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[1] A coincident observation that occurred on 24 March 2000 between the irregularity structure measured by ROCSAT-1 and the scintillation experiment at the Ascension Island has been studied. The study of scintillation statistics is carried out first, and the results show that the Nakagami distribution can portray the normalized intensity of the L-band scintillation at various S4 values, up to S4 equal to 1.4. Moreover, the departure of frequency dependence on S4 predicted by the weak scintillation is noticed due to multiple forward scattering effects. The coincident feature between the characteristics of irregularity structure and the scintillation variation are then studied. The causal relationship between the fluctuation of ion density and the scintillation variation is obtained. A numerical simulation using the parabolic wave equation has been carried out with the ROCSAT-1 data in space to compare with the ground scintillation observation. The results show the reasonable scintillation level at the coincident time to indicate a direct relationship between the irregularity structure and the scintillation in both temporal and amplitudinal variations. Finally, some assumptions and limitations of the simulation model are discussed.

[1] In this paper we present a numerical and step by step ray-tracing method on a phenomenological ionospheric electron density (Ne) model, the TaiWan Ionospheric Model (TWIM), which is constructed from the FormoSat3/Constellation Observing System for Meteorology, Ionosphere and Climate (FS3/COSMIC) ionospheric radio occultation data. With the Earth's magnetic field and horizontal Ne gradient effects included, efficient methods for calculating ray parameters such as the ground range, reflection height, phase path, and group path are presented. The three-dimensional TWIM consists of vertically fitted α-Chapman-type layers, with distinct F2, F1, E, and D layers, for which the layer parameters such as peak density, peak density height, and scale height are represented by surface spherical harmonics. This way the continuity of Ne and its derivatives is maintained. This is important for practical schemes for providing reliable radio propagation predictions. The methodology is successfully applied to a practical high-frequency transmitter for oblique incidence ray tracing and further evaluated by comparing synthetic vertical ionograms generated by the method with experimental ionosonde observations.

During the polar mesosphere summer echo (PMSE) campaign in 1988 the first multiple-frequency mesospheric measurements were carried out using the European incoherent scatter (EISCAT) 224-MHz radar. A case study of nearly simultaneous measurements of coherent backscatter, collected on two closely spaced frequencies on July 3, 1988, is presented in this paper. The data are used to investigate the frequency coherence of the radar echoes and to perform frequency domain interferometry (FDI) analysis. The FDI technique provides precise information about the thickness and relative position of isolated scattering layers. The results indicate that scattering layers with thicknesses in the range 85–120 m are sometimes present in the polar summer mesosphere. Such a layer is shown to exist for a period of approximately 10 min, and its position is tracked as it descends over more than 1 km in altitude and transits from one range gate to the next. In addition, the FDI technique is used to study a case where a sudden frequency jump is observed in the Doppler spectrum. Spectral jumps appear to be a characteristic of the 224-MHz PMSE echoes observed at EISCAT. The FDI analysis and Doppler sorting are employed to study the coherence spectrum of the two-frequency data before, during, and after the jump. The frequency jump as well as the signatures that are observed in the coherence spectrum can be explained if the radar is observing a thin scattering layer which has been rippled by a steepened gravity wave.

The spaced antenna method for VHF/UHF radar applications is discussed for the general observational configurations including the off-zenith observational mode. On the basis of the assumptions of “locally frozen-in” and volume scattering a physical model is constructed. Cross-correlation and autocorrelation functions are derived and applied for the discussion of the various aspects of the full correlation analysis. Spectral width, aspect sensitivity, and characteristic length are compared for different echo mechanisms in this paper. Some observational results based on the model predictions will be discussed.

[1] A numerical and phenomenological model of global ionospheric electron density (Ne) is investigated. The three-dimensional Ne model has been named the Taiwan Ionospheric Model (TWIM) and constructed from monthly weighted and hourly vertical Ne profiles retrieved from FormoSat3/COSMIC GPS radio occultation measurements. The TWIM exhibits vertically fitted Chapman layers, with distinct F2, F1, E, and D layers, and surface spherical harmonics approaches for the fitted Chapman layer parameters including peak density, peak density height, and scale height. These results are useful in investigation of near-Earth space and large-scale Ne distribution with diurnal and seasonal variations, along with geographic features such as the equatorial anomaly (EA). This paper also investigates the diurnal and seasonal variations of EA within different ionospheric layers and specifically attempts to account for the latitudinal and longitudinal structures caused by atmospheric tides.

Simultaneous VHF radar observations of the troposphere and lower stratosphere were carried out on August 17–19, 1988, near Urbana, Illinois, using the Flatland radar and the Urbana stratosphere-troposphere (ST) radar, which are operated by the Aeronomy Laboratory of the National Oceanic and Atmospheric Administration and the University of Illinois Department of Electrical and Computer Engineering, respectively. The two radar sites are located on the vast plain area of central Illinois, separated by approximately 25 km. The geographical and observational configuration is considered most suitable for investigating mesoscale structures in the troposphere-stratosphere region. One horizontally stratified layer at about 15.5 km related to the tropopause, and another in the troposphere at about 8 km were observed at both radar sites for a long period of time. Velocity fluctuations with periods of 100 min < T < 200 min were observed to be well correlated during a period of quiet horizontal wind. A convective thunderstorm on the evening of August 18 coincided with the dissipation of the tropospheric layer observed at 8 km. We present here a qualitative comparison of low-pass and band-pass filtered echo power and radial velocities, and a comparison of vertical power profiles from the two radars.

High-latitude scintillation data show that the strength and spectral index of intensity scintillation are dependent on the propagation geometry. It will be shown that anisotropic irregularity spectra, with different indices along and across the magnetic field, lead to geometrical effects similar to those observed. In general, the spectrum along the magnetic field is steeper than that across the field, and the difference is more pronounced for nighttime conditions. Spectral anisotropy can be interpreted as a size-dependent irregularity anisotropy. Our data indicate that large-scale irregularities in the daytime and nighttime ionosphere are almost isotropic, while small-scale irregularities are anisotropic and considerably more so at night than during the day. It will be shown that anisotropic irregularity spectra could account for the observed scintillation and in situ temporal spectra with frequency-dependent slope. The effect depends strongly on the geometry.

Ionospheric total electron content (TEC) measurements, obtained simultaneously at several locations, can be processed using computerized tomography (CT) algorithms to obtain two-dimensional images of ionospheric electron density. Using TEC data, computerized ionospheric tomography (CIT) reconstructs an image of the electron density structures in a vertical slice above the receiving stations. We successfully applied this technique to realistic simulations of ionospheric density variations over 16° of latitude and a height range of 50 to 1000 km. A method for approximating the peak height and scale height of the electron density profile will be discussed as well as a reconstruction technique based on the multiplicative algebraic reconstruction technique algorithm and a back projection based initial guess. The quality of reconstructions is considered for two geometries and image resolutions. In particular, the image of a mid-latitude trough with background horizontal density gradient and large-scale irregular structures has been reconstructed from TEC data generated from a model based on an incoherent scatter radar observation. The CT reconstructed image was compared with the original contour map obtained by the incoherent scatter radar. Good agreement has been achieved. The CIT technique has also been applied to a modeled ionosphere to calculate the range rate corrections for a Doppler-tracking radar.

The particular characteristics of the VHF mesosphere-stratosphere-troposphere (MST) radar and wind profiler system, operated at the National Central University in Chung-Li, Taiwan, Republic of China, are described. These are the dual-mode applications of the Doppler and the spaced antenna technique, where the latter is used in the conventional mode to determine the wind velocity as well as in the novel interferometer mode. A brief outline of the scientific rationale and the technical layout of this particular configuration of the Chung-Li VHF radar is given. A generally applicable method for system performance checks by deducing principle radar data parameters before the data analysis has been developed and is briefly described. Receiver system and antenna calibration measurements with celestial radio sources are reported and prove the appropriateness of the antenna system. Radar reflectivity profiles, measured with vertical as well as with off-vertical antenna beams, are presented and discussed. We also present height-time-reflectivity plots for quiet and disturbed weather conditions and reflect on their peculiarities. We show that the wind profiles measured with the conventional Doppler method and the spaced antenna method are in good agreement with radiosonde measurements. The spatial correlation parameters, deduced with the spaced antenna method, are consistent with results from other radars. We also discuss measurement capabilities to deduce the tropopause height with the Chung-Li VHF radar. We also describe echo power variations due to focusing from reflectivity structures modulated by gravity waves and a brief case study of Kelvin-Helmholtz instability. We finally outline future research directions which could be performed with the Chung-Li VHF radar.

A model, based on the principle of volume scattering and the assumption of locally frozen-in refractive index irregularities, is proposed for mesosphere-stratosphere-troposphere (MST) radar observations in the spaced antenna mode. Autospectrum, cross-correlation function, cross-spectrum, and coherence function for the received signals are derived and related quantitatively to the atmospheric parameters. The model predicted results are compared with observational results. It will be shown that under observational and atmospheric conditions with appropriate time and spatial scales the model is consistent with experimental results. Those conditions and scales are discussed in the paper.

In this paper the mean gradient of the generalized potential refractive index, denoted by M, calculated from the meteorological data observed at Pan-Chiao rawinsonde station and the vertical echo power measured with the Chung-Li VHF radar are studied. It is found that the ratio of wet term to dry term in M varies from 20 dB at 1 km to −10 dB at 10 km, where 0 dB is occurred at 8 km. This indicates that the magnitude of M is dominated by the contribution of humidity below 8 km. The correlation between echo power and M2 is good. The slope of the regression line relating the echo power and M2 is found to change for different weather conditions. Furthermore, the echo power profiles during the period of typhoon passage are analyzed. The variation of tropopause height and the maximum radar detectable height during the typhoon passage will be studied.

The Chung-Li VHF radar consists of three phase-coherent transmitting-receiving antenna systems, which allow an optimum application of interferometer and incidence angle measurements of radar echoes from the troposphere and the stratosphere. We briefly describe the applications of the spatial domain interferometry and present here the first measurements of cross spectra and the corresponding phases, which vary as function of frequency due to the mean wind. We also present the first incidence angle measurements and show that the scattering-reflecting structures in the troposphere can be inclined to the horizontal by a tilt or inclination of l°–2°. We also notice a periodic change of this inclination as well as the radial velocity measured with vertical antenna beam as a function of altitude and time which we attribute to long-period waves or mountain waves. There are clear indications that the radial velocity measured with the vertical beam is diluted by the projection of the horizontal wind in the presence of inclined or tilted reflectivity structures. We also describe observations of long-period waves seen in the horizontal wind pattern, which could be of the same origin as the quasi-periodic pattern observed in the inclination and the reflectivity.

Aspect sensitivity at tropospheric heights measured with the vertically pointed broad antenna beam (half power beam width is 7.4°) of the new Chung-Li VHF radar will be presented and discussed. The angular dependence of the echo power is shown to be Gaussian, and the echo power lapse rate at heights between 2 and 8 km is about 0.5 dB/deg to 1.05 dB/deg. This angular dependence levels off at approximately 4° to 10 °, depending on the heights. The observed aspect sensitivity is analyzed and related to background atmospheric parameters.

[1] The middle- and upper-atmosphere (MU) radar (34.85°N, 136.10°E) was operated in the incoherent scatter power-only mode to observe the ionosphere during 17 June 2001. Pronounced 200- to 300-min. waves in the echo power appeared in the F2 region during 0240–1250 local time on 17 June 2001. A procedure of Fourier analyses is conducted to derive power spectra, vertical phase, and group velocities of the pronounced waves. Results show that the center frequency of the waves is a function of the wave number. The opposite directions of the vertical phase and group velocities imply the presence of atmospheric gravity waves.

Multifrequency amplitude scintillation data at L and C bands from the equatorial region at Ascension Island are used to study the spectral index n for the scintillation index S4. The average frequency dependence of the scintillation index (S4) is found to be f−1.68. It is shown that the spectral index tends to be larger for events which occur after 2030 local time than for events which occur before 2030. This may indicate temporal evolution of the irregularity spectrum. Model studies based on a two component power law irregularity spectrum are applied to relate changes in n to spectral evolution and to show that the observations are consistent with recent in situ measurements. Possible geophysical implications are also discussed.

Recently, gravity waves and two-dimensional turbulence have been proposed as possible causes for the observed mesoscale wind fluctuations in the atmosphere. In order to use wind velocity data measured by MST radars to investigate atmospheric gravity wave spectra, it is important to apply the correct relation between the observed wind fluctuation spectrum and the wave spectrum. In this paper, based on acoustic-gravity wave theory and radar observation principle, this relationship is quantitatively derived for the general case of acoustic-gravity waves. Examples are given to show how the theoretical results can be used to interpret the observational data as well as to derive parameters for the model wave spectrum. From the theoretical results, tests for the consistency of the gravity wave model for atmospheric wind fluctuations will be proposed.

In situ data measured on board AE satellites and rockets reveal spiky and wedgelike electron density structures inside the equatorial ionospheric bubbles. Two models are constructed to simulate the initial stage and fully developed stage of a bubble. Effects of radio propagation through such bubbles are simulated by solving the parabolic equation numerically. The results show that even though the amplitude scintillation at 136 MHz appears to be stationary, such is not the case at gigahertz frequencies. Instead, the amplitude at gigahertz frequencies shows outbursts with large excursions whenever the direct ray intersects the spicky ionization structure. Both the peak-to-peak excursion and the amplitude distribution cannot be predicted by the scintillation theory that assumes the medium to be random.

The structure of intensity scintillation is characterized by the fourth-order complex signal moment Γ4. The differential equation that governs the behavior of Γ4 is written in terms of dimensionless variables to isolate parameters that can be inferred from intensity scintillation data without a priori knowledge of scale sizes, layer thickness, propagation angles, etc. It is shown, for example, that when the outer scale is large compared to the Fresnel radius, the scintillation index measured under weak scatter conditions can be used to derive a universal scintillation index curve. Multifrequency scintillation data are presented to demonstrate the concept.

Simultaneous scintillation data from the ATS-6 Radio Beacon Experiments for signals at 40, 140, and 360 MHz offer the opportunity to study the frequency dependence of the scintillation phenomenon. Using these data variations of the spectral index, correlation coefficient, and the correlation interval are investigated. It is found that for weak scintillations, the spectral indices lie between 1.5 and 1.7. When the scintillation is strong, the spectral indices vary from about 1.4 to 0.7. The correlation coefficients are found to decrease for increasing scintillation level. The interesting behavior of the correlation intervals as functions of signal frequency is also discussed. The observational results are compared with theoretical predictions.

It is proposed to describe the temporal characteristics of a wave propagating in a random medium in terms of its temporal moments. The first two moments are related to the mean arrival time and the mean pulse width. It is shown that the one-position two-frequency mutual coherence function enters in the formulation naturally. The form of the expression suggests expanding the mutual coherence function in a narrow-band expansion whose coefficients can be solved exactly from the parabolic equation that takes into account all multiple scattering effects except the backscattering. A brief survey of the literature shows that the irregularity spectrum, under various conditions, has a power-law dependence. In order to conform to this observation a Bessel function spectrum proposed by Shkarofsky is found convenient to use since it not only reduces to the desired power-law form in the proper range of wavenumber space, but also has all the finite moments. Exact expressions for the mean arrival time and mean square pulse width are obtained; some numerical examples are given. Finally, the effect of noise on these moments is discussed.

The morphological aspect of gigahertz equatorial scintillations in the Asian region has been reported. As a follow-up, this paper studies the statistical aspect of equatorial scintillations in the same region. Power spectra of prominent scintillation events collected over a 16-month period during the solar maximum years in sunspot cycle 21 were analyzed. The slope ν of the spectrum at the high-frequency end was analyzed with respect to the strength of scintillation as indicated by scintillation index S4. The values of S4 were compared with theoretical calculations based on either phase screen formulation or Rytov approximation. These comparisons were used to assess ionospheric parameters such as the height and thickness of the irregularities layers, rms fluctuation of the total electron content, and the axial ratio of the irregularities. Autocorrelation calculation provided a characteristic coherent interval τ. The study suggests that equatorial ionospheric irregularities in the F region, with subkilometer sizes in the evening hours after local sunset, are the main cause of the gigahertz scintillations observed. The spectra of the irregularities appear to be the power law type, with spectral indices p that generally have values greater than 4. The characterizations of S4, ν, and τ for both the Pacific and Indian Ocean region links provide an important basis for improved modeling of ionospheric scintillation phenomena in the Asian region.

HF wave propagation in the turbulent stratified ionosphere is investigated using the multiple phase-screen simulation method. For waves incident along the axis of the background stratification, generalized parabolic equations for the modified complex amplitude u are derived which are applicable even in the strong scattering case. Based on these parabolic equations, several one-dimensional random phase screens are numerically generated to represent the effect of the random irregularities on the wave. For plane wave incidence, various statistical properties of the field, such as correlation, power spectrum, scintillation index, etc., can be directly computed using spatial averaging under the ergodicity assumption. The simulation method is also used to examine the effect of the velocity profile on the drift pattern on the ground.

In this second paper, we shall concentrate on the “background wave spectra” which were observed during several magnetically quiet days in the Worldwide Atmospheric Gravity Wave Study (WAGS) campaign. The observed parameters used in this study are the ionization density and the line-of-sight ion velocity. This provides more information than in most of the previous investigations of traveling ionospheric disturbances, in which only electron density perturbations were used. The data will be analyzed and compared with a theoretical model to yield information about the background gravity wave spectrum in the neutral atmosphere. It will be shown that the neutral vertical velocity spectrum can be modeled as a power law type of spectrum. The overall kinetic energy of this spectrum will be calculated and compared with that associated with the special event observed on a magnetically active day.

Two possible mechanisms are responsible for the temporal broadening of pulses propagating in a turbulent medium. The ensemble averaged pulse may be broadened owing to the fact that each realization of the ensemble is spread in time as a consequence of scattering. It may also come about because of the wandering of the pulse. In this paper these two mechanisms are studied. First, the two-frequency and the four-frequency mutual coherence functions for the field are obtained for both the Rytov approximation and the asymptotic saturated condition. They are then used to compute the spreading and wandering of the pulse. It is found that under the condition of weak scattering, pulse wandering dominates the contribution to the broadening of the pulse. In the saturated region, however, pulse spreading becomes the dominant factor. Explicit expressions for the spreading and wandering are derived for some examples.

Recent development in the optical scintillation theory has been adapted to the ionospheric geometry in order to study the ionospheric scintillation phenomenon in the presence of multiple scattering. Under approximations well satisfied in typical ionospheres for a frequency above about 20 MHz, the first through fourth moment equations have been derived and some analytic solutions given. The fourth moment equation has also been solved numerically. The numerical results show clearly the occurrence of focusing and saturation phenomena. The new multiple-scatter effects are emphasized.

An electromagnetic signal randomized by scattering from plasma irregularities and by subsequent diffraction in the nonrandom part of the medium is known to bear statistical information about the plasma turbulent irregularities. For example, if the turbulent spectrum is of the form κ−p in its wavenumber dependence, the received amplitude of the electromagnetic signal will fluctuate with a high frequency spectral asymptote of the form υ1−p. However, a power-law turbulent spectrum of the form κ−p has certain nonphysical difficulties if cutoffs at both the inner scale and the outer scale are not introduced. In addition, in this paper it is shown that the mean arrival time and the mean square pulse width are rather sensitive to values of the outer and inner scales of ionospheric turbulence. Information concerning the values of these scales is rather meager at present. It is therefore suggested that pulsed experiments be made so that the inner scale and the outer scale can be determined. Possibilities of making similar measurements on a laboratory plasma are also implied.

In the Worldwide Atmospheric Gravity Wave Study (WAGS) campaign, the source-response relationship between the auroral activities and the gravity waves observed in the ionosphere was studied. Ionospheric parameters observed with the incoherent scatter radars at Sondrestrom and Millstone Hill were compared with predicted results based on gravity wave theory. In the observed data, usually two types of disturbances can be identified. One is the distinct, semiperiodic traveling ionospheric disturbance. The other is the ever present, semirandom perturbations. The first type will be classified as the “special event,” and in this paper, we shall concentrate on the “special event” which was observed on October 18, 1985 during a moderately magnetically active period. The observed parameters used in this study are the ionization density and the line-of-sight ion velocity. This provides more information than in most of the previous investigations of traveling ionospheric disturbances, in which only electron density perturbations were used. The data are analyzed and compared with theoretical models to yield information about the special gravity wave event, such as the vertical and horizontal wavelength, the horizontal phase and group speeds, and the kinetic energy density carried by the waves. The observed waves at the two radar sites are related to a possible source region in the auroral zone.

In the derivation of Booker-Gordon scattering cross sections in a turbulent atmosphere, certain assumptions have been made so that the power scattered within the scattering volume will add coherently. This results in a scattered power that is proportional to the effective scattering volume. As the scattering volume increases without bound, it leads to a physically unreasonable result of infinite scattered power. In this paper we examine these assumptions. In particular, we study the scattering cross sections, taking into account the possible phase incoherence of the scattered fields within the scattering volume. In addition, the effect of a thin turbulent layer on the complex autocorrelation function is investigated. The turbulence is assumed to be locally frozen. Expressions for both the Doppler shift and the correlation time have been derived.

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.

Previous work has shown that a primary gravity wave of sufficient amplitude will always decay through resonant wave-wave interactions with two secondary gravity waves. The interaction among the resonant trio can be reasonably rapid and may be an important process responsible for energy exchange among gravity waves of different wavelengths in the atmosphere. By taking statistical ensemble averages to the interaction equations we obtain an hierarchy of moment equations, the closure condition of which can be effected by making a random phase approximation. The obtained kinetic equation is Boltzmann-like and describes the time evolution of wave action. The nonlinear kinetic equation is impossible to solve in general except numerically, but the equation is drastically simplified in three limiting cases identified as elastic scattering, parametric subharmonic instability, and induced diffusion processes. Through elastic scattering, an upgoing wave is scattered into a downgoing wave by interacting resonantly with a vertical shear. This process is thus responsible for making the atmospheric spectrum vertically symmetric if it is not so initially. The parametric subharmonic instability process is responsible for transferring energetic large-scale waves to small-scale waves at one-half the frequency. The induced diffusion process is responsible for time evolution of small-scale waves by a three-wave process involving two nearly identical waves of small scales interacting resonantly with a large-scale vertical shear. The rapidity with which these three processes take place in the atmosphere and their implication in the atmospheric spectrum are investigated and discussed.

The problem of beam waves propagating through a turbulent layer is studied by using both the stochastic and the deterministic approaches. In the statistical approach exact analytical expressions of beam wander and spread are derived for the turbulence with Shkarofsky spectrum by using phase screen model. The beam spread is found to be dependent, among other factors, on the spectral index of the power law spectrum. In the deterministic approach, the beam wave is propagated through a numerically simulated ionospheric bubble. Hot spots in the intensity and fast fluctuations in the phase are found to appear across the beam. Numerical examples are given. Applications to various transionospheric beam wave systems are discussed.

Theoretical and experimental aspects of using radio scintillation to study ionospheric irregularities will be reviewed in this paper. Both weak and strong scintillation theories will be presented. Theoretical results will be compared with typical experimental data to demonstrate the procedure. Discussions will be concentrated on what information about ionospheric irregularities can be extracted from scintillation data and how. Also, a recently developed simulation technique for radio wave propagation through ionospheric irregular structures will be discussed. It will be shown that by applying this technique, one can obtain information about the properties of the irregularities that are of either statistical or deterministic nature. Specific examples of applying this technique to study equatorial ionospheric bubbles will be reviewed.

Spaced-receiver scintillation measurements are modeled applying scintillation theory together with model spectral representations of nonfrozen turbulent media. The effects of velocity distribution of scatterers, diffusion of irregularities and velocity gradient across the scattering layer on parameters derived from spaced-receiver scintillation experiments are studied. Both correlation and dispersion analyses are considered. The results from modeling are compared with observational data from the equatorial region. It will be demonstrated that self-consistent models can be constructed in interpreting the data and information about the drift velocity field in the ionosphere can be obtained from spaced-receiver experiments.

Ionosphere scintillation data at 4 GHz received in Hong Kong are used to study the statistics of scintillating signals. The data were taken during the last solar maximum (1979–1980) and covered two ionospheric locations, POR (123°E, 20°N) and IOR (108°E, 20°N). The study includes two parts. First, the cumulative distribution functions of the signal are generated from the data base and compared with theoretical distributions. Signal statistics such as the decibel levels of maximum peak, 5% peak, 95% fade and maximum fade are recorded and compared to the scintillation index S4. Empirical relations between S4 and these decibel levels are obtained through statistical analysis. It will be shown that simple linear relations exist between S4 and peak/fade decibel levels. These relations were compared with the results obtained from the “third peak” method for determining the SI index. The second part of the study involved a statistical investigation of the variations of the decorrelation interval of the signal and the roll-off slope of the power spectrum. Diurnal and seasonal variations are investigated. Geophysical interpretation of the results are presented.

Nonlinear oscillations averaging method applied to resonant interactions of acoustic gravity waves

We study the propagation of a wave in an arbitrarily stratified medium in the presence of small random irregularities. The technique of two-dimensional Fourier-Stieltjes spectral representation for the random field is used to formulate this problem. With high frequency wave propagation in mind, we applied the W.K.B. method to yield approximate expressions for structure (correlation) functions for the logarithmic amplitude and phase departure of the wave field. The results are compared with those derived for a random medium with homogeneous background. An example is given in which the effect on the amplitude and phase fluctuations due to the stratified background is explicitly computed.

Wave propagation in random plasma medium with inhomogeneous parabolic electron density profile background for ionospheric propagation applications

Coherent wave propagation in warm turbulent plasma, using perturbation method for wave dispersion

Ionospheric irregularities explained by gravitational field and positive electron density gradient joint effect on ionospheric region below electron distribution peak