Booker H.G., 1979, "The role of acoustic gravity waves in the generation of spread-F and ionospheric scintillation", Journal of Atmospheric and Terrestrial Physics, 41, pp 301-315.
In the aggregate, acoustic gravity waves in the F-region constitude a spectrum of geophysical noise extending from the frequencies involved in diurnal variations up to the Brunt-Väisälä bouyancy frequency. They drive a roughly uniform power spectrum of travelling ionospheric disturbances (TIDs) with vertical scales of the order of the atmospheric scale height H and with horizontal scales extending from the radius of the earth down to H. It has been known since the 1950s that this permits multiple normals onto the F-region from an ionosonde, thereby creating the multiple-trace type of spread F on ionograms. At shorter scales the spectrum of the TIDs decreases in strength and, below the mean free path of the neutral atmosphere, creates a spectrum of plasma turbulence aligned along the Earth's magnetic field. Progressivley shorter scales are responsible for phase scintillations, for amplitude scintillation and for blur-type spread-F on ionograms. A weak extension of the spectrum to scales less than the ion gyroradius is responsible for spread F and transequatorial propagation in the VHF band. Under evening conditions in equatorial regions a band of TIDs with wavelengths of the order of 600 km can, at times, have phase velocity that matches the drift velocity of the plasma (RÖTTGER 1978). This band of TIDs is then amplified until it breaks (KLOSTERMEYER 1978). The associated explosive increase in plasma turbulence creates the plume phenomena discovered by WOODMAN and LA HOZ (1976).
Booker H.G., 1981, "Application of refractive scintillation theory to radio transmission through the ionosphere and the solar wind, and to reflection from a rough ocean", Journal of Atmospheric and Terrestrial Physics, 43, pp 1215-1233.
The results of BOOKER and MAJIDIAHI (1981) concerning refractive scattering by large-scale irregularities in a phase-changing screen are combined with the theory of diffractive scattering by small-scale iregularities in order to study three intensity scintillation phenomena. The first is the reflection of radio and optical waves from an ocean surface disturbed by a spectrum of water waves. The second is the scintillation of VHF, UHF and SHF radio waves traversing the ionospheric F-region. The third is the scintillation of VHF, UHF and SHF radio waves traversing the solar wind. In each case appropriate values are chosen for the mean square fluctuation of phase, for the outer scale, for the inner scale and for the spectral index. Spectral diagrams are drawn to show how the outer scale, the inner scale, the Fresnel scale, the focal scale, the lens scale and the peak scale vary with a relevant parameter (electromagnetic wave-frequency for the ocean, RMS fractional fluctuation of ioniztion density for the ionosphere, and distance of closest approach to the Sun for the solar wind). For the ionosphere and the solar wind, multiple refractive scattering by wave irregularities occurs in practice whereas it is strong single scattering that is assumed in the thin-screen theory; potential consequences of this are discussed qualitatively.
Bramley E.N. and Browning R., 1978, "Mid-latitude ionospheric scintillation of geostationary satellite signals at 137 MHz", Journal of Atmospheric and Terrestrial Physics, 40, pp 1247-1255.
The results are given of a twelve-month series of scintillation measurements at a frequency of 137 MHz, using signals from a quasi-geostationary satellite. In addition to the usual night-time minimum in the occurrence of scintillations, a pronounced daytime maximum was observed at all seasons. A spaced-aerial receiving system was used, enabling the geometrical statistics of the ground diffraction pattern, and hence those of ionospheric irregularities, to be investigated. A combination of these results with the observed frequency spectra confirmed the F-region and E-region origins, respectively of the night-time and daytime scintillations.
Chytil B., 1975, "A note on the spectral density function of ionospheric irregularities", Journal of Atmospheric and Terrestrial Physics, 37, pp 815-823.
Three possible spectral density functions for ionospheric irregularities are considered. The resulting frequency spectrum of amplitude fluctuations in a wave passing through these irregularities is compared with that experimentally observed in satellite signals. It is found that a power-law spectrum of ionospheric irregularities gives a better fit to the data than a Gaussian spectrum.
Clark D.H., 1971, "The latitude variation of sizes of the ionospheric irregularities producing radio-satellite scintillation", Journal of Atmospheric and Terrestrial Physics, 33, pp 1267-1272.
The sizes of the small-scale ionospheric irregularities producing radio-satellite scintillation have been found from an auto-correlation analysis of scintillation records. At night irregularity sizes are found to be typically greater at mid-latitudes than at sub-auroral latitudes. They do not appear to depend on ionospheric height or Kp condition.
Clark D.H. and Ireland W., 1975, "Quasi-periodic scintillations of radio-satellite signals", Journal of Atmospheric and Terrestrial Physics, 37, pp 1277-1279.
Quasi-periodic scintillation of radio-satellite signals has been
attributed to a variety of possible causes; these include site effects,
diffraction by ionospheric irregularities, and interference between
transmissions from two satellites or between a single satellite and ground
transmissions.
Evidence is presented showing that fading produced by interference effects
can readily be distinguished from scintillation of ionospheric origin, one
distinct class of which is confirmed by experiment to originate in the
ionospheric E-region. The suggested grouping of all quasi-periodic
amplitude fluctuations under the broad classification 'QP Scintillations' is
not satisfactory, and this term should be resticted to fluctuations
originating in the ionosphere.
Das Gupta A. and Kersley L., 1976, "Summer daytime scintillation and sporadic-E", Journal of Atmospheric and Terrestrial Physics, 38, pp 615-618.
Scintillation of transionospheric transmissions from geostationary satellites observed at a mid-latitude site during daytime in summer has been shown to be associated with sporadic-E. It has been found that a high critical frequency and an extended vertical structure of the sporadic-E layer, as indicated by range spread on ionograms, are linked with scintillation occurrence. There are indications that at times of scintillation the vertical distribution of ionisation in the layer may be influenced by short period gravity waves.
Davies K. and Whitehead J.D., 1977, "A radio lens in the ionosphere", Journal of Atmospheric and Terrestrial Physics, 39, pp 383-387.
Using a modified version of the classical Cornu spiral, fading patterns in
agreement with observations of radio signals on 140 and 360 MHz from the
geostationary satellite ATS6, have been obtained. The particular fading
patterns chosen show modulated quasi-periodic fading before and after a
deep central minimum. It is shown that a cylindriccal lens in the
ionsophere required to produce this is only about 100 m across (an order of
magnitude smaller than the size of the pattern on the ground) and if it were
circular in cross-section would have a maximum plasma frequency of over 40
MHz. This suggest that the reason why calculations based on a transparent
phase screen did not give the observed fading pattern for the 40 MHz signals.
It was not possible to deduce the height of the lens above the ground,
though we would incline to an E-region origin.
Doan J.W. and Forsyth P.A., 1978, "Mid-latitude quasi-periodic scintillations of satellite beacon signals", Journal of Atmospheric and Terrestrial Physics, 40, pp 981-990.
Simultaneous observations of amplitude fluctuations at two stations and of the relative phase of the arriving signals are used to study quasi-periodic scintillations of the kind that are sometimes called 'ringing irregularities'. Since one set of measurements is sufficient to locate the irregularity it is possible to assess the utility of a model proposed by Elkins and Slack by using it in a computer simulation to predict the temporal behaviour of the other observed quantities. The resulting agreement leaves no doubt that scintillations arise in the ionosphere by a mechanism having the gross features of the one suggested, although the additional redundant observations permits the derivation of information about the ionospheric irregularities not encompassed by the Elkins and Slack model. This simple geometric model which assumes specular reflection is extremely useful and the more complete scattering analysis is needed only where detailed information about the irregularity is required. Evidence is also presented for the occassional occurrence of large angle scattering from ionospheric irregularities.
Dyson P.L., 1971, "Comparison of scintillation, spread F and elctrostatic probe observations of electron density irregularities", Journal of Atmospheric and Terrestrial Physics, 33, pp 1185-1192.
A comparison is made of Aloutte II topside sounding and electrostatic probe measurements of electron density irregularities near simultaneous BE-B scintillation observations and ground-based ionosonde data. The topside sounding technique was found to be the most sensitive means of detecting irregularities followed by scintillation, bottomside sounding and electrostatic probe. Hence combining the results of different experiments can present difficulties in interpretation. The results indicate the need for further direct measurements of irregularity characteristics particularly near the F2 layer peak.
Fremouw E.J., 1980, "Geometrical control of the ratio of intensity and phase scintillation indices", Journal of Atmospheric and Terrestrial Physics, 42, pp 775-782.
Early observations of complex-signal scintillation revealed a sizeable difference in the ratio of the intensity scintillation index, S4, to the phase scintillation index, when measured at mid-latitude, auroral-zone, and equatorial stations. The differences observed between auroral and equatorial stations receiving a beacon signal from a polar-orbiting satellite have now been found to persist, for non-staurated values of S4. The phase-screen theory for the production of scintillation is employed in this paper to indentify four factors that control the S4 ratio, and the behaviour of two of them is explored for models describing both sheetlike and rodlike plasma-density irregularities. The analysis permits rejection of the effects of static diffraction by field-aligned irregularities (whether rodlike or sheetlike) as the factor controlling the different behaviours observed. It is shown, on the other hand, that geometrical control of the effective outer scale imposed by detrend filtering in the presence of highly anisotropic irregularities can readily explain the observed behaviour. Such effects arise in virtually all experiments and radio systems operating in the presence of a power-law spectrum with a very large outer scale, and they are important in controlling the relationship between phase and intensity scintillation.
Fremouw E.J., Livingston R.C. and Miller D.A., 1980, "On the statistics of scintillating signals", Journal of Atmospheric and Terrestrial Physics, 42, pp 717-731.
The statistics that best describe optical and radio signals that have been
scattered by random refractive-index irregularities have presented an open
question for some time. Different models have been used close to the
medium (log-normal) and far from it (Rican), and signal behaviour in the
intermediate zone has been particularly difficult to characterize. In this
work, we address experimentally the problem of a general and systematic
description in all Fresnel-zone regimes and for all strengths of scatter.
We make use of multi-frequency, phase-coherent radio signals transmitted
through the ionosphere to obtain a bivariate representation of complex-signal
statistics and then form conclusions based on chi-squared tests of four
hypotheses against histograms of intensity and phase.
We find that neither the log-normal nor the Guassian generalization of
Rican statistics provides a generally valid and complete description of
scintillation but that a two-component model based upon them does. We
suggest, further, that equal or superior efficacy might be achieved from
a simpler model based on the Nakagami distribution for intensity and the
normal distribution for phase. At present no such model exists that can
also account for correlation between intensity and phase, which is a
salient feature of our observations.
Fremouw E.J. et al., 1978, "Early results from the DNA Wideband satellite experiment - Complex-signal scintillation", Radio Science, 13, pp 167-187.
A multifrequency (ten spectral lines between VHF and S band) coherent radio beacon is presently transmitting continuously from a 1000-km, high-inclination orbit for the purpose of characterizing the transionospheric communication channel. Its high phase-reference frequency (2891 MHz) permits direct observation of complex-signal scintillation, and its very stable, sun-synchronous orbit allows repeated pre-midnight observations at low latititudes and near-midnight observations at auroral latitudes. We present here early results of the observations; salient points include the following. First, most of the data are consistent with phase-screen modeling of the production of ionospheric scintillation, including an f-2 frequency dependence for phase variance. Second, propagation theories invoking weak, single scatter seldom are adequate, because even moderate intensity scintillation usually is accompanied by phase fluctuations comparable to or greater than a radian. Third, under conditions producing GHz scintillation (near the geomagnetic equator), lower frequencies show marked diffraction effects, including breakdown of the simple f-2 behaviour of phase variance and loss of signal coherence across a band as narrow as 11.5 MHz at UHF.
Fujita M. et al., 1978, "1.7 GHz Scintillation measurements at midlatitude using a geostationary satellite beacon", Journal of Atmospheric and Terrestrial Physics, 40, pp 963-968.
Preliminary results of 1.7 GHz scintillation measurements made in Japan using a geostationary satellite during May-August in 1977 are presented. Since the propagation path below about 100 km altitude is nearly parallel to the magnetic field, it was possible to observe irregularities along the field direction. The scintillation activity was enhanced at night in June and the maximum peak-to-peak variation of scintillation observed was about 2.3 dB. Simultaneous measurement of the total electron content show that irregular electron density structures play an important role in 1.7 GHz scintillation.
Fujita M., Sinno K. and Ogawa T., 1982, "Frequency dependence of ionospheric scintillations and its application to spectral estimation of electron density irregularities", Journal of Atmospheric and Terrestrial Physics 44, pp 13-18.
Analytical results of simultaneous observations of 136 MHz and 1.7 GHz ionospheric scintillations at mid-latitude during summer are presented. The causal relation between scintillation occurrence and ionospheric condition is discussed to examine the influences of spread-F and sporadic-E on the scintillation. The diurnal variations of scintillation occurrences show that the time of maximum occurrence for the nighttime scintillation depends on the scintillation amplitude. the frequency dependence of the scintillation depth is, on average, ft-1.38 during the nighttime and ft-1.52 during daytime, where ft is the transmitted wave-frequency, which may reflect the difference in the spectral form of electron density irregularities. Finally, the temporal variations of the frequency dependence index are investigated for the nighttime peiod. The result indicates a clear variation of the spectral form of irregularities with time.
Hajkowicz L.A., 1971, "VHF phase detection of magnetic field aligned irregularities in mid-latitudes", Journal of Atmospheric and Terrestrial Physics, 33, pp 1685-1692.
A new phase recording technique, based on elimination of the phase ramps, was used to record the angle-of-arrival variations in the vicinity of London, Ontario, using the ISIS-1 beacon signal at 136.410 MHz. A conventional technique was used to record the ISIS-1 signal at 137.950 MHz. The new technique made it possible to record small angular scintillations of short periods which were undetectable by conventional methods (i.e. phase ramp or amplitude scintillations). The scintillations, in a period range of 0.2-0.5 sec, showed considerable enhancement in magnitude in the regions (south of London) where the angle between the ray-path and magnetic field is close to a minimum value.
Hajkowicz L.A., 1974, "Radio transmissions from two satellites as a possible cause of quasiperiodic scintillations in amplitude recordings", Journal of Atmospheric and Terrestrial Physics, 36, pp 1689-1693.
A numer of reports have been written on the occurrence and causes of regular fadings, or quasiperiodic (QP) scintillations, in amplitude and phase of satellite radio-transmissions in the VHF range. QP scintillations have been associated with the E- or F-region ionospheric phenomena. Further analysis of the amplitude data suggests that QP scintillations may be closely linked with an interference effect of electromagnetic waves simultaneously transmitted by two satellites moving within the beamwidth of the receiving antenna. A certain type of QP scintillations could be due to an interference effect between the satellite and ground transmissions.
Hajkowicz L.A., 1975, "Morphological aspects of ionospheric scintillations from a multi-satellite radio transmission system", Journal of Atmospheric and Terrestrial Physics, 37, pp 1255-1261.
Radio transmissions at a frequency of 150 MHz from five U.S. Navy
Navigational Satellites were used to detect amplitude scintillations in
southern mid-latitudes. The frequent radio scans of the ionosphere made it
possible to follow the development of scintillation regions at night-time.
At first, scintillations tended to occur polewards of the station in the
evening. This was followed by the equatorwards drift of scintillations with
a typical velocity lying between 70-130 m/sec. Later at night the majority
of scintillations occurred equatorwards of the station. The time of the
evening occurrence of scintillations coincided with the sunset curve at
the auroral F-region.
The equatorwards drift of the scintillations is in agreement with the
earlier finding on the equatorwards expansion of the polar scintillation
ovals. It is suggested that the polar scintillation oval is a source of
scintillation activity in mid-latitudes.
Hajkowicz L.A., 1977, "Morphological and ionospheric aspects of quasiperiodic scintillations", Journal of Atmospheric and Terrestrial Physics, 39, pp 833-841.
Multi-satellite scintillations, at a frequency of 150 MHz, and associated
vertical-incidence ionosonde data were recorded at Brisbane from November
1973-January 1976. A distinct type of regular amplitude fadings, so-called
quasiperiodic (QP) scintillations, was most frequently recorded in a time
interval: 2200 to 0200 LT in the southern summer, and to a lesser extent in
autumn. The maximum in the occurrence number of QP scintillations coincided
with the largest simultaneous increases in the intensities of nocturnal
sporadic-E (Es) and spread-F. QP scintillations were rarely
recorded in winter at the time of pronounced Es activity.
The majority of QP scintillations occurred at zenith angles in excess of 70°,
and at north-west azimuth angles centered on 330°. The azimuth preference
in the occurrence of QP scintillations is similar to the prevailing
north-west direction of arrival of ionospheric reflections at Brisbane. It
appears that the generation of these scintillations is associated with the
frontal structures of irregularities responsible for spread-F and
Es in southern midlatitudes.
Hajkowicz L.A., 1977, "Multi-satellite scintillations, spread-F, sporadic-E over Brisbane -1", Journal of Atmospheric and Terrestrial Physics, 39, pp 359-365.
Associated amplitude scintillations and vertical-incidence ionosonde data
were obtained during a two-year recording period at Brisbane.
Scintillations were recorded using radio-satellite transmissions at a
frequency of 150 MHz from six U.S. Navy Navigational Satellites (NNSS). It
was found that a consistent decrease of scintillations in the morning from
0200 to 0600 LT coincided with an increase in the occurrence and intensity
of the frequency spread of spread-F, especially in the southern
Winter. A midnight (2200 to 0200 LT) maximum in scintillations coincided
with increases of the range spread of spread-F and nocturnal sporadic
E(Es), especially in the Summer. A second increase in
scintillations was consistently recorded in the afternoon from 1400 to 1800
LT in the Winter, and was associated with a pronounced enhancement in the
occurrence and range spread of daytime Es; the occurrence
of spread-F was insignificant during this period. The Winter of 1974
was associated with an unusually high occurrence of Es in
the afternoon period. Simultaneously, average scintillation index reached
its highest level.
The diurnal variation in the spatial occurrence pattern of scintillations
indicates an equatorwards drift in scintillation patches as the night
progresses. Scintillations tended to occur at relatively large zenith
angles, especially durng the post-midnight hours. The eqatorwards drift
direction of scintillations is in agreement with the reported movement of
ionization patches responsible for spread-F and Es
at Brisbane.
It appears that the spatial difference in the reflection of ionosonde echoes,
associated with the frequency and range spread, is responsible for the
varying degree of correlation of scintillations with these two types of
spread-F.
Hajkowicz L.A., 1978, "Mid-latitude scintillations, spread-F and sporadic-E over Brisbane - 2", Journal of Atmospheric and Terrestrial Physics, 40, pp 99-104.
Amplitude scintillations of radio transmissions from six U.S. Navy
Navigational Satellites at a frequency of 150 MHz have been recorded at a
southern mid-altitude station over a number of years. Scintillations were
most pronounced in winter daytime and summer night-time. The winter maximum
coincided with maxima of range spread (Se) and critical frequency (foEs) of
sporadic-E (Es), and range spread of spread-F (Sr) was negligible or absent.
The summer scintillation maximum was associated with simultaneous maxima of
nocturnal of Se, Sr and high values of foEs.
The well-known occurrence of intense Es in summer daytime, characterised by
the diurnal maxima of Se and foEs, coincided with small scintillation
activity. This appears to be due to the fact that the Es which occurs at
this time is of the "sequential" type (Ess) the structure of which is too
uniform to cause scintillations. On the other hand, the summer night-time
and winter daytime maximum in scintillation activity coincided with the
occurrence of so-called "constant height" Es (Esc) which is believed to have
a small scale irregularity structure. It is evident that Esc is responsible
for daytime scintillations even in the UHF range of satellite transmissions.
Hajkowicz L.A., 1981, "A horizontal structure of random and quasiperiodic scintillations over a wide range of latitudes", Journal of Atmospheric and Terrestrial Physics, 43, pp 165-170.
VHF amplitude transmissions, from a large number of non-synchronous satellite passes, were recorded to deduce ionospheric scintillation occurrences from low to auroral latitudes during a geomagnetically quiet period. An intense region of random scintillation-producing irregularities was centered near a mid-latitude station. Simulatneously, the records obtained from satellites moving in meridonial planes indicated the presence of pronounced, regular fading, or quasiperiodic (QP) scintillations, at large zenith angles and equatorwards of the station. Other stations, positioned away from scintillation-producing irregularities, recorded signals which were free of QP scintillations. It is suggested that reflection and interference of the transmitted radio waves, due to the presence of tilted ionization surfaces embedded in the random scintillation-prodcuing structure, are responsible for the preferential occurrence pattern of the regular fading.
Hajkowicz L.A., 1982, "Equatorwards limits of the southern scintillation oval", Journal of Atmospheric and Terrestrial Phsyics, 44, pp 539-545.
Radio signals in the VHF range were recorded and compared with ionograms over a wide range of southern latitudes during a few equinoctial months for which a large variation in the magnetic distrubance level was observed. It is evident that the equatorwards edge of the auroral scintillation oval extends well into mid-latitudes for high values of magnetic K-index. The range-spreading type of spread-F and scintillation-producing irregularities show a high degree of spatial coincidence from the polar cap to mid-latitudes. It is suggested that the inhomogeneities responsible for both ionospheric phenomena are associated with the equatorwards propagation of travelling ionospheric distrubances (TIDs) generated in the auroral zone.
Hajkowicz L.A., 1982, "Topside and ground ionosonde observations of a mid-latitude scintillation region", Journal of Atmospheric and Terrestrial Physics, 44, pp 173-178.
Ionospheric amplitude scintillations of transmissions in the VHF range from orbiting satellites were compared with topside and ground (bottomside) ionograms of an inhomogenous region in southern mid-latitudes. It is evident that, for the event considered, there is a good spatial correlation between intense topside and bottomside spread-F and scintillations. The ionospheric disturbance pattern appears to agree with a quasi-sinusoidal model of frontal disturbances (derived from the angle-of-arrival experiments) in the F-region at these geographic latitudes.
Hajkowicz L.A., Bramley E.N. and Browning R., 1981, "Drift analysis of random and quasiperiodic scintillations in the ionosphere", Journal of Atmospheric and Terrestrial Physics, 43, pp 723-733.
Radio signals in the VHF/UHF range from the geostationary satellite ATS-6
were recorded using a system of three spaced antennas at Slough.
Simultaneously, the integrated electron content (TEC) was monitored between
the satellite and ground. Full correlation analysis and similar fade
techniques were used to deduce the drift velocities of irregularities
responsible for random and quasiperiodic (QP) 'ringing' scintillations.
Similar drift velocities were found for the disturbances responsible
for both types of scintillations at times when QP and random scintillations
occurred in a sequential pattern. A southward-drifting disturbance was
responsible for rare, multiple QP scintillations which were followed by
large scale fluctuations in electron density. In general,
QP-scintillation-producing irregularities drifted southward, with
velocities whose median magnitude and azimuth were 64 ms-1
and 178°E of N respectively.
The sequential occurrence pattern of QP-random scintillations as well as
the time delay between occurrences of large fluctuations in TEC and QP
scintillations, appear to be consistent with a reflection model of
generation of the ringing fading of the signal.
Kersley L. and Chandra H., 1984, "Power spectra of VHF intensity scintillations from F2- and E-region ionospheric irregularities", Journal of Atmospheric and Terrestrial Physics, 46, pp 667-672.
An experiment is described for the routine study of scintillations and ionospheric irregularities at high-latitudes using NNSS satellites with coordinated observations by means of the EISCAT ionosphere radar facility. Early results, obtained during the development phase of the experiment, are presented of a power spectra of intensity fluctuations at 150 MHz observed at the equatorwards edge of the high-latitude irregularity zone. The spectra of 165 samples of night-time scintillation recorded during October 1982 to May 1983 show a spectral index with a mean value of -3.58 and a steepening of the spectral slope with increasing S4. Some examples of scintillation arising from irregularities at E-layer heights show spectral indices of magnitude generally smaller than for F-region cases. A few spectra have been found with a clear break in spectral slope at around 10 Hz, suggesting two regimes for irregularities of different scale sizes.
Liu C.H. and Yeh K.C., 1977, "Model computations of power spectra for ionospheric scintillations at GHz frequencies", Journal of Atmospheric and Terrestrial Physics, 39, pp 149-156.
Recently, two models of ionospheric electron density irregularities have been proposed to interpret the GHz scintillation phenomenon. One is an irregularity slab of thickness about 200 km or so around the F-region peak with the electron density fluctuations of the order of 20% about its background value. The other assumes an ensemble of field-aligned irregularities throughout the large part of the magnetosphere as the cause for signal fading. Power spectra of GHz scintillation signals for these two models are investigated in this paper from the viewpoint that comparisons between experimental results and model computations may yield important information about the irregularities.
MacDougall J.W., 1981, "Distributions of the irregularities which produce ionospheric scintillations", Journal of Atmospheric and Terrestrial Physics, 43, pp 317-325.
The distribution of nighttime irregularities which produce satellite scintillation has been examined for a midlatitude location using a large array of receivers. The irrgularities are aligned along the earth's magnetic field and appear to extend from the top to bottom of the F-region, being preferentially observed near the F-region ionization peak where they produce the strongest scintillations. A new method of mapping the horizontal distribution shows patches of various shapes and sizes but with no systematic structure.
MacDougall J.W., 1981, "Measurements of Ionospheric Electric Field Convection by the Long-Line Technique", Journal of Geophysical Research, 86, pp 4781-4789.
Ionospheric ExB convections are measured by a new technique that uses
satellite scintillations. The measurements are for an ionospheric region centered on
39°N, 82°W geographic or 53° invariant latitude. Results are presented for
spring equinox 1980. The quiet condition eastward convection drift is approximately
. During disturbed conditions at nighttime the westward convection
becomes large and highly variable. The northward perpendicular ExB
convection is approximately 
m/s during quiet conditions.
During disturbed conditions the semidiurnal component of the northward convection
increases by about a factor of 3 and becomes larger than the diurnal.
Moorcroft D.R. and Arima K.S., 1972, "The shape of the F-region irregularities which produce satellite scintillations - Evidence for axial asymmetry", Journal of Atmospheric and Terrestrial Physics, 34, pp 437-450.
Correlation analysis of three-station observations of satellite amplitude
scintillations, recorded at London, Canada during the summer of 1968, have
been interpreted to give information on the height, size and shape of the
ionospheric irregularities.
The irregularities had a mean height of 390 km, and when interpreted in
terms of the usual axially-symmetric, field-aligned model, had a mean axial
ratio of 6.5, and a mean dimension transverse to the magnetic field of 0.7
km. None of these parameters showed any systematic trend with magnetic
latitude.
The data for one of the passes analysed was inconsistent with axial
symmetry, and when examined in terms of a more general model, 3 of 9
passes showed evidence of irregularities which were elongated both along
and transverse to the Earth's magnetic field, the elongation transverse to
the field tending to lie in a north-south direction. The formation of such
irregularities appears to require some sort of instability which involves a
preferential direction perpendicular to the Earth's magnetic field. A
qualitative examination of the cross-field or gradient instability indicates
that it might produce irregularities with the observed characteristics.
Ogawa T. and Sinno K., 1980, "Severe disturbances of VHF and GHz waves from geostationary satellites during a magnetic storm", Journal of Atmospheric and Terrestrial Physics, 42, pp 637-644.
Severe night-time scintillations of VHF and GHz waves (1.136, 1.7, 4
and 11.5 GHz) emitted from the three Japanese geostationary satellites
were observed during a geomagnetic storm on February 15, 1978. The GHz
scintillations were strongly enhanced when irregular fluctuation of
total electron content (TEC) were superposed on the background TEC which
was varying sharply with time. This indicates a close relationship between
the scintillations and irregularities. Detailed analysis shows that the
one-dimensioanl wavenumber power spectrum of irregularities obeys a form
of k-2 and that the scintillation spectra vary as f
s-3. The scintillation index S4, seems
to have a frequency dependence of f-0.5 for
0.136<f<1.7 GHz, f-1 for 1.7<f<4 GHz and
f-2 for 4<f<11.5 GHz.
It is found that this scintillation event was accompanied with large
decrease in the plasmaspheric electron content, which continued for one
and a half days after the strom onset, and with appearance of localized
electron density trough in the F-region ionosphere.
Rino C.L., 1979, "A power law phase screen model for ionospheric scintillation 1. Weak scatter", Radio Science, 14, pp 1135-1145.
In this paper the weak scatter scintillation theory is reformulated to show explicitly the ramifications of an arbitary large ionospheric outer scale. The measured temporal phase spectrum, for example, is effectively truncated at a fixed frequency corresponding to the detrend time or the length of the data interval over which is measured (whichever is smaller). As a consequence, the rms phase exhibits a complicated dependence on the relative irregularity drift velocity and the propagation geometry. This effect has not been included in previous analyses. By comparison, intensity scintillation data are intrinsically high-pass filtered by the diffraction process. By taking advantage of this fact a simple closed form expression for the S4 intensity scintillation index has been derived. The theory is applied to representative data sets from the Wideband satellite. The interpretation of the ionospheric parameters deduced from the analysis is also discussed.
Rino C.L., 1979, "A power law phase screen model for ionospheric scintillation 2. Strong scatter", Radio Science, 14, pp 1147-1155.
The multiple-scatter theory of wave propagation in randomly irregular media is now well developed. Morever, work in fields such as coherent optics and radio astronomy has stimulated the development of asymptotic formulas that can be used in various scattering regimes. In this paper the power law phase screen model is used to derive the form of the intensity correlation function for strong ionospheric radio wave scattering when the Fresnel radius lies within the power law contimuum. The model allows fully for the anisotropy of the scattering medium. Asymptotic formulas valid under conditions of very strong scattering are developed. It is shown that the results depend critically on the power law index such that an important transition in the structure of a strongly scattered field occurs when the three-dimensional index is greater than 4.
Rufenach C.L., 1971, "A radio scintillation method of establishing the small-scale structure of the ionosphere", Journal of Atmospheric and Terrestrial Physics, 33, pp 1941-1951.
The power spectra of the intensity fluctuations for the radio source Cygnus A were analyzed for 44 nights during the summer of 1970. When the scattering was weak, oscillations were observed in the power spectra. These oscillations are attributed to a Fresnel filtering effect. When present, these oscillations are used to calculate the velocity and to estimate the irregularity scale size and the rms electron density fluctuations for irregularities smaller than the Fresnel radius. On many occassions the power law intensity spectra for structure smaller than the Fresnel radius may be attributed to a power law electron density spectrum.
Rufenach C.L., 1975, "Power spectra of large scintillation signals", Journal of Atmospheric and Terrestrial Physics, 37, pp 569-572.
Scintillation spectra using radio stellar sources at the time of large scintillation levels show a monotonically decreasing spectral density with increasing frequency in contrast to a spectral flatness for v< vf previously reported for small levels.
Sinno K. and Kan M., 1978, "Mid-latitude ionospheric scintillations of VHF radio signals associated with peculiar fluctuations of Faraday rotation", Journal of Atmospheric and Terrestrial Physics, 40, pp 503-506.
Simultaneous measurements of the scintillation and Faraday rotation of
136 MHz radio waves radiated by the Japanese geostationary satellite ETS-2
have been studied at Koubunji Japan during April to May, 1977.
These preliminary results show that there is a close association between
scintillations and the peculiar fluctuations of the Faraday rotation due to
ionospheric spread F, and an empirical formula relating them is presented.
Furthermore, the successive daily values of the two parameters show a close
correspondence with a cross correlation coefficient of about 0.8. An
unexpected result is that cross-correlation between the incidence of Es and
the Faraday fluctuations on a daily basis is found to be about 0.65.
Sinno K. and Minakoshi H., 1983, "Experimental results on satellite scintillations due to field-aligned irregularities at mid-latitudes", Journal of Atmospheric and Terrestrial Physics, 45, pp 563-567.
Experiments using multi-station networks receiving signals from the VHF beacon of a geostationary satellite have been carried out in order to clarify the geometrical factor involved in ionospheric intensity scintillations due to field-aligned irregularities. The characteristics of scintillation observed in the daytime agree with the theoretical value expected for weak diffractive scattering by ionospheric irregularities with an elongation of 10 along the geomagnetic field. However, those in the night-time show much marked enhancement along the field-line due to strong refractive scattering by irregularities having the same elongation. Finally, it is shown that the geometrical factor in scintillation at mid-latitudes can be expressed as a function of the propagation angle between the radio path and the geomagnetic field in the ionosphere. The maximum values of the geometrical factor are respectively about 5 in the daytime and 14 at night.
Slack F.F., 1972, "Quasiperiodic scintillation in the ionosphere", Journal of Atmospheric and Terrestrial Physics, 34, pp 927-939.
The hypothesis is advanced that a regular cyclic type of fading seen occasionally on chart recordings of HF and VHF radio frequency signals that have penetrated the ionosphere is a special case of the more normal irregular ionospheric scintillation. Analysis of satellite signals containing this special type of anomaly leads to a better understanding of ionospheric scintillation in general. The paper shows how properties of normal scintillation are consistent with the two ray interference formula derived for the more orderly pattern. As an illustration we have included the analysis of an ionospheric irregularity appearing over Thule that provides height and electron density measurement. Emphasis is given to the part reflection plays in scintillation, a process generally considered non-existent in HF and VHF propagation.
Tanaka T., 1982, "Spatial and temporal distributions of midlatitude ionospheric scintillations observed by low-altiude satellites", Journal of Atmospheric and Terrestrial Phsyics, 44, pp 719-729.
Spatial and temporal distributions of ionospheric scintillations have been observed at Kashima (36.0°N, 140.7°E) using VHF and UHF signals from low-altitude satellites. From these observations, three different types of prevailing ionospheric scintillations seen from Japan are identified. Scintillations of type I are rather weak scintillations, occur most frequently during the daytime in summer and are primarily associated with the sporadic E-layer. However, considerable occurrences of type I scintillations are also observed during the night in summer and autumn, not necessarily due to the sporadic-E layer but occassionally due to F-layer irregularities which originate from lacalized midlatitude processes. Type II scintillations are much stronger than type I and occur near the equatorward horizon during spring, summer and autumn. Their occurrences start after sunset, raech maximum before midnight and decrease subsequently, with a tendency for negative and positive correlations with the magnetic and solar activities, respectively. It is concluded that type II scintillations are the midlatitude aftermath of equatorial plume-associated irregularities and cause transequatorial propagation of VHF waves. From observations of type I and II scintillations, the boundary between midlatitude and equatorial scintillations is clearly identified. Type III scintillations area as strong as type II and appear only during magnetically active periods. They cab be regarded as another aspect of the severe scintillation events observed on gigahertz waves from geostationary satellites as reported by TANAKA (1981).
Titheridge J.E., 1971, "The diffraction of satellite signals by isolated ionospheric irregularities", Journal of Atnospheric and Terrestrial Physics, 33, pp 47-69.
Procedures are given for the rapid calculation of refraction and diffraction
patterns produced by isolated ionospheric irregularities. These patterns
are observed experimentally, and a sensitive polarisation angle recorder is
also used to determine the associated changes in electron content. Large
scale irregularities in the F-region are shown to cause variations
of several decibels in the amplitude of 20 and 40 MHz satellite signals.
Dense, isolated irregularities produce patches of 'scintillations' on 20
Mhz. The common assumption that scintillations are caused by a large number
of small irregularities, acting as a random diffracting screen, is therefore
incorrect on many occassions.
Small isolated irregularities produce diffraction patterns which depend on
the total number of electrons in the irregularity, and the height.
Irregularities of all sizes commonly occur in trains; in such cases the
height of the irregularities can be determined by comparing the depth of the
fluctuations in amplitude and polarisation. Calculated heights are mostly
in or above the F-region. For large isolated irregularities, their
position with respect to the peak of the F-layer can be obtained
directly from the different times at which amplitude fluctuations occur on
20 and 40 Mhz.
Vickrey J. F. and Kelley M.C., 1982, "The effects of a Conducting E Layer on Classical F Region Cross-Field Plasma Diffusion", Journal of Geophysical Research, 87, pp 4461-4468.
The rate of cross-field plasma diffusion in the F region ionosphere is significantly
is significantly increased when the magnetic field lines thread a highly conducting E
region below. This reduces the lifetime of small-scale F region electron density
irregularities in the polar ionosphere where the presence of a highly conducting E region is commonplace. A simple model is developed to describe the effects of a conducting
E layer on classical F region plasma diffusion. In the abscence of an E
region, the difference in ion and electron diffusion rates leads to a charge separation and,
hence, to an electrostatic field that retards ion diffusion. When the highly conducting
magnetic field lines are tied to a conducting E region, however, electrons can flow
along B to rduce the ambipolar diffusion electric field, and ions can proceed perpendicular to B at a rate approaching their own (higher) diffusion velocity. It is
shown that the enhanced total diffusion rate that results depends strongly on the height of the
F layer and on the ratio of the E to F region Pedersen conductivities.
Although the enhanced classical diffusion rate hastens the removal of irregularities once their
production source is removed, it is not a strong enough damping mechanism to prevent instabilities from operating routinely in the polar ionosphere. However, the E region
probably plays an important role in determining the scale size of the irregularities that are
favoured. E region 'images' may be important for low E electron densities
and small scale sizes, in which case the diffusion rate is lowered. However, if the E-
region conductivity is high, the prescence of images only reduces the F region cross-
field plasma diffusion rate by about 25% from the ion rate. We hypothesize that the
spectrum of high-latitude plasma density irregularities is controlled at large scales
(
> 10 km) by structured soft electron precipitation and
classical diffusion. Smaller scale waves are produced by plasma instabilities operating on
the edges of the large scale structures. The generalized ExB instability
(including the current convective process) acts to strengthen waves in the intermediate scale
size (100 m < < 10 km)in regions where the geometry is
appropriate or where field-aligned currents are significant. Universal drift waves transfer
energy from the intermediate scale to smaller structures but are ineffectual at large scales.
The classical diffusion process described herein is applied (in conjunction with a model of
irregularity production and convection) to the problem of explaining the morphology of the
large scale high-latitiude irregularities in a companion paper (Kelley et al., this issue). The
anomalous diffusion due to the instabilities mentioned above is also described in more detail.
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Last updated 07/02/1997 by Mark Keir