Investigations Of Ionospheric Total Electron Content Behavior At Conjugate Points And During A Solar Eclipse

The Faraday rotation data were collected a Cold Bay, Alaska in an effort to correlate with similar data collected at Invercargill, New Zealand. Cold Bay and Invercargill form an approximate conjugate pair. Day-to-day variations of content at these two stations have been compared and studied. It has been found that these changes were negatively correlated during periods of magnetic quiet, uncorrelated during weak magnetic activities and increasingly positively correlated with increasing magnetic activities. In the second experiment two field stations were set up along the path of March 7, 1970 solar eclipse. These data, when combined with data obtained by others, show that the delay between the time of maximum obscuration and the time of minimum content varies systematically with latitude. The theoretical study is concerned with studying the effect of a dynamo electric field on the thermospheric winds. (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).

Observations of the ionosphere during the 20 July 1963 solar eclipse at Bedford, Massachusetts are presented. A C-4 vertical incidence sounder was used. Critical frequencies and virtual heights of the ionosphere are plotted and compared with a 10-day average curve. Ionograms of the time of first contact, maximum eclipse and fourth contact are included. A series of optical photographs of the sun in eclipse, taken at ground level, are presented. (Author).

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).

The Earth's Ionosphere: Plasma Physics and Electrodynamics emphasizes the study of plasma physics and electrodynamics of the ionosphere, including many aeronomical influences. The ionosphere is somewhat of a battleground between the earth's neutral atmosphere and the sun's fully ionized atmosphere, in which the earth is embedded. One of the challenges of ionosphere research is to know enough about these two vast fields of research to make sense out of ionospheric phenomena. This book provides insights into how these competing sources of mass, momentum, and energy compete for control of the ionosphere. Some of the topics discussed include the fundamentals of ionospheric plasma dynamics; equatorial plasma instabilities; high-latitude electrodynamics; and instabilities and structure in the high-latitude ionosphere. Throughout this text only the region above 90 km are discussed, ignoring the D region entirely. This publication is a good source of information for students and individuals conducting research on earth’s ionosphere.