes of the system. Moreover, it is found possible to isolate certain situations in which the R.w.c.l. within the shear enhances over-reflexion. The situation when the shear is linear and thin is studied analytically. Explicit expressions for the reflexion and transmission coefficients are obtained. It is then shown that over-reflexion is present in a stable shear in which case the energy is extracted from the mean flow primarily at the R.w.c.l. The influence of a general flow on the R.w.c.l. is also studied in a special case to show that the reflectivity and stability properties of the thin shear are strongly dependent on the type of shear present. Comparison of these results with those obtained for the corresponding vortex sheet show wide disagreement. A general criterion for determining whether a vortex sheet will adequately represent the corresponding thin shear layer is offered in the final section.

Cross-equatorial waves, with applications to the low-level East-African jet

Abstract: The problem of a wave disturbance propagating meridionally along a western boundary is considered first for an f-plane and then for an equatorial β-plane. On an f-plane small-amplitude waves travel at speed c with no attenuation, but when the amplitude is increased, energy is lost to inertia-gravity waves. On the β-plane, inertia-gravity waves are excited even in the linear case, though this process is enhanced by nonlinearity. Some energy can go into trapped equatorial wave modes, but for the parameters used in this study, most of the energy initially in the coastal waves is radiated across the equator as inertia-gravity waves. The relevance to cross-equatorial flow in the low-level East African jet is discussed.

Equations of kinetic and available potential energy evolution in wave-number frequency space

Abstract: The equations of kinetic and available potential energy for the analysis of the growth and decay of atmospheric waves in wave-number-frequency space are derived. The effects of linear and nonlinear interactions of waves in the velocity and temperature fields, the conversions between the available potential and kinetic energies, and the Reynolds and molecular stresses on wave growth and decay are discussed.

Atmospheric waves from large meteors

Abstract: The body of airwave data taken by the U.S. Government for the purpose of atmospheric monitoring of distant nuclear explosions, contains fortuitously waves of natural origin as well. We have recently received a portion of this original data base which contains only those signals which are presumably of meteoric origin; other natural signals such as from aurora, volcanic eruptions, meteorological phenomena, etc. having been previously removed from the sample. The ten meteoroid related events have amplitudes of about 0.5 to 10 dynes/cm2 and periods at maximum signal amplitude of about 3 to 45 s at horizontal ranges of about 800 to 14 000 km from the source. Using appropriate signal characteristics with models for the source and for propagation of these waves, source energies can be inferred. For these events energy estimates range from about 0.1 kT to as much as 550 kT (TNT equivalent) assuming that a low altitude point source explosion model is applicable. This detailed data set, having been recorded at sev...

An energy equivalent for viscous dissipation of atmospheric disturbances

Abstract: A means of representing the effect of viscous diffusion comprehensively for both horizontally and vertically propagating atmospheric waves is developed. This is accomplished by replacing the viscou...

Topographic coupling of surface and internal Kelvin waves. [of ocean]

Abstract: Abstract An analytical method is developed to compute the diffraction of a barotropic Kelvin wave by a localized topographic irregularity on an otherwise flat-bottom ocean with an arbitrary vertical stratification. The bump topography is assumed to be small in height compared to the water depth of the flat-bottom ocean. It is found that all baroclinic mode Kelvin waves will be generated downstream of the bump, with the first baroclinic mode having the largest amplitude. At subinertial frequencies (ω f) cylindrical Poincard waves with certain anisotropy are generated at (x = x0, y = 0) and (x = −x0, y = 0), where (x0,0) is the center of the bump topography, and the y axis is the coastline. The Poincare waves favor the lowest few modes, with the baroclinic modes having stronger tendencies to be directionally anisotropic. The baroclinic Poincare waves radiating offshore from the...

Dynamics of the equatorial middle and upper atmosphere based on incoherent scatter type radar observation

Abstract: Recent development of incoherent scatter radar (ISR) technique has made it possible to observe motions of the middle atmosphere as well as the upper ionized atmosphere, an important step forward which enables us to understand dynamic coupling of the atmosphere extending vastly from the ground to the outerspace. Especially, the equatorial atmosphere is abundant in various atmospheric waves which behave very distinctly from those in other latitudes. These waves travel vertically from the lower to the upper atmosphere transporting both dynamical energy and various atmospheric constituents, an important role in the general circulation of the earth's whole atmosphere. There are now two radars, one at Jicamarca and the other at Arecibo, both having been built originally as incoherent scatter radars in the 1960's for exploring the ionospheric plasma. These facilities are now making outstanding contributions for the study of these equatorial atmospheric waves and also the mean flows which couple with the atmospheric waves. The present review may reveal that this radar atmospheric sciences present promising and rewarding fields in the future of geophysics.

ON THE DISPERSIVE NATURE OF F2-REGION TIDs OVER WALTAIR

Abstract: Studies on F2-region TIDs are carried out at Waltair (Geo.lat.17.7°N, long.83.3° E) using phase path technique. The data obtained during the period 1974-:75 have been analysed to study the propagational characteristics of TIDs. The observed range of disturbances contains both the acoustic wave mode as well as gravity wave mode relevant to F-region heights, the maximum response occurring at a period of about 33 min. The speed of the disturbance is found to be varying with period in both the cases, thereby indicating a dispersion in the observed velocities. The observed nature of dispersion in the propagation of these TIDs has been discussed on the basis of the dispersive nature of the atmospheric waves in the ionosphere.