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Total ionospheric electron content (TEC) has been determined from the measurements of the Faraday rotation of a plane polarized wave that have been returned from the geostationary satellite ATS 6 transmitting at a frequency of 140 MHz. The results of the computations have been presented in the form of diurnal curves in order to investigate the effect of the solar eclipse of 29 April 1976 on the TEC over Ankara longitudes. (Author).
Variations of the total ionospheric electron content are assumed to indicate the motion of eclipse-produced internal atmospheric gravity waves. Variation of the electron content before, during, and after the eclipse of 7 March 1970 was obtained from polarization of ATS-3 and S-66 BEC satellite signals. The resolution of the content data is better than 2 degrees in polarization or 5 x 10 (to the power of 10) e/sq. cm in content. The maximum possible error of the content-variation measurements using our automatic ATS system is less than plus or minus 6 degrees of polarization or less than plus or minus 1.4 x 10 (to the power of 11) e/sq. cm in electron content. The average period of the content variations was found to be 18 plus or minus 3 minutes. From BEC observations across the predicted wake of the gravity waves, an estimate was made of the wavelength and velocity of the atmospheric undulations and found to be 320 km and 296 m/s, respectively. (Author).
IPSE OF July 10, 1972. Technical rept., Soicher, H. ;Gorman, F.J., Jr;ECOM-4097DA-1-T-061102-B-31-A1-T-061102-B-31-A-01(*ionospheric disturbances, solar eclipses), electron density, atmospheric temperature, polarization, scientific satellitesats-3 satellitePolarization measurements at Fort Monmouth, N.J., using ATS-3 emitted signals and bottomside ionospheric sounding measurements at the subionospheric point were performed during the partial solar eclipse of 10 July 1972. A decrease in the total electron content and the plasma temperature ensued with corresponding diffusive particle fluxes into heights of maximum ionization. The diffusion rate to the height of maximum ionization was comparable to the recombination rate at that altitude. (Author).
Positive ion composition measurements in the D and E regions were performed on three rocket flights during the 1966 solar eclipse program conducted at Cassino, Brazil. The E region results showed that, at totality, NO+ and O2+ decreased in density while the ratio NO+/O2 increased. Long-lived meteoric ions appeared to be unaffected during the short period of the eclipse. A submerged layer of meteoric ions became prominent at totality when the molecular ion densities were smallest and produced a sporadic E layer. The D region results indicated that the decay in the water cluster ions at totality was probably less than a factor of four in the vicinity of 80 km. This work represents part of a continuing Air Force program to study lower ionospheric processes which affect communications. (Author).
This thesis focuses mainly on two topics: one is the ionospheric signature of solar eclipses, the second is the Hole vs Enhancement debate about earthquake precursors. On the 21st August 2017 the shadow of a total eclipse drastically changed the state of the ionosphere over the USA. This effect is visible in the total electron content (TEC) measured by ~3000 GNSS stations seeing multiple GPS and GLONASS satellites. This tremendous dataset allows high-resolution characterization of the frequency content and wavelengths -using an omega-k analysis based on 3D Fast-Fourier-Transform (FFT)- of the eclipse signature in the ionosphere in order to fully identify traveling ionospheric disturbances (TIDs). We confirm the generation of TIDs associated with the eclipse including TIDs interpreted as bow waves in previous studies. Additionally we reveal, for the first time, short (50-100 km) and long (500-600 km) wavelength TIDs with periods between 30 and 65 min (Eisenbeis et al., 2019). On 2nd July 2019 another total solar eclipse happened across the South American continent at magnetic conjugate latitudes as the Great American Eclipse, and consequently useful to visualize the difference response. Although for the South American eclipse we have only data from more than hundred GNSS stations and located in a zone close to the sunset, we can show the clear evidence of the ionospheric signature of the eclipse (Eisenbeis & Occhipinti in prep.a).The second major topic in this work is the still ongoing debate about the possibility of earthquake precursors. Heki (2011) sparked this debate when he published results of the Tohoku earthquake showing a TEC enhancement before the earthquake. The enhancement claimed by Heki (2011) has been interpreted as a decrease in the background TEC after the seismic event, the so called ionospheric hole in literature. The existence of the enhancement has been promoted by several papers (e.g. He & Heki, 2017) extending the observation to several events with moderate magnitude (M> 7.5) and proposes a new vision of the rupture dynamics. By trying to reproduce their results we show that the reference curve used by Heki (2011) to define the TEC background is strongly affected by the order of polynomial fit as well as the selected time windows. This shows that the TEC enhancement could be, in fact, just an artifact, subjectively selected to create the presumed precursor (Eisenbeis & Occhipinti in prep.b).
Ionospheric total electron content (TEC) observations were carried out from eight stations during the total solar eclipse of 26 February 1979 over North America by monitoring changes in the Faraday rotation of the plane of polarization of vhf signals from geostationary satellites. Additionally, TEC data from ionospheric group-delay measurements were made at Vanderberg, Calif., from two 12-h synchronous NAVSTAR/Global Positioning System (GPS) satellites which crossed over the eclipsed region. Local times of totality of the eclipse in the ionospheric observed from the various stations ranged from 0730 h to 1400 h. Depletion of the ionospheric TEC from the non-eclipse average behavior varied up to a maximum of 40 percent for the ionosphere experiencing 100 percent eclipse. Maximum TEC depletion occurred, on average, 33 min after maximum obscuration. Most of the stations showed a rapid rate of depletion of TEC about 30 min after first contact, the rate of depletion reaching a minimum value at or before maximum obscuration. Before fourth contact was reached, the rate of increase of TEC generally had overshot the non-eclipse day average, gradually returning to that average after fourth contact. Ionosonde data showed that the peak density of the F region and the TEC varied by approximately the same amount at those stations for which the E region had formed before first contact of the eclipse. Slab thickness, a first order F-region shape parameter, was not significantly changed during the eclipse. (Author).