Showing papers on "Total electron content published in 1971"

Determination of electron content at a low‐latitude station with off‐zenith transverse point

Abstract: The importance of the choice of mean ionospheric height (hM) in the determination of latitude variation of total electron content (TEC) from satellite transmissions at a low-latitude station is investigated. By considering the concept of magneto-ionic mode coupling in the vicinity of the transverse region, the Faraday rotation as a function of latitude for a frequency of 40 MHz has been theoretically computed for Calcutta (12°N geomagnetic) by using typical electron concentration profiles representing different ionospheric conditions. This result was used to determine the criterion for the proper choice of hM consistent with least error in the determination of TEC over the entire latitude range of interest. It is found that the correct choice corresponds to the height of the transverse point at that latitude (TP) for which the Faraday rotation is a minimum. An incorrect choice of this height leads to substantial error in the computed electron content at latitudes to the north of TP, the error being as large as 3% per 10 km deviation from the best choice of hM. A method of deriving the correct choice of hM from actual Faraday rotation records is indicated.

Simultaneous Sudden Frequency Deviations and Sudden Enhancements of the Total Electron Content of the Ionosphere

Abstract: THE response of the ionosphere to solar flares has been studied mostly by the sudden changes which develop in the D-region. A study of the ionosphere as a whole during flare events is much more instructive but also much more difficult, because ionospheric sounders cease to function because of the greatly enhanced absorption in the D-layer. Sudden frequency deviations (SFD) in h.f. radio signals reflected from the ionosphere provide a very useful technique and have been used extensively for the study of the rapid changes which occur in the E and F-regions during solar flares1.

Measurement of total electron content with a geostationary satellite during the solar eclipse of March 7, 1970.

Abstract: This note deals with the measurement of the total electron content of the ionosphere at the Goddard Space Flight Center, looking towards the geostationary satellite ATS 3 during the solar eclipse of Mar. 7, 1970. Obscuration at this site was nearly total. Faraday rotation was measured with a stationary circularly polarized antenna and a dual-channel phase-lock receiver tuned to 137.350 MHz. By comparing the electrical phase of the two opposite circularly polarized components, a continuous chart recording was made of Faraday rotation vs local time. A depletion of about 25% in electron content was observed from first contact to the time of minimum electron content. The time variations of the electron content during the eclipse are briefly examined in the light of current theories of ionospheric processes.

Total Electron Content during the Great Magnetic Storm of March 8,1970

Abstract: TOTAL electron content data were obtained at Fort Monmouth, New Jersey, from polarization measurements of the ATS-3 satellite beacon on 137·35 MHz (Fig. 1). The bottomside ionosphere was simultaneously explored by bottomside vertical sounding. These ionograms were converted to true height electron density profiles. Curves of height variations were drawn for F-region plasma frequencies (Fig. 2). For comparison, reference is made to the storm magnetograph (Fig. 3) from Fredericksburg, Virginia.

Studies on Ionospheric Electron Content and Irregularities of Electron Concentration at Low Latitudes.

Abstract: : The low latitude ionosphere has a special character of its own owing to a strong control of geomagnetic field over the topside ionosphere. In order to explore the extent of this control, studies on total electron content and irregularities of electron concentration in the ionosphere were carried out at Haringhata Field Station (22 degree 58 minutes N, 88 degrees 30 minutes E). The investigation on electron content were mainly oriented towards the determination of its latitude variation under varying geomagnetic conditions while those on the irregularities sought to obtain their axial ratio and spatial distribution. (Author)

Combined Differential Faraday and Differential Absorption Measurements at 40 Megahertz

Abstract: Differential Faraday rotation measurements of the 40- and 41-MHz beacons of satellite 1964–64A/BE-B were made at London, Ontario (43°N, 81°W) through the use of a continuous output polarimeter of the phase comparison type, and simultaneous differential absorption measurements were made by use of the ordinary and extraordinary mode amplitudes at 40 MHz. Sufficient measurement accuracy was obtained to employ the second-order expansion of the magnetoionic refractive and absorption index equations to extract total electron contents, the ratio of the density squared integral to the total electron content, a mean ionospheric electron collision frequency, and a parameter sensitive to the height of an electron density irregularity, from the data. Two passes, orbit 17239, March 17, 1968, and orbit 17280, March 20, 1968, were selected for analysis. Peak electron densities, mean plasma scale heights, and mean electron temperatures were computed from the reduced data by the assumption of an electron density height profile; they were found to correspond to within experimental error with comparable published measurements. During both passes examined, F region electron density profile broadenings were detected that were, for March 20, attributed to adiabatic expansions of the F region electron gas, which was driven by localized neutral gas motions, and for March 17 the broadenings were attributed to thermal expansions of the F region plasma. On both occasions, the fractional errors in the data were sufficiently small over some portions of the pass to permit a determination of the dominant ionospheric absorption mechanism.