A total eclipse occurred on 11 August 1999 with its path of totality passing over central Europe in the lat- itude range 40 -50 N. The ionospheric responses to this eclipse were measured by a wide ionosonde network. On the basis of the measurements of foE, foF1, and foF2 at six- teen ionosonde stations in Europe, we statistically analyze the variations of these parameters with a function of eclipse magnitude. To model the eclipse effects more accurately, a revised eclipse factor, FR, is constructed to describe the vari- ations of solar radiation during the solar eclipse. Then we simulate the effect of this eclipse on the ionosphere with a mid- and low-latitude ionosphere theoretical model by using the revised eclipse factor during this eclipse. Simulations are highly consistent with the observations for the response in the E-region and F1-region. Both of them show that the max- imum response of the mid-latitude ionosphere to the eclipse is found in the F1-region. Except the obvious ionospheric response at low altitudes below 500 km, calculations show that there is also a small response at high altitudes up to about 2000 km. In addition, calculations show that when the eclipse takes place in the Northern Hemisphere, a small ionospheric disturbance also appeared in the conjugate hemi- sphere.

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The ionospheric responses to the 11 August 1999 solar eclipse: observations and modeling

[1] In this study, we statistically analyze the latitudinal dependence of F2-layer peak electron densities (NmF2) and total electron content (TEC) responses to solar eclipses by using the ionosonde observations during 15 eclipse events from 1973 to 2006 and the GPS TEC observations during six solar eclipse events from 1999 to 2006. We carried out a model study on the latitudinal dependence of eclipse effects on the ionosphere by running a theoretical ionospheric model with the total eclipse occurring at 13 latitudes from 0 Nt o 60N at intervals of 5. Both the observations and simulations show that the NmF2 and TEC responses have the same latitudinal dependence: the eclipse effects on NmF2 and TEC are smaller at low latitudes than at middle latitudes; at the middle latitudes (>40), the eclipse effect decreases with increasing latitude. The simulations show that the smaller NmF2 responses at low latitudes are mainly because of much higher heights of hmF2 at low latitudes and electron density response decreasing rapidly with increasing height. For the eclipse effects at the middle latitudes (>40), the simulations show that the smaller NmF2 or TEC response at higher latitude is mainly ascribed to the larger downward diffusion flux induced by the larger dip angle at this region, which can partly make up for the plasma loss and alleviate the depression of electron density in the F region. The simulated results show that there is an overall decrease in electron temperature throughout the entire height range at the middle latitude, but for the low latitudes the eclipse effect on electron temperature is much smaller at high heights, which is mainly because of the much smaller reduction of photoelectron production rate at its conjugate low heights where only a partial eclipse with small eclipse magnitude occurs.

http://www.igg.cas.cn/xwzx/yjcg/200911/W020091126310555897309.pdf

Latitudinal dependence of the ionospheric response to solar eclipses

Effects of the August 11, 1999 total solar eclipse as deduced from total electron content measurements at the GPS network

Satellite beacon observations during eclipses have provided much information on the behavior of the ionosphere. A combination of Faraday rotation and differential phase measurements as well as ionosonde data can provide information on the topside and bottomside ionospheric behavior during an eclipse as well as on the production rate. Recent attention has been directed toward a study of the dynamics of the F region during an eclipse and the relation between the amount of depletion in the total electron content and the percent obscuration of the sun. Of particular interest is the time delay from the maximum obscuration to the maximum depletion of the total electron content. Further modeling studies are required in order to reproduce the experimental results. Further observations are also required in order to establish whether TID's are generated following a total solar eclipse as predicted theoretically. In particular, it appears that a more sensitive technique such as differential Doppler rather than Faraday rotation is required. The total solar eclipse of June 11, 1983, with its long totality time of 4–5 min over Indonesia and Papua New Guinea will provide an ideal opportunity for further studies of these unanswered questions.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/RS019i003p00769%4010.1002/%28ISSN%291944-799X.BEACSAT1

The study of the effect of solar eclipses on the ionosphere based on satellite beacon observations

National Natural Science Foundation of China[40725014, 40674090, 40636032]; National Important Basic Research Project[2006CB806306]

/pdf/the-midlatitude-f2-layer-during-solar-eclipses-observations-x96473mfpc.pdf

The midlatitude F2 layer during solar eclipses: Observations and modeling

FOUR stations were set up in southern and eastern Africa (Table 1) to observe variations of total electron content during the eclipse of the Sun on June 30, 1973. Each station was equipped with a conventional Faraday rotation recording system consisting of a receiver and a mechanically rotating aerial. We recorded the amplitude fading of the 137 MHz signals from the geostationary satellite, Intelsat IIF3, located at approximately 14°W. The four stations were operating for a total period of 10 d, including June 30, the day of the eclipse.

D. G. Feldgate

Papers

Faraday rotation studies in Africa during the solar eclipse of June 30, 1973