Showing papers in "Radio Science in 1974"

An improved equation for the radio refractive index of air

Abstract: New constants are derived for the equation relating the radio refractive index, n, at frequencies below 20 GHz to the pressure, temperature, and humidity of the air. The new equation is (n-1)×106=N=77.6(Pa/T)Za-1+64.8(e/T)Zw-1+3.776×105(e/T2)Zw-1 where Pα is the partial pressure of dry air (mb), T is the absolute temperature (K), e is the partial pressure of water vapor (mb), and Zα−1 and Zw−1 are the inverse compressibility factors for dry air and water vapor, respectively. Improved values of the constants are obtained by considering the relationship between the radio and optical portions of the electromagnetic spectrum. With the use of the full three-term equation including non-ideal gas law effects, the accuracy of the new radio refractive index equation ranges from 0.018%, or about 0.05N, for dry air to 0.048%, or 0.21N, for extremely moist air.

Geometrical optical approach for electromagnetic wave propagation in rectangular mine tunnels

Abstract: Electromagnetic wave propagation inside an empty rectangular mine tunnel with imperfect walls is considered. The modal expansion of the fields is complicated by the coupling of the basic modes by the imperfect walls. To avoid this difficulty, and in view of the large guide dimensions relative to the free space wavelength, a geometrical ray approach is proposed. To provide a theoretical foundation for the method, we first consider an idealized waveguide model with two perfectly reflecting side walls. The modal field expansion for this prototype model is fully analyzed to provide a satisfactory comparison between the modal and the geometrical ray sums. The proposed general ray method is then applied to the rectangular waveguide when all four walls are imperfectly conducting. Finally, the influence of wall roughness is considered by a relatively simple method.

Field-aligned scattering from a heated region of the ionosphere—Observations at HF and VHF

Abstract: Radio scattering measurements have been made of a region of the ionosphere above the Institute for Telecommunication Sciences' ionospheric heating facility at Platteville, Colorado. Strong scattering was observed at frequencies in the HF and VHF bands. The scattering has been shown to originate from electron density fluctuations that are highly elongated in the direction of the geomagnetic field. Radar scattering cross sections of 70 to 80 dbsm are measured in the HF and low VHF bands. The scattering cross section decreases at a rate of 20 to 30 db per octave at the high end of the VHF band. The scattering irregularities are produced by operation of the heating facility with o-mode polarization at frequencies that reflect within the ionosphere. The strength of the scattered energy decreases at a rate of at least 10 db per degree for observation geometries that do not match the geometry for specular reflections from long cylinders aligned with the geomagnetic field. The spatial distribution of irregularities has been estimated for both E- and F-region heating. The temporal properties of the scattering have also been determined including the frequency spectrum of the scattered signals. The processes by which ionospheric heating produces these irregularities are not yet fully explained. Several potentially useful applications of radio scattering from such irregularities are discussed.

Radio frequency scattering from a heated ionospheric volume: 1, VHF/UHF field-aligned and plasma-line backscatter measurements

Abstract: It is observed that an ionospheric volume in the F layer subjected to high power HF illumination becomes an effective scattering medium for radio signals in the VHF/UHF frequency range. The experimental results are representative of a field-aligned scattering geometry for which the first such observations of VHF/UHF scattering from a heated ionospheric volume are presented. Two distinct scattering modes are observed, center-line and plasma-line scattering. Center-line scattering is observed at the transmitted radar frequency f; plasma-line scattering is observed as a pair of sidebands at f ± fh where fh is the heater frequency. The two scattering modes are observed to have markedly dissimilar characteristics. Center-line scattering is highly aspect sensitive with respect to the direction of the geomagnetic field, B; plasma-line scattering is found to be much less aspect sensitive, if at all. The region of maximum backscatter for the center-line mode is found from these measurements to consist of the locus of points within the heated volume over which perpendicularity between the radar line of sight and B is achieved, independent of the location of maximum heating. The backscattering region for the plasma-line mode is found from these measurements to be determined by the altitude of maximum heating, independent of geometrical considerations involving B. The longitudinal coherence length, L, for center-line scattering is found from these measurements to be greater than the maximum antenna diameter of 85 ft; no more exact estimate for L is possible. A striking reversal in frequency dependence is found between the center-line and plasma-line modes. The per-unit-volume center-line backscatter cross section is found to be about 7 db greater at VHF than at UHF; the per-unit-volume plasma-line backscatter cross section is found to be at least 11 db less at VHF than at UHF. Preliminary results concerning time-dependent behavior are presented. For both modes the scattering cross section is found to be effectively turned on and off very rapidly in response to the heater excitation; the spectral width of the scattering for both modes is found to be quite narrow (about 10 Hz). The spatial configuration of the heated volume is investigated; significant differences are observed depending on whether fh/f0F2 is greater or less than unity.

Tidal oscillations of the meridional neutral wind at midlatitudes

Abstract: The meridional neutral wind values estimated over St. Santin (44 deg 65'N, 2 deg 19' E, geographic) from incoherent scatter observations, during the years 1971 and 1972, have been analyzed in terms of Fourier components in the whole thermospheric altitude range. Seasonal averages of the height structure of amplitude and phase for each harmonic term are presented and compared with relevant theoretical predictions. The high thermosphere results exhibit clear annual and semiannual effects and the steady meridional wind is found to depend on magnetic activity and solar flux. The discussion of the experimental results, in connection with predictions of the tidal theory, suggests future work in this field which is outlined in the conclusion. (auth)

Midlatitude thermospheric winds from incoherent scatter radar and theory

Abstract: Ionospheric plasma vertical drifts measured by the Millstone Hill incoherent scatter radar are decomposed into estimates of meridional neutral particle motion by accounting for ion diffusion and semidiurnal electric fields. For two equinoctial days with relatively high F-region electron densities the resulting neutral circulation at 300 km is composed of equatorward winds of 100 to 150 m sec/sup -1/ at night and poleward winds of 25 to 50 m sec/sup -1/ during the day. Harmonic analysis of the wind pattern yields a diurnal northward component of 80 to 100 m sec/sup -1/ with a maximum near noon, a semidiurnal component of 35 m sec/sup -1/ at 0600 LT and a prevailing southward wind of about 20 m sec/sup -1/. The observations are compared with tidal theory predictions and are interpreted by means of a simplified integration of the horizontal equations of motion through which effects of zonal advection, ion drag, viscosity, and pressure gradients are studied. Although the observed wind pattern is consistent in general with that derived from global models based on satellite drag observations, various discrepancies concerning the amplitude and phase of the diurnal bulge are noted and discussed. (auth)

Arecibo heating experiments

Abstract: Enhancements of various features of the incoherent scatter spectrum are observed when the ionosphere is illuminated with powerful, high frequency radio waves. The radio waves excite plasma instabilities producing lines or more complex spectral features near the local plasma frequency, at the local ion acoustic frequency, near the local gyrofrequency, and near twice the gyrofrequency. The enhancements occur in a thin slab as observed by the incoherent scatter radar and at both upshifted and downshifted frequencies with respect to the probing radar frequency. The enhancements are observed to vary with time when the excitation is held constant and is turned on or off. The high power radio waves are produced by a 160 kw transmitter feeding a log-periodic pair of curtains mounted at the focus of the 1000-ft reflector and covering the frequency range from 5 to 12 MHz. The effects are observed with the incoherent scatter radar using the same reflector and with ionosondes and photometers. The frequencies of the enhanced plasma line and the ion line and their relation to the pump (high frequency radio wave) frequency are predictable from available parametric instability theory. Other spectral features are being explained as the theory develops with the help of the observations. There remain some discrepancies, in particular the asymmetries in intensity, width, and fluctuations of the upshifted compared to the downshifted plasma lines.

A model of the enhanced airglow excited by RF radiation

Abstract: 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.

A summary of vertical incidence radio observations of ionospheric modification

Abstract: Within the past four years, experiments with high power, high frequency radio waves have proved the feasibility of temporarily altering the ionosphere's properties. Many different radio and photometric effects have been observed as a result of the ionospheric modification. This paper provides a survey of some of the effects observed with vertical incidence radio techniques when the US Department of Commerce's Platteville facility, near Boulder, Colorado, is used to illuminate the overhead ionosphere with an equivalent isotropically radiated power of the order of 100 Mw. A variety of different and repeatable phenomena are observed to occur in the F region. A few always occur; for others, apparently, certain ionospheric conditions must exist. E-region effects observed by these techniques are small, but substantial effects are noted in the D region.

Recent developments and outstanding problems in the theory of the D region

Abstract: The present understanding of the ionization processes, and of the positive and negative ion chemistry of the D region, is reviewed with particular attention being given to outstanding problems. Rocket-borne mass spectrometer observations carried out in the past decade have shown that the change in positive ion composition with height (from NO+, O2+ and metallic ions above to water cluster ions H+· (H2O)n below) is a general feature of the D region at all latitudes and under all geophysical conditions. Furthermore, these observations indicate that this change occurs over a very small range of heights, between 82 and 86 km under normal conditions and at lower heights during auroral or Polar Cap Absorption conditions. These results are discussed in terms of current ideas concerning the formation of water cluster ions from O2+ and NO+ ions. Mass spectrometer observations by two experimental groups have provided conflicting results concerning the negative ion composition in the D region and cannot be used to test theoretical models. Such models have been derived from laboratory measurements, and involve reaction schemes leading from O2− ions, formed by electron attachment, to ions O3−, O4−, CO3−, CO4−, NO2− and NO3−. The effect on these models of including recent laboratory measurements of negative ion hydration is considered, and the importance of photodetachment is also mentioned.

Electromagnetic scattering by random dielectric constant fluctuations in a bounded medium

Abstract: The electromagnetic scattering properties of a medium bounded by a plane surface and whose (scalar) dielectric constant is the sum of a nonrandom part assumed to vary only with depth and a small random part are investigated by means of an approximate, first-order perturbation method. It is shown that the equivalent dielectric constant to be used in calculating the average reflected power in the specular direction is a function of depth even in the case where the nonrandom part of the dielectric constant is independent of depth. Further, the equivalent dielectric constant is shown to be a tensor. Nonspecular scattering is also considered.

A theoretical model for short‐scale field‐aligned plasma density striations

Abstract: The short-scale (about 3 m), field-aligned plasma density striations found in ionospheric modification experiments are generated by the plasma turbulence resulting from ion acoustic-plasma wave parametric decay instabilities. The field-aligned geometry results from the fact that nonlinear wave coupling arises from thermal, ohmic heating terms rather than ponderomotive force (radiation pressure). The theory shows that field-aligned striations increase rapidly in intensity as the wavelength increases—in agreement with experiment.

Simultaneous measurement of ion and neutral motions by radar and optical techniques

Abstract: 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 A 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. Copyright 1974 by the American Geophysical Union.

Incoherent scatter observations of the ionospheric response to a large solar flare

Abstract: Incoherent scatter observations at Millstone Hill were made during the importance 3B solar flare which occurred at 15:00 UT on 7 August 1972. Measurements were obtained of the electron density profile over the height range 125 to 1200 km, together with observations of the electron temperature, ion temperature, and vertical drift velociy above 225 km. The Ne(h) results showed electron density enhancements of nearly 100% at 125 km and 60% at 200 km; Ne enhancements were also observed throughout the topside, with the percentage enhancement increasing with height above 400 km. The total electron content up to 1200 km showed an increase of 3.8 × 1016 el m−2 (≃30%). The temperature and drift data represent the first Thomson scatter measurements of these parameters during flare conditions. While the electron temperature results showed substantial increases at all altitudes examined, the ion temperatures were only slightly perturbed. The drift data provided the most interesting results. In response to the flare, a dramatic upward surge was observed in which the drifts increased nearly linearly with height over the height range 300 to 750 km. In discussing the overall results obtained during this event, estimates are made of the flare-induced electrodynamic and thermal processes which contribute to the observed effects.

Thermal microwave emission from a halfspace containing scatterers

Abstract: 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.

Comparisons of techniques for measurement of D‐region electron densities

Abstract: This paper reviews the ground-based and rocket techniques that are presently being used to determine electron density profiles in the ionospheric D region. Ground-based techniques include VLF, LF, and MF sounding; differential absorption and differential phase measurements using partial reflections; wave interaction; and incoherent scatter. Rocket techniques include differential absorption and Faraday rotation in association with high-resolution dc probes calibrated by means of the radio measurements. The characteristics of the aforementioned techniques are presented, including time and height resolution, accuracy estimates, preferred height ranges, and problems encountered. Electron density profiles obtained with these techniques are presented for comparable solar zenith angles and undisturbed solar and geophysical conditions.

Evidence for the existence of nighttime F-region polarization fields at Arecibo

Abstract: Recent measurements are presented of F-region ion drifts made at Arecibo using a new continuous beamswinging technique. The measurements are applied to the question of the origin of the F-region electric field over Arecibo. It is shown that the daytime electric fields are probably caused by E-region tidal winds, while the nighttime electric fields appear to be generated in the F region itself by thermospheric winds.

Guided electromagnetic waves in a curved rectangular mine tunnel

Abstract: 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.

Ionospheric heating by powerful radio waves

Abstract: In addition to the communication applications that stem from the generation of field-aligned irregularities, ionospheric heating by powerful HF waves also holds promise for establishing new techniques in D-, E-, and F-region aeronomy. This paper concentrates on the application of the theory of plasma heating by ohmic and nonlinear dissipation to the special conditions of the lower ionosphere where the electron collision and disturbing wave frequencies are comparable and the upper ionosphere where electron thermal transport is large and restricted by the earth's magnetic field. We predict the magnitude and distribution of large-scale changes in the electron temperature and density in both the D and F layers under a variety of conditions. These results are compared with direct measurements or inferred changes whenever possible. We also examine the effects of specular-height mismatch, multiple frequency operation involving heater-power sharing, and antenna beam tilt on the total cross section for field-aligned scattering. The analysis is based on the concept that the energy-density distribution on the heater reflectrix computed by means of a ray-tracing technique can be related directly to the density-fluctuation intensity through an appropriate scattering model. Lastly, potential applications to aeronomy are discussed, particularly in regard to D-region measurements of the effective recombination coefficient magnitude and temperature dependence and the relative water cluster ion concentration.

Estimation of raindrop size distribution using multiple wavelength radar systems

Abstract: The possible use of multiple wavelength radar systems to determine raindrop size distributions is examined. Pairs of radars at 1, 3, and 10 cm, respectively, are considered; the method involves measurements of rain reflectivities at two wavelength and at two range intervals separated by about one km. Assuming a general exponential form for the drop distribution, equations are derived relating the distribution parameters to the measurements. From these analytical forms the sensitivities of these parameters to radar inaccuracies are examined. The results show that one needs combined 2-radar accuracies of 1 dB to get even marginal drop distribution accuracies. Such accuracies are considered impractical at present. Other impractical constraints implicit in the results are the assumed uniformity of reflectivity over distances of approximately 1 km, and the requirement to average as many as 104 independent power samples.

Fetch and wind speed dependence of Doppler spectra

Abstract: Previous measurements of Doppler spectra in microwave backscattering in a wind wave tank at 9.375 GHz and 23.9 GHz have been extended to 70.1 GHz at 3 m fetch and to longer fetches and higher winds at the two lower microwave frequencies. At high depression angles, the scatterers appear to be specular points moving at approximately the speed of the dominant wind wave. At lower depression angles, the scatterers can be thought of as comprising systems which are respectively bound to and free of the dominant wave. The free scatterers are low-order Bragg scatterers and it is natural to treat them as free waves or free wave systems in their own right. The bound scatterers are the familiar parasitic capillary waves at low winds, but at higher winds they appear to be associated with the breaking water at the crest of the dominant wave.

Microwave radiometer measurements of the Cape Cod Canal

Abstract: Microwave radiometer measurements were conducted from a railroad bridge which spans the Cape Cod Canal in Massachusetts. Data were collected as a function of viewing angle and polarization at frequencies of 1.4, 4.0, and 7.5 GHz. The results compare differences in the microwave emmissivity of a smooth vs rough water surface. Results are also given which show the effects of roughness on the bistatic scattering of sunlight.

HF phased array observations of heater-induced spread-F

Abstract: A large circular HF phased array radar has been used to study the angular spectrum of spread-F returns from an ionosphere modified by the intense radio waves from the high power Platteville transmitter. The results obtained are presented to show the dependence of angular spectrum on range delay, Doppler shift, operating frequency, and on the power of the heater transmitter. The phenomenon of wideband attenuation observed with the o-mode diagnostic wave is examined for its dependence on the angle of arrival of the received signal. The angular spectrum of the spread-F returns exhibits a systematic behavior. It is found that the angle of arrival migrates from north to south and the Doppler changes from positive to negative as the range delay examined is changed from the leading edge of the return to the trailing edge. The height dependence of the angular spectrum shows that the volume containing the spread-F irregularities is aligned along the earth's magnetic field. The dependence on the heater power is such that the angular extent of the returns is reduced by a factor of 3 when the heater power is reduced to -9 db of its maximum value of 1.8 Mw. The attenuation suffered by the diagnostic o-mode upon heater turn-on changes with the angle of arrival to reach a maximum with the signal returns arriving from the south. It is shown by means of ray-tracing simulation that the observed interdependence of angle of arrival, Doppler shift, and range delay is consistent with a model of field-aligned ducts for the heater-induced spread-F irregularities. The model, when applied to the conditions at Arecibo and the results compared to that for Platteville, reveals that the range delay spread is about the same and the angular spread is approximately in the same ratio as the heater beamwidths at the two places.

First observations of RF backscatter from field-aligned irregularities produced by ionospheric heating

Abstract: 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.

Accuracy of rocket measurements of lower ionosphere electron concentrations

Abstract: 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.

Seasonal variations in the thermosphere above Millstone Hill

Abstract: Incoherent scatter radar measurements gathered since 1969 at Millstone Hill (42.6°N, 71.5°W) are used to study the seasonal variations of the neutral gas temperature, composition and wind velocity in the thermosphere. Between 110 and 120 km, the mean temperature is found to oscillate with a 20 K annual amplitude, 10 K semiannual amplitude, and maxima in July; the mean density oscillates with an annual amplitude of 13% of the mean and a semiannual amplitude of 6% of the mean with maxima in November. Similarly, the mean daily exospheric temperature possesses a 100 K amplitude variation with a maximum in summer; the semiannual component is only about 10 K. Moreover, a weak winter maximum characterizes the neutral density at 400 km, and the neutral wind at 300 km is found to blow northward for a longer period during the day in winter than in summer. The amplitude and phase of the daily semidiurnal tides in the lower thermosphere do not vary systematically with season but a large variability is observed from day to day, particularly in the phase of the oscillation during winter. In contrast, the semidiurnal harmonic of the exospheric temperature varies seasonally in amplitude and phase and reflects the controlling influence of the length of the day on the shape of the daily temperature oscillation. In the middle thermosphere, the neutral composition ratio O/N2 is larger in winter than summer, with a rapid transition at the equinox.

The horizontal wire antenna over a conducting or dielectric half space: Current and admittance

Abstract: The wave number, the distribution of current, and the admittance of a horizontal wire antenna over a homogeneous isotropic half space are determined when the complex wave number characteristic of the half space is large in magnitude compared with the real wave number of the air. The axial electric field at the surface of the half space is described. The properties of the antenna are obtained from those of the eccentrically insulated dipole in a general medium in the limit as the radius of the insulation is increased without limit while the distance of the dipole from the boundary is kept constant. Application of the new theory to the Beverage or wave antenna is discussed.

A numerical study of electromagnetic scattering from ocean-like surfaces

Abstract: The integral equations describing electromagnetic scattering from cylindrical, perfectly conducting surfaces are formulated and numerical results are presented. The results are compared with those obtained using approximate methods such as physical optics, geometrical optics, and perturbation theory. The integral equation solutions show that the surface radius of curvature must be greater than 2.5 wavelengths for either the physical optics or geometrical optics to give satisfactory results. It has also been shown that perturbation theory agrees with the exact fields as long as the root-mean-square surface roughness is less than one tenth of a wavelength.

Electron densities within aurorae and other auroral E-region characteristics

Abstract: The L-band incoherent scatter radar located at Chatanika, Alaska (L ≃ 5.6) has been used to measure the characteristics of the auroral E layer. In this paper, the term auroral E layer refers to nighttime ionization between altitudes of 90 to 150 km produced by particle precipitation. Electron density profiles have been measured using time resolutions as short as 0.2 sec and range resolutions of 5 to 10 km. For the shortest integration time, the statistical accuracy of the measurement is on the order of 10%. Results obtained to date show auroral ionization to align with the earth's magnetic field and to have lengths along the field of typically 20 to 30 km and thicknesses across the field of less than 5 km (both distances measured between the half-peak-density points). Within the auroral ionization, the maximum electron density at times approaches 2 × 106 el cm−3. The measured quantities have been analyzed to deduce (a) energy of the particle precipitation, (b) flux of particle precipitation, (c) production rates, and (d) effective recombination coefficients. For a few cases, estimates of the pitch-angle distribution of the primary electrons have been made.

Inversion of sweep‐frequency sky‐wave backscatter leading edge for quasiparabolic ionospheric layer parameters

Abstract: A method is presented for the derivation of quasiparabolic ionospheric layer parameters from a set of three data points on the leading edge of a sweep-frequency sky-wave backscatter ionogram. The method is illustrated with a numerical example. Possible extensions of the method are discussed.