bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamo Currents, Winds, and Electric Fields
Authors: Matsushita S.
Published: February 2008

After a brief presentation of Sq and L electric current systems deduced from geomagnetic data, electric conductivities and wind models in the dynamo region are discussed. It is then shown that the solar negative‐mode thermal diurnal tide and the lunar semidiurnal gravitational tide having a phase shift with altitudes produce the best fit Sq and L current systems, respectively. Distributions of electrostatic fields are computed, and electromagnetic drift speeds in the ionospheric F region are also examined. These calculated values agree well with observed results.
Equatorial Anomaly During a Period of Declining Solar Activity
Authors: Rush C. M. , Rush S. V. , Lyons L. R. , Venkateswaran S. V.
Published: February 2008

This paper is an observational study of the equatorial anomaly during a period of declining solar activity. The anomaly is studied at two different longitudes, 75°W and 105°E. Data from both the topside and the bottomside of the F region are used. The topside data were obtained by the satellite Alouette 1. Seasonal and daily variations, longitude dependence, and geomagnetic storm‐time distortions of the anomaly are treated.
Empirical Studies of Atmospheric Structure and Spectra in the Free Atmosphere
Authors: Vinnichenko Nikolay K. , Dutton John A.
Published: February 2008

This review paper summarizes present knowledge about turbulence in the free atmosphere. Data from various sources allow the construction of an average spectrum of atmospheric motions which covers almost the entire range of periods from 1 second to 1 year. It is shown that the micrometeorological maximum, which probably exists in cases of moderate and severe CAT (clear air turbulence), is not separated from synoptic scale motions by a deep mesoscale gap. Theoretical considerations and observations in the laboratory, the ocean, and the free atmosphere suggest that CAT is a manifestation of the Kelvin‐Helmholtz instability. This implies that for better understanding of CAT, for forecasting, and for planning of air‐borne measurements, isentropic analysis of the meteorological situation is advisable. Sophisticated aircraft instrumentation is now beginning to yield data sufficiently accurate and detailed to make feasible the use of the powerful tool of energy budget analysis for CAT studies. Recent experiments in the atmosphere have not clarified the problem of the existence of the buoyant subrange and the corresponding behavior of the spectrum. Development of a high‐resolution vertical sounding technique permits the measurement of the spectra of the horizontal winds in the vertical direction, which may make possible the prediction of microturbulence features from vertical wind profile analysis. Temperature spectra in the free atmosphere are discussed, and the values of the temperature dissipation rate and of the structure function coefficient are calculated for CAT of several different intensities.
Turbulence Spectra in a Stably Stratified Boundary Layer
Authors: Plate Erich J. , Arya S. P.
Published: February 2008

Some experimental spectra of the v', w', and t' fluctuations in a stably stratified boundary layer are discussed that were obtained in the constant stress region of a laboratory boundary layer. It is shown that no buoyant subranges exist and that temperature‐fluctuation and velocity‐fluctuation spectra are roughly described at high frequencies by the universal laws of Kolmogoroff and Corrsin for the viscous subrange. Better agreement for the velocity spectra is found, however, by extending formally the k−1 law of Tschen and Gisina to higher wave numbers.
Mean Vertical Gradient of Potential Refractive Index in Turbulent Mixing and Radar Detection of CAT
Authors: Ottersten Hans
Published: February 2008

Radar backscattering from the turbulent clear atmosphere is determined by the small‐scale variability in the radio refractive index and is therefore related to the mean gradient of potential refractive index and to the degree of turbulence. Consequently, the mean gradient of potential refractve index is considered in works concerned with radar detection of CAT (clear air turbulence). This note clarifies the role of potential quantities and their vertical gradients in quantitative discussions of the generation of small‐scale atmospheric inhomogeneities by turbulent mixing. If potential quantities are referred to a standard pressure of 1000 mb, as is common, the mean vertical gradient of potential refractive index cannot be used directly to evaluate the small‐scale refractive‐index variability resulting from adiabatic mixing. It is convenient to define a generalized potential refractive index, and a generalized potential temperature as potential quantities referred to the mean pressure at the level under consideration. The refractive‐index inhomogeneities produced by turbulent mixing are directly related to the mean vertical gradient of generalized potential refractive index (generalized potential temperature if specific humidity is negligible). The terminology already adopted in several works on radar detection of CAT is preserved if it is emphasized that the potential quantities employed are generalized. Errors of several decibels may result if the ordinary potential quantities referred to 1000 mb are used mistakenly to determine the smale‐scale refractive‐index variability.
On Resonant Interactions of Acoustic Gravity Waves
Authors: Yeh K. C. , Liu C. H.
Published: February 2008

The method of averaging in the study of nonlinear oscillations is applied to the problem of resonant wave‐wave interaction of a nonlinear dispersive wave system. The simplicity and directness of the method make it possible to study rather general and complex systems. Two examples are treated, one is posed as an initial value problem and the other as a boundary value problem. The second example deals with the acoustic‐gravity wave system in the atmosphere. It is found that resonant condition can be satisfied for the three‐wave system for which one of the waves is the zero frequency gravity wave. Through resonant interaction, the other two waves become trapped. The trapping depth is plotted for typical atmospheric parameters.
Numerical Computations of Terrestrial ELF Electromagnetic Wave Fields in the Frequency Domain
Authors: Jones D. Llanwyn
Published: February 2008

The zero‐order term of the residue series has been employed to calculate the variation of field strength with distance over the earth's surface in the frequency band 7.8 Hz to 1 kHz. Spherical symmetry is assumed for the earth and ionosphere. The ionosphere is taken to be isotropic, but radial inhomogeneity is allowed. A vertical electric dipole source and a realistic propagation‐constant model were assumed. The computations indicate the accuracy of the usual approximations to the residue series and enable the magnitude of the standing wave effects in the earth‐ionosphere cavity to be assessed.
Total Electron Content Studies in Equatorial Regions
Authors: Hunter A. N.
Published: February 2008

This paper reviews current knowledge of the diurnal variation and spatial distribution of total electron content in the equatorial ionosphere. The problems of data reduction peculiar to stations near the equator are considered. There is a large diurnal variation up to 40∶1 that is greatest at the equinoxes and least in local winter. An ‘equatorial anomaly’ in total electron content similar to the anomaly observed in f0F2 exists and is largely associated with the topside. Considerable differences in detail, particularly with regard to the time of disappearance of the anomaly, occur at different longitudes. Peaks of ionization have been observed around 2300 LT at about 26° of magnetic dip. Although little correlation has been found with magnetic activity on individual days, collective data indicate a reduction in the depth of the equatorial trough with magnetic disturbances, with the maxima occurring closer to the dip equator. More detailed work is indicated on the effects of longitude and magnetic activity, on the nighttime content, and on large‐scale irregularities.
Impedance of a Short Dipole Antenna in a Warm Isotropic Plasma
Authors: Schiff M. L.
Published: February 2008

The impedance of a short dipole antenna with a finite radius is considered using the Vlasov theory of the plasma rather than the simpler hydrodynamic theory. Analytic and numerical computations are presented for the longitudinal portion of the impedance. The results of this paper are compared with similar calculations for spherical antennas and filamental dipole antennas.
High‐Frequency Hall Current Instability
Authors: Lee K. , Kennel C. F. , Kindel J. M.
Published: February 2008

In a partially ionized gas, if electrons and ions have a relative drift Vd perpendicular to a static B field, Farley and Buneman have shown that an electrostatic wave with propagation vector K perpendicular to B and wavelength λ ≥ 0.375 meter will be unstable if K·Vd/Kexceeds the ion thermal speed. We have extended Farley's calculation for K perpendicular to B by the following procedure. First, we examine modes of higher frequencies and shorter wavelengths. Second, we retain the term K2λDE2 (λDE is the electron Debye length), since this term cannot be neglected for short wavelength modes. This makes the dispersion relation density dependent. Third, we obtain plots of growth rate versus frequency for various values of K· Vd/K. With the use of the Culler‐Fried on‐line computer system, the dispersion relation has been solved numerically by contour integration. There are four results of the numerical calculation. First, there is an electron density threshold for excitation of higher frequency modes. Second, for a fixed electron density of 3.5 × 105/cm3, the fastest growing mode shifts to higher frequency as K·Vd/K increases. For K·Vd/K equal to three times the ion thermal speed, 3al, the fastest growing mode oscillates at ωr ≃ 0.7(ΩEΩl)½, where ΩE and Ωl are electron and ion cyclotron frequencies. The frequency ωr is far above those calculated by Farley. Third, the same behavior cited above is also exhibited for fixed K·Vd/K but increasing electron density. Fourth, modes with oscillating frequency ωr ≃ (ΩEΩl)½ can be excited for K·Vd/K ≥ 2.3al and current density greater than 1.0 × 10−5 amp/m2. These are reasonable values for the equatorial electrojet and the auroral electrojet in the ionosphere during disturbed times.
The Formation by Electric Fields of Field‐Aligned Irregularities in the Magnetosphere
Authors: Park C. G. , Helliwell R. A.
Published: February 2008

A possible mechanism for the formation of electron density irregularities in the magnetosphere is examined quantitatively. The mechanism involves localized E × B convection cells in which tubes of ionization with different total content are mixed. Under reasonable initial conditions, it is shown that a 0.1‐mv/m electric field in the equatorial plane can produce electron density enhancements and depressions of the order of 5% at L = 4 in about one‐half hour. These enhancements are large enough to trap whistler waves, whereas the depressions can trap HF waves. It is also shown that small‐scale density irregularities can be produced by a much larger scale electric field. It is suggested that thundercloud electricity may be a possible source of the electric field responsible for the irregularities.
Observation of F Region Vertical Velocities at Millstone Hill, 1, Evidence for Drifts Due to Expansion, Contraction, and Winds
Authors: Evans J. V.
Published: February 2008

The theory for the drift of ions in the F region is briefly reviewed, and it is shown that, for the restricted case of no external electric fields or neutral air motion, the velocity of the ions along the magnetic field lines in the upper part of the F2 region can be derived from the continuity equation. Experimental results for the electron density, electron and ion temperatures, and O+ vertical velocity obtained by the incoherent (Thomson) scatter technique at Millstone Hill are presented for two 24‐hour periods taken a year apart in March 1969 and 1970. The largest vertical velocities encountered occur around sunrise and sunset and give rise to vertical fluxes of the order of 5 × 108 ions/cm2/sec through 600‐km altitude. It is shown that these fluxes are a result primarily of the growth or decay of the layer, though in the case of sunset the thermal contraction resulting from the decrease in the electron temperature with time assists in establishing the observed fluxes. The vertical velocity observed near 300 km is compared with the expected ambipolar diffusion velocity that should result from the observed pressure gradients in the plasma and from acceleration due to gravity. The difference between the observed and computed velocities is attributed to thermospheric neutral winds which have diurnal behavior similar to those determined by Vasseur (1969a, b) from incoherent scatter observations in France.
Observed and Predicted VLF Phase Behavior for the Solar Eclipses of September 11, 1969, and March 7, 1970
Authors: Noonkester V. R. , Sailors D. B.
Published: February 2008

A VLF propagation and a D‐region aeronomy model have been used to predict the effect of two solar eclipses on VLF propagation to Aztec, Arizona. Transmissions at 12.2 kHz from Hawaii were monitored during the eclipse on September 11, 1969; and transmissions at 12.0 kHz from Trinidad, at 24 kHz from transmitter NBA, at 12.5 kHz from Forestport, New York, and at 17.8 kHz from transmitter NAA were monitored during the eclipse on March 7, 1970. The VLF phase predictions were found to agree with measurements except for the two nearly coincident northerly paths from Forestport and NAA.
Ground Backscatter Observed With High Resolution Oblique Sounders
Authors: Basler Roy P. , Scott Thomas D.
Published: February 2008

The amplitude of ground backscatter at high frequency (HF) recorded with oblique sounding equipment that utilizes azimuthal antenna beamwidths of about 6° and effective pulse lengths of about 50 μsec is characterized by sharp spikes that rise 10 to 20 db above the diffuse background clutter and have a range extent as short as the pulse length. These spikes suggest that the backscattering efficiency of the ground is highly nonuniform as a result of the occasional presence of a localized surface feature with a backscatter cross section one or two orders of magnitude larger than any object in the surrounding countryside. When short‐pulse ground backscatter echoes are displayed as intensity modulated range versus azimuth records, these sharp spikes produce discrete echoes with an azimuthal extent approximately equal to the effective beamwidth of the antenna. The sources of many of these discrete echoes have been identified with specific topographic and geographic features, including cities and mountains in the western United States and islands in the Caribbean Sea.
The Structure of Sporadic E From a Radio Experiment
Authors: Whitehead J. D.
Published: February 2008

An ionosonde has been used to measure the ordinary and extraordinary critical and blanketing frequencies separately. While the results support the idea that transparent sporadic‐E reflections occur from small volumes within the E region, it is likely that the plasma density even in these volumes is often less than that required to cause total reflection. The structure of sporadic E is probably as follows: The peak plasma frequency varies by roughly equal amounts above and below a mean value often by a megahertz or so, within a few kilometers. Some intense blobs cause total reflection; other small volumes of increased plasma frequency strongly scatter radio waves of somewhat greater frequency.
The Integral Equation and Boundary Conditions for a Cylindrical Antenna in a Warm Plasma
Authors: Preis Douglas H.
Published: February 2008

The linearized, continuum fluid‐dynamical equations for a warm, collisional electron plasma with independent source terms are presented, and their applicability to boundary‐value problems is discussed. Boundary conditions are developed for a perfectly conducting cylindrical antenna immersed in the warm collisional plasma and excited by a delta‐function generator. An integral equation relating the antenna surface current and charge is derived based upon all the conventional boundary conditions and the requirement that proper continuity be maintained between the antenna and the plasma. The deficiency of other integral formulations, including the grid‐type dipole, is discussed.
The triaxial‐accelerometer system on Atmosphere Explorer
Authors: Champion K. S. W. , Marcos F. A.
Published: February 2008

A triaxial‐accelerometer system will be included in each of the Atmosphere Explorer (AE) payloads. The instrument consists of three uniaxial miniature‐electrostatic‐accelerometer units mounted mutually at right angles. This paper provides a description of the accelerometer system being designed for AE. It includes the principles of the instrument operation, the measurement capabilities, and the relation between the measured data and the scientific and engineering results. The functions of the instrument are to determine the density of the neutral atmosphere, monitor the thrust of the orbit‐adjust propulsion system, determine the satellite minimum altitude, measure spacecraft roll, and provide some attitude‐sensing information. Measurements will be made four times per second or approximately once every 2 km of flight path. Density variations will be determined with an accuracy ranging from approximately 1% below 200 km to 10% at 350 km, not including any error in ephemeris or drag coefficient.
Atmosphere Explorer pressure measurements: Ion gauge and capacitance manometer
Authors: Rice C. J. , Carter V. L. , LaValle S. R. , Chater W. T. , Jones D. A. , King C. G. , Nelson D. F.
Published: February 2008

Absolute pressure measurements are made by two instruments aboard Atmosphere Explorer (AE) : a cold‐cathode ion gauge and a capacitance manometer. The dual sensors feature coverage from 120 to 370 km with double coverage below 200 km, differing and complementary sensing techniques, usable output in the spinning and both normal and inverted despun satellite modes, simple formatting to facilitate data use for real‐time monitoring of spacecraft operation, and cross‐calibration in the laboratory and in space.
Ionospheric structure from oblique‐backscatter soundings
Authors: Basler Roy P. , Scott Thomas D.
Published: February 2008

Oblique ionograms are made monostatically by using an HF sounder to record the delay times of echoes from known ground targets as a function of operating frequency. Cooperative sources, such as repeaters, or distinctive terrain features, such as cities, serve effectively as known ground targets. An analytic method is developed to transform oblique‐backscatter ionograms into the h'‐f curves recorded by conventional ionosondes at vertical incidence, from which ionospheric electron‐density profiles can be derived. The validity of the transformation technique is demonstrated by comparing h'‐f data recorded simultaneously at oblique incidence and at vertical incidence near the midpoint of the oblique path.
Far‐field, extremely‐low‐frequency propagation measurements, 14 March to 9 April 1971
Authors: Bannister Peter R. , Wolkoff Edwin A. , Katan J. Robert , Williams Frederick J.
Published: February 2008

From 14 March through 9 April 1971, the New London Laboratory of the Naval Underwater Systems Center conducted a far‐field, extremely‐low‐frequency (ELF) attenuation‐constant measurement test. Two sites located along the same great‐circle path were utilized. One site (3.9 Mm) was in St. John Island, Virgin Islands; the other (1.7 Mm) was near Swansboro, North Carolina. The horizontal magnetic‐field strengths were measured at a band of frequencies centered at 45 Hz and at 75 Hz to determine the attenuation rates for daytime and nighttime propagation conditions. The EW antenna of the US Navy ELF Wisconsin Test Facility, Clam Lake, Wisconsin, was the transmission source. The principal results obtained from these measurements were that (a) the daytime attenuation rate is higher than the nighttime rate at both 45 and 75 Hz and (b) the ionospheric excitation factors are quite different for daytime and nighttime propagation conditions. A comparison of these results with the data taken previously and concurrently shows excellent agreement.
Active experiments, magnetospheric modification, and a naturally occurring analogue
Authors: Kivelson Margaret G. , Russell C. T.
Published: February 2008

Active experiments in the magnetosphere include some intended to be primarily diagnostic (barium release, electron guns) and others designed to perturb the system to generate instabilities (VLF or ULF wave injection from ground stations, ionospheric heating). Recently, a scheme has been proposed which would modify the magnetosphere by injecting plasma near the equator beyond the plasmapause and initiating wave‐particle instabilities. The expected effects have been examined theoretically. Injection of plasma into this region is also a naturally occurring phenomenon produced by the cross‐tail electric fields which are associated with geomagnetic activity. For further investigation of magnetospheric instabilities, the advantages of examining artificially injected plasma (control of time and location of injection and of the volume of plasma injected) contrast with the advantages of studying natural enhancements (no extra payload, frequent occurrence). Thus, the two types of experiments are complementary. In preliminary studies of natural plasma enhancements both ULF and ELF emissions have been observed. The ELF noise is consistent with generation by the electron cyclotron instability.
Simultaneous measurement of ion and neutral motions by radar and optical techniques
Authors: Nagy A. F. , Cicerone R. J. , Hays P. B. , McWatters K. D. , Meriwether J. W. , Belon A. E. , Rino C. L.
Published: February 2008

The results of simultaneous thermospheric neutral wind and ionization drift measurements from near College, Alaska (L = 5.6, Λ = 65°) are presented. The neutral wind data were obtained by observing the Doppler shift of the 6300 Å atomic oxygen line with the 15‐cm Fabry‐Perot interferometer of the Michigan Airglow Observatory which is located temporarily at Ester Dome, Alaska. Ionization drifts were measured by the Chatanika incoherent scatter radar facility. These simultaneous measurements indicate that in the premidnight sector both the neutral wind and the ionization drift are generally westward. This westward ionization drift is consistent with the general magnetospheric convection pattern but the measured neutral wind is in a direction opposite to the diurnal pressure gradients and thus must be driven by ion drag. In the postmidnight sector the ionization drift turns eastward while the neutral wind direction turns south. Again, the ion drift is consistent with previously published results; the reasons for the absence of significant zonal neutral winds and the significant southward meridional wind in the postmidnight sector are not well understood at this time, but are probably a combination of a decrease in the ion drag force following magnetic midnight, Coriolis force, and pressure gradients due to both the diurnal and auroral heat sources.
Generation of ULF by a horizontal electric dipole
Authors: Greifinger Carl , Greifinger Phyllis
Published: February 2008

A horizontal electric dipole antenna at the ground operating at ULF can excite hydromagnetic TE waves in the hydromagnetic waveguide centered at the F2 ionization maximum. Propagation in the waveguide accompanied by leakage into the earth‐ionosphere cavity provides a mechanism by which magnetic fluctuations may be transmitted to ground receivers some thousands of kilometers from the transmitter. At ULF, the optimum direction for this mode of operation is broadside to the dipole. Under favorable ionospheric conditions, a dipole 30 km in length and driven at a peak current of 500 amp could produce a ground signal of the order of a milligamma at a distance of 2000 km.
The relative daily variability of f0F2 and hmF2 and their implications for HF radio propagation
Authors: Rush C. M. , Miller D. , Gibbs J.
Published: February 2008

The effect of the daily variability of f0F2 and hmF2 on the propagation conditions of an HF communication circuit has been studied in an empirical manner. The daily variability of f0F2 and hmF2 was determined by a detailed statistical analysis and the results were incorporated into a three‐dimensional ionospheric model and ray‐tracing program. During hours surrounding local noon, the relative day‐to‐day changes seen in both f0F2 and hmF2 are comparable while at all other times the daily variability of f0F2 substantially exceeds that of hmF2. In terms of HF propagation changes resulting from these changes in f0F2 and hmF2, it can be concluded that a knowledge of the critical frequency of the F2 region is much more important than that of hmF2 if account must be taken of the propagation changes resulting from the normal daily variability of the F2 region.
The Platteville high power facility
Authors: Carroll J. C. , Violette E. J. , Utlaut W. F.
Published: February 2008

The Department of Commerce's Platteville transmitter facility has been used to modify the ionosphere since 1970. Design concepts and a description of major components at the facility are discussed. When used for ionospheric modification studies, one of two 10‐element ring‐array antennas, each producing right‐ or left‐handed circularly polarized signals, is excited by a transmitter which develops up to 2 Mw of average power. These arrays permit operation in the frequency range from 2.7 to 10 MHz, as required to approximately match varying ionospheric critical frequencies.
A theoretical study of the ionospheric scintillation behavior caused by multiple scattering
Authors: Yeh K. C. , Liu C. H. , Youakim M. Y.
Published: February 2008

We investigate in this paper the behavior of transionospheric radio signals in the presence of irregularities with a power‐law spectrum. The roles played by multiple scattering and irregularity selection through the Fresnel filtering effect are delineated. The effect of competition between these two processes on the scintillation index and on the transverse correlation is discussed.
Ion effects on ionospheric electron resonance phenomena
Authors: Benson Robert F.
Published: February 2008

Ion effects are often observed on topside‐sounder‐stimulated electron plasma wave phenomena. A commonly observed effect is a spur, appearing after a time delay corresponding to the proton gyroperiod, attached to the low frequency side of an electron plasma resonance. The spurs are often observed on the resonances at the electron plasma frequency, fN, the harmonics nfH of the electron cyclotron frequency fH (n = 2, 3, 4, ···), and occasionally on the upper hybrid frequency (fN2 + fH2)1/2. The spurs on the fN resonance are usually quite small unless the fN resonance overlaps with an nfH resonance; very large spurs are observed during such overlap conditions. Proton spurs are only observed on the nfH resonances when the electron plasma waves associated with these resonances are susceptible to the Harris instability and when the electromagnetic z wave can be initiated by the sounder pulse. This instability is the result of a sounder‐stimulated anisotropic electron velocity distribution. The observations suggest that energy is fed into the nfH longitudinal plasma wave from the z wave by means of wave‐mode coupling.
Diffracted field computations by a series expansion
Authors: Inada Hitoshi
Published: February 2008

The possibility of a series expansion for the diffracted fields by a dielectric sphere or circular cylinder is considered by first expanding the Mie scattering coefficients into a geometric series (Debye expansion), and then applying a modified Watson transformation to each term of the series. The diffracted fields can then be obtained by finding poles of the Debye expansion, and evaluating the residues. The locations of the poles due to the Debye expansion as well as the Mie scattering coefficients themselves are discussed. Numerical values of the poles are tabulated. The diffracted field contributions associated with the first five terms of the Debye expansion are presented in the form of a radar scattering cross section. The geometrical optics contribution arising from each term of the Debye expansion is asymptotically evaluated. To compare the magnitude of a sum of the geometrical optics and diffracted field contributions, the radar scattering cross section of the total backscattered field, obtained from the exact Mie theory, is also plotted.
Scattering by a dielectric‐loaded slit in a conducting plane
Authors: Hurd R. A. , Sachdeva B. K.
Published: February 2008

A low frequency solution to the diffraction problem of an E‐polarized plane wave incident on a dielectric‐loaded slit in a perfectly conducting plane is obtained. The dielectric loading consists of a circular cylinder just filling the slit and concentric with the slit center. The method used is a significant improvement over the traditional pseudo‐power‐series method of solution. Thus, when the dielectric is absent, our values differ by less than 2.1% from the exact Mathieu function solution at ka = 2.4, a being the half width of the slit. The gap between the high and low frequency solutions has therefore been bridged. When a dielectric is present, the limit ka = 2.4 will be multiplied by 1/∈1/21. It is found that the transmission usually increases with the dielectric constant. Some curves are given to illustrate the effects.
Radio measurements of oceanic winds at long ranges: An evaluation
Authors: Stewart Robert H. , Barnum James R.
Published: February 2008

Oceanic winds were measured locally by anemometers and remotely by an HF skywave radar at ranges exceeding 3000 km. Wind velocity was deduced from sea backscatter Doppler spectra. These spectra were often perturbed by ionospheric motion, yet wind direction was measured to within ±16° and wind speed to within ±4 m sec−1. Better measures of wind speed should exist at shorter ranges or with better ionospheric conditions.
Satellite microwave observations of the Utah Great Salt Lake Desert
Authors: Ulaby Fawwaz T. , Dellwig Louis F. , Schmugge Thomas
Published: February 2008

Microwave data acquired over the Great Salt Lake Desert area by sensors aboard Skylab and Nimbus 5 indicate that the microwave emission and backscatter were strongly influenced by contributions from subsurface layers of sediment saturated with brine. This phenomenon was observedby Skylab's S‐194 radiometer operating at 1.4 GHz, S‐193 RADSCAT (Radiometer‐Scatterometer) operating at 13.9 GHz, and the Nimbus 5 ESMR (Electrically Scanning Microwave Radiometer) operating at 19.35 GHz. The availability of ESMR data over an 18‐month period allowed an investigation of temporal variations.
A simple way of solving transient thin‐wire problems
Authors: Marin Lennart , Liu Tom K.
Published: February 2008

A simple way of calculating the transient response of a thin wire is presented. The method is based on (i) the asymptotic antenna theory for thin wires and (ii) an expansion of the induced current in terms of the so‐called natural modes. An explicit series representation of the transient induced current in terms of the resonances of the wire is obtained and this representation is used to numerically evaluate the wire current using a desk calculator. A comparison is made between the results obtained using the asymptotic theory presented here and those obtained from a numerical solution of a space‐time integral equation. Good agreement between the results is found except for early times. The method points to a fast way of estimating the transient induced currents on more complicated structures such as a wire model of an aircraft.
Propagation of low and medium frequency radio waves in a coal seam
Authors: Emslie Alfred G. , Lagace Robert L.
Published: February 2008

A theoretical model has been developed to explain the unexpectedly long communication ranges of over 300 m obtained, and the marked polarization effects observed, during recent radio transmission measurements in a conductor‐free area in a coal mine at frequencies in the range of 57.5 to 920 kHz. The model is based on a dipolar cylindrical TEM mode of propagation, with E vertical and H horizontal, in a low‐conductivity horizontal coal seam bounded by high‐conductivity rock. The best overall fit to the experimental data over the frequency range 57.5 to 920 kHz is found for coal and rock conductivities of 1.4 × 10−4 mho/m and 1.0 mho/m, respectively, for an assumed coal dielectric constant of 7. A better fit to the data at 57.5 kHz can be obtained if, in the model, the conductivity of the surrounding rock is allowed to be high for only a short distance above and below the coal seam and of a substantially lower value elsewhere. If the coal conductivity is changed from 1.4 × 10−4 mho/m, which is near the lower end of the range of expected values for bituminous coals, to 1.0 × 10−2 mho/m, which is near the upper bound of values for such coals, the attenuation is markedly increased with corresponding reductions in communication range.
A very‐long‐baseline interferometer system for geodetic applications
Authors: Whitney A. R. , Rogers A. E. E. , Hinteregger H. F. , Knight C. A. , Levine J. I. , Lippincott S. , Clark T. A. , Shapiro I. I. , Robertson D. S.
Published: February 2008

A very‐long‐baseline interferometer system was designed and built for geodetic applications. Each interferometer terminal records a 360‐kHz spectral band of noise from a compact extragalactic radio source. The center frequency of the spectral band can be selected to sample sequentially bands covering a much wider frequency range to obtain subnanosecond accuracy in group‐delay measurements. A tunnel‐diode pulse generator is used to calibrate the delays in the receiver. The necessary sets of algorithms and computer programs have been developed to analyze the data and have allowed the system to be employed to make accurate determinations of vector baselines, radio‐source positions, polar motion, and universal time.
On the sheath surrounding a conductor emitting photoelectrons in an isotropic collisionless plasma
Authors: Lafon Jean‐Pierre J.
Published: February 2008

The structure of the sheath surrounding a cylindrical or spherical body immersed in an isotropic collisionless plasma is investigated for a wide range of parameters corresponding to regions in space where the electron photoemission by the surface can produce small, strong, or even dominant effects (in this last case, the photoemission is also assumed to have cylindrical or spherical symmetry). The collected currents are also considered.
Slots in a parallel plate waveguide
Authors: Quintenz J. P. , Dudley D. G.
Published: February 2008

The problem of one or more infinite transverse slots in a parallel plate waveguide wall is considered. An integral equation is derived for the aperture electric field for the TMz case. The integral equation is solved by the method of moments. Steady state results are presented for the case where the exciting field is a TEM mode in the waveguide. Both transient and steady state results are presented for the case where the exciting field is a plane wave incident from outside the guide.
An experiment to measure variations in nighttime E‐region neutral concentration
Authors: Cogger L. L. , Carlson H. C.
Published: February 2008

The entire thermosphere responds strongly to changes in the composition and relative number density of the upper atmosphere near 100 km. However, the atmosphere at altitudes near 100 km is difficult to probe experimentally, and complex to treat theoretically. Time‐continuous incoherent scatter daytime observations of profiles of ion‐neutral collision frequencies υin (providing net neutral concentration) and neutral temperatures Tn have significantly extended our knowledge of this region over the past few years, but low signal strengths have to date precluded application of that technique to the nighttime period. Here, an experimental procedure is demonstrated which holds serious potential for the nighttime measurement of υin by combining incoherent scatter data with appropriate photometric measurements. Data illustrating the technique are applied to comparing, near 100 km, relative variations in atomic oxygen concentrations n (O) (from the E‐region component of the OI 5577 Å emission) to those in υin or net neutral concentration (from combined incoherent scatter data and Tn extracted from Fabry‐Perot measurement of the OI 5577 Å spectral line profile). For the data presented, the independently determined variations in these two concentrations vary in close proportion to one another, supporting the validity of studying the dynamical behavior of the atmosphere near 100 km by analyzing the temporal variation of the 5577 Å E‐region airglow.
Generation of artificial spread‐F by a collisionally coupled purely growing parametric instability
Authors: Cragin B. L. , Fejer J. A. , Leer E.
Published: February 2008

The threshold and growth rate of conventional stimulated Brillouin scattering are first calculated for a uniform magnetoplasma. Approximate calculations of the threshold and growth rate are then carried out for a new instability which could be termed thermally stimulated Brillouin scattering; in this instability the nonlinear Lorentz force (ponderomotive force) is replaced by a pressure force due to differential heating in the interference pattern of the pump wave and the generated electromagnetic wave. The threshold for this new instability in a uniform medium is much lower than for conventional Brillouin scattering if the low‐frequency wavelength measured along the magnetic field is much longer than the electron mean free path. The threshold is then calculated for the purely growing version of the new instability numerically, taking both the inhomogeneity of the medium and the effect of the geomagnetic field on wave propagation into account. The growth rate is also calculated and it is concluded that this new instability is probably responsible for the generation of large‐scale field‐aligned irregularities associated with artificial spread‐F produced by ionospheric heating.
Optically activated switch/modulator using a photoconductor and two channel waveguides
Authors: Goldberg Lew , Lee Sing H.
Published: February 2008

An optically activated switch was fabricated on LiNbO3 substrate by deposition of photoconductor‐metal electrode structure on two channel waveguides obtained by the outdiffusion process. One waveguide was overcoated with a CdS film, and served as a light detector which converted the optical signal in that waveguide into an electrical signal. Utilizing the electrooptic effect, this electrical signal modulated the light propagating in the second waveguide by changing the refractive index, and the cutoff condition, of the waveguiding channel between two metal electrodes. (The second waveguide and associated electrodes constituted an electrically activated electrooptic modulator.) The waveguides in the optically controlled switch can be either single or multimode. The length of the device can be short in comparison with other switching schemes. When binary optical signals are applied to the two waveguides, the switch can perform logic AND, NEGATION, OR and pseudo‐amplification operations.
Radiation from a circular bend between two discontinuities in surface waveguiding structures
Authors: Maley S. W.
Published: February 2008

Surface waveguides radiate energy at bends. The asymptotic problem of solving for the radiated power and the radiation pattern for large radius of bend has been studied theoretically for the slab waveguide and for the circular cylindrical waveguide. The slab configuration consists of two semi‐infinite slabs joined by a circular bend. The cylindrical configuration consists of two straight circular cylinders joined by a circular bend. The results indicate that the discontinuities at the transitions between the straight sections and the bend cause the radiation to differ significantly from the radiation of a bend of the same size but being part of a uniform circular structure rather than being joined to two straight sections. The radiated power for both the slab and circular cylinder configurations is found to vary inversely as the square of the radius of curvature, and the radiation pattern is composed of many closely spaced narrow lobes. As the radius of curvature of the bend increases, the lobes become more numerous and more closely spaced.
Classification of hybrid modes in cylindrical dielectric optical waveguides
Authors: Safaai‐Jazi A. , Yip G. L.
Published: February 2008

The classification of hybrid modes in cylindrical dielectric waveguides consisting of two or three layers is studied. A new mode designation based upon the separation of the characteristic equation is introduced. That is, separate characteristic equations for HEnm and EHnm modes are derived. This new scheme covers dielectric rods, dielectric tubes, cladded optical fibers and any three‐layer structure in general. It is analytically shown that no crossover exists between HE and EH modes with the same order of azimuthal variation (n).
Inhibition of tumor growth in mice by microwave hyperthermia, Streptolysin S and Colcemide
Authors: Szmigielski Stanislaw , Pulverer Gerhard , Hryniewicz Waleria , Janiak Marek
Published: February 2008

Mice with transplanted Sarcoma 180 were irradiated 2 hours daily; 1st through 14th day after transplantation with 3‐GHz microwaves at a power density of 40 mW/cm2. The irradiation resulted in an increase of rectal temperature by 3 to 4 °C. Some animals that were exposed to radiation received daily an IP injection of 1 mg/kg of Colcemide (synthetic Colchicine) or of 0.5 mG/kg of purified Streptolysin S or of both compounds. On the 14th day after transplantation half of each group of mice received 1 μCi/g IP 3H‐thymidine; the other halves 3H‐uridine, 1 μCi/g IP. Three hours later all of the mice were killed; the tumors were dissected, then measured for mass and radioactivity. Mean tumor mass, number of regressed tumors and averaged counts of radioactivity were calculated for each group. Microwave hyperthermia resulted in reduction of tumor mass by about 40%; the reduction was enhanced when microwave hyperthermia was combined with Colcemide and/or Streptolysin S. In the combined treatment with all three factors the tumor mass was reduced by about 70%. Inhibition of the tumor's growth was accompanied by reduced uptake of 3H‐thymidine and 3H‐uridine into the tumorous tissues.
Characteristics of microwave‐induced cochlear microphonics
Authors: Chou Chung‐Kwang , Guy Arthur William , Galambos Robert
Published: February 2008

Cochlear microphonics (CM) have been recorded from guinea pigs and from cats of differing body mass during irradiation by 918‐ and by 2450‐MHz pulsed microwaves. Both horn applicators and a cylindrical waveguide exposure system were used to radiate the animals. The CM frequency and duration were similar irrespective of carrier frequency and mode of application. Parameters of the CM (except amplitude) were not influenced by orientation of the body axis to the electrical field or by pulse width of microwaves for pulses less than 30 μsec wide. The frequency of the CM correlated well with the longest dimension of the brain cavity and poorly with several dimensions of the head. Extrapolations of these animal findings to the human being indicates that the frequency of the microwave‐induced CM in man should be between 7 and 10 kHz.
Auditory and visual sensations stimulated by low‐frequency electric currents
Authors: Adrian Donald J.
Published: February 2008

Auditory (electrophonic) and visual (phosphene) sensations were generated in human subjects through direct stimulation by low‐frequency electric currents. The effects occurred at frequencies in and near the ELF (extremely low frequency) communication band. Frequency‐response characteristics for both effects were measured. Both sensory modalities were found to behave much like frequency‐selective filters but with a number of important nonlinearities. The minimum thresholds of current for the phosphene and auditory effects occur, respectively, at 18 to 22 Hz and 60 to 90 Hz. The effects were also generated by the application of two simultaneous sine waves well above the cutoff frequency when the difference frequency was near the minimum threshold. Habituation of the phosphene and of the auditory response was noted. These effects and difference‐frequency effects received emphasis because of potential implications for the understanding of sensory processes. Potential diagnostic and therapeutic applications are described.
Fixed interval behavior of rats exposed to microwaves at low power densities
Authors: Sanza James N. , de Lorge John
Published: February 2008

Behavioral effects of 2.45‐GHz microwaves (100% amplitude modulated at 120 Hz) were studied at averaged power densities of 8.8, 18.4 and 37.5 mW/cm2 of incident radiation as measured in the absence of the animal subjects. Four rats were exposed for 60 min while performing in a response chamber of Styrofoam. Lever pressing was reinforced by food pellets on a fixed‐interval 50‐sec schedule and produced high rates of responding in two rats and low rates of responding in the other two rats. Radiation at 37.5 mW/cm2 disrupted the lever response in the two rats that responded at high rates during baseline measures. Radiation at the two lowest power densities had no observable effect on the rate of responding. For the two rats that responded at low rates, no effects on rate of lever pressing were observed at any of the power densities. However, ambulatory activity of all rats decreased during radiation at 18.4 and 37.5 mW/cm2. This decrease was associated with a tendency of the rats to remain in areas of the response chamber with lower power densities of irradiation. The results are believed to be due to an interaction between higher metabolic rates in the more frequently responding rats and exogenous heating by microwave radiation.
Early results from the DNA Wideband satellite experiment—Complex‐signal scintillation
Authors: Fremouw E. J. , Leadabrand R. L. , Livingston R. C. , Cousins M. D. , Rino C. L. , Fair B. C. , Long R. A.
Published: February 2008

A multifrequency (ten spectral lines between VHF and S band) coherent radio beacon is presently transmitting continuously from a 1000‐km, high‐inclination orbit for the purpose of characterizing the transionospheric communication channel. Its high phase‐reference frequency (2891 MHz) permits direct observation of complex‐signal scintillation, and its very stable, sun‐synchronous orbit allows repeated pre‐midnight observations at low latitudes and near‐midnight observations at auroral latitudes. We present here early results of the observations; salient points include the following. First, most of the data are consistent with phase‐screen modeling of the production of ionospheric scintillation, including an ƒ−2 frequency dependence for phase variance. Second, propagation theories invoking weak, single scatter seldom are adequate, because even moderate intensity scintillation usually is accompanied by phase fluctuations comparable to or greater than a radian. Third, under conditions producing GHz scintillation (near the geomagnetic equator), lower frequencies show marked diffraction effects, including breakdown of the simple ƒ−2 behavior of phase variance and loss of signal coherenceacross a band as narrow as 11.5 MHz at UHF.
Singularity extraction in kernel functions in closed region problems
Authors: Howard A. Q. , Seidel D. B.
Published: February 2008

A general method of obtaining the free space particular solution and the required homogeneous solution decomposition in closed region problems in electromagnetics is described. This allows the singular nature of the kernel function to be handled analytically. The remaining homogeneous solution which is expressed in an eigenfunction series is rapidly convergent. The method should be of particular value in vector integral equation formulations where the dyadic kernel is highly singular. The method is applied to the rectangular cavity dyad.