Equivalent Slab Thickness Research Articles

Ionospheric total electron content and slab-thickness at low latitudes in Indian zone

Observations of Faraday rotation of beacon signals from low orbiting satellite BE-B recorded at one station near the dip equator (Kodaikanal, dip 3·4° N) and at another station near the peak of the equatorial anomaly (Ahmedabad, dip 34° N) give a complete coverage of the equatorial anomaly belt in Indian zone. Contours of total elctron content (TEC) are obtained on a grid of latitudeversus local time for the different seasons of low (1964–66) and high (1967–69) solar activity epochs in the latitude belt 10° S to 26° N dip latitude. The development of the equatorial anomaly and its dependence on season and solar activity are discussed. Using similar contours of F2 layer critical frequency, f0F2 contours of equivalent slab-thickness, τ are also constructed. The dependence of τ on season and solar activity and its implications on temperature are discussed.

Day-to-day variability of ionospheric electron content at mid-latitudes

By using the data of total electron content (TEC) obtained from the Faraday rotation of signals from geostationary satellites recorded at several locations, the day-to-day variability of the daily range and hour of maximum of TEC is studied. Fluctuations sometimes as large as ±50% in the magnitude of TEC and ±4 hours in the time of the maximum are observed, even on quiet days. Changes in TEC and Nmax even at the same location are not always completely parallel. Also TEC changes at locations separated by more than about 3000 km in latitude or longitude show poor correlations. No relation with changes in solar EUV is indicated. It is suggested that erratic neutral winds blow away from the polar regions toward the equator even during quiet times and create convection cells which may result in ionospheric irregularities of scale lengths of about 3000 km which wander about the globe slowly and give the observed day-to-day variability of TEC and the equivalent slab thickness τ.

Measurement of primary cosmic-ray electrons and positrons from 4 to 50 GeV

view Abstract Citations (97) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Measurement of primary cosmic-ray electrons and positrons from 4 to 50 GeV. Buffington, A. ; Orth, C. D. ; Smoot, G. F. Abstract We have used a bremsstrahlung-identification technique to measure electron and positron spectra in the primary cosmic rays from 4 to 50 GeV. Above our average geomagnetic cutoff of 4.0 GV/c, we find fluxes of 4.4 (plus or minus 0.3) electrons and 0.37 (plus or minus 0.09 positrons) per sq m/sr/sec. The electron events follow a differential power law whose spectral index is 2.8 (plus or minus 0.1). Our ratio electrons/(electrons + positrons) = 0.08 (plus or minus 0.02) implies traversal of an equivalent slab thickness of 4.3 (plus or minus 1.5) g/sq cm of interstellar and source material. Publication: The Astrophysical Journal Pub Date: August 1975 DOI: 10.1086/153736 Bibcode: 1975ApJ...199..669B Keywords: Bremsstrahlung; Cosmic Ray Showers; Electron Flux Density; Positrons; Primary Cosmic Rays; Abundance; Balloon-Borne Instruments; Data Acquisition; Data Reduction; Energy Spectra; Interstellar Matter; Space Radiation full text sources ADS |

Ionospheric electron content and equivalent slab thickness in the equatorial region

The ionospheric total electron content and equivalent slab thickness in the equatorial region around 75°E have been studied. It is found that the slab thickness exhibits a strong latitudinal dependence with a maximum at the magnetic equator and a minimum around the crest of the F2 anomaly, indicating that the F region is thick near the equator and most skewed near the crest. The results are consistent with the electrodynamic drift and diffusion in the equatorial ionosphere.

Investigations of the ionosphericFregion using multistation total electron content observations

A network of stations near the 70°W meridian has been used to monitor continuously the polarization of the VHF beacon signal from the geostationary satellite ATS 3. Measurements of the amount of Faraday rotation experienced by the signal in traversing the ionosphere permit continuous observations of the ionospheric total electron content (TEC) to be made over the invariant latitude range 34°–73°. When the TEC data are combined with ground-based ionosonde data from nearby locations, it is also possible to monitor the peak density (Nmax) of the F2 region and the equivalent slab thickness (τ = TEC/Nmax). Observations from six stations made in December 1971 were used to construct computer-generated contour maps of the TEC, Nmax, and τ monthly median behavior on an invariant latitude (Λ) versus local time grid. Comparisons between daily TEC contours and the monthly median contours reveal dramatic effects induced by substorms (December 8–9) and major geomagnetic activity (December 17–18).

Total electron content of the equatorial ionosphere

Total electron content ( N t ) variations in the ionosphere above the magnetic equator (Thumba dip 0.6°S) obtained by the Faraday rotation measurements of beacon signals from S66 satellites are described for the period December 1965–August 1968. The N t value reaches a minimum around 05 hr and a broad maximum between 14–18 hr, the diurnal ratio being more than 20. During no-echo condition at pre-sunrise hours, N t is found to be abnormally low. The equivalent slab-thickness at Thumba is between 150 and 250 km except around 14 hr when it reaches a high value around 500 km. The electrons are almost equally distributed above and below the peak for the daytime hours, but in the latter part of the night the ratio of top-side to the bottom-side electron content exceeds the value of 5. This high ratio is suggested as being due to very low value of maximum electron density which during the pre-sunrise period becomes comparable to the electron density at great heights where there is no diurnal change of electron density. Combining the data of Thumba and Ahmedabad, the diurnal development of the equatorial anomaly in N t is described.

An empirical relationship between ionospheric equivalent slab thickness and mean gradient of the electron temperature in the f-region

It is shown that it is possible to define an empirical law between ionospheric slab thickness and mean gradient of the electron temperature in the F-region. This law is obtained by using data of the incoherent scatter of Saint-Santin (France) and can be used under certain conditions in connexion with ionograms to find the electronic temperature and density profiles above the ionization maximum level.

The behavior of total electron content and equivalent slab thickness during magnetic disturbances

The total electron content ( TEC) and equivalent slab thickness data reduced from observations of 137 MHz transmissions from the geo-stationary satellite AT-3 at a sub-ionospheric point near 50°N and 68°W were statistically investigated. We observed that: 1. (a) there exists a positive correlation between ΔTEC and K p max nearly all the time in winter. 2. (b) the coefficient of correlation is, in general, positive in the case of equivalent slab thickness during daytime, and negative after dark for all seasons: it changes from positive to negative during local sunrise, and 3. (c) the decrease of TEC with increasing disturbance is usually accompanied by an increase of the equivalent slab thickness in daytime hours in equinox and summer, but not in winter.

Temporal and spatial changes of the electron content of the ionosphere

Measurements of the electron content of the ionosphere are analysed in order to study temporal and spatial variations of this parameter. Observations relating to a large part of a solar cycle are available for Australian and North American stations. Furthermore, measurements exist for a wide range of latitudes since October 1964 after the launching of Explorer 22. The analysis clearly shows the increase of the annual averages with solar activity and the decrease of the electron content with increasing geographic latitude. There is strong evidence for the existence of a semiannual variation of the electron content. Its amplitudes depend on solar activity and latitude similar to the mentioned annual averages. In general the variation is more marked in the afternoon and evening than in the morning of the days around the equinoxes. A semiannual variation is also known for the maximum electron density of the ionosphere and the temperature of the high atmosphere, and thus the same variation is expected for the equivalent slab thickness. But instead of the expected result there is only a semiannual variation of the daily change of this parameter. All these observed phenomena support the assumption that the semiannual variation in the studied ionospheric region is partly caused by plasma transport.

Measurements of total electron content at Huancayo, Peru

Measurements of total electron content of the ionosphere above Huancayo, Peru by observation of Faraday fading of satellite signals during January through March 1967 are reported. The data are examined to study principally the diurnal variation of total electron content and of equivalent slab thickness as well as the latitudinal variation of the electron content. The diurnal variation is characterized by the occurrence of a midday biteout. The equivalent slab thickness reaches a peak around midday besides exhibiting a hump in the early morning hours. The latitudinal variation of electron content in the afternoon shows a dip around the magnetic equator.

Abnormal Diurnal Variation of Total Ionization

IT has long been known that magnetic storms may be associated with major changes in the F2 region of the ionosphere. Recently interest has been concentrated on the relationship between the level of magnetic activity, and three ionospheric parameters, namely NT, the total electron content; NM, the maximum ionization density; and T=NT/NM, the “equivalent slab thickness”. The exact nature of the relationship is not yet clear, and published results are to some extent conflicting. It has been shown, however1,2, that a moderate or severe storm is often accompanied by the following effects, (a) During the first day after the start—a “sudden commencement” or “gradual commencement” — NT is unusually high. It may remain so for 12–24 h, and then change fairly rapidly to become unusually low. It may then take as long as 24 – 36 h to return to a normal value. (b) NM follows a similar pattern to that of NT, although the effect is not always so pronounced, (c) The slab thickness increases considerably during the day after the commencement of a storm. The amount and duration of the increase are very variable.

Incoherent backscatter study of electron content and equivalent slab thickness

Electron content and equivalent slab thickness from radar backscatter measurements, noting F layer peak height and electron and ion temperatures diurnal variation

Faraday rotation measurements of electron content near the magnetic equator

At the Electronics Laboratory of the Military Research and Development Center, Bangkok, Thailand (13.7°N latitude, 100.1°E longitude), Faraday rotation observations of the 54-MHz signal from the Transit 4-A (1961 Omicron 1) satellite were made during 10 months of a sunspot minimum period (1964). The satellite has an essentially circular orbit with an inclination of 67° and a spin-stabilized linear-polarized antenna. In this paper, two methods of analysis, involving rotation rate and total number of rotations, are applied to the Bangkok observations. The rotation-rate method is used to determine the electron content when the angle between the ray path and the geomagnetic field is 90° (transverse position). The total-rotations method is used to determine the latitudinal variations of the electron content for five selected satellite passes from a joint analysis of observations at three stations, Singapore, Bangkok, and Hong Kong. A comparison of the calculated critical frequency with observed ionosonde critical frequencies at Singapore, Bangkok, and Macao shows some evidence that the equivalent slab thickness may be considered independent of latitude near the magnetic equator.

Variations in total electron content and other ionospheric parameters associated with magnetic storms

The storm-time variations of the ionosphere in middle latitudes during ionospheric storms are described. Usually the total electron content is increased during the first 24 hours of the storm. The total content then falls to below its quiet-day value and recovers after one or two days. The peak electron concentration in the F region is similarly increased at the beginning of the storm and is later depressed. The fall in peak electron concentration commences some hours earlier than the fall in total electron content. The equivalent slab thickness is increased above the quiet-day value throughout the storm, corresponding to an increase in the electron-ion temperature. In weak magnetic storms the ionospheric disturbance may not last longer than one day, and only the initial elevation of total electron content occurs.

Lunar tidal variations in the equivalent slab thickness of the ionosphere over Hawaii

For many years, lunar tidal variations in several ionospheric parameters deduced from bottomside soundings have been extensively studied. These investigations have led to the establishment of an essentially global pattern of the lunar variations that in turn have contributed to an understanding of the dynamical structure of the ionosphere. Summaries of lunar tidal analyses of observational data as well as theories of lunar variations are given by Martyn [1950] and Matsushita [1961]. With the advent of geostationary satellites, it has now become possible to extend this study to include the topside ionosphere.

The high-latitude trough in ionospheric electron content

Results of 15 months observations of the ionospheric electron content made at Kiruna, Sweden are presented. Observations were made using the 40 and 41 MHz beacon of the S-66 satellite. Most of the night-time observations, except for the summer period, show a distinct trough in the electron content. Seasonal and diurnal variations of the trough and of the electron content are studied. Also the corresponding equivalent slab thickness obtained using ƒ 0F2 data from six Scandinavian ionosondes and geomagnetic control of the trough are investigated. Some features of the diurnal variation of electron content during the summer agree with the hypothesis of ionospheric heating by photoelectrons from the sunlit magnetic conjugate ionosphere.

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.

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.

Total electron content of the ionosphere in middle latitudes

A study is made of measurements of the total electron content nT in the ionosphere, derived from satellite Doppler measurements. These are combined with simultaneous ionosonde measurements of the true height of Nmax and the electron content below Nmax. The following are the principal results obtained, nT varies diurnally, and at night it decays approximately exponentially with a mean effective attachment coefficient of 0.8×10−4 sec−1. The daytime maximum electron content was greater in winter than in summer in 1961–1962, but the difference was much less than in 1958–1960. The daytime electron content increases with the 10.7-cm solar radio noise flux S, and the rate of increase is greater in winter than in summer; a similar result holds over a large part of the solar cycle. The equivalent slab thickness, nT/Nmax is greater in daytime and in summer and increases with S. The ratio of the electron contents na/nb above and below hm is about 1.8 in the daytime, increases after sunset and before sunrise, and has a minimum in the middle of the night.

Measurements of the total electron content and the equivalent slab thickness of the midlatitude ionosphere

Total electron content and equivalent slab thickness of midlatitude ionosphere determined from radio transmissions of Transit IVA Earth satellite