bluuebunny/crossref_metadata_2025 huggingface dataset:
Low‐altitude convection, precipitation, and current patterns in the baseline magnetosphere
Authors: Gussenhoven M. S.
Published: February 2008

Three states of the magnetosphere may be identified from polar auroral and magnetic activity: the active auroral oval state, the active polar cap state, and the quiet state. The quiet time magnetosphere occurs when the energy transfer from the solar wind has been maintained at a minimum level for several hours. The conditions for minimal energy transfer occur for low solar wind velocity and for small IMF B and Bz. The quiet magnetosphere is characterized by minimal, but nonzero, cross‐cap electric field potentials (6–20 kV) and, therefore, low earthward convection velocities in the plasma sheet. The auroral oval shrinks to a circle of radius 20° geomagnetic latitude (MLAT) offset, as in active times, toward midnight. Diffuse auroral precipitation is continuous throughout these periods but has low average energy and number flux. Discrete arcs are weak (subvisual) and multiple, often extending to extremely high latitudes, particularly on the dayside of the cap. The cusp lies between 77° and 84° MLAT at noon. The total particle energy flux into both hemispheres is ∼ 10 GW. Region 1 and region 2 field‐aligned current systems frequently are not observed during extended periods of magnetic quiet. However, small‐scale current systems, which are associated with the weak discrete arcs, are still seen. Cusp currents in the sunlit hemisphere remain strong. Of particular interest in modeling the quiet magnetosphere are the following topics: the entry and transport of cusp particle populations, stable convection in the plasma sheet, and the closure of tail lobe magnetic field lines.
The “Greenhouse” effect and climate change
Authors: Mitchell John F. B.
Published: February 2008

The presence of radiatively active gases in the Earth's atmosphere (water vapor, carbon dioxide, and ozone) raises its global mean surface temperature by 30 K, making our planet habitable by life as we know it. There has been an increase in carbon dioxide and other trace gases since the Industrial Revolution, largely as a result of man's activities, increasing the radiative heating of the troposphere and surface by about 2 W m−2. This heating is likely to be enhanced by resulting changes in water vapor, snow and sea ice, and cloud. The associated equilibrium temperature rise is estimated to be between 1 and 2 K, there being uncertainties in the strength of climate feedbacks, particularly those due to cloud. The large thermal inertia of the oceans will slow the rate of warming, so that the expected temperature rise will be smaller than the equilibrium rise. This increases the uncertainty in the expected warming to date, with estimates ranging from less than 0.5 K to over 1 K. The observed increase of 0.5 K since 1900 is consistent with the lower range of these estimates, but the variability in the observed record is such that one cannot necessarily conclude that the observed temperature change is due to increases in trace gases. The prediction of changes in temperature over the next 50 years depends on assumptions concerning future changes in trace gas concentrations, the sensitivity of climate, and the effective thermal inertia of the oceans. On the basis of our current understanding a further warming of at least 1 K seems likely. Numerical models of climate indicate that the changes will not be uniform, nor will they be confined to temperature. The simulated warming is largest in high latitudes in winter and smallest over sea ice in summer, with little seasonal variation in the tropics. Annual mean precipitation and runoff increase in high latitudes, and most simulations indicate a drier land surface in northern mid‐latitudes in summer. The agreement between different models is much better for temperature than for changes in the hydrological cycle. Priorities for future research include developing an improved representation of cloud in numerical models, obtaining a better understanding of vertical mixing in the deep ocean, and determining the inherent variability of the ocean‐atmosphere system. Progress in these areas should enable detection of a man‐made “greenhouse” warming within the next two decades.
Do internal solitions exist in the ocean?
Authors: Ostrovsky L. A. , Stepanyants Yu. A.
Published: February 2008

A short survey of results related to solitary internal waves in the ocean is presented. We discuss observations of solitary waves in shallow seas and deep ocean regions accumulated over the last two decades. Work containing more or less complete hydrodynamical data that allow one to construct adequate theoretical models and to compare theory with experimental results is considered in more detail. The relation between the features of observed solitary formations and those of solitons known in theory is also developed. A summary of theoretical models describing nonlinear internal wave propagation, including the basic evolution equations and their soliton solutions, is presented in an appendix.
Global scale, physical models of the F region ionospere
Authors: Sojka J. J.
Published: February 2008

During the last decade, ionospheric F region modeling has reached an accurate climatological level. We now have global computer models of the F region which simulate the interactions between physical processes in the ionosphere. Because of their complexity, these climatological models are confined to modern day supercomputers. This review focuses on the development and verification of these physical ionospheric models. Such models are distinct from local models, steady state models, and empirical models of the ionosphere, which are, by their conception, unable to represent physically the range of F region variability or storm dynamics. This review examines the limitations of the physical models, which are at the present time mainly associated with inputs to the ionospheric system. Of these, the magnetospheric electric field and auroral precipitation are by far the most dominant and yet the least well‐defined dynamic inputs. Several developments are currently under way which could well lead to meteorological modeling capabilities in the next decade. For this the use of higher‐resolution inputs, both temporal and spatial (for example, auroral imagery), is critical. Coupling the ionospheric models with thermospheric and magnetospheric models will lead to self‐consistency and probably a predictive capability. Coupling to thermospheric models is currently under way; however, coupling with the magnetosphere must await the development of a magnetospheric model.
The representation of continental surface processes in atmospheric models
Authors: Avissar Roni , Verstraete Michel M.
Published: February 2008

This paper provides a general overview of the issues related to the modeling of surface processes in atmospheric models. The role of surface processes is first discussed as an essential coupling between the surface and the atmosphere. The issue of parameterization of small‐scale processes in large‐scale atmospheric models is addressed next, paying special attention to the cases of bare ground and vegetated surfaces. The paper focuses on the issues rather than the details of implementation, and extensive citations to the published literature are given for further investigations.
The geological interpretation of side‐scan sonar
Authors: Johnson H. Paul , Helferty Maryann
Published: February 2008

Recent developments in side‐scan sonar technology have increased the potential for fundamental changes in our understanding of ocean basins. Developed in the late 1960s, “side looking” sonars have been widely used for the last two decades to obtain qualitative estimates of the acoustic properties of the materials of the seafloor. Modern developments in the ability to obtain spatially correct digital data from side‐scan sonar systems have resulted in images that can be subsequently processed, enhanced, and quantified. With appropriate processing, these acoustic images can be made to resemble easily recognizable optical photographs. Any geological interpretation of these images requires an understanding of the inherent limitations of the data acquisition system. When imagery is collected, these limitations are largely centered on the concept of resolution. In side‐scan sonar images, there are several different types of resolution, including along‐ and across‐track resolution, display resolution, and absolute instrumental resolution. All of these parameters play a critical role in our ability to calibrate and ultimately to interpret the new pictures of the ocean floor. Acoustic image processing is a new application of an old and well‐established technique. Digital optical images have benefited from several decades of development in processing techniques. These relatively sophisticated techniques have been applied to photographic images from satellites and spacecraft, images which are “noisy” and difficult to obtain but extremely valuable. Side‐scan sonar systems, on the other hand, have only recently been able to produce spatially correct, digital images of the seafloor. The application of digital signal‐processing techniques to side‐scan sonar data will now allow us to quantify what had been previously very subjective and qualitative interpretations of images of the seafloor. The goal of all this processing of acoustic images remains clear: the development of an interpretable map of the geology of the seafloor.
Pressure Broadening of the 1.63‐mm Water‐Vapor Absorption Line
Authors: Hemmi C. O. , Straiton A. W.
Published: February 2008

This paper describes an experimental investigation of the 1.63‐mm H2O absorption line for nitrogen‐water‐vapor mixtures and for oxygen‐water‐vapor mixtures. Frequency sweep measurements were made at pressures between 1 and 5 mm of mercury and measurements at discrete frequencies were made for pressures between 200 and 760 mm of mercury. These measurements were made over a range of temperatures from 242° to 325°K. Data for the attenuation and line breadth constant as a function of temperature are presented.
Bearing Deviation in High‐Frequency Transionospheric Propagation: 3. Ray Tracing Investigation of the Magnetoionic Effect
Authors: Rao N. Narayana
Published: February 2008

The influence of an earth‐centered dipole magnetic field upon the bearing deviation of medium range HF ray paths in the ionosphere is investigated by using the ESSA three‐dimensional computer ray tracing program for a variety of conditions involving quasi‐parabolic layer models and actual electron density profiles deduced from ionograms gathered during a direction finding experiment. The adequacy of the dipole model is examined by comparing the bearing deviations obtained from it with those for a magnetic field based upon spherical harmonic expansion using Gaussian coefficients.
Cross Modulation in a Nonlinear Dispersive Plasma
Authors: Ram Sant
Published: February 2008

Expressions for the electric vector of the first‐ and the second‐order cross modulation have been derived for an amplitude‐modulated wave propagating in a nonlinear dispersive medium as well and for a normally incident wave reflecting back into free space from the plasma freespace interface. In the discussion, some numerical results illustrating the variation of the cross modulation with different plasma parameters are presented in tabular form.
Statistics of Instantaneous Frequency and Amplitude as Related to the Doppler Spectrum
Authors: Srivastava R. C. , Carbone R. E.
Published: February 2008

The distribution of the instantaneous frequency and power of the signal associated with a given Doppler spectrum is investigated for two cases: (case A) where the power at any frequency of the Doppler spectrum is exponentially distributed and (case B) where the power at each frequency is determinate. It is found that in case A the joint distribution of the instantaneous power and frequency depends only on (1) the total power, (2) the mean, and (3) the variance of the Doppler power spectrum. This result holds to a first approximation for case B also. The distributions of (1) instantaneous power, (2) instantaneous frequency, (3) average power as a function of instantaneous frequency, (4) average frequency as a function of instantaneous power, (5) variance of frequency as a function of instantaneous power, and (6) variance of power as a function of instantaneous frequency are also obtained. In particular, it is shown that the mean of the instantaneous frequency is equal to the mean power‐weighted frequency of the Doppler spectrum in case A. In case B, this result is only approximately valid.
Direct D‐layer Reflection as a Factor in Oblique Propagation on the Lower High Frequencies
Authors: Bain W. F. , Buckley R. J.
Published: February 2008

Recently available D‐region profiles are used to determine a model in which direct D‐region reflection is assumed to be the dominant daylight mode in the 2‐ to 5‐MHz region. This model is applied to the calculation of daylight absorption as a function of frequency and path length at oblique incidence. Good agreement with measurement is found, in contrast to early absorption calculation techniques, which show discrepancies of up to 50 decibels in this frequency range. Evidence suggesting direct D‐region reflection higher in the HF band is presented.
On the Moments and Tails of the Spectrum of an FM Wave
Authors: Blachman Nelson M.
Published: February 2008

The first three moments of the normalized spectrum of an FM wave equal the corresponding moments of the distribution of instantaneous frequency deviations. The fourth spectral moment contains an additional term given by the product of the mean‐squared deviation times the second moment of the normalized modulating spectrum. These moments are used to bound the power in the spectral tails.
VLF Modes Below an Idealized Anisotropic Ionosphere
Authors: Galejs Janis
Published: February 2008

The cylindrical shell between the earth and a homogeneous or exponentially varying ionosphere model is excited by vertically or horizontally polarized line sources; these fields are related to dipole fields in a spherical shell. Because of ionospheric anisotropy, the vertically polarized source also excites TM field components with wave numbers corresponding to TE modes, and a horizontally polarized source excites TE fields corresponding to TM modes, particularly for the higher frequencies at nighttime and for propagation westward. Among thefield components tangential to the ground surface, TM fields tend to dominate with the exception of TE modes at daytime and for lower frequencies at night. TM modes dominate in the nighttime mode sum (or interference pattern) for propagation eastward, but the two lower TE modes contribute significantly if propagation is westward. Simplified computational models that neglect the radial component of the earth's static magnetic field are justified under daytime conditions. At nighttime such calculations provide extreme changes in the attenuation rates and phase velocity variations, which are opposite to the ones observed with a dipping static magnetic field. The direction dependence of the phase velocity is eliminated by decreasing the strength of the static magnetic field.
Computation of Topside Ionograms From N (h) Profiles
Authors: Colin L. , Chan K. L. , Lee J. G. K.
Published: February 2008

Model profiles of plasma frequency and electron gyrofrequency are chosen to simulate typical conditions observed in the topside ionosphere by the Alouette 1 sounder (1000 km) and the Alouette 2 sounder near apogee (3000 km). Examples of group refractive index profiles for these models are presented. Applying parabolic‐in‐log X lamination techniques to the plasma frequency profiles, ‘cumulative delays’ are computed to illustrate the relative delays contributed by each lamination to the formation of topside ionograms. Complete ionograms (ordinary, extraordinary, and Z traces) are presented for all the models. Implications of the results to the inverse experimental problem of scaling ionogram data and computing electron concentration profiles are discussed. It is concluded that high‐altitude (sounder height above 1500 km) ionograms cannot be reliably and accurately reduced to electron concentration profiles using standard open‐loop procedures (i.e., N(h) profile computed from scaled extraordinary trace data alone). To process high‐altitude ionograms satisfactorily, closed‐loop procedures, as follows, are required: (1) compute N(h) profile and ordinary and Z traces from extraordinary trace data; (2) compare computed and scaled ordinary and Z traces on a CRT display unit; (3) correct extraordinary trace scaling and iterate computations in (1) and comparisons in (2), until computed and scaled values agree. An operational, man/CRT/computer on‐line system (FILMCLIP: Closed‐Loop Ionogram Processor for the analysis of topside sounder ionogram Films) based on this approach has been developed at Ames Research Center.
On the Coherent Wave Motion in Bounded, Randomly Fluctuating Regions
Authors: Rosenbaum Shalom
Published: February 2008

Some aspects of the propagation of scalar waves in bounded, randomly fluctuating media are considered. Specifically emphasized are the interface effects on the coherent wave motion in the limit of small‐scale fluctuations. It is shown that the procedure whereby a bounded, fluctuating region is replaced by an effectively homogeneous medium whose properties follow from the analysis of the appropriate unbounded domain may not be applicable, and an effectively inhomogeneous profile is generally required. In the case of fluctuations in a one‐dimensional medium bounded by a planar interface (for which explicit solutions are found), we conclude that the interface perturbs the coherent wave motion to a significant extent over a large distance from it. The three‐dimensional model reveals several deviations from the corresponding one‐dimensional case; the most significant stems from the observation that the interface effects are now confined to a well‐defined ‘transition’ layer of the order of a wavelength in thickness.
Low‐Latitude Ionospheric Electron Content Measurements During Half a Solar Cycle
Authors: de Mendonça F. , Kantor I. J. , Clemesha B. R.
Published: February 2008

This paper presents the results of total electron content measurements made at São José dos Campos (23.22°S, 45.98°W) between 1963 and 1968. The 1963 measurements were made by using the differential Doppler shift technique, and from December 1964 onwards the close‐spaced‐frequency method was employed using the 40 and 41 MHz transmission from the BE‐B and BE‐C satellites. An analysis is made of the variation of electron content with local time, dip angle, season, solar activity, and magnetic activity. Special attention is given to the equatorial anomaly and the region of the Brazilian magnetic anomaly.
The Variation of Pi 2 Micropulsation Waveform with Time
Authors: Orr David
Published: February 2008

Pi 2 micropulsations observed ‘simultaneously’ at two widely separated low‐latitude stations: M'Bour, Senegal, in West Africa, and Makerere, Uganda, in East Africa have been compared. The variation in the waveforms has been measured in terms of an average damping coefficient and the number of excursions taken for events to reach their peak amplitude. The differences in the waveforms are discussed in terms of dispersion varying with distance from the Pi 2 source and the damping coefficient varying with time. Shorter period activity has been noted in association with some Pi 2 events and an estimate of the relative apparent phase velocity of the higher‐frequency component has been made.
Laser Beam Broadening in Atmospheric Propagation
Authors: Gilmartin Thomas J. , Schultz Floyd V.
Published: February 2008

By using the Born approximation and the Gaussian model for the correlation of refractive index fluctuations in the atmosphere, an expression for the power in the first‐scattered field of the TEM∞ mode is obtained. It is demonstrated that the second‐scattered field does not contribute to beam broadening in the lowest‐order approximation. The total power in the first‐scattered field is found. The transverse profile of the scattered power is shown to be a function of a single parameter ΘL, which depends strongly on the ratio of the beam radius to the scale of turbulence a/lo. Values of lo and the mean square fluctuation of the refractive index (n12) are determined in an illustrative comparison with experimental data of the theoretical profile of a broadened beam.
An Expansion of the Helmholtz Integral and Its Evaluation
Authors: Dougherty H. T.
Published: February 2008

The Helmholtz integral theorem for the scattering or radiation of radio waves from surfaces is examined to obtain a more general approximation of the observed field distribution. The resulting new integral expansion is particularly responsive to evaluation by the method of stationary phases, yielding a quantitative solution applicable to a more general class of surfaces and aperture boundaries than was previously feasible. The problem of reflection from finite irregular surfaces, such as terrain or atmospheric layers, is evaluated formally. The result indicates a source of significant reflections not generally treated by ray theory.
Individual Sky Wave Mode Loss Statistics Measured on a North–South Path
Authors: Shepelavey Bohdan
Published: February 2008

The HF propagation loss behavior, in general, and the observed losses over the north‐south path reported here, in particular, can be explained in terms of a deterministic and a random component. Thus, the results are presented as the cumulative distributions of loss by frequencies and by modes in terms of their median and decile values. The most significant aspect of these data and the accompanying statistics is that the propagation losses were observed and analyzed strictly on the individual mode basis. Among these propagation modes are included 2‐hop E, 1‐hop F2, 2‐hop F2, 2‐hop E8, and N. From the medians and the deciles of the loss distributions of these various modes, it is quite apparent that propagation losses are mode dependent, day and night dependent, and sometimes high‐ and low‐ray dependent. The E‐mode losses also appear to be dependent on the ratio of the operating frequency and the maximum observed frequency of the path.
Scattering of a Plane Wave at a Plane Interface Separating Two Moving Media
Authors: Censor Dan
Published: February 2008

The problem of reflection and transmission of a plane electromagnetic wave at an interface separating two moving media is discussed. Contrary to previous studies, the model does not exclude normal components of the velocities with respect to the interface. The general formalism yields dyadic reflection and transmission coefficients. The results are applied to the Cerenkov radiation phenomenon, the Fizeau experiment, clear‐air scattering (when the two media have the same constitutive parameters in their respective rest frames), and ray optics in moving media.
Some Aspects of the Fine Structure of Elevated Layers in the Troposphere
Authors: Lane J. A.
Published: February 2008

This paper summarizes a series of measurements, with a balloon‐borne, spaced‐cavity refractometer, of the fine structure layers of large variance in refractivity. The measured height variation of the intensity of small‐scale fluctuations often shows clear evidence of some degree of stratification, even in nonanticyclonic conditions, with local parcels within which the value of ((ΔN)2)/l may reach 10−11 meter−1, where l is the scale size in the parcel. The results of forward‐scatter and beam‐swinging experiments must therefore be interpreted with due regard for this inhomogeneity. Furthermore, the spectral characteristics of refractivity in the region of scale layers vary widely in space and time. The value of Richardson's number across the layer is generally appreciably greater than 1, the exponent in the one‐dimensional spectrum is usually —2 to —2.5, and the spectra often tend to converge at wave numbers of 10–100 meters−1.
A Review of Line‐of‐Sight Propagation Studies of the Small‐Scale Structure of the Atmosphere
Authors: Lee R. W.
Published: February 2008

The present state of theory and experiment are reviewed. Theory is adequate for line‐of‐sight propagation in weakly inhomogeneous media; theory treats a wide variety of situations with potential for the probing of small‐scale atmospheric phenomena, using acoustic, microwave, and optical transmission. Thus far experiments have served mainly as tests of theory; useful information about the atmosphere will follow upon more intensive concern with the interpretive aspects of the problem.
Investigations of the Turbulence in Convective Atmosphere Using Radar and Aircraft
Authors: Chernikov A. A. , Mel'nichuk Yu. V. , Pinus N. Z. , Shmeter S. M. , Vinnichenko N. K.
Published: February 2008

A joint experiment using Doppler radar technique and instrumented aircraft has produced comparative measurements of wind‐speed fluctuations under convective conditions in the lowest 500 meters. Preliminary results show a good agreement between radar and aircraft spectra of a longitudinal wind‐speed component at scales from 50 meters to 1 km. There is an indication that, at scales larger than 1 km, Taylor's hypothesis is not valid.
A Modified Hypothesis on Turbulence Spectra in the Buoyancy Subrange of Stably Stratified Shear Flow
Authors: Lin J.‐T. , Panchev S. , Cermak J. E.
Published: February 2008

For a stationary process in the wave‐number range investigated (the buoyancy subrange of stably stratified flow) under the assumption of local homogeneity of the flow, two governing spectral equations derived from equations of motion and energy are solved by means of a generalized eddy‐viscosity approximation. Asymptotic solutions are obtained in the buoyancy subrange, where the local production and local dissipation of turbulence energy are negligible when compared with the inertial transfer and vertical heat‐flux terms when the flow conditions satisfy the frequency criterion
. The power law for the velocity and temperature spectra is not universal but varies with the flow conditions in the way ϕ(k) ∼ kn and ϕTT(k) ∼ km, where −11/5 ≥ n ≥ −3 and −1 ≥ m ≥ −7/5.
Boundary Between Laminar and Turbulent Flow
Authors: Thorpe S. A. , Strohbehn J. , Birkemeier W. P. , Plate E. J. , Scorer R. S.
Published: February 2008

This group was asked to consider the characteristic structure of the boundary between laminar and turbulent flows (the L‐T boundary) and to answer the following specific questions. If we consider the boundaries at the top and bottom of a patch of intense turbulence in a stratified medium,

a. Can we predict the two‐dimensional spectrum of the height deviations of the boundary?

Answer: no.

b. Will there be density fluctuations induced in the laminar layers where the stratification still remains?

Answer: yes.

c. If so, what spectrum can we predict for these fluctuations?

Answer: refer to Townsend [1964].

d. How intense will the fluctuations of a passive scalar quantity be at the boundary relative to a point in the middle of the thoroughly mixed zone (patch)?

Answer: it is not known.
The Application of Stationary Phase to Radio Propagation for Finite Limits of Integration
Authors: Dougherty H. T.
Published: February 2008

The application of the stationary phase method is investigated for a dimensionless line integral encountered in wave propagation. Evaluation of the integral for a first‐order point of stationary phase may be expressed, characteristically, by the Fresnel‐Kirchhoff function or its derivative. A related function is found for the isolation factor required for finite limits of integration. Curves for evaluating this factor, K(u2 u1), are presented.
The Origin and Nature of Lunar Mascons
Authors: Gilvarry J. J.
Published: February 2008

The origin of the mascons is explained in terms of a primordial atmosphere and hydrosphere of the moon lasting of the order of 1 b.y. from the origin 4.5 b.y. ago. On this basis, the mascons arose in four steps: (1) excavation of a large crater by meteoritic impact at a time close to the moon's origin, (2) subsequent isostatic adjustment of its rim and true floor, (3) rigidification of the crater and extensive depositon of sediments in its interior while an atmosphere and hydrosphere existed, and (4) eventual dessication of the sediments in the floor when the atmosphere and hydrosphere vanished. Rigidification of the crater (within a time about 1 m.y. after the moon's origin) prior to the main deposition of the sediments implies that the mascon load is supported by the strength of the underlying rock to produce a positive gravitational anomaly (independently of sediment density). The same history of the hydrosphere explains the presence of negative mascons in the irregular maria as a consequence of low sedimentation in these areas. The thicknesses of the mascons (at the apex, for a conical shape) in the prominent circular maria are obtained by scaling from the computer results of Conel and Holstrom for a sediment density (2.4 g/cm3) corresponding to shale. By means of Haskell's equation, it is shown that the lunar craters exclusive of those forming mascon basins cannot be compensated isostatically. It follows that the curves of Baldwin and of Gilvarry for the diameter‐depth and diameter‐rim relations for lunar craters can be extrapolated to infer the uncompensated depths and uncompensated rim heights of the primordial mascon craters. Available measurements of these parameters for the present time permit evaluation of isostatic adjustments in dimensions of mascon craters. On the basis of these data, a plot of the change in rim volume corresponding to isostatic subsidence of the crater rim against the volume corresponding to isostatic elevation of the cratic floor yields equality over two powers of 10 in the variables, within the accuracy of the data. This quantitative check tends to confirm strongly the isostasy of the true floors of the mascon craters and the support by the mantle rock of the mascon loads, as postulated in the theory.
Radio and Radar Studies of Venus and Mercury
Authors: Goldstein R. M.
Published: February 2008

Recent radio and radar studies of Mercury and Venus conducted since the last Symposium on Planetary Surfaces and Atmospheres are reviewed briefly.
Refractive Index and Group Velocity in Moving Dispersive Media
Authors: Nicolis John S. , Lin C. C.
Published: February 2008

We study the variations of the refractive index of a moving homogeneous dispersive half‐space (cold plasma or conventional dielectric) under the incidence of a plane quasi‐monochromatic wave entering from vacuum. The medium is moving parallel or perpendicular to the boundary, and the plane of incidence, containing either the magnetic or the electric vector, has an arbitrary azimuthal orientation with respect to the velocity of parallel motion.
Characteristics of the Sporadic E Layer at Waltair Using the Phase Path Technique
Authors: Reddi C. Raghava , Rao B. Ramachandra
Published: February 2008

The Es‐echo phase path records on 5.6 MHz have shown that the bottom surface of the Es was sometimes very sharply bounded. Some evidence showing that the formation of Es is a highly localized phenomenon has been obtained. The phase path variations of ‘O’ and ‘X’ components in the F2‐region echo during the formation of Es showed that the increase in the ionization in the Es is not totally from a vertical redistribution of the ionization along the ray paths.

From spaced phase path records of Es echoes taken during the daylight hours, apparent drift speeds in the range 40–130 m/sec with an eastward sense of the east‐west components of Es apparent drifts were observed. This is opposite to the sense of the east‐west components of E‐region drifts during the daylight hours but is the same as that during the nighttime hours. An attempt is made to interpret these observations.
The Comparison of Electron Density Profiles Obtained from Backscatter Observations and Ionogram Analysis
Authors: Smith D. H.
Published: February 2008

A large number of ionograms recorded at Arecibo have been converted to electron density profiles. It is shown that the method of analysis can give very high accuracy for a single layer, but the presence of an E layer can result in systematic errors in the shape of the F layer. Backscatter observations taken at the same times as the ionograms have been analyzed to give electron density curves with a height resolution of 9 km. Although there is a wide range of variation in the shape and height of the ionospheric layers, there is in general close agreement between the profiles obtained by the two methods.
Electromagnetic Fields of a Pulsed Dipole in Dissipative and Dispersive Media
Authors: Wait James R.
Published: February 2008

Exact expressions are obtained for the fields of a step‐function excited electric dipole in a homogeneous medium of infinite extent. Special cases include a conducting dielectric medium and a cold lossless plasma.
Simulation and Analysis of Faraday Rotation of Beacon Satellite Signals in the Presence of Traveling Ionospheric Disturbances
Authors: Rao N. Narayana , Hamrick L. T.
Published: February 2008

Records of Faraday rotation of signals from radio beacon satellites during traveling ionospheric disturbances are simulated for spaced stations. These synthetic records are used to discuss, first, observational differences using geostationary satellites and low‐orbiting satellites and, secondly, the effect of assuming a height value for the disturbance in the analysis of the low‐orbiting satellite data.
Ray Tracing in Warm Magnetoplasma and Applications to Topside Resonances
Authors: Bitoun J. , Graff Ph. , Aubry M.
Published: February 2008

A procedure for determining ray trajectories in warm magnetoplasmas is presented; it is based on mathematical treatments of the wave dispersion relation. This procedure is used to interpret topside resonance at the upper hybrid frequency as oblique echoes. The following results are obtained: when ƒτ < 2 ƒH, two Doppler shifted echoes are received after reflection from above the emitting satellite; their frequencies are plotted as functions of time. The absence of such echoes is observed for ƒτ > 2ƒH.
Effects of Positioning Errors on Grating‐Lobe Reduction in Uniform Linear Arrays
Authors: Zaghloul Amir I. , MacPhie Robert H.
Published: February 2008

In this paper we consider the effect of element positioning errors on the pattern of a uniform linear array. An error in positioning each element in the longitudinal direction relative to the previous one is assumed to occur with a Gaussian distribution of zero mean and variance σ2. An important effect of this type of error is that although the main beam remains practically unchanged, there is a suppression of the grating lobes whose expected levels can be made less than the first sidelobe by increasing the number of elements and/or σ. In the side‐lobe region, far from the mainlobe, the mean and variance of the pattern approach a constant whose value is inversely proportional to the number of elements. This permits one to use larger element spacings that give higher resolution without grating‐lobe ambiguities. An example is given in connection with the mapping of two incoherent point sources. Expressions are derived and graphs are given for the mean and Standard deviation of the field pattern and for the mean and standard deviation of the power pattern. The theory was verified statistically by means of a computer that generated Gaussian random numbers. It also provided relative frequency histograms of power at the first grating lobe.
Transient Propagation of Electromagnetic Waves in a Stratified Plasma
Authors: Field John C.
Published: February 2008

The method of characteristics is applied to the study of transient electromagnetic wave propagation in a stratified plasma. The technique is applicable to lossy, anisotropic, time‐varying plasmas whose parameters may vary in the direction of wave propagation. Numerical results demonstrate good agreement with theory.
Current Distribution on a Grid Type Dipole Antenna Immersed in a Warm Isotropic Plasma
Authors: Schiff Maurice L.
Published: February 2008

The current distribution on a grid type dipole antenna immersed in a warm isotropic plasma is formulated from two viewpoints. The first method is a direct source approach; it yields a new integral equation that is an extension of Hallen's equation. The second method is based on a boundary value analysis introduced by Einarsson. The equivalence between the two methods will be shown. A solution to the integral equation valid for thin antennas shows that the current is sinusoidal in form with a propagation constant Ke = (ω2–ωp2)½/C. This result will be compared with the work of Monroe.
A Laboratory Model for VLF Propagation Experiments
Authors: Schwartz K. , Brown G. L.
Published: February 2008

A laboratory model of a section of the earth‐ionosphere has been designed and constructed to provide a means for systematically investigating the effect of ionospheric perturbations on long range VLF paths. This model provides a capability for the investigation of a wide variety of different disturbed ionospheric conditions. For any given configuration, all the pertinent parameters are clearly defined and repeatable. This is in contradistinction to naturally occurring events, for which many parameters that are important for a clear interpretation are either unknown or, at best, poorly known. The design rationale and the construction methods are presented in this paper with initial experimental data obtained from the model for uniform propagation paths. It is shown that these data are in good agreement with theoretical data obtained for the modeled conditions. Data are also presented for propagation paths through a nuclear type ionospheric perturbation. These data exhibit both amplitude loss and phase advance caused by the perturbation.
Group‐Theoretic Implication for Statistically Self‐Similar Atmospheric Turbulence
Authors: Rosen Gerald
Published: February 2008

The group‐theoretic consistency of a random variable scaling law implies that the associated spectrum function is proportional to a power of the frequency.
Time‐Response Waveforms for a Cube From Measured Data and Diffraction Analysis
Authors: Ryan C. E.
Published: February 2008

The geometrical theory of diffraction has been applied to analysis of the backscattered fields of a cube in the plane normal to four edges of the cube. The results of this diffraction analysis are used to calculate the backscattered fields at harmonically related frequencies, which are then combined with experimental data and transformed to obtain impulse, step, and ramp responses in the time domain. The inclusion of the calculated high‐frequency data results in a more precise determination of the time‐response waveforms than is possible with only low‐frequency measured data. As an example of the results, the impulse, step, and ramp responses for vertical and horizontal polarization are presented for θ = 0° (specular direction), 30°.
Admittance of Dipolar RF Probes in a Simulated Ionosphere
Authors: Hall T. A. , Landauer G.
Published: February 2008

This paper describes a laboratory investigation of two types of dipolar RF admittance probes which could be of use in the ionosphere and inner magnetosphere. Simple theoretical models are presented, using the quasi‐static approximation and vacuum sheath. Independent accurate measurements of both the electron density and temperature are made, using Langmuir probes and the dispersion properties of Bernstein waves, and the results are compared with the RF probe predictions. In general, good agreement is obtained, indicating both the usefulness of the probes as a way of measuring electron densities in space and the applicability of the model used. These results also give an estimate of the effective sheath thickness around the probe, which is smaller than previous measurements have suggested.
Radiation From Magnetic Line Source Covered with a Moving Sheath
Authors: Kojima T. , Itakura K. , Higashi T.
Published: February 2008

In this paper we investigate the radiation from magnetic line source covered with a moving uniaxial or isotropic sheath (nondispersive dielectric or cold plasma). The far‐zone radiated fields and the radiation pattern for the four cases, (a) uniaxial dielectric sheath, (b) isotropic dielectric sheath, (c) uniaxial plasma sheath, and (d) isotropic plasma sheath are obtained, and the effects of the motion of the sheath on the far‐zone radiated fields and the radiation pattern for each case are discussed by showing some numerical results of the radiation pattern.
Method of Conjugate Gradients for Antenna Pattern Synthesis
Authors: Fong T. S. , Birgenheier R. A.
Published: February 2008

The computational method of conjugate gradients for linear operator equations is given. This technique is applied to the solution of the integral equation that relates the aperture distribution and the far‐field pattern. This problem is treated from the variational setting by minimizing an error functional. In searching for the solution, a sequence of expanding subspaces in a function space is generated via the Frechet differential of the error functional. The error functional is minimized in each of the subspaces and thus forms a sequence of approximating solutions. This iterative procedure may be conveniently implemented on a computer. Two synthesis problems are treated using this technique, and the results are discussed.
Radiation From a Short Electric Dipole in a Hot Uniaxial Plasma
Authors: Singh N. , Gould R. W.
Published: February 2008

The effects of electron temperature on the radiation fields and the resistance of a short electric dipole antenna embedded in a uniaxial plasma have been studied. The radiation condition for solving Maxwell's equations is discussed, and the phase and group velocities for propagation are given. It is found that for ω < ωρ the antenna excites two waves, a slow wave and a fast wave. These waves propagate only within a cone whose axis is parallel to the biasing magnetostatic field B0 and whose half‐cone angle is slightly less than sin−1 (ω/ωρ). In the case of ω > ωρ the antenna excites two separate modes of radiation. One of the modes is the electromagnetic mode, while the other mode is of hot plasma origin. A characteristic interference structure is noted in the angular distribution of the field. The input and the radiation resistances are calculated and are shown to remain finite for nonzero electron thermal velocities. The effect of Landau damping and the antenna length on the input and the radiation resistances has been considered.
A Theory of Scattering From Irregularities in a Magneto‐Ionic Medium
Authors: Simonich D. M. , Yeh K. C.
Published: February 2008

A theory is developed to describe scattering from irregularities in a magneto‐ionic medium. The theory makes use of the asymptotic Green's dyadic. Since the medium is anisotropic, crossmode scattering in addition to self‐mode scattering is possible. Several examples are given.
Transmission and Reflection of a Wave Obliquely Incident on a Nonuniform Magnetized Plasma
Authors: Peratt A. L. , Kuehl H. H.
Published: February 2008

A theory is given describing the conversion of obliquely incident fast waves to slow waves when propagation is perpendicular to a static magnetic field in a warm inhomogeneous plasma for frequencies near and below the second electron cyclotron harmonic. The half‐space and thin slab are treated with collisional effects included. The results are compared with those of a previously considered normally incident wave case. In particular, the analysis points out that wave conversion is proportional to the scale length of the density gradient at a hybrid resonance point provided the scale length is small compared to a free space wavelength. Both analytical and numerical solutions for the reflection and transmission coefficients and fields within the slab are presented. Between the hybrid resonances the electric field is found to consist of a longitudinal Bernstein mode contribution with rapid spatial variation and a slow variation extraordinary mode contribution. With appreciable losses, a pure standing wave is predicted at the center of the plasma whereas near the hybrid resonance points the longitudinal field is predominantly a traveling wave with an outwardly directed phase velocity. Although the coupling is small, the longitudinal field attains a large amplitude producing strong reflection of the incident wave when resonances occur with even symmetry about the center of the slab. Furthermore, the numerical computations indicate a perturbation in the position of the resonances from those of the normally incident case. This shift is analogous to the azimuthally asymmetric modes of a plasma column. Finally, for a large angle of incidence, the formulation leads to the impedance of a nonuniform plasma capacitor in a magnetic field.
On the Maximum and Minimum Energy Transmitted Through Thin, Dispersive, Dielectric Media
Authors: Mayhan Joseph T.
Published: February 2008

The electromagnetic energy transmitted over a path in which a thin, dispersive, dielectric medium is introduced is studied from the viewpoint of maximizing the transmitted energy. Two cases are treated in detail: a dispersionless dielectric and a plasma dielectric, including the effects of collisions. It is shown that the form of the solution that maximizes the energy transmitted through a dispersionless dielectric minimizes the energy transmitted through a plasma dielectric. Expressions specifying the energy transferred in each case are presented. The cases treated illustrate the importance of dispersion in choosing a suitable pulse shape for maximum energy transmission.
Comments on the First Intensive Period of Observation of ES in Europe
Authors: Bossy L. G.
Published: February 2008

More than twenty European vertical‐sounding stations participated in an intensive period of observation of ES on June 15, 16, and 17, 1971. Results show that, using values of ƒ0ES from this network, useful information can be obtained about the structure and movement of ES clouds.
Atmospheric Metal Ion Chemistry
Authors: Ferguson E. E.
Published: February 2008

The role of metal ion chemistry in the atmosphere is briefly reviewed. The available relevant thermal energy binary and three‐body reaction rate data are tabulated. The importance of a two‐step hydration of metal ions is pointed out, first three‐body association of metal ions to CO2 (or possibly O2 or N2) followed by a fast binary ‘switching’ reaction, M+·CO2 + H2O → M+·H2O + CO2 which should be particularly effective for metal ion loss in the D region.
Winds in E Region
Authors: Whitehead J. D.
Published: February 2008

It is important to determine whether regular tidal winds or irregular gravity waves dominate the transport processes in the E region. This depends on their relative amplitudes. The question became prominent when Chimonas [1971] claimed that ‘the dominant winds in the E region are the solar tidal winds.’ This was a misquotation from another source. The best estimates seem to be that gravity wave amplitudes are rather greater than either of the major solar tidal wind amplitudes at E‐region heights. Consequences of assuming otherwise are discussed.
Three‐Dimensional Analysis of the Cross‐Field Instability in the Ionosphere
Authors: Sato Tetsuya , Tsuda Takao
Published: February 2008

A three‐dimensional linear analysis is made of the cross‐field instability for a geometry in which the magnetic field lines make an arbitrary angle with the direction of density gradient. A general formula of the growth rate is obtained for a perturbation over whose scale the background quantities do not change appreciably. Applying the formula to the lower ionosphere, we find that the results of an earlier analysis [Tsuda et al., 1966] are recovered as a special case; that is, the present instability is a potential source of small‐scale irregularities in temperate latitude E region, as well as in the equatorial E region.