Ionospheric Electron Content Measurements During A Solar Eclipse

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).

It is a 10ng-standing tradition in this country for any event re1ated to solar activity to enjoy special importance. Because we enjoy the advantage of pro10nged sunny periods, we consider the incidence of some thirty c10udy days each year as a personal af front. I cannot say that we have the facu1ty to produce solar ec1ipses in order to justify an Institute on this subject to be held in Athens, but I can say that the occurrence of a solar ec1ipse over Greece wou1d present, for optica1 and solar astronomers, the highest possibi1ity of exce11ent conditions for observation. We had this opportunity during the May 20, 1966 annu1ar solar ec1ipse over North Africa and southern Europe. At that time we had the p1easure to co11aborate with a 1arge number of research groups of various nationa1ities, who insta11ed optica1 and radio instru ments near or in Lagonissi, which 1ay a10ng the centra1 path, in order to fo110w the ec1ipse. A first meeting was then organized in order to discuss methods of data handling and avai1abi1ity of resu1ts. After a pre1iminary discussion it was suggested that a 1ater meeting shou1d be organized when final resu1ts were avai1ab1e.

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).