bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous rocket probe, scintillation, and incoherent scatter radar observations of irregularities in the auroral zone ionosphere
Authors: Kelley M. C. , Baker K. D. , Ulwick J. C. , Rino C. L. , Baron M. J.
Published: February 2008

Two rocket payloads carrying plasma density probes with high spatial resolution have been flown in the auroral zone during active conditions. Simultaneous Wideband satellite scintillation and Chatanika incoherent scatter radar observations were made in order to study the properties of high‐latitude irregularities and their effects on radio wave transmission. Unlike barium cloud striations and bottomside equatorial spread F, the observed power law dependence of the irregularities does not seem to be due to steepening of kilometer‐scale structures, rather, a turbulent process seems to occur. In addition the power law indexes determined both from the probe and from the scintillation measurements indicates an in situ one‐dimensional spectrum less steep than the k−2 value often reported. Both the probe and the scintillation data indicate absolute electron density fluctuations (Δn2e)½ of several times 109 m−3 during the expansion phase of an auroral substorm, with a layer thickness of several hundred kilometers. The observed S4 levels at VHF were in the range of 0.1–0.4. This level of scintillation, as well as the absolute density fluctuation levels and the power spectral density at the kilometer scale, are shown to be comparable with bottomside equatorial spread F. It is suggested that differences between the power spectral index in the present data set and the other ionospheric experiments mentioned above may be due to a highly conductive E layer and its effects upon the nonlinear evolution of irregularities. During another flight with lower magnetic activity but several bright auroral areas in the trajectory, much lower levels of absolute and relative density fluctuations were observed with a corresponding lower value for S4. Two very sharp changes in electron density were observed (e‐folding scales of 1.45 and 0.7 km) near the field line projected position of the auroral arcs. The associated density spectra were peaked at short wavelengths. The detection of very structured plasma within minutes of the poleward expansion phase of a substorm suggests that the F layer irregularities were formed in the precipitation event. On the other hand, evidence is also presented for production or enhancement of irregularities in the presence of horizontal density gradients which suggests that plasma instabilities also play a role in the production of auroral zone irregularities.
An ionospheric ray tracing technique
Authors: Cummack C. H.
Published: February 2008

The method of Jones used for the ray tracing of internal gravity waves has been applied to radio waves in the ionosphere. This method avoids problems usually encountered near a reflection point and, consequently, may be used to trace both reflected and refracted rays. The method is particularly efficient when the propagation effects of the magnetic field are neglected.
Tropospheric refractive angle and range error corrections utilizing exoatmospheric sources
Authors: Mano K. , Altshuler E. E.
Published: February 2008

Tropospheric refractive range and angle errors limit the performance of radar and navigation systems that operate at low elevation angles. For some locations and for many applications, antenna pointing corrections based on surface refractivity alone or, if necessary, a vertical refractivity profile are adequate. However, new systems that operate at very low elevation angles require improved accuracies. More accurate angle error corrections can be obtained by utilizing calibration sources (often referred to as ‘targets of opportunity’), such as the limb of the sun, radio sources, or satellites, the angular positions of which are precisely known. Since the angle error is dependent on the target distance, an expression for angle error as a function of target height is derived. Unfortunately, radio sources cannot be used for range calibration, and since the ranges of most satellites are not known to a sufficient accuracy, the range error correction is still a problem. It is shown in this paper that it is possible to develop a method for obtaining an improved range error correction by utilizing measured angle error data for the same ray path. An expression for the refractive angle error correction for a target based on the measured angle error of the calibration source is first derived; also the angular refraction is expressed as a function of the angle error. It is then shown that the range error correction for a target can be expressed as a function of the angular refraction and can thus be calculated from a set of angle error measurements, thereby providing an improved correction. In the formulation of this problem a time independent spherically stratified nonionized atmosphere with a monotonically decreasing index of refraction with altitude is adopted, so the solution is only valid at frequencies above which ionospheric effects are negligible and for atmospheres which do not have inversion layers in refractivity. Also, it is assumed that both the calibration source and target are above the troposphere.
Coherence bandwidth loss in transionospheric radio propagation
Authors: Rino C. L. , Gonzalez V. H. , Hessing A. R.
Published: February 2008

In this paper a theoretical model that predicts the single‐point, two‐frequency coherence function for transionospheric radio waves is developed. By using an asymptotic approximation a single parameter was isolated, which gives the functional dependence on perturbation strength, propagation distance, and fractional frequency separation. The model is compared to the measured complex frequency correlation function by using data from the seven equispaced, phase‐coherent UHF signals transmitted by the Wideband satellite. The model and data agreement is very good when allowance is made for a varying spectral index. The pulse delay jitter induced by the coherence bandwidth loss is also computed and compared with the actual delay jitter observed on synthesized pulses obtained from the Wideband UHF comb. Again, the data are in good agreement with the theory. The ramifications of the asymptotic approximation vis a vis the more commonly used quadratic approximation are also discussed.
Scintillation of VHF/UHF and L band satellite signals at Guam
Authors: Paulson M. R.
Published: February 2008

An investigation of the equatorial scintillation of satellite signals at 257.55 and 1541.5 MHz for about 10° and 50° elevation angles is reported. Diurnal and seasonal variations are shown for the two frequencies and the two elevation angles. A periodicity in the occurrence of the scintillation was observed and is attributed to the gravitational field of the moon. It is proposed that the moon's gravity may affect the occurrence and intensity of equatorial scintillation by modulating the velocity of the zonal winds at ionospheric heights. An additional possible contribution to the periodic variation in the scintillation is a periodic variation which occurred in the geomagnetic activity during the first half of the year.
Scattering from a Rayleigh layer with an irregular interface
Authors: Fung A. K. , Chen M. F.
Published: February 2008

A theory of wave scattering from an inhomogeneous irregular layer has been developed with the radiative transfer method. It is shown that there is a basic difference between the plane and irregular layer formulation. When the inhomogeneities are represented by the Rayleigh scatterers, the plane layer problem can be solved with three Fourier components, whereas the irregular layer requires additional Fourier components until convergence is achieved. In general, smaller numbers of Fourier components are required for thicker layers. Comparisons between the backscattering coefficients of a plane versus an irregular Rayleigh layer indicate that the rough surface boundary causes the level difference between the like and the cross polarized returns to be smaller than the plane case. In addition, polarized returns may be dominated by surface roughness effects near vertical incidence. While the cross polarized return continues to be dominated by volume scattering parameters, the interaction between rough surface and volume scattering can cause significant change in both its angular shape and its level.
On the application of phase screen models to the interpretation of ionospheric scintillation data
Authors: Rino C. L.
Published: February 2008

Phase screen models have been used for nearly three decades to facilitate the application of the scintillation theory to data interpretation. Only recently, however, as large amounts of multifrequency phase‐coherent beacon data have been analyzed, has the full potential of the model been realized. This paper presents a review of the application of the phase screen model to the interpretation of data from the Defense Nuclear Agency's Wideband satellite (international designation P76‐5), which was operational from May 1976 until August 1979. The signal structure and experiment configuration allowed measurements of temporal, spatial, and frequency coherence for a wide variety of scintillation conditions. The derived scintillation parameters are in excellent agreement with the phase screen theory. Moreover, the inferred irregularity structure has been confirmed by recent in situ measurements. The principal results can be summarized with simple algebraic formulas for the scintillation level, spatial/temporal coherence, and frequency coherence or coherence bandwidth. With appropriate manipulations, the formulas fully accommodate the propagation angle dependence in highly anisotropic media.
Constant‐dose microwave irradiation of insect pupae
Authors: Olsen Richard G.
Published: February 2008

Pupae of the yellow mealworm Tenebrio molitor L. were subjected to microwave irradiation for 1.5–24 hours at power density levels adjusted to produce a total dosage of approximately 1123 J/g in each insect for every experiment. Insects without visible blemishes were exposed in a standing wave irradiation system such that half of them were exposed in the plane of maximum electric field (E field) and the other half were exposed in the plane of maximum magnetic field (H field). Both E field and H field insects exhibited nearly the same specific absorption rate (SAR) for pupal orientation parallel to the magnetic field vector at 5.95 GHz. Irradiations were conducted both with and without the use of a ventilating fan to control the temperature rise in the irradiation chamber. Abnormal development as a result of the microwave exposure was seen only in the high‐power, short‐duration experiment without chamber ventilation. This result suggests a thermal interaction mechanism for explanation of observed microwave‐induced abnormalities. A study of the time course of the average temperature rise in the irradiated insects indicates that teratological effects for this configuration have a temperature threshold of approximately 40°C.
Comparison of measured and predicted characteristics of microwave‐induced sound
Authors: Lin James C. , Meltzer Richard J. , Redding Foster K.
Published: February 2008

Microwave pulse‐evoked potentials at the vertex show a series of waves occurring in the first 10 ms following delivery of the pulse. The sources of these waves, as in the case of acoustic click‐evoked responses, are action potentials generated in the cochlea and auditory brain stem nuclei. We shall show, using microwave‐induced auditory brain stem responses, that the experimentally observed characteristics agree with previously derived theoretical predictions in regard to pulse width and frequency of impinging microwaves, pattern of absorbed microwave energy, frequency of vibration, and threshold of sensation.
Interaction of ambient temperature and microwave power density on schedule‐controlled behavior in the rat
Authors: Gage Michael I. , Mark Guyer W.
Published: February 2008

Most guidelines of microwave exposure do not explicitly address effects of ambient temperature. Our experiment revealed that ambient temperature potentiates the behavioral effects of intensity of irradiation. Sixty‐four adult male Long‐Evans rats were trained to insert their heads into a food cup to obtain food pellets on a 1‐min variable‐interval schedule of reinforcement. Two groups of four rats each were then exposed to 2450‐MHz CW microwaves for 15.5 hours under one of the following eight combinations of power density and air temperature: 8 or 14 mW/cm2 at 22°C; 0, 8, or 14 mW/cm2 at 26°C; and 0, 8, or 14 mW/cm2 at 30°C (relative humidity was 50% in all cases). Response rate of each rat following exposure was compared with its control rate at 0 mW/cm2 and 22°C. After exposure at 8 mW/cm2, response rates were reduced by a mean of 13.8% at 22°C, 27.5Percnt; at 26°C, and 77.5% at 30°C. After exposure at 14 mW/cm2, rates were reduced by a mean of 21.1% at 22°C, 43.7% at 26°C, and 80.0% at 30°C. In the absence of microwaves the higher temperatures caused only slight decreases in response rate.
A morphological study of gigahertz equatorial scintillations in the Asian region
Authors: Fang D. J. , Liu C. H.
Published: February 2008

Concerted efforts were made from 1978 to 1980 to monitor ionospheric scintillations in the Asian region. Two geostationary satellites (Intelsat IV F8, Pacific Ocean Region, and Intelsat IV‐A F1, Indian Ocean Region) and five earth stations (Hong Kong, Singapore, Thailand, Hawaii, and Sri Lanka) with a total of eight up/downlink signals at 4 and 6 GHz, respectively, were involved. Twenty‐nine months of 4‐GHz data received at the Hong Kong earth station were used for analysis. This measurement period coincided with the solar maximum period of the current solar cycle 21. Scintillations of severe intensity with peak‐to‐peak fluctuations of up to 14 dB were recorded. This paper examines the morphological aspect of scintillations in the Asian region, including the equinoctial occurrence pattern, diurnal onset characteristics, relationship between scintillations along the eastward and westward links during sunset, and correlation with sunspot numbers. These findings, complementary to information already available from American and European‐African regions, provide an essential element in understanding the global behavior of gigahertz ionospheric scintillations.
Calculation of ionospheric conductivity profiles by inverting VLF/LF reflection data: 1. Isotropic propagation
Authors: Field E. C. , Warren R. E. , Warber C. R.
Published: February 2008

A method for inverting VLF/LF ionosounder data to obtain ionospheric conductivity profiles is described. The method is applied to altitudes below about 70 km, where the propagation can be assumed to be isotropic. Two cases are evaluated: (1) model ionospheres for which artificial data are generated by calculating reflection coefficients and (2) actual ionospheres for which reflection coefficients are measured by VLF/LF ionosounders during a strong solar proton event. Estimates are given of altitude ranges inside which ionosounder data contain information about conductivity and outside which the inversion breaks down. Calculated profiles are shown to agree well with model profiles within those altitude ranges. Profiles calculated for the solar proton event of September 23, 1978, are similar in magnitude and structure to those which occurred during earlier strong solar proton events.
Coordinated measurements of low‐energy electron precipitation and scintillations/TEC in the auroral oval
Authors: Basu Sunanda , MacKenzie Eileen , Basu Santimay , Carlson H. C. , Hardy D. A. , Rich F. J. , Livingston R. C.
Published: February 2008

A case study of coordinated observations of low‐energy (<500 eV) electron precipitation in the auroral oval from DMSP/F2 and phase and amplitude scintillations from Goose Bay, using a geostationary satellite transmitting at 244 MHz, is presented. The precipitation event took place during the expansion phase of an intense evening substorm, when the equatorward boundary of the diffuse aurora reached 59° invariant latitude. Particularly large phase scintillations (>10 radians for fluctuation frequencies >0.0067 Hz) were found to be well correlated with intense fluxes (>109 particles (cm2 s sr)−1) of precipitated low‐energy electrons. Total electron content and magnetometer measurements indicate that the onset of the precipitation event was about 10 min prior to the DMSP pass. Within this time scale, the ionization generated in the F region could reach the topside so that the thermal sensor on board the DMSP satellite was able to measure a factor of 2–3 density enhancement at 840 km. The latitudinal width of these density structures is consistent with that of F region blobs observed at Chatanika. The gradient scale length measured in the topside was only 30 km, which was probably responsible for the fast growth rate of the scintillation‐producing irregularities. The phase to amplitude scintillation ratio changed rather drastically compared to quiet magnetic times, however, implying that increased convection velocities during these magnetic disturbances were partially responsible for the enhanced phase scintillation.
The inflection point method of determining riometer quiet day curves
Authors: Krishnaswamy S. , Detrick D. L. , Rosenberg T. J.
Published: February 2008

A computer technique is described for determining the quiet day curve (QDC) from riometer measurements of cosmic radio noise. In this technique, the QDC value for a given sidereal time interval is taken to be the signal level corresponding to the inflection point on the high‐signal side of the peak of the distribution of the measured cosmic radio noise power for that interval. A comparison is made with earlier methods of calculating the QDC and the superiority of the present method is demonstrated. This method has been applied to 30 MHz riometer data from Siple station, Antarctica (75°36'S, 83°36'W) for 1975 and 1980. Despite the presence of high levels of propagated interference during some months in 1980, the technique is able to generate useable QDC's for each month. The uncertainty in the determination of the QDC is estimated to be about 0.1 dB when interference is present, but much lower at other times. Changes in the QDC levels from month to month have been found which are qualitatively consistent with expected seasonal (i.e., solar zenith angle) effects. The technique described here provides an objective operational definition of the QDC which is relatively easy to adapt to computer calculation, and it appears to be a promising tool for the detection and monitoring of long‐term variations in background radio‐wave absorption by the ionosphere.
On the altitudinal profile of auroral radar backscatter
Authors: Uspensky M. V.
Published: February 2008

It is assumed that an aspect sensitivity value of 10 dB/deg is a common and inherent property of any auroral backscatter radar. Based on this assumption the altitudinal profiles of auroral backscatter (APB) are calculated. For radar frequencies smaller than about 70 MHz and moderate to high E layer electron densities the APB's have double maxima structures due to the radio wave ionospheric refraction. For frequencies 70–120 MHz, the APB's exhibit only single‐maximum profiles. However, even in this case, there remains an altitudinal control of the APB's by the E region electron densities. It is found that there exists strong restriction on the E region altitudes producing auroral radar backscatter for all frequencies. This effect, which is closely related to the height variation of the zero aspect angle surfaces, also causes variations of the APB with range and azimuth.
An updated model for millimeter wave propagation in moist air
Authors: Liebe Hans J.
Published: February 2008

A practical atmospheric Millimeter‐Wave Propagation Model (MPM) is formulated that predicts attenuation, delay, and noise properties of moist air for frequencies up to 1000 GHz. Input variables are height distributions (0–30 km) of pressure, temperature, humidity, and suspended droplet concentration along an anticipated radio path. Spectroscopic data consist of more than 450 parameters describing local O2 and H2O absorption lines complemented by continuum spectra for dry air, water vapor, and hydrosols. For a model (MPM*) limited to frequencies below 300 GHz, the number of spectroscopic parameters can be reduced to less than 200. Recent laboratory measurements by us at 138 GHz of absolute attenuation rates for simulated air with water vapor pressures up to saturation allow the formulation of an improved, though empirical water vapor continuum. Model predictions are compared with selected (2.5–430 GHz) data from both laboratory and field experiments. In general, good agreement is obtained.
On‐line data processing techniques for MST radars
Authors: Farley D. T.
Published: February 2008

We review the principles of pulse compression, frequency stepping, and coherent integration in some detail; coarse quantization and the calculation of spectral moments are treated very briefly. Pulse compression and/or frequency stepping permit full use of the average power capability of the radar transmitter, while maximizing the height resolution and minimizing problems of range ambiguity. Barker codes, complementary codes, cyclic codes, and quasi‐complementary codes have all been employed for pulse compression. Complementary codes are particularly useful in mesosphere‐stratosphere‐troposphere observations, since the correlation time of the medium is usually very long. Only binary codes have been used to date, but quaternary codes might also prove to be useful. Another topic worth exploring further is sample weighting, or windowing. Such “unmatched” decoding slightly reduces the signal‐to‐noise ratio, substantially reduces the range sidelobes associated with matched decoding, and significantly increases the computation required for decoding, since multiplications are needed. The sidelobe reduction might be worth both added costs in some cases. Coherent integration is a crude but effective and easily implemented form of digital frequency filtering which can reduce drastically the subsequent computations required. Coarse quantization, usually combined with special purpose hardware, is another way of reducing the computation load, with usually only a small loss in statistical accuracy. Computation is also reduced by calculating spectral moments directly from only a few lagged products, but these moments alone may not be sufficient if ground clutter or other contamination is important.
A numerical consideration on edge effect of planar dipole phased arrays
Authors: Fukao Shoichiro , Sato Toru , Hojo Hiroshi , Kimura Iwane , Kato Susumu
Published: February 2008

The edge effect of planar phased hexagonal arrays is numerically investigated by comparing exact solutions of active impedance and array element pattern of finite arrays with those determined with infinite array approximation. The analysis incorporates the improved circuit theory, which has a higher accuracy than the electro‐motive‐force method. Considerations are also made for the edge effect on the total array pattern. It is found that the edge effect is in reverse proportion to array size. It can be neglected for arrays composed of more than 200 elements, for which the array pattern can be well approximated by the product of the array factor and array element pattern of an infinite array.
Theoretical and experimental aspects of ionospheric structure: A global perspective on dynamics and irregularities
Authors: Szuszczewicz Edward P.
Published: February 2008

Perspectives on ionospheric plasma processes have expanded from narrow views on local phenomenology to more global approaches that recognize the importance of a multitude of coupling mechanisms. This includes attempts to develop truly predictive capabilities for such diverse phenomena as equatorial spread‐F and high latitude ionospheric responses to substorm activity. The approach now recognizes and perhaps even emphasizes that the ionospheric domains are not isolated subsystems but are active and interactive elements in the much larger solar‐terrestrial network. In fact, it is an accepted principle that the ionosphere can exert important feedback on magnetospheric events. A number of these aspects will be considered in this review, with a focus on a developing understanding of dynamic and irregular ionospheric structures and associated relationships to local and remote geophysical plasma controls.
Scattering from a random rough surface: Linear equations for coefficients of Wiener‐Hermite expansion of the wave field
Authors: Nakayama J.
Published: February 2008

This paper describes an exact formulation of random surface scattering by a probabilistic theory. No Rayleigh hypothesis and no approximate boundary condition are used in this formulation. Using the translation invariance property of a homogeneous random surface, we first determine a form of the scattered wave, which is written as a product of unknown homogeneous random function and an exponential phase factor. Regarding the scattered wave as a stochastic functional of the Gaussian random surface, we then develop the scattered wave in terms of orthogonal stochastic functionals (Wiener‐Hermite expansion) with unknown coefficients. As a result, the problem of finding the scattered wave is mathematically reduced to determining the coefficients. In the external region above the highest excursion of the random surface, each stochastic functional is physically represented by a linear combination of outgoing plane waves (and evanescent waves). Then Green's theorem and the ergodic theorem relate the surface field to the coefficients to get two sets of new equations; a set of equations determines the surface field, whereas the other set of equations gives the coefficients in terms of the surface field. Suggestions for solving these equations are described.
Interference detection and correction applied to incoherent scatter radar power profile measurements
Authors: German M. J. , Mathews J. D.
Published: February 2008

Incoherent scatter radars are used principally to measure “power profiles” (total power versus range) from which electron concentration is inferred. When applied to the ionosphere D region this measurement is, due to very small signal‐to‐noise ratios and the range involved, especially susceptable to aircraft and meteor returns and to interference from other radars. We report a power spectrum based interference detection scheme which allows correction of the power profile. The power spectrum used is formed from the same data sequence used to form the power profile. This scheme has been successfully applied to Arecibo D region data.
Analysis of the transverse electromagnetic mode linearly tapered slot antenna
Authors: Janaswamy Ramakrishna , Schaubert Daniel H. , Pozar David M.
Published: February 2008

A theoretical analysis of the radiation characteristics of the transverse electromagnetic mode linearly tapered slot antenna is presented. The theory presented is valid for antennas with air dielectric and forms the basis for analysis of the more popular dielectric‐supported antennas. The method of analysis involves two steps. In the first step, the aperture distribution in the flared slot is determined. In the second step, the equivalent magnetic current in the slot is treated as radiating in the presence of a conducting half‐plane, and the far‐field components are obtained. Detailed comparison with experiment is made and excellent agreement is obtained. Design curves for the variation of the 3‐dB and 10‐dB beamwidths as a function of the antenna length, with the flare angle as a parameter, are presented.
VHF radar for ocean surface current and sea state remote sensing
Authors: Broche P. , Forget P. , de Maistre J. C. , Devenon J. L. , Crochet M.
Published: February 2008

A meteorological ST radar operating at a frequency of 47.8 MHz has been used for remote sensing of sea state. General features of the Doppler spectra of the echoes are found to be the same as those obtained at HF; however, space resolution and intrinsic accuracy of the current velocity measurements can be significantly improved. Arguments are presented to suggest a potential range of a few tens of kilometers on the open sea if the full capabilities of ST radars are used. The experiment also shows that, when it is possible, the range could be extended by increasing the altitude of the radar.
A systematic error in MST/ST radar wind measurement induced by a finite range volume effect: 1. Observational results
Authors: Fukao Shoichiro , Sato Toru , May Peter T. , Tsuda Toshitaka , Kato Susumu , Inaba Motoyuki , Kimura Iwane
Published: February 2008

Wind measurement by MST/ST radars may be accompanied by a systematic error due to a finite range volume effect which works when a thin turbulent layer is simultaneously located in several adjacent range volumes. The error occurs when the layer coincides with a cross section through the range volume which is not symmetric with respect to the center of the beam. The finite range volume effect appears as a false vertical shear of horizontal wind in a vertical scale of the order of a few hundred meters, even if the ambient wind field is uniform. The false wind shear sometimes exceeds 40 ms−1 km−1 in magnitude or the critical value to induce the Kelvin‐Helmholtz instability. Also the effect leads to a false temporal variation of the wind measurement, although the wind field does not change at all. The false wind shear with a magnitude less than 40 ms−1 km−1 cannot be discriminated from a true one in the observed data. It seems hard to indicate directly that the finite range volume effect appears as theoretically conceived. Judging from wind velocity and echo intensity data obtained by the MU radar in Japan, this effect appears quite frequently in the atmosphere. The small vertical scale wind shear as well as the temporal variation found only at a specific range should be treated with great care except when the ambient wind field is weak, where the finite range volume effect is not so important.
High‐resolution synoptic scale measurement of ionospheric motions with the Jindalee sky wave radar
Authors: Anderson S. J. , Lees M. L.
Published: February 2008

The Jindalee HF sky wave radar has been developed to carry out surveillance and remote sensing missions over Australia's northern Exclusive Economic Zone. Offering an unequaled combination of versatility, resolution, and signal processing capability, Jindalee is also a powerful instrument for observing the structure and dynamics of the ionosphere, as illustrated by the examples shown here. The interpretation of HF sky wave backscatter in terms of ionospheric phenomena is more complicated than for conventional ionosondes, but this is compensated for by the vast spatial coverage and the use of clutter analysis techniques which enable the relationship between group range and ground range to be estimated.
The effects of magnetic storm phases on F layer irregularities below the auroral oval
Authors: Aarons J. , Gurgiolo C. , Rodger A. S.
Published: February 2008

Through the study of two periods in September and October 1981 it was possible to observe F layer irregularity development and intensity primarily over subauroral latitudes in the area of the plasmapause. Using sets of data which include in situ measurements of low‐energy (< 12 eV) electron precipitation, ionosonde measurements of spread F, and a series of scintillation measurements, we observed the following phenomena: (1) the descent of the auroral irregularity region to include subauroral latitudes in the general area of the plasmapause during the main phases of a series of magnetic storms, and (2) the “subauroral or plasmapause storm” case when irregularities were noted primarily at lower latitudes, which took place during the recovery phase of magnetic storms when local magnetic activity was low or moderate. Irregularities at these latitudes appearing during both magnetic quiet and magnetically disturbed conditions make statistical modeling of intense F layer irregularities for latitudes in this region very difficult. Dynamic modeling, which would follow the phases of a magnetic storm from commencement through injection to recovery, would more likely be successful in predicting periods of spread F, scintillations, and other manifestations of F layer irregularities at subauroral latitudes. We suggest that the subauroral irregularities in the recovery phase of magnetic storms are the result of energy stored in the ring current which then is slowly released. The appearance of intense F layer irregularities at subauroral latitudes over several days in the recovery phase of magnetic storms is similar to the recovery pattern of Dst, the measure of ring current energy density.
Ionic mobility, mean mass, and conductivity in the middle atmosphere from near ground level to 70 km
Authors: Swider William
Published: February 2008

Mean ionic mass and conductivity, the product of mobility and ion concentration, are important in calculations of low‐frequency propagation. Progress made mostly over the last decade concerning these parameters is reviewed. The mean positive ion mass has a range of about 90±35 amu with lighter masses more prevalent at the higher altitudes. The mean negative ion mass is generally greater and reaches a peak value of 300 amu near 35 km. Reduced mobilities μ0 for both positive and negative ions appear to lie within 1.6±0.6 cm2 (V s)−1. Somewhat finer resolution of μ0 with altitude is tabulated in the text. It is argued that ion concentrations and hence total conductivities are easily and well defined where galactic cosmic rays are the dominant ionization source and electron concentrations are negligible.
The second‐order multiple scattering theory for the vector radiative transfer equation
Authors: Kuga Yasuo , lshimaru Akira , Ma Qinglin
Published: February 2008

Vector radiative transfer (RT) and first‐order multiple scattering (FOMS) theories are often used for analyzing the depolarization effect by the random medium. However, the numerical solution for the RT theory is limited to moderate‐sized particles because of the numerical stability. In order to analyze the depolarization effect by large particles near the backscattering direction, we obtained the second‐order multiple scattering (SOMS) theory for the vector RT theory. The derivation was based on the second‐order solution of each Fourier component of the Stokes vector. The numerical results were compared with FOMS and RT theories. It was shown that the SOMS theory was most useful for large particles and near the backscattering direction. Experimental results for large spherical particles were compared with the SOMS theory. The second‐order ladder term which was included in the SOMS theory was not sufficient to explain the sharp peak observed in the backscattering direction in the depolarized intensity. The peak appears to be caused by the backscattering enhancement effect.
Mesospheric wind and aspect sensitivity measurements at Jicamarca using radar interferometry and poststatistics steering techniques
Authors: Kudeki Erhan , Sürücü Fahri , Woodman Ronald F.
Published: February 2008

Spectral and cross‐spectral signatures of lower mesospheric radar returns are investigated and modeled. Aspect sensitivity of radar echoes and the horizontal, vertical, and random components of atmospheric fluid velocity are estimated. Estimated random velocity magnitudes of ∼0.2 m/s during a specific lower mesospheric scattering event are smaller than corresponding Doppler spectral widths of ∼1 m/s. During the same event, aspect sensitivity variations as large as ∼10 dB/deg were observed. Higher mesospheric returns generally indicate stronger random velocity amplitudes and weaker aspect sensitivity variations. The extreme conditions encountered in the lower mesosphere can introduce systematic errors in wind and turbulence studies, but simple interferometric methods are suggested to cope with such problems. Data analysis in this paper includes first examples of the implementation of the recently introduced poststatistics steering (PSS) technique. A cross‐spectral model developed in the appendix should be suitable for the analysis of most middle atmospheric radar interferometer data.
Comparison of VHF Doppler beam swinging and spaced antenna observations with the MU radar: First results
Authors: Van Baelen J. S. , Tsuda T. , Richmond A. D. , Avery S. K. , Kato S. , Fukao S. , Yamamoto M.
Published: February 2008

We present a comparison between wind measurements in the 5–21 km altitude range over the middle and upper atmosphere (MU) radar obtained by two different techniques: Doppler beam swinging (DBS) and spaced antenna (SA). The SA data are analyzed by full correlation analysis (FCA) to extract the apparent and true velocities. The period analyzed, December 14–18, 1988, had strong zonal winds that often exceeded 80 m/s at around 11 km altitude and also had substantial (> 1 m/s) vertical winds that existed over extended regions of height and time. It is essential to account properly for the vertical wind when extracting the horizontal winds from the oblique DBS beams, but no obvious influence of the vertical velocity on the FCA is detected. In different altitude regions of the atmosphere (below and above the jet stream peak and above 17.7 km), the DBS amplitude alternately agrees better with the true or the apparent velocity obtained by the FCA method. The directions of all three wind estimations agree well, although the apparent direction displays more variability with altitude than do the true and DBS directions. When a smaller spacing for the receiving array is used, it yields a smaller true velocity estimate.
Computer processing for deriving drop‐size distributions and vertical air velocities from VHF Doppler radar spectra
Authors: Sato Toru , Doji Hiroshi , Iwai Hisato , Kimura Iwane , Fukao Shoichiro , Yamamoto Mamoru , Tsuda Toshitaka , Kato Susumu
Published: February 2008

A fully automated data processing procedure has been developed for deriving the precipitation parameters from VHF Doppler radar spectra simultaneously with the background atmospheric parameters such as the mean wind velocity. The procedure has largely enhanced our capability in analyzing the data from continuous observations, which was hardly possible with human‐attained analysis. The accuracy of the derived parameters are quantitatively evaluated by means of numerical simulations. It is found that the rain parameters can be determined with an accuracy of 15% at a time and height resolution of 10 min and 600 m, respectively, for high signal‐to‐noise ratios, for example. Parameters for the background atmospheric turbulence are estimated with an accuracy more than twice the fitting procedure currently used to analyze clear‐air data. Experimental results of the MU radar observations are compared with the rain intensity measured on the ground for the first time. It is confirmed that the radar has a capability of measuring rain parameters with a rainfall rate sensitivity of about 1 mm h−1.
Gravity waves in the mesosphere observed with the middle and upper atmosphere radar
Authors: Tsuda T. , Kato S. , Yokoi T. , Inoue T. , Yamamoto M. , VanZandt T. E. , Fukao S. , Sato T.
Published: February 2008

We have observed wind motions from 60 to 90 km altitudes with the middle and upper atmosphere (MU) radar during daylight hours (0800–1600 LT) from October 13 to 31, 1986. Gravity waves with fairly sinusoidal vertical structure were evident on 16 days of the 19 days of observations. They were characterized by a typical vertical wavelength of 5–15 km and intrinsic periods centered at about 8.6 hours. The propagation velocity of these waves was determined using the linear gravity wave theory. All of the waves propagated downward and had an equatorward component of the meridional propagation. The median direction of horizontal propagation was slightly east of south, and the mean horizontal phase speed was 35.3 m/s. The vertical wave number spectra of horizontal components of mesoscale wind fluctuations agree well with the theoretical spectrum of saturated gravity waves. At frequencies from 1 × 10−5 to about 4 × 10−5 c/s frequency spectra of vertical and radial wind components had logarithmic slopes of 1/3 and −5/3, respectively, which agree fairly well with a model gravity wave spectrum. The effects of Doppler shifting on frequency spectra are most obviously recognized at large frequencies near the Brunt Väisälä frequency. We have also determined the upward flux of horizontal momentum induced by waves with periods from 10 min to 8 hours and further estimated the westward and northward body force of 5.1 and 4.0 m/s/d, respectively.
Anisotropic electromagnetic wave propagation modeling using parabolic approximations
Authors: Brent R. I. , Siegmann W. L. , Jacobson M. J. , Jacyna G. M.
Published: February 2008

A new method for the investigation of anisotropic electromagnetic wave propagation in the atmosphere is developed using parabolic approximations. Model equations for the electric field components are formulated which include the effects of both the inhomogeneous atmosphere and the static magnetic field of the Earth. Application of parabolic‐type approximations produces different systems of coupled parabolic equations. Each is valid for different relative magnitudes of components of the electric field. All admissible cases are then synthesized into one system which can be numerically examined, yielding solutions without a priori knowledge of electric field ratios. A specific example is presented and examined to understand static magnetic field effects on electromagnetic wave propagation. The influences of the Earth's magnetic field are discussed and displayed in terms of electric components and the Poynting vector. Results demonstrate that the geomagnetic field can significantly influence HF atmospheric propagation.
Group paths and dispersion coefficients of pulsed radio signals reflected from model ionospheres
Authors: Park Ikmo , Yeh K. C.
Published: February 2008

When pulsed electromagnetic signals propagate through a stratified, inhomogeneous, isotropic ionosphere, their shapes are usually distorted because of dispersion. To the first‐order approximation, this distortion is determined by the dispersion coefficient ф″, the second derivative of the phase with respect to the angular frequency. In order to derive analytic expressions of the group path and the dispersion coefficient in model ionospheres for the spherical Earth‐ionosphere geometry the quasi‐linear and quasi‐parabolic electron density models already in existence in the literature have been used. When generalized to an ionosphere with known virtual height, the secant law applicable to the plane geometry must be modified for application to the spherical geometry. In this regard, a correction factor can be introduced. This correction factor is computed, and a dispersion coefficient in terms of a correction factor is derived using a modified secant law and the geometry of a spherical Earth‐ionosphere. All calculations are made under conditions which neglect the Earth's magnetic field, absorption, and horizontal gradients. The results show the dependence of the group path and the dispersion coefficient on propagation geometry and ionospheric parameters.
Microwave scattering and emission from a half‐space anisotropic random medium
Authors: Mudaliar Saba , Lee Jay Kyoon
Published: February 2008

This paper is a sequel to our earlier paper (Lee and Mudaliar, 1988) where the backscattering coefficients of a half‐space anisotropic random medium were obtained. Here we calculate bistatic scattering coefficients by solving the modified radiative transfer equations under a first‐order approximation. The effects of multiple scattering on the results are observed. We also calculate emissivities and compare them with those obtained using the Born approximation (single scattering). Several interesting properties of our model are brought to notice using numerical examples. Finally, as an application, we use our theory to interpret the passive remote sensing data of multiyear sea ice in the microwave frequency range. We observe a quite close agreement between our theoretical prediction and the measured data.
Analysis of electromagnetic scattering from buried cylinders using a multifilament current model
Authors: Leviatan Yehuda , Meyouhas Yossef
Published: February 2008

The problem of transverse magnetic (TM) electromagnetic scattering from buried cylinders is analyzed by means of a multifilament current model. The basic idea is to use two sets of fictitious filamentary sources, with adjustable constant complex amplitudes, to simulate the fields in the various regions of the problem. One set, which is placed in the region originally occupied by the cylinder and assumed to radiate in the presence of the interface, is used for simulating the scattered field. This simulation of the scattered field would naturally require an evaluation of various Sommerfeld‐type integrals in two dimensions. These integrals are calculated using a new procedure which combines simplicity and efficiency. The other set, which is placed outside the region originally occupied by the cylinder and assumed to radiate in a homogeneous unbounded space, is used for simulating the field inside the cylinder. The fields due to the filamentary sources are forced to satisfy the boundary conditions in the point‐matching sense. This requirement is cast into a matrix equation, which is solved for the filamentary current amplitudes. The fields and field‐related parameters of interest can be subsequently determined in a straightforward manner. The procedure is simple and general. A selection of illustrative examples is considered and compared with available data.
Observations of ULF pulsation electric fields in the D region using the high‐power auroral simulation heater facility
Authors: Olson John V. , Ferraro A. J. , Lee H.‐S.
Published: February 2008

During the two week interval from October 12 to 24, 1987, an experiment was conducted using the high‐power auroral simulation (HIPAS) ionospheric heating facility near Fairbanks, Alaska. During the experiment the beam was modulated at ELF and ULF frequencies, and the data were recorded at the Geophysical Institute of the University of Alaska approximately 50 km from the HIPAS site. On several occasions naturally occurring ULF waves were present in the overhead ionosphere and were detected in the ELF polarimeter data and in the ground magnetometer data. The amplitudes of the ELF signals show high correlation with the magnitude of the naturally occurring ULF pulsations. Our analysis indicates that the ELF returns were produced by currents generated in the D region, near 75 km, where the bulk of the heater energy was deposited. The ULF pulsation signatures detected by the ground magnetometers reflect Hall currents flowing principally in the E region above 100 km. We believe that the correlation between ELF and ULF signals is produced as the naturally occurring ULF electric field penetrates to D region altitudes where it can drive currents in the heated ionosphere. It is the modulation of those currents by the heater beam which produces the ELF signals detected on the ground. ELF signal levels indicate pulsation fields of approximately 5 mV/m in the D region.
Major lineaments and the Lake Erie‐Maryland crustal block
Authors: Lavin Peter M. , Chaffin David L. , Davis Willard F.
Published: February 2008

Analyses of regional gravity and magnetic patterns, LANDSAT images and geological information have revealed two major lineaments crossing western Pennsylvania and parts of surrounding states. These lineaments are inferred to be expressions of fracture zones which penetrate deeply into the crust and possibly the upper mantle. The extensions of the Tyrone‐Mt. Union and the Pittsburgh‐Washington lineaments bound a distinct crustal block (Lake Erie‐Maryland block) over 100 km wide and probably more than 600 km in length. Evidence exists for the lateral displacement of this block at least 60 km northwestward during late Precambrian to Lower Ordovician time. Subsequent movements have been mainly vertical with respect to neighboring blocks.