bluuebunny/crossref_metadata_2025 huggingface dataset:
An Investigation of the Ionospheric D Region at Sunrise: 3, Time Variations of Negative‐Ion and Electron Densities
Authors: Turco R. P. , Sechrist C. F.
Published: February 2008

The growth over sunrise of the C and D layers of the ionosphere is investigated for a model which includes: the negative ion species O−, O2−, O3−, O4−, NO2−, NO3−, CO3−, and CO4−; ion‐pair production by galactic cosmic rays, precipitated electrons, photoionization of NO by scattered Lyman‐α radiation, and the photoionization of NO and O2(1Δ) by direct solar radiation; the photodetachment of most of the negative ions; and the time variations of all these parameters. It is found that the inclusion of the reaction NO3− + O → NO2 + O2− with a rate constant of 5×10−14 cm3 sec−1 in combination with fast electron‐ion recombination (α ∼ 10−5 cm3 sec−1) can accurately reproduce both the development of the C layer at sunrise and the correct magnitude and form for the D‐layer development. The photodetachment of NO3− is not a suitable alternate source of sunrise electrons because of the large electron affinity of NO3. The photodetachment of lower‐affinity negative ions, such as hydrated species, could replace the NO3− + O → NO2 + O2− reaction if indeed the presunrise mesospheric ions are predominantly hydrated. The dominant ions in the present scheme are NO3−, CO4−, and CO3−. Atomic oxygen greatly limits the quantity of negative ions above 75 km at all times of the day by associative detachment and is responsible for the nighttime D‐layer ledge of electron density. The 98 and 94° VLF radio propagation effects are explicable on the basis of this model.
VLF Emissions in the Magnetosphere
Authors: Rycroft M. J.
Published: February 2008

Recent observations of both naturally occurring and triggered VLF emissions (a few KHz) made on the ground, aboard rockets, and aboard satellites are discussed. Although reference is made to auroral‐zone emissions, attention is concentrated on midlatitude discrete emissions such as chorus. FollowingBrice[1964] andKennel and Petschek[1966], the signals are interpreted as arising from the transverse resonance (or cyclotron) instability of magnetospheric plasma in the equatorial plane in the vicinity of the plasmapause. The energy of the gyroresonant electrons is estimated; the precipitation of these energetic electrons from the radiation belts is a consequence of the interaction.
On D‐region Electron Heating by a Low‐Frequency Terrestrial Line Current With Ground Return
Authors: Row R. V. , Mentzoni M. H.
Published: February 2008

A horizontal current‐carrying wire near the surface of the earth will maintain a tangential electric field in the ionosphere overhead. The questions of how large this field must be to produce a given local increase in electron temperature in the D region and the corresponding required current (dipole moment) in the wire are addressed here. To achieve a 20 K modulation (about 10% of ambient temperature) of the local electron temperature at an altitude of 70 km under daytime conditions would require an rms current of 2730 amp at 45 Hz over a length of at least 300 km where the ground conductivity is 1.4×10−4 mho m−1. A parallel array of 23 wires spaced at 10‐km intervals will produce the same temperature modulation with only 139 amp in each wire.
The Atmosphere Explorer mission
Authors: Dalgarno A. , Hanson W. B. , Spencer N. W , Schmerling E. R.
Published: February 2008

A short description is presented of the general scientific objectives of the Atmosphere Explorer mission.
The magnetic ion‐mass spectrometer on Atmosphere Explorer
Authors: Hoffman J. H. , Hanson W. B. , Lippincott C. R. , Ferguson E. E.
Published: February 2008

The magnetic ion‐mass spectrometer is designed to measure the abundances of the ambient positive ions in the ionosphere. It will be calibrated in flight against the retarding‐potential analyzer and the cylindrical electrostatic probe to give absolute concentration data for the ion species detected. These parameters can be measured to approximately ±10% in well‐behaved regions where concentrations are above 103 cm−3. However, in highly structured polar regions, some degradation in accuracy may be expected.

Three mass ranges, covered simultaneously by the scan of the instrument, 1 to 4, 4 to 16, and 16 to 64 amu, permit measurement of the entire mass range, 1 to 64 amu, in 1 sec in the main (peaks) mode. An alternate mode, analog‐long, will extend the mass range to 90 amu with a 9‐sec period. Capability is provided to lock onto any set of mass numbers in the ratio 1:4:16 to give very high spatial resolution, e.g., 500, 250, and 125 m in the low‐, mid‐, and high‐mass ranges, respectively. This mode will be most useful in the despun satellite orientation to provide fine‐structure data on ion concentrations. In the spinning mode the phase shifts between roll modulation maxima of heavy and light ions determine the vertical component of the individual ion‐drift velocities. Values from a few km sec−1 to over 20 km sec−1 can be determined. Such data are applicable to the study of polar wind phenomena.
The Bennett ion‐mass spectrometer on Atmosphere Explorer‐C and ‐E
Authors: Brinton H. C. , Scott L. R. , Pharo M. W. , Coulson J. T.
Published: February 2008

The Bennett spectrometer to be flown on Atmosphere Explorer‐C and ‐E (AE‐C and AE‐E) is designed to measure, throughout the 120 to 4000‐km orbit, the concentrations of all thermal positive ions in the mass range 1 to 72 amu and number density range 5 to 5 × 106 ions cm−3. To reduce the buildup of ram pressure and facilitate measurements at low altitude, the analyzer is vented, and a multigrid ion‐current collector is employed. An extensive command capability permits optimization of instrument parameters for particular measurement objectives; commandable functions include mass‐scan range and period, the sensitivity‐resolution characteristic of the analyzer, orifice potential, and in‐flight calibration. Any combination of three mass ranges (1 to 4, 2 to 18, 8 to 72 amu) may be selected as the mass‐scan mode; each range is normally scanned in 1.6 sec, corresponding to a distance of 12 km along the orbit. Ion spectra will be simultaneously telemetered in both analog and digital form; the digital data result from on‐board processing of the analog spectra and consist only of ion‐peak coordinates. The three overlapping mass ranges will enable in‐flight evaluation of mass discrimination within the ion analyzer. Verification of absolute instrument sensitivity will require correlation of the spectrometer data with results from the companion electrostatic probe and retarding‐potential analyzer. Such correlations should permit individual ion concentrations to be determined with an accuracy of ±10%.
The electromagnetic response of a buried sphere for buried‐dipole excitation
Authors: Hill David A. , Wait James R.
Published: February 2008

The effect of a spherical inhomogeneity on the surface fields of a buried magnetic dipole source is determined from the reradiated fields of induced electric and magnetic dipole moments. For small spheres where the theory is valid, the errors introduced in source location are shown to be small. The results have possible application to rescue operations following coal mine disasters.
High latitude electric fields and the modulations related to interplanetary magnetic field parameters
Authors: Heppner J. P.
Published: February 2008

The meaning and characteristics of basic and average convection (i.e., electric field) patterns are described. The continuous existence of the basic convection pattern argues against treating magnetic field merging mechanisms as the fundamental cause of magnetospheric convection. However, whether related to merging or to some other mechanism, interplanetary magnetic field conditions significantly modulate the distribution, magnitudes, and boundaries of the convection pattern. A previous correlation between azimuthal, ф, angles of the inter‐planetary magnetic field and asymmetries in polar cap electric field distributions as seen by OGO‐6 is reviewed. A new approach is taken to reveal correlations with the north‐south, θ, angle and magnitude, B, of the interplanetary field as well as additional features which correlate with the ф angle. Both significant correlations and conditions which show a lack of correlation are found. Several aspects of the correlations appear to be particularly important. One is that for a given ф angle, correlations exist relative to θ independent of B and relative to B independent of θ. A second is that shifts in the latitude of the low altitude limit of the auroral belt convection are strongly correlated with all parameters (ф, θ, B).
Analytical determination of propagation paths near gyroharmonics
Authors: Bitoun J.
Published: February 2008

The propagation of waves in a hot magnetoplasma near gyroharmonics is studied by means of analytical ray tracing. To get the parametric equations of the paths a dispersion relation is first obtained through the electrostatic hypothesis and some mathematical approximations. For this case, it is shown that, except near reflection, waves transmitted from an ionospheric sounder travel almost along the static magnetic field and that the gradient of the magnetic field may be responsible for their reflection back to the spacecraft antenna. In certain cases two distinct trajectories can simultaneously intersect the receiving antenna thus giving rise to beats which are sometimes observed experimentally. The theoretical formulas are applied to a 3fH resonance.
Physics and chemistry of the E region: A review
Authors: Strobel Darrell F.
Published: February 2008

A review of physical and chemical processes in the E region is given with emphasis on the absolute ionization balance and relative ion composition. The importance of transport processes in the nighttime E region is emphasized. It is concluded that the electron, ion, and neutral gases are in thermal equilibrium.
The F1 region during a solar eclipse
Authors: Oliver W. L. , Bowhill S. A.
Published: February 2008

Temperature and ion composition results obtained during the eclipse of 7 March 1970 at Millstone Hill are presented. The temperature variations appear to be controlled by the high degree of magnetic activity present on the eclipse day. Ion composition variations may be explained in terms of photochemical processes and the distribution of ionizing radiation across the solar disk. The data indicate the quality of ion composition determination by incoherent scatter radar, and it is concluded that these data are more useful when averaged in quantity to determine diurnal, seasonal, and solar cycle variations rather than short‐term temporal variations on a given day.
Accuracy of rocket measurements of lower ionosphere electron concentrations
Authors: Mechtly E. A.
Published: February 2008

Measurements of electron concentration taken at the same time and at the same place in the lower ionosphere by independent instrumentation mounted on the same rocket are described. The technique utilizes Faraday rotation and differential absorption of radio waves propagating from the ground to the rocket at two different frequencies. Agreement near 90 km within ±7%, ±6%, ±8%, and ±3% is demonstrated by the four available cases of coincidence in time and altitude. Maximum dispersion at other altitudes is calculated from known random errors. Stronger variation of electron collision frequency with altitude than with season is indicated by 34 measurements between 75 and 100 km. Insensitivity of electron concentration determinations at 72 km to errors in extrapolated collision frequency models is demonstrated. Partial reflection data are compared with rocket results in the one case of commonality in time and place.
Thermal microwave emission from a halfspace containing scatterers
Authors: England A. W.
Published: February 2008

The microwave brightness of heterogeneous materials is decreased by internal scattering. This study, based upon radiative transfer theory, shows that for low loss media darkening can be many tens of degrees, that the effect is greater for materials of lower dielectric constant, that darkening depends upon the dominance of scattering over absorption, that volume scattering tends to mask a temperature gradient, that darkening is slightly greater for V‐ than for H‐polarized radiation, and that darkening increases slightly with view angle. For isotropic scattering, the analysis yields the brightness temperature as a function of the scattering albedo, the complex dielectric constant, thermal temperature, and the temperature gradient.
Guided electromagnetic waves in a curved rectangular mine tunnel
Authors: Mahmoud Samir F. , Wait James R.
Published: February 2008

The transmission of VHF electromagnetic waves in a curved mine tunnel is analyzed using an idealized model in a cylindrical geometry. The tunnel cross section is assumed to be rectangular and the broad curved walls are imperfectly reflecting. The computations of the modal characteristics are facilitated by using a modified Airy function approximation of the rigorous cylindrical wave functions. The results indicated that the curvature of such tunnels will seriously increase the attenuation of the dominant low‐order modes that are used for communications.
A discussion of possible negative ion detachment mechanisms in the sunrise D region
Authors: Turco R. P.
Published: February 2008

Many recent measurements of photochemical rate constants and atmospheric ion composition have changed our understanding of D‐region sunrise processes. In this paper several new sunrise mechanisms are suggested in the light of the recent data. It is concluded that very stable hydrated negative ions will probably be converted by chemical reaction at sunrise into less stable hydrates which can be photodetached.
Resonance cone and Bernstein wave interference patterns in a magnetoplasma
Authors: Muldrew D. B. , Gonfalone A.
Published: February 2008

General dispersion relations for a hot magnetoplasma are used to explain the interference observed between electrostatic waves and the electromagnetic field in an afterglow plasma. Observations are made near both oblique resonance cones (connected with whistler and Z‐propagation modes) and in the frequency region corresponding to “Bernstein” waves. Independent measurements of the lower (whistler) and upper (Z‐mode) resonance cones, for a particular case, lead to the same isotropic temperature in the late afterglow, namely 540 K. Independent measurements of the lower resonance cone and of Bernstein waves in the early afterglow also lead to consistent isotropic temperatures. As the real and imaginary components of the wave number increase, a point of inflection is reached on the various dispersion curves for homogeneous plane waves beyond which these curves can no longer be used to explain the observed interference fringes. For homogeneous waves with a wave number smaller than that corresponding to the inflection point, reasonable values of Landau damping are obtained which agree roughly with observed damping.
First observations of RF backscatter from field‐aligned irregularities produced by ionospheric heating
Authors: Thome George D. , Blood David W.
Published: February 2008

A series of experiments was conducted with HF and VHF radars at White Sands, New Mexico, during the months of October 1970 and June 1971 to search for direct RF backscatter from ionospheric irregularities produced by the Platteville heater. The observations were made from White Sands because radars at this location view the heated volume normal to the earth's magnetic field lines. Direct echoes from the heated volume were unquestionably observed. Returns were obtained at frequencies up to the highest available at the HF radar site: 30 MHz during the first series of observations and 54 MHz during the second. The echoes were observed only after sunset, at times when the local plasma frequency over Platteville was of the order of 5 MHz at the layer maximum. The total radar scattering cross section of the heated volume was found to decrease with increasing frequency and to vary from less than 104 m2 (the minimum detectable cross section) to 109 m2, depending on frequency and time of day. The Doppler spectrum of the returns indicated that the drift velocity of the scatterers through the heated volume was greater than the relative velocity between scatterers and comparable to the drift velocity of natural irregularities at midlatitudes.
VHF and UHF bistatic observations of a region of the ionosphere modified by a high power radio transmitter
Authors: Carpenter G. B.
Published: February 2008

VHF and UHF bistatic radar investigation of a region of the ionosphere modified by a high power transmitter has revealed two modes of scatter. The modes are described in association with parameters of the scatter region and of the received signals.
A model of the enhanced airglow excited by RF radiation
Authors: Haslett J. C. , Megill L. R.
Published: February 2008

A phenomenological model of the enhanced airglow produced by the Department of Commerce ionospheric modification facility is presented. This model is based primarily on airglow data taken from two sites for triangulation. These data show that it is not necessary for the region in which RF power is deposited (interaction region) to be coincident with the region in which the modified airglow is emitted (excitation region). The two are coincident at altitudes below 280 ± 15 km; but, as the interaction region rises, the two may separate with the excitation region remaining at altitudes around 280 km. It is also shown that a non‐Maxwellian energy distribution for electrons is generated by the transmitter. Further, using this model, we present estimates of the efficiency for converting the radio wave energy into energetic electrons. This can typically be 1%, although observations indicating efficiencies 10 to 15 times higher have been made. A variety of experimental data which are not clearly understood are also presented.
Multiple scattering of waves in a medium of randomly distributed particles and derivation of the transport equation
Authors: Furutsu K.
Published: February 2008

In a previous paper, the characteristic functional of the wave function has been found to be the solution of a basic equation which has the same form as the original wave equation and is given in terms of the characteristic functional of the refractive index. In this paper, the theory is applied to the case of scalar wave propagation in a medium of randomly distributed particles, and the transport equation is derived by use of an analytical procedure. The renormalization of the medium and of the one‐particle scattering matrix is explicitly introduced, and is found to play an essential role for energy conservation. The Fourier transform of the resulting single Green's function (in the infinite medium) has a set of poles of infinite number. The transport equation is expressed by a series of residue values at the poles of the original and complex conjugate Green's functions, and has a wider range of applicability than that of the conventional transport equation. As a method of solving the transport equation, a set of eigenfunctions is introduced, and the solution is obtained in terms of the eigenfunction series. The diffusion function associated with each eigenfunction is also obtained.
Numerical studies of type 2 equatorial electrojet irregularity development
Authors: McDonald B. E. , Coffey T. P. , Ossakow S. L. , Sudan R. N.
Published: February 2008

A computer simulation based on fluid equations of motion seems to account for basic observational features of short wavelength type 2 (subsonically propagating) ionization irregularities in the equatorial electrojet. The short wavelengths (less than 28 m for parameters taken here) are excited only after long wavelength, horizontally propagating waves grow to an amplitude sufficient to trigger the nonlinear growth of secondary vertically propagating modes. The result is a complicated two‐dimensional turbulent flow, with convective elements moving with comparable vertical and horizontal velocities. The density fluctuation power spectrum obeys approximately a power law κ−3.5. These results agree with theory and observation.
An estimate of the global‐scale joule heating rates in the thermosphere due to time mean currents
Authors: Roble R. G. , Matsushita S.
Published: February 2008

An estimate of the global‐scale joule heating rates in the thermosphere is made based on derived global equivalent overhead electric current systems in the dynamo region during geomagnetically quiet and disturbed periods. The total neutral gas heating rate due to joule dissipation is proportional to the Pedersen conductivity and the square of the total electric field perpendicular to the geomagnetic field line. The equivalent total electric field distribution is calculated from Ohm's law as applied to the dynamo region using the equivalent overhead currents estimated from geomagnetic data and the components of the two‐dimensional conductivity tensor determined from global empirical models of the electron and neutral gas number density distributions. The global‐scale joule heating rates are calculated for various monthly average periods in 1965. The calculated joule heating rates maximize at high latitudes in the early evening and postmidnight sectors. During geomagnetically quiet times the daytime joule heating rates are considerably lower than heating by solar EUV radiation. However, during geomagnetically disturbed periods the estimated joule heating rates increase by an order of magnitude and can locally exceed the solar EUV heating rates. The results show that joule heating is an important and at times the dominant energy source at high latitudes. However, the global mean joule heating rates calculated near solar minimum are generally small compared to the global mean solar EUV heating rates.
Principles for the radar determination of the polarization properties of precipitation
Authors: McCormick G. C. , Hendry A.
Published: February 2008

The principles for determining certain parameters of precipitation particles by means of a radar with two‐channel orthogonal polarization capability are discussed. The parameters are or are related to the mean shape, mean orientation angle, the degree of randomness of the particle orientation, and also to particle size and phase state. The preferred orientation of such particles results in the medium being anisotropic. The propagation aspects of the problem are considered in terms of additional parameters which include the differential attenuation, the differential phase shift, and the tilt angle of the anisotropy axes. Formulas are derived for determining the parameters in terms of radar observables. A limited sample of results from 16.5 GHz data is presented in order to illustrate the radar determination of each parameter.
The impedance of a dipole antenna in the ionosphere: 1. Experimental study
Authors: Vernet N. , Manning R. , Steinberg J. L.
Published: February 2008

The impedance of a short electric dipole antenna has been measured from rockets in the ionosphere. The EIDI I experiment was launched in conditions where the plasma was expected to be nearly isotropic (operating frequencies 4.48 and 6.09 MHz, f0F2 ⋍ 9 MHz, fH ⋍ 1 MHz). It was designed to detect and measure or to eliminate most of the unwanted effects which complicated the data reduction of previous experiments: outgassing, telemetry radiation, etc. The number of parameters measured simultaneously on board (impedances with variable bias and RF excitation level, resonance frequencies, Te, dc current drawn by the antennas, vehicle potential) and from the ground or an overhead satellite was large enough to provide numerous cross checks and to determine the sheath dimensions.

The impedance is very weakly spin‐modulated over most of the flight; the collision frequency is very low (v/ω ⋍ 10−5) unlike some of the previous experiments where collision losses were dominant. The measured values of the impedance are given as a function of X=f2p/f2 where the other parameters are known.
Theoretical and experimental sunrise mode conversion results at VLF
Authors: Pappert R. A. , Morfitt D. G.
Published: February 2008

Previously a mode conversion model was presented which allowed for both the vertical inhomogeneity and anisotropy of the ionosphere. Horizontal inhomogeneity along the direction of propagation was modeled by a slab approximation. The required height gain functions were determined by full‐wave solutions and their associated integrals evaluated numerically. In this paper results of a modified mode conversion model are compared with those of the original. In the modified model, height gain functions are discarded above some height h in the guide and are approximated below height h by Airy functions. Merits of the modified version are that a full‐wave program for height gains is not required, and that the associated integrals may be performed analytically. An obvious disadvantage is the free parameter h. The modified mode conversion model can be implemented with about the same ease as a WKB method and has one distinct advantage over the latter, namely, that mode numbering in any given slab is immaterial. Results of both mode conversion models are compared at several frequencies in the VLF band with experimental sunrise results obtained with a multifrequency oblique sounder system located on the island of Hawaii. In particular, comparisons are made with vertical field measurements in southern California. Approximate agreement is found. Discrepancies between modelling results and data are generally larger than the differences between the two mode conversion models.
The VLF complex permittivity of deep Antarctic ice measured in situ
Authors: Rogers James C. , Peden Irene C.
Published: February 2008

The results of the first in‐situ measurement at VLF of the complex permittivities of deep Antarctic ice are presented as functions of depth, projected along the vertical. Measurements made with an electrically short dipole probe at five frequencies to a depth of 1500 m below the ice surface are reported. Temperature is identified as a dominant factor affecting the ice permittivity. This fact, coupled with the measurements of complex permittivity to 1500 m depth, is used to estimate ice permittivities from 1500 m to the bottom of the ice sheet at 2164 m. Comparison of the in‐situ measurements with those of surface measurements is made; it is concluded that for the purpose of VLF antenna and propagation studies the Antarctic ice sheet cannot be considered to be an isotropic homogeneous material, but must be treated at least as a horizontally stratified medium whose dielectric and loss properties vary in the vertical direction with temperature.
Some early results from the ATS‐6 Radio Beacon Experiment
Authors: Davies K. , Fritz R. B. , Grubb R. N. , Jones J. E.
Published: February 2008

The multifrequency satellite radio beacon enables the measurement of the columnar electron content of the ionosphere and plasmasphere along the ray path and its spatial and temporal structure. Measurements include modulation phase, Faraday rotation, and amplitude. The characteristics of the beacon transmitter and its design are presented together with the design of the Boulder receiver and antennas and the calibration procedures. A shape factor F is defined which depends on the electron density and geomagnetic field distributions. It is found that F varies by about 30% from day to night. It is shown that the ratio of the plasmaspheric content to total content varies from about 0.08 during the day to about 0.35 at night. Other examples which are presented to illustrate the uses of the radio beacon include sunrise effects, solar flare enhancements of total content, and the ionospheric storms of early July 1974.
Dielectric coated wire antennas
Authors: Richmond J. H. , Newman E. H.
Published: February 2008

The problem considered is an electrically thin dielectric insulating shell on an antenna composed of electrically thin circular cylindrical wires. The solution is a moment method solution and the insulating shell is modeled by equivalent volume polarization currents. These polarization currents are related in a simple manner to the surface charge density on the wire antenna. In this way the insulating shell causes no new unknowns to be introduced, and the size of the impedance matrix is the same as for the uninsulated wires. The insulation is accounted for entirely through a modification of the symmetric impedance matrix. This modification influences the current distribution, impedance, efficiency, field patterns, and scattering properties. The theory will be compared with measurement for dielectric coated antennas in air.
Constraints affecting through‐the‐earth electromagnetic signalling and location techniques
Authors: Geyer Richard G. , Keller George V.
Published: February 2008

Over the past several years much effort has been expended in the development of through‐the‐earth communication links. The development of such links would improve the chances of survival following coal mine disasters by allowing miners to make their circumstances known to rescue teams. In order to implement effective electromagnetic communication links for signalling between mine workings and the surface, the electrical properties of the rock overlying mine workings and ambient background noise levels in several mining provinces are studied. The results of both CW and pulse field transmission tests show good agreement with theoretical considerations, and several techniques for locating either a buried finite line current source or a buried finite vertical‐axis loop are demonstrated. The effect of loop size on the latter location criteria is considered, as well as the relative merits of a pulse or CW system.
Theory relating to remote electromagnetic probing of a nonuniform‐thickness coal seam
Authors: Lytle R. Jeffrey , Lager Darrel L.
Published: February 2008

The effect of lateral inhomogeneities on electromagnetic remote probing of layered structures is considered. The excitation is taken to be an incident transverse electric (TE) plane wave. The fields, the surface admittance, and the wave tilt depend upon the angle of incidence, the distance from the air‐coal interface, the electrical contrast, and the layer profile (e.g., sinusoidal, step, and slant profiles). Both low‐ and high‐frequency cases are illustrated and compared with corresponding results having no lateral inhomogeneities. Results indicate that the surface admittance and the fields tangential to the surface are “good” indicators of the local structure, whereas the field normal to the surface and the wave tilt are not. However, the wave tilt and the field normal to the surface give good indication of subsurface anomalies. As the observation point is moved away from the air‐coal interface, the “information content” regarding the lateral inhomogeneities rapidly decreases. Thus, measurements performed on the surface, or measurements dependent upon the fields at the surface, e.g., reflection coefficients, are more sensitive to lateral inhomogeneities than measurements performed away from the surface.
Scattering and depolarization of microwaves by spheroidal raindrops
Authors: Warner C. , Hizal A.
Published: February 2008

With a view to calculating depolarization and differential attenuation of microwaves by rain, with allowance for the variable shape and orientation of raindrops, the theory of P. C. Waterman is applied to the calculation of cross sections and depolarization ratios of spheroids, and drops of the shapes determined by H. R. Pruppacher and R. L. Pitter. Use of Waterman's extended boundary condition facilitates computation. The scattering characteristics of spheroids appear similar in nature to those of spheres, in the regimes considered. Marked singularities in the characteristics of backscattering depolarization appear at optical size 1.5. The Pruppacher and Pitter drops scatter similarly to equivalent oblate spheroids. Implications for weather radar measurements are briefly discussed.
Radar measurements of the latitudinal variation of auroral ionization
Authors: Vondrak Richard R. , Baron Murray J.
Published: February 2008

The Chatanika, Alaska, incoherent scatter radar has been used to measure the spatial variation of auroral ionization. A two‐dimensional (altitude, latitude) cross‐sectional map of electron densities in the ionosphere is produced by scanning in the geomagnetic meridian plane. The altitude variation of ionization is used to infer the differential energy distribution of the incident auroral electrons. The latitudinal variation of this energy distribution and the total energy input are obtained by use of the meridian‐scanning technique. Examples are shown of observations made during an active aurora.
A model of the midlatitude nighttime E region including metallic ions
Authors: Harris R. D. , McGhan M.
Published: February 2008

The midlatitude nighttime E region was modeled with three ion species including a metallic ion species, Mg+. Time‐dependent ionization profiles, including diffusion, were calculated for five wind profiles measured over Wallops Island, Virginia, on 22 February 1968. Model‐generated profiles are compared with electron density measurements from the same night.
Observed temporal amplitude and phase spectra from ATS‐6 radio beacon experiment at 40, 140, and 360 MHz
Authors: Ott R. H.
Published: February 2008

A large selection of temporal amplitude and phase spectra for the ATS‐6 beacon experiment has been analyzed. Those time periods exhibiting relatively high scintillation show two scattering mechanisms in the amplitude spectra for different ranges of the scintillation frequency whereas those periods appearing quiet show a single scattering mechanism. Unlike the amplitude spectra, the phase spectra shows a single power‐law dependence with scintillation frequency that provides information on the full range of electron density fluctuations.
A refracting radio telescope
Authors: Bernhardt Paul , da Rosa A. V.
Published: February 2008

Observations of extraterrestrial radio sources at the lower end of the radio frequency spectrum are limited by reflection of waves from the topside ionosphere and by the large size of antenna apertures necessary for the realization of narrow beamwidths. The use of the ionosphere as a lens is considered. The lens is formed by the release of chemicals such as H2 and H2O at the F2‐layer peak. These chemicals promote dissociative recombination of O+ in the ionosphere resulting in a local reduction in plasma density. Gradients in electron density in the vicinity of the gas release tend to focus rays propagating through the depleted region. Preliminary calculations indicate that a lens capable of focusing cosmic radio waves in the 1 to 10 MHz frequency range may be produced by the release of 100 kg of H2 at the peak of the nighttime F layer. The beamwidth of a refracting radio telescope using this lens may be less than 1/5 degree.
Extraction of wave parameters from measured HF radar sea‐echo Doppler spectra
Authors: Barrick Donald E.
Published: February 2008

Computerized techniques for extracting rms wave height and dominant wave period from HF radar sea‐echo Doppler spectra are derived. Earlier theoretical models for first‐ and second‐order sea backscatter (derived elsewhere) are employed to obtain the simple, closed‐form inversion equations giving these two radar‐deduced quantities. The results are general in that no specific models for the radial or azimuthal form of the wave height directional spectrum need be assumed; the resulting formulas are only weakly dependent upon the radar/wind direction. Approximations made in the derivation are stated, and they are ultimately tested by comparing wave heights and periods extracted from the inversion model with the actual values input to the original equations for scatter. The derived relationships are then tested against some eighty hours of radar measurements taken at a variety of frequencies and buoy‐measured sea conditions. Theoretically predicted and empirically determined correction factors for wave height and period are in agreement. Finally, the measurements show that when sea wave height is greater than one twentieth of the radar wavelength, wave height extraction (rms) errors are less than 23%, and wave period extraction errors less than 12%.
The night and day relationships between polar cap riometer absorption and solar protons
Authors: Sellers Bach , Hanser Frederick A. , Stroscio Michael A. , Yates G. Kenneth
Published: February 2008

The relationship between riometer‐measured absorption of 30 MHz cosmic radio waves at Thule, Greenland, and the extramagnetospheric 1‐100 MeV solar proton event fluxes observed by satellite OV5‐6 during 1969–1972 is studied, with night and day conditions at Thule being separated. In the 70–90 km region in which most nighttime absorption occurs, ionization conditions are, in fact, relatively simple. This leads to a nighttime relationship between absorption and the square root of the integral proton flux, which is similar to that for daytime contlitions. Based on previously measured effective recombination coefficients, theoretically optimum energy thresholds are determined for use in this approximate relationship. The values are 2.2 MeV and 5.2 MeV for night and day conditions, respectively. Both the approximate absorption, and that calculated by a reformulation of the standard approach, compare satisfactorily with extensive riometer measurements at Thule. The approximate relationships are employed in a real‐time system that uses satellite proton data for prediction of radio wave (riometer) absorption.
Two‐dimensional maximum entropy reconstruction of radio brightness
Authors: Wernecke Stephen J.
Published: February 2008

This paper describes a procedure for maximum entropy reconstruction of two‐dimensional radio brightness maps from noisy interferometer measurements. The method defines a map that obeys the nonnegativity constraint and is, in a sense, the smoothest of all brightness distributions that agree with the visibility measurements within the errors of observation. This approach acknowledges the fact that signal‐to‐noise considerations have a strong influence on useful resolution; fine structure appears only to the extent justified by measurement accuracy. Iterative computing is needed to find the maximum entropy image. It is shown that the primary computational burden of maximum entropy reconstruction involves calculations that are efficiently performed by fast Fourier transform techniques. Different techniques are used depending on whether visibility data are irregularly distributed in the u,v plane or interpolated onto a rectangular lattice prior to reconstruction. The efficiency of the fast Fourier transform provides a tremendous computational advantage with the result that maximum entropy reconstruction on a moderately large grid (64×64) is practicable at reasonable cost. Several comparative examples are shown, and some of the limitations of the present theory of maximum entropy imaging are identified.
Cold plasma diagnostics using electromagnetic impulses
Authors: Gray K. G. , Bowhill S. A.
Published: February 2008

A diagnostic method is described in which the impulse response of a cold, lossy, magnetoplasma half space is used to infer the characteristic parameters of the plasma, namely, angular plasma frequency, electron collision frequency, and electron gyrofrequency. The method uses observations of measurable quantities from the early‐time portion of the impulse response. Using these quantities, plasma parameters can be obtained directly from a contour map. Numerical results are presented to illustrate the diagnostic technique.
HF excited instabilities in space plasmas
Authors: Carlson H. C. , Duncan L. M.
Published: February 2008

Radio waves delivering sufficiently strong electric field strengths to a plasma can excite parametric instabilities in the plasma for properly matched conditions. Technology had advanced by 1970 to the stage where this could be effected in the ionospheric plasma by ground‐based installations. High‐power HF transmitters, in the nominal 3–12 MHz range, deposited substantial energy in the ionospheric plasma, raising thermal plasma temperatures, exciting a rich spectrum of waves and irregularities in the plasma, and leading to extrathermal electron fluxes sensible to energies of the order of 10 eV. The results of experiments utilizing such controlled effects on the ionospheric plasma as diagnosed by remote sensors in a very broad RF band as well as in the optical band, have been followed with great interest by workers in fields as diverse as nuclear fusion, plasma physics, communications, and aeronomy from ionospheric thermal balance to spread‐F. Significant checks on and advances in relevant theory have already accrued, but much of the potential is yet untapped. Experiments of this nature can also be performed from space vehicles. These could not only supplement studies possible from ground‐based sites, but also permit some qualitative advances by virtue of the spacial trajectory and in situ nature unique to the vehicle. A number of specific features of the phenomena bear importantly on the practicality of such an experiment, including: instability rise times and decay times, irregularity scale sizes, power dependence, frequency spectra and implied physics, thermal plasma time constants, and field geometry dependences. The results of ground‐based “HF heating experiments,” particularly as diagnosed by incoherent scatter techniques, are reviewed with this in mind.
Whole‐body dosimetry of microwave radiation in small animals: The effect of body mass and exposure geometry
Authors: Kinn James B.
Published: February 2008

Whole‐body absorption of 2450‐MHz radiation was measured in rats that ranged from 6 to 440 grams and in mice that ranged from 30 to 50 grams. Simultaneous exposure of groups of animals in varying numbers and in various configurations were made under free‐field conditions in an electrically anechoic chamber. Measurements of whole‐body absorption were made with twin‐well calorimeters. The results indicate that, for animals within a given narrow range of body mass, individual rates of absorption may, at the extreme, vary by a factor of seven. One implication of this variability is that studies of dose‐response relations may be confounded unless power densities of incident radiation are sufficiently different to provide nonoverlapping dose rates. Comparisons of measured doses to predicted values as derived from a spherical shell model show considerable variations of observed from predicted values. Specific relationships of the SAR to the position and mass of the animals are presented.
A microwave exposure system for primates
Authors: Heynick Louis N. , Polson Peter , Karp Arthur
Published: February 2008

Development of a system for exposing nonhuman primates of sizes to and including stumptail macaques (Macaca arctoides) at 2.45 GHz for long periods without constraining the animals (except for cage confinement) is described. The exposure chamber is a multimode mode‐stirred cubical microwave cavity of edge length about 90 cm internally; within the cavity is a dielectric cage sufficiently large to house a 15‐kg primate. The cavity is excited by a Type 2M53 magnetron. Radiopaque windows are provided for viewing and ventilation. Forward and reflected powers are measured with calibrated diode detectors in a bidirectional coupler between the magnetron and the cavity. Power values are set by phase‐angle selection and are held constant by detector‐output feedback to a thyristor control circuit. Containers of saline were used as phantoms, i.e., as first approximations to the RF loads presented by monkeys. Calorimetric measurements were made to determine energy absorption values for various quantities and spatial distributions of saline. The results indicate that the dose rate at any given input power is insensitive to phantom location (indicative of isotropy) and is inversely related to the mass of saline within. After the development of the prototype, 12 units were constructed for concurrent chronic irradiation of two squirrel monkeys in each module. A summary is presented of calorimetric measurements on saline‐containing dolls serving as phantoms; these measurements were performed to determine net values of RF input power into a cavity unit that are thermally equivalent to specified power‐density values of plane‐wave irradiation for the same duration of exposure.
Oxygen‐consumption rate of mice under differing dose rates of microwave radiation
Authors: Ho Henry S. , Edwards William P.
Published: February 2008

Controversy exists over thermal versus nonthermal biological effects of microwave radiation. Rectal measurements of temperature, which are often used as indicators of thermal stress, may not be sufficiently reliable. In this investigation, the oxygen‐consumption rate was used as a biological indicator of thermal stress from microwave radiation. Male CFI mice were irradiated with 2450‐MHz CW microwave energy in a waveguide at forward power levels of 0 (sham), 0.09, 0.3, 0.6, 1.7, and 3.3 W, which resulted in corresponding averaged dose rates of 0, 1.6, 5.5, 10.4, 23.6, and 44.3 mW/g. The environmental conditions were: temperature 24 °C, relative humidity 55% and rate of air flow 78 ml/min. The rate of oxygen consumption of the mouse was determined for successive 5‐minute periods by means of a paramagnetic oxygen analyzer, before, during, and after irradiation. Each of the stages lasted for 30 minutes. Across time, there was a reduction of oxygen consumption which correlated with a reduction in the averaged rate of energy absorption. The rate of oxygen consumption also decreased across time when the dose rate did not exceed 10.4 mW/g. The mouse apparently compensates homeostatically for large doses of microwave radiation by adjusting its metabolic rate downward to compensate for thermal loading from the radiation. Rebound of metabolic activity occurred after irradiation.
Irradiation of rats by 918‐MHz microwaves at 2.5 mW/cm2: Delineating the dose‐response relationship
Authors: Lovely Richard H. , Myers David E. , Guy Arthur W.
Published: February 2008

Eight male rats were exposed for 13 weeks to 918‐MHz CW microwaves at an averaged power density of 2.5 mW/cm2. The rats were exposed ten hours every night for a total of 910 hours of irradiation. The exposure system consisted of (1) cylindrical waveguides that were capable of delivering guided, circularly polarized waves (TE11 mode); and (2) Plexiglas living chambers that provided standard laboratory conditions for the rodents. The waveguides allowed for easy quantification of incident and absorbed energy in each chamber independent of the number of rodents being simultaneously exposed. Daily measures of body mass and of intake of food and water revealed no significant differences between the eight irradiated and the eight sham‐irradiated controls. Blood sampled after 4, 8, and 12 weeks showed no differences in most parameters of serum chemistry (e.g., calcium, sodium, potassium, chlorine, blood urea nitrogen, carbon dioxide, ion gap and glucose). During the 11th week, serial assessments were made of colonic temperature and behavioral repertoire but neither demonstrated a significant effect of the microwave exposures. Serum corticosterone levels sampled after 910 hours of radiation gave no indication of stress. Finally, neither one‐ nor two‐bottle preference tests for a saccharin solution suggested the presence of radiation‐related malaise. The significance of these results is discussed with respect to comparable exposures of rats to 10 mW/cm2, which do influence several of the assessed parameters.