Showing papers on "Total electron content published in 1975"

Investigations of the ionospheric F region using multistation total electron content observations

Abstract: 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).

Latitude dependence of ionosphere total electron content: Observations during sudden commencement storms

Abstract: The latitude dependence of the changes in the ionosphere total electron content (TEC) has been studied during 12 magnetic storms. TEC observations were obtained at Hamilton, Massachusetts, and Arecibo, Puerto Rico. Definite latitude differences are observed in the TEC responses during the magnetic storms: both TEC enhancements and TEC depletions are observed at Hamilton, while only enhancements are measured at Arecibo. A pre-local midnight TEC ‘ledge’ is frequently observed in the Arecibo storm data but is seldom observed in the higher-latitude Hamilton data. These enhanced ledges in the Arecibo TEC, together with the nighttime TEC depletions measured at Hamilton, produce large south-to-north differences in the ionosphere TEC. The ledges at Arecibo may arise from electrodynamic drift effects associated with westward electric fields; the role of the motion term in the continuity equation for the TEC is assessed under these conditions. The local evening enhancements in the TEC during certain large storms are discussed in the context of the latitude dependence of the storm time magnetic field variations measured from Great Whale River to San Juan. It is shown that the large TEC enhancements appear to be associated with large positive geomagnetic bays at middle to high latitudes.

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

Abstract: 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.

ATS-6 Radio Beacon Experiment: The First Year

Abstract: The Radio Beacon Experiment is designed to measure the total electron content and ionospheric content between the satellite and any observer within its field of view. Since Applications Technology Satellite-6 (ATS-6) is visible from about 43 percent of the Earth's surface, an international community of observers have made measurements using it. The radio parameters have to be measured to an accuracy of a few percent, which requires good system calibration and stability. The spaceborne beacon transmits signals on frequencies of 40, 140, and 360 MHz with amplitude modulations of 1 MHz and/or 0.1 MHz for the measurement of modulation phase, Faraday rotation, and amplitude. The overall system objectives and requirements are discussed along with the design of the ATS-6 transmitter and the receiver in Boulder, Colo. The role of the principal investigator in the context of the international program is considered with particular reference to the joint National Oceanic and Atmospheric Administration (NOAA)/Max Planck Institute (MPI) observation program. Monthly median hourly values of total content, plasmaspheric content, and shape factor show distinct diurnal and seasonal variations. A specific event is described to illustrate the use of a spaced receiver network.

Polarization of VHF waves emitted from geostationary satellites

Abstract: Measurements of Faraday polarization rotation of VHF radio waves transmitted from geostationary satellites have been made by many workers at various locations throughout the world to study the total electron content (TEC) of the earth's ionosphere. In order to determine the absolute amount of total Faraday rotation a knowledge of the initial plane of polarization as transmitted from the satellite with respect to a known reference is necessary. A knowledge of this initial polarization angle is particularly important when the total Faraday rotation is small, such as at near-equatorial regions, and at all locations during nighttime, particularly under solar minimum conditions. By using a VHF lunar radar at a time when the moon passed nearly behind each satellite this initial polarization has been determined with respect to a known reference for 10 different geostationary satellites. The initial polarizations of the signals emitted from the ionospheric beacon on the ATS 6 satellite were measured before the satellite launch. One of these initial polarizations, the one at the VHF frequency most often used for Faraday measurements, was confirmed by the lunar technique.

ATS-6 radio beacon experiment

Abstract: SINCE ATS-6 was launched into a geostationary orbit at 94°W in late May 1974, measurements of the total electron content (TEC) using the Faraday polarisation-rotation1 and group dispersive-delay techniques have been made at Fort Monmouth (40.18°N; 74.06°W). Comparison of TEC rate of change obtained by the two techniques yields the temporal variation of the integrated number of free electrons above the ionosphere. This variation indicates a flow of electrons from regions above the ionosphere into the ionosphere at night, while during the day the direction of flow is reversed. The rate of the electron flux is estimated using the continuity equation.

Storm-time increases in the ionospheric total electron content

Abstract: CHANGES in the total electron content of the mid-latitude ionosphere during the first day of each of 20 geomagnetic storms have been monitored by Papagiannis et al.1. They have shown that during the positive phase of the storms the magnitude of the increase in total electron content exhibits a very pronounced maximum near sunset. Although Rishbeth and Hanson2 have shown that plasma convergence in the F region itself cannot account for the observed increases, an inward meridional E×B drift of the plasma may compress the H+ gas at great heights1,2, giving rise to a field-aligned flow of H+ into the ionosphere. We have investigated the consequences of fieldaligned H+ flow by integrating the F region–protonosphere equations of motion and continuity for O+ and H+ along magnetic tubes that are undergoing E×B drift. The range of integration is from the lower F region to the equatorial crossing point of the magnetic tube, the method of integration being essentially that of Moffett and Murphy3. Our results support the idea that an influx of ionisation from the protonosphere may be partly responsible for some storm-time increases in ionosphere content.

The response of the lower ionosphere to the great solar flare of August 7, 1972.

Abstract: The response of the ionosphere in an altitudinal range of 50-200km to the great solar flare that occurred at about 1500UT on 7 August 1972 is studied. Sudden increases in electron concentration, Pedersen and Hall electric conductivities (SIEC), total electron content (SITEC) and sudden cosmic noise absorption (SCNA) due to solar X-ray flux increments at 1530, 1600, 1700 and 2100UT are calculated for the location of 40°N latitude and 75°W longitude, and some of the results are compared with observed values. The solar X-ray emissions concerned in this study are those with wavelengths of 1-100A, of which emission fluxes measured from the SOLRAD 10 satellite are available for the 1-20A band, while emission spectra for other wavelength bands are assumed. Two altitudinal profiles of increased electron concentrations at each time are first derived based on two assumed effective recombination coefficient profiles, then associated increments in 30MHz cosmic noise absorption and Pedersen and Hall electric conductivities are derived. It is found that the calculated 30MHz SCNA's (SCNA values) and SITEC's (50-200km) at 1530, 1600 and 1700UT for one of the increased electron concentration profiles are in reasonably good agreement with the observed ones, but the SITEC's roughly corrected for the entire ionosphere at 1530 and 1600UT seem to be greater by more than 20 and 30% than the observed ones, respectively. These results seem to imply that the derived electron concentration enhancements in the ionosphere above about 100km are overestimated.

The Global Pattern of 6300 Å Atomic Oxygen Emission as Seen from the ISIS-2 Spacecraft

Abstract: The 6300 A line of O is a useful detector of low energy ionospheric processes. The 100 eV magnetosheath-type electrons incident in the dayside cleft produce red auroras, and red-enhanced auroras appear as polar cap arcs and at high latitudes on the nightside. During storms, thermal excitation inside the plasmapause generates SAR Arcs. Outside the plasmapause conjugate photoelectrons produce significant increases of 6300 A emission by electron impact. Dissociative recombination of O2 + produces 6300 A emission, dramatically evident at the equator. All of these mechanisms are identifiable in the ‘instantaneous’ global maps produced by the Red Line Photometer (Shepherd et al., 1973a) on the ISIS-2 spacecraft. The Auroral Scanning Photometer (Anger et al., 1973) also yields data at 5577 A and 3914 A. Parameters measured in the circular orbit at 1400 km include (Shepherd et al., 1973b) electron density and temperature, ion composition and temperature, and energy spectra of electrons and protons; while the electron density profile down to the ionosphere is traced by the topside sounder.