Scintillation Occurrence Research Articles

Estimation of the Cumulative Amplitude Probability Distribution Function of Ionospheric Scintillations

The fading characteristics of ionospheric amplitude scintillations can be described by a cumulative amplitude probability distribution function (cdf). The cdf expresses the probability (percentage of time) that the signal amplitude will equal or exceed a given amplitude. Distributions of amplitude variations are made with the use of ionospheric scintillations observed on beacon signals from synchronous satellites transmitting at 136 MHz. The resulting distributions are divided into six groups corresponding to ranges of the scintillation index, the predominant measure in scintillation studies. The model distributions are then combined with the occurrence of scintillations in various index ranges to produce cumulative amplitude probability distributions. These have been done for long‐term observations made at Hamilton, Massachusetts, Narssarssuaq, Greenland, and Huancayo, Peru. The results allow engineers to determine margins necessary for communication and navigation systems. Individual 15‐min distributions have been compared to the theoretical distributions obtained by Nakagami [1960] in his m‐distribution method of characterizing amplitude scintillation and were found to be in good agreement. The m parameter is shown to be a measure of the frequency dependence of scintillations and can be used to determine a spectral index for interpolating the amplitude distributions to other frequencies of interest.

Seasonal, diurnal and magnetic dependence of ionospheric scintillation at 64° invariant latitude

F layer irregularities at the invariant latitude of 64° were studied by observing amplitude scintillations at 137 MHz of the synchronous satellite, ATS-3; observations were made from Narssarssuaq, Greenland. In the 2 yr of data analyzed (1968–1970) consistent seasonal effects were noted. Quiet day winter records showed little diurnal variation. Quiet day summer daytime values showed extremely low occurrence of scintillation. These seasonal patterns must now be integrated into the model of the high latitude irregularity region. The occurrence of high amplitude fluctuations correlated sensitively with the magnetic index. Nightly means of scintillation index showed a positive correlation of 0·46 with night means of K p . The autocorrelation function of the nightly scintillation index reveals that a long time constant of several days exists for the irregularity pattern. During magnetic storms the time of maximum occurrence of scintillation shifts from the quiet day peak of 2200 to a peak between 0300 and 0500 when K p = 4−9. The morphology of the irregularity region is becoming more evident with the addition of the seasonal pattern and the long term consistency of the irregularities.

A graphic solution for wave velocities of sound in crystals: Bond, W.L., Vol 48, No 5 (November 1970) pp1084–1085

In this study we have used VHF and GPS-SCINDA receivers located at Nairobi (36.8°E, 1.3°S, dip −24.1°) in Kenya, to investigate the ionospheric scintillation and zonal drift irregularities of a few hundred meter-scale irregularities associated with equatorial plasma density bubbles for the period 2011. From simultaneous observations of amplitude scintillation at VHF and L-band frequencies, it is evident that the scintillation activity is higher during the post sunset hours of the equinoctial months than at the solstice. While it is noted that there is practically no signatures of the L-band scintillation in solstice months (June, July, December, January) and after midnight, VHF scintillation does occur in the solstice months and show post midnight activity through all the seasons. VHF scintillation is characterized by long duration of activity and slow fading that lasts till early morning hours (05:00 LT). Equinoctial asymmetry in scintillation occurs with higher occurrence in March–April than in September–October. The occurrence of post midnight VHF scintillation in this region is unusual and suggests some mechanisms for the formation of scintillation structure that might not be clearly understood. Zonal drift velocities of irregularities were measured using cross-correlation analysis with time series of the VHF scintillation structure from two closely spaced antennas. Statistical analyses of the distribution of zonal drift velocities after sunset hours indicate that the range of the velocities is 30–160 m/s. This is the first analysis of the zonal plasma drift velocity over this region. Based on these results we suggest that the east–west component of the plasma drift velocity may be related to the evolution of plasma bubble irregularities caused by the prereversal enhancement of the eastward electric fields. The equinoctial asymmetry of the drift velocities and scintillation could be attributed to the asymmetry of neutral winds in the thermosphere that drives the eastward electric fields.

Mechanical or electromechanical resonance: Jagodzinski, Z. Vol 23, No 6 (December 1970) pp355–361

In this study we have used VHF and GPS-SCINDA receivers located at Nairobi (36.8°E, 1.3°S, dip −24.1°) in Kenya, to investigate the ionospheric scintillation and zonal drift irregularities of a few hundred meter-scale irregularities associated with equatorial plasma density bubbles for the period 2011. From simultaneous observations of amplitude scintillation at VHF and L-band frequencies, it is evident that the scintillation activity is higher during the post sunset hours of the equinoctial months than at the solstice. While it is noted that there is practically no signatures of the L-band scintillation in solstice months (June, July, December, January) and after midnight, VHF scintillation does occur in the solstice months and show post midnight activity through all the seasons. VHF scintillation is characterized by long duration of activity and slow fading that lasts till early morning hours (05:00 LT). Equinoctial asymmetry in scintillation occurs with higher occurrence in March–April than in September–October. The occurrence of post midnight VHF scintillation in this region is unusual and suggests some mechanisms for the formation of scintillation structure that might not be clearly understood. Zonal drift velocities of irregularities were measured using cross-correlation analysis with time series of the VHF scintillation structure from two closely spaced antennas. Statistical analyses of the distribution of zonal drift velocities after sunset hours indicate that the range of the velocities is 30–160 m/s. This is the first analysis of the zonal plasma drift velocity over this region. Based on these results we suggest that the east–west component of the plasma drift velocity may be related to the evolution of plasma bubble irregularities caused by the prereversal enhancement of the eastward electric fields. The equinoctial asymmetry of the drift velocities and scintillation could be attributed to the asymmetry of neutral winds in the thermosphere that drives the eastward electric fields.

Optical measurements of ultrasonic attenuation and reflection losses in fused silica: Krischer, C., Vol 48, No 5 (November 1970) pp1085–1092

In this study we have used VHF and GPS-SCINDA receivers located at Nairobi (36.8°E, 1.3°S, dip −24.1°) in Kenya, to investigate the ionospheric scintillation and zonal drift irregularities of a few hundred meter-scale irregularities associated with equatorial plasma density bubbles for the period 2011. From simultaneous observations of amplitude scintillation at VHF and L-band frequencies, it is evident that the scintillation activity is higher during the post sunset hours of the equinoctial months than at the solstice. While it is noted that there is practically no signatures of the L-band scintillation in solstice months (June, July, December, January) and after midnight, VHF scintillation does occur in the solstice months and show post midnight activity through all the seasons. VHF scintillation is characterized by long duration of activity and slow fading that lasts till early morning hours (05:00 LT). Equinoctial asymmetry in scintillation occurs with higher occurrence in March–April than in September–October. The occurrence of post midnight VHF scintillation in this region is unusual and suggests some mechanisms for the formation of scintillation structure that might not be clearly understood. Zonal drift velocities of irregularities were measured using cross-correlation analysis with time series of the VHF scintillation structure from two closely spaced antennas. Statistical analyses of the distribution of zonal drift velocities after sunset hours indicate that the range of the velocities is 30–160 m/s. This is the first analysis of the zonal plasma drift velocity over this region. Based on these results we suggest that the east–west component of the plasma drift velocity may be related to the evolution of plasma bubble irregularities caused by the prereversal enhancement of the eastward electric fields. The equinoctial asymmetry of the drift velocities and scintillation could be attributed to the asymmetry of neutral winds in the thermosphere that drives the eastward electric fields.

F-region irregularities that cause scintillations and spread-Fechoes at low latitude

The temporal variations of two types of spread-F echoes and scintillation of stationary satellites observed at a low-latitude site are studied. The correlations among the three phenomena and with the Kp index are also investigated. Each type of spread F has quite simple variational characteristics, unlike the admixture of both types. The range spread is maximum at 2100–0100 hours during equinoxes and at high sunspot numbers, whereas the frequency spread is maximum at 0300–0500 hours during summer and at low sunspot numbers. The correlation with Kp is statistically significant for range spread, but not for frequency spread. The association of scintillation occurrence with range spread is excellent, whereas that with frequency spread is scarcely significant. The existing models of F-region irregularities that may cause the spread-F echoes and scintillations at low latitude are also discussed in the light of our findings.

The Equatorial F‐layer Irregularity Extent as Observed From Huancayo, Peru

Simultaneous observations of propagation paths to two synchronous satellites transmitting at 137 MHz have revealed distinctive characteristics of the equatorial irregularity structure. Data were taken between July 1967 and February 1969. The abrupt onset of scintillations on a particular path within minutes led to the concept that a sharp boundary of about 10 km exists between quiet non‐scintillating regions and regions of irregularities. Once the scintillation has started, a region over 5000 km wide from east to west may contain irregularities. Within such a region there is strong localized control of irregularities. Comparison of scintillation onset on two paths spaced 1 to 2 hours apart at their subionospheric points reveals that, in the mean, scintillation onset is a function of local time. However, many days show nearly simultaneous onset on two paths that are 1 hour apart in local time. Other days show onset of scintillations on the westerly satellite path before onset at the eastern intersection; this variability is clearly a negation of the diurnal pattern. Maximum occurrence of scintillation has been observed in September, October, and November. A somewhat lower occurrence of high‐amplitude scintillation is noted in the December–January solstice period. A secondary maximum exists in March, according to other South American data. A very low occurrence of scintillation is observed in May, June, and July. The scintillation phenomenon is correlated in the mean with the downward motion of the F layer after 2100 local time at Huancayo. A hypothesis is advanced that after 2100 the westerly F‐layer maximum is higher in altitude and has a greater electron density than the easterly maximum. This west‐east gradient of electron density produces (either through electrodynamic forces or diffusion) the irregularities that show an apparent eastward drift. The diurnal pattern, with its nighttime maximum of scintillation occurrence, is a westward motion, but the irregularity drifts noted are clearly eastward in the direction of lower electron density profiles.

Scintillation Studies of a Synchronous Satellite's Radio Signals at a Low‐Latitude Station

Scintillation observations at 136 MHz were made with the Canary Bird synchronous satellite during the winter of 1967–1968 and the spring and early summer of 1968. The diurnal pattern of scintillations is similar for the two periods. The mean scintillation index is higher during the spring and early summer, however, because of the increase in the percentage of occurrence of mild scintillations during this period. There is a positive correlation between nighttime scintillations and magnetic activity. On the other hand, daytime scintillations are only slightly dependent on magnetic activity.

Interplanetary Scintillations V. a Survey of the Northern Ecliptic

view Abstract Citations (59) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Interplanetary Scintillations V. A Survey of the Northern Ecliptic Harris, Daniel E. ; Gundermann Hardebeck, Ellen Abstract Source structure on the scale 0'.' '.'5 was examined at the Arecibo Ionospheric Observatory by inter- planetary-scintillation observations of 5(x) Parkes and 4C sources. These sources were observed only when the angular distance to the Sun was between 10 and 20 . This assured the presence of detectable scintillations at 430 MHz for this scale. Slightly over half of all the sources displayed scintillations. For most of these, we were able to find rough values for the fraction of the source scintillating ( ) and upper limits to the diameter of the small component (4,). The results corroborate earlier deductions that most scintillating sources are complex, with at least one component being very small and containing a significant fraction of the total intensity. Because a large number of sources were examined, the occurrence of scintillations can be correlated with source intensity, source identification, and source spectra. The results indicate that: 1. There is no evidence for a statistical distance effect; that is, the scintillation index is not correlated with source intensity. However, the optically faint galaxies do scintillate more than the bright galaxies. 2. Three-quarters of the QSOs and one-half of the galaxies showed scintillation. 3. Most of the QSOs for which little or no scintillation was observed have normal or steep spectra. The strongly scintillating QSOs are more likely to have fiat or curved spectra. Publication: The Astrophysical Journal Supplement Series Pub Date: December 1969 DOI: 10.1086/190201 Bibcode: 1969ApJS...19..115H full text sources ADS | Related Materials (4) Part 1: 1967ApJ...147..433S Part 2: 1967ApJ...147..449C Part 3: 1969ApJ...155..645C Part 5: 1968AJS....73R..17H

The occurrence of scintillation-producing irregularities over Australasia

An analysis has been made of the occurrence of satellite scintillations using observations of the Beacon Explorer satellites at a number of sites throughout Australasia. Time versus latitude contour diagrams of occurrence and mean index for the geomagnetic latitude range 20° to 55° are described. These are compared with similar contour diagrams of the occurrence of the frequency-spreading component of bottomside spread F, sporadic-E ionization, and the ducting and scattering components of topside spread F. Similarities are noted in the occurrence patterns of scintillations and topside scattering on one hand and bottomside frequency spreading and topside ducting on the other. However, these two patterns are complementary in that the occurrence of scintillation and of topside scattering are minimal in the latitude range 30° to 40°, while the occurrence of frequency spreading and topside ducting maximizes in this latitude range. It is inferred that of the F-layer irregularities, those that produce topside scattering are more able to cause scintillation than are those that result in topside ducting and bottomside spread F. It is further postulated that there exists, in the F layer, a continuous spectrum of irregularity sizes, the peak of which shifts from a dimension (normal to the earth's magnetic field) of less than 1 km at high latitudes to greater than 1 km between latitudes 30° and 40° and back to less than 1 km at the lower latitudes.

The F-region equatorial irregularity belt as observed from scintillation of satellite transmissions

Scintillation occurrence studies have been made on 40/41 MHz recordings of satellites BE-B and BE-C at Addis Ababa, Nairobi and Dar-es-Salaam. The results are presented in the form of latitude plots for the different seasons, each divided into pre- and post-midnight periods, and quiet and disturbed conditions. The equatorial irregularity belt is found to vary in shape and extent. The existence of north-south elongated patches is indicated.

Ionospheric electron content and scintillation studies at widely-spaced low-latitude stations

Results of measurements of electron content, of ionospheric slab thickness and of scintillations from three low latitude stations are presented. The three stations are Nairobi (Kenya), Kingston (Jamaica) and Haifa (Israel). Measurements were made at the three stations, of the Faraday polarization rotation of radio signals from the ionospheric beacon satellites S-66 and BE-C, during the period March–June 1965. The results show similar diurnal variations of electron content for the three stations, with a ratio of daytime maximum to predawn minimum of 8–10. Large variation in daytime values of electron content appear between Nairobi and Haifa, indicating large latitudinal gradients. The daytime values at Kingston and Haifa differ by about 25 per cent. There are similar results of slab thickness and of scintillation occurrence at Haifa and Kingston, while at Nairobi the slab thickness values are lower and there is an increase in the percentage of scintillation occurrence during daytime, in comparison to the other two stations.

Scintillation on S.Marco 1 satellite signals

An analysis is reported of the scintillation observed on the 20·005 MHz signals from the S.Marco 1 satellite. The observations were made by six stations situated at middle and low latitudes in both the north and south hemispheres. Results are presented of the scintillation occurrence and of the geographical distribution of the scintillation index.

Some evidence of Es-layer effects upon 137 MHz radio waves

The occurrence of pronounced scintillation of radio waves transmitted from synchronous satellite Early Bird (1965-28A) appears to be correlated with the growth of the E s layer frequency ƒ 0E s . The scintillation disturbances are usually short term but occasionally exist for as much as an hour. A number of the disturbances have well defined quasi-periodic edges although they generally exhibit a noisy spectrum.

Electron content observations at Brisbane for 1965

Observation of Faraday Fading of 40 Mc/s Signals from satellites Explorer 22 (BE-B) and Explorer 27 (BE-C) at Brisbane (27.4°S, 207.5°W) has yielded values of electron content for 435 passes in the period October 1964 to November 1965. Diurnal and seasonal variations of electron content and diurnal variation of equivalent slab thickness are investigated. Special interest is attached to the relation between electron content and scintillation occurrence.

Seasonal Variations in Occurrence of Scintillation

Observations of scintillation on signals radiated on a frequency of 20.005 Mc/s from a series of satellites are used to derive diurnal variations in the appearance of scintillation. Marked seasonal changes in daytime scintillation are apparent, but it is shown that summarizing for the four conventional seasons may mask some of the more significant changes.

Some Results of Electron Content Measurements at Delhi From Faraday Fading of S‐66 Transmissions

This paper contams the results of analysis of the total electron content (Is) measurements made from the recordings of Faraday rotation at Delhi of the 20‐ and 40‐Mc/s transmissions of the satellite Explorer 22 (S‐<16) for the period October 1964 through June 1965, the period of low solar activity. The results show that the diurnal maximum is reached around 1300‐1400 1ST, while at night the electron content falls to low values, decreasing slowly with time until 0600 when it starts to increase. The variations in Isclosely follow the f0F2, variations. The ratio I, smax/Isminincreases from 7 for OctoberDecember 1964 through 10 for January‐March 1965 to about 25 for April‐June 1965. It is interesting to note that electron content values are more or less independent of solar activity until the 10‐cm solar flux exceeds about 80 units. Above 80 units, there is a positive correlation. The study of dependence ofIson magnetic activity shows that there is posiiive correlation during daytime, while nighttime values do not show any dependence on magnetic activity. In addition, the electron content seems to have a correlation with solar zenith angle. General features of the thickness parameter T and the ratio of total to subpeak electron contemIs//b are also given. The variations ofT are correlated with both solar flux anJ hm‐F~ variations. Preliminary examination of occurrence of scintillations is also given.

Ionospheric Measurements by Means of the Early Bird Geostationary Satellite

The VHF emission of the Early Bird geostationary satellite during the period June 23 to July 9, 1965, has been used for ionospheric measurements at Florence, Italy (43°48' N, 11°13' E). Electron content daily variation curves obtained from Faraday rotation measurements show a maximum‐to‐ minimum ratio of about 5. The equivalent slab thickness ranges from 140 to 310 km. The scintillation occurrence shows maxima at night and at noon.

On Scintillation of Radio Sources

In a communication concerning scintillation of discrete radio sources and geomagnetic activity, relative to transit observations (within 45� of zenith) Slee (1962) found correlation between scintillation and geomagnetic indices. Scintillation activity was assessed as low if none of the radio sources showed detectable scintillation or if scintillation occurrence was isolated and high when all sources exhibited intense scintillations for several hours during the night.

Amplitude Scintillation of Radio Star at Ultra-High Frequency

Observations of radio star scintillation at a frequency of 915 Mc over a 12-month period (October, 1957-September, 1958) are described. By daily observations of Cygnus A (IAU 19N4A) over a wide range of elevation angles, both the amplitude and rate of scintillation were studied. It was found that the amplitude scintillation is strongest near the horizon and decreases rapidly as the altitude increases. The amount of the intensity fluctuation ranges from less than 3 per cent to over 50 per cent of the undisturbed intensity, while the rate of fluctuation varies from ? to 8 peaks per minute. A fluctuation amplitude greater than 10 per cent was observed at low-altitude angles for 71 per cent of the total observations. The frequency of occurrence of scintillation follows a seasonal variation having two maxima; one in the winter and the other in the summer. During these two maximum periods, the mean fluctuation amplitude was found to be higher than during other periods. It was also found that the mean fluctuation rate in the winter is about three times faster than that in the summer. It was also observed that the scintillation characteristics are markedly affected by the presence of auroras and/or geomagnetic disturbances. During the winter months, the fluctuation rate is roughly proportional to the three-hour geomagnetic K index.