Showing papers on "Total electron content published in 1983"

Modeling the total electron content observations above Ascension Island

Abstract: Recent Faraday rotation (136 MHz) measurements between Ascension Island (8/sup 0/ S geographic latitude; 345/sup 0/ E geographic longitude; 15/sup 0/ S. dip latitude) and the Sirio satellite (azimuth 0/sup 0/, elevation 80/sup 0/)= reveal two characteristic features associated with the undisturbed ambient ionosphere: a late afternoon decrease in TEC followed by a postsunset enhancement that lasts for two to three hours. We theoretically investigate the ambient ionosphere above Ascension Island by numerically solving the time-dependent plasma continuity equation, including the effects of ionization production by solar ultraviolet radiation, loss through charge exchange and transport by diffusion, E-bar x B-bar drift and neutral wind (both zonal and meridional components) appropriate for an equinoctial, solar cycle maximum period. It is found that the postsunset enhancement in upward E-bar x B-bar drift, which is a characteristic feature observed by the Jicamarca incoherent scatter radar facility during solar cycle maximum periods, is primarily responsible for the postsunset increase in TEC observed at Ascension Island between 1900 and 2300 LT. The late afternoon decrease in TEC is caused by an increase in the poleward neutral wind velocity, which lowers the F layer into a higher loss rate region. Inclusion of the meridional wind notmore » only reproduces the observed decrease but also modulates the postsunset peak in TEC so that it is in much better agreement with the observed values. Calculated north-south asymmetries in TEC caused by a zonal wind component are also discussed.« less

Equatorial anomaly in ionospheric electron content and its relation to dynamo currents

Abstract: Using the ATS 6 satellite radio beacon data collected over a chain of stations in the Indian zone, a study has been made of the equatorial anomaly in total electron content (TEC) and its relation to the E region currents. Two parameters, ΔHd, the difference in the magnetic field perturbation between the equator and a low-latitude station, and Vd, the backscatter radar measurement of the draft velocity of the electrojet irregularities, are used to represent the equatorial current strength. The results, presented in the form of regression plots relating the strength of the anomaly and that of the current, indicate that the anomaly dependence on the current strength is about the same for all the three seasons. It is also noted that, regardless of the season, the anomaly crest moves toward a farther latitude from the equator with increasing current strength. The total ionization inventory, Σ TEC, of the anomaly belt is found to increase linearly with the strength of the equatorial current and this result seems to bear some significance for the correlation observed between TECmax and ΔHdmax at the equator.

Coordinated measurements of low-energy electron precipitation and scintillations/TEC in the auroral oval

Abstract: A case study of coordinated observations of low-energy ( 10 radians for fluctuation frequencies >00067 Hz) were found to be well correlated with intense fluxes (>109 particles (cm2 s sr)−1) of precipitated low-energy electrons Total electron content and magnetometer measurements indicate that the onset of the precipitation event was about 10 min prior to the DMSP pass Within this time scale, the ionization generated in the F region could reach the topside so that the thermal sensor on board the DMSP satellite was able to measure a factor of 2–3 density enhancement at 840 km The latitudinal width of these density structures is consistent with that of F region blobs observed at Chatanika The gradient scale length measured in the topside was only 30 km, which was probably responsible for the fast growth rate of the scintillation-producing irregularities The phase to amplitude scintillation ratio changed rather drastically compared to quiet magnetic times, however, implying that increased convection velocities during these magnetic disturbances were partially responsible for the enhanced phase scintillation

Influence of solar sector boundaries on ionospheric variability

Abstract: A latitudinal network of total electron content (TEC) observations has been used to assess the contributions to day-to-day F region variability associated with a wide variety of solar-terrestrial phenomena. Recent discussions of a proposed “sun-weather coupling” effect related to solar wind sector boundary (SB) crossings prompted a systematic search to document any upper atmospheric components of such a linkage. TEC data from several North American sites close to the 70°W meridian (Narssarssuaq, Greenland (L = 5); Goose Bay, Labrador (L = 4); Sagamore Hill, Massachusetts (L = 3); and the Kennedy Space Center, Florida (L = 2) were examined during the years 1973–1975. Average daytime (0900–1700 LT) TEC values were compared with a 27-day mean centered on the day of an SB crossing. The resultant percentage deviations were examined for sector polarity (plus to minus versus minus to plus) effects and for overall latitudinal patterns during a period of ±5 days from the SB crossings. Average results for the entire data set show peak excursions well within the ±20–25% deviations associated with day-to-day variability. There is, however, a remarkable consistency in the coherence of the small amplitude latitudinal patterns. At middle to high latitudes (L = 3–5), the TEC variations show an ordered transition from enhancements to depletions following an SB crossing. At lower latitudes (L = 2), the opposite pattern of depletions to enhancements occurs. An identical analysis for geomagnetic activity variations (using the planetary index Ap) reveals the well-known pattern of a transition from relatively quiet to relatively disturbed activity as a sector is crossed. A merging of these two results suggests that the manifestation in the F region of SB crossings is nothing more than a small-scale version of the average “geomagnetic/ionospheric storm effect” that is well documented over the L = 2–5 range. The latitudinal patterns for ΔTEC, and their seasonal variations, are consistent with the morphology of O/N2 variations during geomagnetic disturbances and southward IMF effects during equinoctial versus solstice periods.

The HILAT program

Abstract: The HILAT satellite is scheduled to be launched June 1983 into a circular, 830-km-altitude orbit with an 82.2° inclination. This spacecraft is a modified U.S. Navy TRANSIT navigation satellite and will conduct a unique combination of experiments: (1) transmissions of radio signals from the spacecraft to surface stations for measurements of ionospheric scintillations and total electron content (TEC), (2) in situ measurements of plasma density, electric fields, magnetic fields, and soft electron fluxes, and (3) visible photometric measurement and UV imaging of aurora and airglow. The objective of this mission is to provide definition information on the formation, development, transport, and decay of plasma density irregularities in the high-latitude ionosphere; the relationship of these plasma processes to auroral and polar cap current systems, electric fields, convective flow patterns, and low-energy electron distributions; and the relationship of these plasma processes to the global distribution of auroral phenomena during quiet and substorm periods and during various interplanetary conditions.

A study of the charged particle calibration requirements for the Deep Space Network

Abstract: A study made of the Deep Space Network charged particle calibration requirements is discussed The effects of charged particles on navigation and timing systems were reviewed and it was proposed that a system based upon the Global Positioning System satellites be used to measure the charged particle content of the ionosphere The system would be required to measure the total electron content of the ionosphere to the order of 10 to the 16th power electron per square meter Two types of systems were suggested as possible candidates for making these measurements

The Conversion of Off-Vertical Observations of Total Electron Content into Equivalent Vertical-Incidence Values.

Abstract: : Observations of total electron content along off-vertical paths are normally converted into an equivalent vertical incidence total content before their application in studies of the ionosphere or in communications predictions. The errors in this conversion have been studied using a numerical model of the ionosphere. The errors are found to vary with the azimuth and elevation of the satellite, the altitude at which the conversion is made, the presence of ionospheric gradients along the ground-satellite path, and with the well-known variations of the ionosphere itself. For elevation angles of 20 deg or greater, the relative errors are usually less than about 10% and often less than about 5%, for a wide range of conditions. Errors of up to 20% are obtained for equatorial stations and for stations near the high latitude trough, especially for low angles of elevation. (Author)

Horizontal gradients and correlation coefficients in total electron content of the ionosphere

Abstract: Horizontal gradients and correlation coefficients in the ionospheric TEC are among the basic parameters in space-physical research of exceeding the limits and surmounting the obstacles. In the present paper, the. horizontal distribution and space correlation of TEC observed in Western Europe under quiet solar condition during phase II of synchronous beacon satellite ATS-6 when it was repositioned at 35 °E over Eastern Africa are analysed. The latitudinal and longitudinal gradients, their diurnal variations and seasonal characteristics are dealt with. It is proposed and discussed that the sun-pointing effect of daytime horizontal gradient vectors in the ionospheric TEC is such that: On the Northern Hemisphere, in winter, daytime course of gradient direction is the southeast-south-southwest; and in summer, the east-south-west. In winter, daytime extent of azimuthal variation, the gradient magnitude and its fluctuation are smaller; and in summer, greater. In other words, the direction of daytime gradient vectors has apparently the co-rotational nature with the sun or the sun-pointing character following the azimuth of the sun, and the corresponing gradient magnitude and its variation, beyond equatorial belt and low latitudes, increase along with the. rise of solar elevation. The manifestation pattern of TEC space correlation coefficient at mid-latitudes and the possible involved dynamic causes are also inquired.