Showing papers on "Atmospheric wave published in 1983"

A Compressible Model for the Simulation of Moist Mountain Waves

Abstract: A two-dimensional, nonlinear, nonhydrostatic model is described which allows the calculation of moist airflow in mountainous terrain. The model is compressible, uses a terrain-following coordinate system, and employs lateral and upper boundary conditions which minimize wave reflections. The model's accuracy and sensitivity are examined. These tests suggest that in numerical simulations of vertically propagating, highly nonlinear mountain waves, a wave absorbing layer does not accurately mimic the effects of wave breakdown and dissipation at high levels in the atmosphere. In order to obtain a correct simulation, the region in which the waves are physically absorbed must generally be included in the computational domain (a nonreflective upper boundary condition should be used as well). The utility of the model is demonstrated in two examples (linear waves in a uniform atmosphere and the Jan. 11, 1972 Boulder windstorm) which illustrate how the presence of moisture can influence propagating waves. In both cases, the addition of moisture to the upstream flow greatly reduces the wave response.

Measurements of wind velocity and pressure with a wave follower during Marsen

Abstract: Air pressure data are used in determining the rate of momentum transfer from wind to waves. On the basis of the wind velocity measurements, the wave-induced airflow and its coherence with waves are obtained for various wind velocities and phase speeds of the ocean waves. The pressure results suggest that momentum transfer to waves can be specified by a certain relation, which is given. The wind-velocity results suggest that the wave-induced airflow is much smaller than the mean wind speed. An empirical equation is proposed for the modulation of atmospheric transfer to short waves caused by the orbital velocity of long waves.

Magneto-atmospheric waves

Abstract: A theoretical treatment of magneto-atmospheric waves is presented and applied to the modelling of waves in the solar atmosphere. The waves arise in compressible, stratified, electrically conductive atmospheres within gravitational fields when permeated by a magnetic field. Compression, buoyancy, and distortion of the magnetic field all contribute to the existence of the waves. Basic linearized equations are introduced to describe the waves and attention is given to plane-stratified atmospheres and their stability. A dispersion relation is defined for wave propagation in a plane-stratified atmosphere when there are no plane-wave solutions. Solutions are found for the full wave equation in the presence of either a vertical or a horizontal magnetic field. The theory is applied to describing waves in sunspots, in penumbrae, and flare-induced coronal disturbances.

A Case Study of Gravity Waves–Convective Storms Interaction: 9 May 1979

Abstract: An analysis is presented of a series of severe storms which occurred in the north central United States on 9 May 1979 and whose spatial distribution and movement correlate well with observed gravity waves. Two gravity wave trains of 2.1-3 mb amplitude, 2.5-3.3 h period and 240-265 km horizontal wavelength were isolated through power spectra analysis and cross-correlation techniques applied to National Weather Service barograph traces. The wave trains propagated in the 200 deg direction, which coincided with the jet axis, with a phase velocity of 20-30 m/s and within a 300 km wide band. The storms were identified on enhanced infrared GOES satellite pictures with the help of radar summaries. These convective systems initially developed in Nebraska and propagated north-northeast at 25 m/s, revealing wave-like characteristics with a separation of 300-400 km. The convective systems were closely linked to the observed wave trains with cell intensity, height and associated rainfall maximized at the wave ridge. One of the two wave trains developed in regions of weak or no convection and appeared to initiate more intense convective clusters downstream from the point of origin. It is shown that the characteristics of the wave trains are consistent with those of gravity waves generated in a region of strong vertical shear associated with the jet. It is suggested that the wave trains continue to extract energy from the basic state all along their track through critical level interaction.

Short-Term Climate Variability and Atmospheric Teleconnections from Satellite-Observed Outgoing Longwave Radiation. Part II: Lagged Correlations

Abstract: As a sequel to Part I of this study, lagged relationships in atmospheric teleconnections associated with outgoing longwave radiation (OLR) are investigated using Lagged Cross Correlations (LCC). The feasibility of extratropical seasonal-to-interannual predictions using satellite-derived observation is also quantitatively assessed. It is found that the global influence of teleconnectivity of the atmosphere is strongest for diabatic forcing located near the equatorial central Pacific, but much reduced for forcings over the maritime continent and to the east of the dateline. The LCC patterns show that at zero-lag, the OLR fluctuation over the equatorial central Pacific is associated with simultaneous excitation of quasi-stationary waves in the tropics. These tropics–tropics teleconnections eventually (in about 5 months) transform into tropics–midlatitude and midlatitude–midlatitude teleconnections associated with possible excitation of extratropical quasi-stationary waves in both hemispheres. Analys...

Resonant Topographic Response of Nearshore Currents to Wind Forcing

Abstract: Model calculations and current meter observations are analyzed in the spectral domain and in the time domain to investigate effects of topographic waves on the response of nearshore currents to wind. The spectral response is computed for a shelf forced by a progressive atmospheric wave, and effects of friction and alongshore depth variations are considered. Comparisons are made with results for standing atmospheric waves and with the response of closed basins forced by winds uniform in space and periodic in time. It is found that coastline curvature is rather unimportant for the scales under consideration, and that the alongshore wind component represents the crucial forcing. Spectral model results are then compared with current meter spectra to show the resonant topographic wave character of the response of currents to wind. Time series of observed and computed nearshore currents are compared, and the alongshore momentum balances are considered for models with and without topographic wave effect...

Short-Period Atmospheric Gravity Waves: A Study of Their Statistical Properties and Source Mechanisms

Abstract: Gravity waves for the one year period beginning 19 October 1976 around Palisades, New York, are investigated to determine their statistical properties and sources The waves have typical periods of 10 min, pressure amplitudes of 3 Pa and velocities of 30 m/s In general, the largest, amplitude waves occur during late fall and early winter when the upper tropospheric winds directly overhead are fastest and the static stability of the lower troposphere is greatest Mean wave amplitudes correlate highly with the product of the mean maximum wind speed and the mean low level stratification directly aloft A distinct diurnal variation of wave amplitudes with the largest waves occurring in the pre-dawn hours is also observed as a result of the increased static stability then The majority of waves are generated by shear instability; however, a number of waves are generated by distant sources such as nuclear detonations or large thunderstorms The waves with distant sources can be distinguished on the basis of their generally much higher coherency across the grid and velocities that depart markedly from the wind velocity at any point in the sounding

On waves in non-isothermal, compressible, ionized and viscous atmospheres

Abstract: A review is given of the properties of waves in atmospheres, with particular emphasis on (Section 1) the variation of amplitude and phase with altitude for propagating waves (Figures 1 to 4) and the waveforms of standing modes (Figure 5). The cases dealt with concern waves under the combined influences of gravity and compressibility, and examine the effects of. (Section 2) temperature gradients in a non-isothermal atmospheric model; (Section 3) external magnetic field, either vertical or horizontal; (Section 4) dissipation by viscosity and electrical resistance. The results are relevant to (Section 5) the assessment of atmospheric wave growth and shock formation, and to the calculation of heating functions describing the deposition of wave energy.

Stratospheric‐tropospheric ozone exchange in Antarctica caused by mountain waves

Abstract: Under suitable meteorological conditions, mountainous terrain may induce atmospheric wave formations that propagate across the tropopause and into the stratosphere. This study presents results of a NSF C-130 research aircraft flight over the Ellsworth Mountains of Antarctica (78°S, 85°W) on December 3–4, 1978. The aircraft was in the study area for more than 6 hours and flew a total of 14 flight tracks generally parallel to the mountain ridge at 4 primary altitudes between 7.3 and 8.7 km, MSL. Data analyses included horizontal and cross-sectional fields of temperature, potential temperature, ozone, frost point, and wind. The results showed that over the mountain area there was a pattern of changes in these variables that could be explained by the apparent vertical motion expected to occur in mountain wave situations. In this case there was vertical displacement of air parcels across the tropopause zone that was shown by ozone and potential temperature patterns. In the patterns at various constant levels the measured values appear to be organized into a series of bands or zones characteristic of wave troughs and ridges oriented across the mean wind direction and parallel to the terrain ridges. Ozone flux calculations were made by using concentrations measured in upwind and downwind zones. The results showed that at about 7.4 km, 1.1 km below the tropopause, the flux of ozone leaving the mountain wave zone was 268 μgm−2 s−1. This was a 61% increase over the incoming ozone flux of 167μgm−2 s−1. This increased flux produces a change in concentration at the 7.4 km altitude from about 12 ppb in the background air flow to about 20 ppb downwind of the mountains. The downwind flux was larger above 7.4 km. It is concluded that the increases in ozone observed in the downwind tropospheric layers were the result of mountain wave-induced downward mixing of ozone-rich stratospheric air parcels.

Structure of Medium-Scale Atmospheric Waves in the Southern Hemisphere Summer

Abstract: Recently reported medium-scale wave dominance of the Southern Hemisphere summer circulation is studied using NMC geopotential height fields for the 1978–79 summer. These features, corroborated by independent analyses of satellite microwave measurements, are apparent in meridional thermal winds derived from the NMC grids. In the time mean, we observe strong medium-scale waves which extend throughout the troposphere and lower stratosphere, in agreement with Kalnay et al. (1981). These zonally asymmetric features attain a maximum in low latitudes, exhibiting an equivalent barotropic vertical structure with maximum amplitude near the tropopause. A longitudinal phase versus time plot from daily analyses of zonal wavenumbers 4–7 (which contain the majority of the time variance) reveals periodic variations in both phase and amplitude: wave 5 frequently dominates, exhibiting eastward phase progression with period near 10 days. During other times, shorter scale waves (waves 6–7) exhibit enhanced amplitude...

The influence of a Critical latitude on Topographically Forced Stationery Waves in a Barotropic Model

Abstract: A nondivergent barotropic model on a sphere is used to study the effects of a critical latitude on stationary atmospheric waves forced by topography. Linear and “quasi-linear” calculations are performed with an idealized wavenumber 3 mountain and with realistic topography. Quasi-linear dynamics, where mean flow changes are due to momentum flux convergence, “form drag” and relation to a prescribed climatological mean flow, produces an S-shaped kink in the zonal mean absolute vorticity gradient near the critical latitude, resulting in enhanced reflection. The component of the quasi-linear solution resulting from enhanced reflection at the critical latitude is computed by taking the difference between the linear and the quasi-linear solutions. In a calculation with realistic topography and zonal flow, this reflected component is found to be dominated by a wave train emanating from the western tropical Pacific and propagating northward and then eastward across the Pacific 0cean and the North American...

On the Frictionless Influence of Planetary Atmospheric Waves on the Adriatic Sea Level

Abstract: The influence of planetary atmospheric waves on the Adriatic sea level is investigated for the year 1976 on the basis of 500 mb surface height and sea level data. Analysis is performed in time and frequency domains. It is found that—in the first approximation—the lower layers of the atmosphere are characterized by barotropic structure in the scope of the mentioned processes, while the equilibrium of sea-elevation gradient with air-pressure gradient is realized in the sea. Accordingly, sea level changes are opposite in phase to the oscillations of a selected isobaric surface; the ratio of their amplitudes is the same as the one between (sea surface) air density and density of the sea. Departures from this simple relationship result from the baroclinic atmospheric disturbances that occasionally influence the sea in the frequency band corresponding to planetary atmospheric waves.

Non-adiabatic oscillations in an isothermal atmosphere

Abstract: The problem of propagation and linear transformation of atmospheric and temperature waves in an isothermal atmosphere with stratified heat exchange has been solved analytically. The cases are discussed where temperature inhomogeneities produced by the waves are either optically thin or optically thick. Formulae have been derived for the absorption, reflection, and transformation of waves when they are transformed from adiabatic into isothermal. The properties of temperature waves are considered. The theory of non-adiabatic atmospheric waves is applied to an analysis of oscillations in a quiet solar atmosphere.

A Quantitative Comparison of the Refractive Index Structure Parameter Determined from Refractivity Measurements And Amplitude Scintillation Measurements at 36 GHz

Abstract: Results are presented of the determination of the atmospheric refractive index structure parameter C2n, deduced from amplitude scintillation measurements made on a 36-GHz radio link and also from refractivity measurements using a turbulence probe. These measurements were made in a town environment (central London) and covered a range of atmospheric conditions. The two methods of measurement give good agreement, particularly in convective conditions, and provide further experimental evidence of the applicability of Tatar-ski's wave propagation theory in a turbulent medium to millimeter wavelengths.

The Response of Stationary Planetary Waves to Tropospheric Forcing

Abstract: The lower boundary forcing of airflow over topography, and the internal forcing that results from the geographical distribution of diabatic heating, are studied in light of a steady state, linear, quasi-geostrophic model of stationary waves on a sphere. The lower boundary vertical motions forced by airflow over topography depend on whether the horizontal deflection of airflow around topographic features is taken into account, the level of the wind profile at which flow over topography is assumed to take place, and the topographic data set that was used in the forcing formulation. The lower boundary forcing is taken to be given by the observed stationary planetary wave in lower boundary geopotential height, and the internal forcing is computed using the planetary wave propagation equation on the observed wave structure.

Planetary wave modelling of the middle atmosphere: The importance of transients

Abstract: A linear planetary wave model of the middle atmosphere is used to diagnose the wavenumber-1 structure for a day during December 1979 given the wave forcing and the time-derivative terms. The time derivatives are calculated using data from the stratospheric sounding unit (SSU) on NOAA 6 for days on either side of the principal day of interest. The effect of the time-derivative terms is significant and the model is found to be in fair agreement with the data in high latitudes although low latitude features are poorly reproduced. The influence of the transient wave components is discussed and in particular some dissipation-like effects are demonstrated which might clarify the role of Rayleigh friction in planetary wave models.

Conservation laws of wave action and potential enstrophy for Rossby waves in a stratified atmosphere

Abstract: The purpose of this article is to discuss the evolution of wave energy, enstrophy and action for atmospheric Rossby waves in a variable mean flow. The presentation is theoretical, but does not represent original research; rather, it is pedagogic in nature. The work of a number of people has been drawn together into a unified account, with much of the algebra implicit in previous work made explicit here. The central results are that wave energy is conserved only when there are no spatial variations in the mean flow, and wave action is conserved even in the presence of such variations as long as they are not in the longitudinal direction. Finally, wave enstrophy is conserved in the presence of arbitrary (slow) mean flow variations.

Solitary waves as aviation hazard

Abstract: Scientists at the Australian National University in Canberra have found that wind shear produced by solitary atmospheric waves is a potentially serious hazard to aircraft operating at low altitudes. In recent years a significant number of aircraft accidents have been attributed to a sudden, unexpected encounter with low-level wind shear during the landing or takeoff stage. In many cases it has been possible to associate the hazardous shear with one of a variety of well known meteorological wind shear conditions including intense thunderstorm down drafts, down-draft-produced density currents, cold frontal systems, and sea breezes. These sources are easily recognized and are usually predictable in the airport environment. In some instances, however, the identity of the wind shear source has been uncertain. Studies of the properties of large amplitude solitary waves in the boundary layer have shown that they produce intense, transient, horizontal and vertical wind shears which are comparable with the well known types of shear. Solitary wave activity may therefore account for some hitherto unexplained aircraft accidents.

A theoretical study of small amplitude waves in the Martian lower atmosphere and a comparison made with those on earth

Abstract: A linearised study of waves in the Martian Atmosphere reveals much similarity with those om the Earth. For motion independent of the meridional direction approximations can be made from the exact solution and those can be regarded as a useful guide to the relevance and importance of waves in the Martian atmosphere. We shall distinguish between acoustic waves, including Lamb Waves, inertial gravity , baroclinic and Rossby waves. The beta effect and Newornian radiative damping will be included for these longer perturbations.

The dynamical response of the lower atmosphere to upper atmosphere forcing and the sun-weather problem

Abstract: A time-dependent, primitive-equation numerical model is used to test the hypothesis that solar variations induce changes in the distributions of basic state variables at high levels in the atmosphere, and thus induce changes in planetary-scale wave structure at lower atmospheric levels. This mechanism was proposed to explain apparent atmospheric responses to solar activity. The changes are brought about in the model by a diabatic heat source, which is taken to be a simple representation of Joule dissipative heating. Lower atmospheric wave structure is found to be insensitive to solar-induced changes in the upper atmosphere. Such changes as do occur are limited to within 25 to 40 km below the level of maximum heating, and are also quite short-lived.

On the Origin of Oscillations in a Solar Diameter Observed through the Earth’s Atmosphere: A Terrestrial Atmospheric or a Solar Phenomenon

Abstract: Interpretations of current and past results from ground-based solar diameter measurements, as well as the planning of scientific programs for the 1980’s, are strongly dependent on the perceived level of the degrading effects of the Earth’s atmosphere. One of the more effective approaches has been to design the observing program and the subsequent data analysis such that the solar diameter measurements themselves could provide an evaluation of atmospheric effects. Many important results have been obtained in studies of this type and these results are collected here to help in appraising the current situation. This evidence all points in one direction: the Earth’s atmosphere, while complicating the design of observational programs, is not the source of the oscillations observed in solar diameter measurements. Further, this same evidence indicates that the Earth’s atmosphere will not pose any serious limitations in ground-based solar diameter studies during the 1980’s.

Dependence of nongeostrophic baroclinic instability of wave disturbances on the vertical resolution of a numerical model

Abstract: A numerical investigation of baroclinic instability of nongeostrophic wave perturbations with different vertical resolutions (N) of the model was made. It has revealed the well known shift in the unstable wave spectrum towards shorter wave lengths and an increase in the growth rates and band width of unstable waves with increasingN. The vertical tilt of troughs and ridges and energy conversion rates of the unstable waves have also shown an increase with the increase in the number of information levels in the model. However, these increases in the growth rates and band width of unstable waves appear to be due to better resolution in the vertical structure of the waves, leading to the increased energy conversions in the model, rather than due to either the relaxation of algebraic restraint on the solutions, as has been shown by Hirota [2] for the case of a quasi-geostrophic model, or due to better resolution in vertical, of the basic state parameters of the numerical model, as has been claimed by Mishra and Salvekar [3].

Upwellings and Kelvin Waves Generated by Transient Atmospheric Fronts

Abstract: Motions generated by transient atmospheric fronts are investigated. Using asymptotic expansions in time, it is shown that the variation of the longshore component of the wind stress generates an interface elevation which propagates along the coast as an internal Kelvin wave front. Strong horizontal baroclinic motions are linked to this wave front. The velocity within the deep layer is in the opposite direction to that of the wind on the surface. Far from the coast, the wind stress curl, associated with the atmospheric front, produces strong interface elevations which increase with time and combine with coastal elevation to give peculiar behaviour of the interface associated with strong currents at the discontinuities.

Random-Medium Propagation Theory Applied To Communication And Radar System Analyses

Abstract: Atmospheric electromagnetic wave propagation plays a crucial role in determining the performance of communication and radar systems that operate at millimeter through visible wave-lengths. Theoretical treatments of atmospheric wave propagation draw upon work on the micrometeorology of the medium, and feed work on the design and performance analysis of communications and radar systems. This paper will illustrate some of the features of the foregoing hierarchy, focusing on the interaction between the propagation and system analyses. Specific examples include: optical communication through atmospheric turbulence, coherent laser radar operation in atmospheric turbulence, and millimeter-wave communication through rain.

Linear Theory of Internal Gravity Waves and Mountain Waves

Abstract: The linearized analysis of internal gravity (buoyancy) waves, including those forced by topography, is surveyed, with particular attention given to the propagation conditions and their variability with the scale of forcing. The exchange of momentum and energy with the mean flow and the effects of reflection and resonance are also discussed.

Stationary, quasi-geostrophic waves of finite amplitude

Abstract: We consider the dynamics of finite amplitude long waves in a quasi-geostrophic atmosphere. It is shown that they satisfy the well known theorems, formulated by Charney and Drazin, for vertical reflection and coupling with zonal flow. It is further shown that the typical critical level effect holds for such waves as well.

On Waves in Non-Isothermal, Compressible, Ionized and Viscous Atmospheres *

Abstract: A review is given of the properties of waves in atmospheres, with particular emphasis on (Section 1) the variation of amplitude and phase with altitude for propagating waves (Figures 1 to 4) and the waveforms of standing modes (Figure 5). The cases dealt with concern waves under the combined influences of gravity and compressibility, and examine the effects of: (Section 2) temperature gradients in a non-isothermal atmospheric model; (Section 3) external magnetic field, either vertical or horizontal; (Section 4) dissipation by viscosity and electrical resistance. The results are relevant to (Section 5) the assessment of atmospheric wave growth and shock formation, and to the calculation of heating functions describing the deposition of wave energy.