Did the solar eclipse of August 11, 1999, show a geomagnetic effect?

Abstract

Abstract. The solar eclipse of August 11, 1999, presented good conditions for the study of associated geophysical effects. Ionospheric measurements clearly show a decrease of electron density due to the reduced solar irradiation during the eclipse. However, contrary to claims elsewhere, the decreased conductivity did not cause an obvious effect in the geomagnetic recordings at the Earth's surface. Recordings of several European geomagnetic observatories and of a temporary variometer network, set up specially to observe an eclipse effect in detail, have been studied directly and in terms of equivalent currents in the ionosphere. We present the results of these studies and discuss possible current configurations that might explain the lack of an eclipse effect in geomagnetic recordings.

Observations of the ionosphere in the equatorial anomaly region using WISS during the total solar eclipse of 22 July 2009

“…An increase in f 0 F2 (the critical frequency of the F2 layer), followed by a decrease, was recorded at three ionosonde stations during the total solar eclipse of 20 July 1963 (Evans, 1965). A decrease in the f 0 F2 during the solar eclipse was reported for other eclipses (Datta et al, 1959;Walker et al, 1991;Cheng et al, 1992;Boitman et al, 1999;Huang et al, 1999;Korte et al, 2001;Afraimovich et al, 2002;Baran et al, 2003). Oscillations in the ionosphere, similar to gravity waves, were observed following some solar eclipse events (Chimonas and Hines, 1970;Cheng et al, 1992;Liu et al, 1998;Altadill et al, 2001).…”

“…The reported results show that different regions behave differently during each solar eclipse event. The generation of electrons in the lower ionosphere (the E and F1 region) is predominantly determined by the amount of solar radiation, so electron density decreases during a solar eclipse (Davis et al, 1964;Evans, 1965;Cheng et al, 1992;Korte et al, 2001;Le et al, 2008). The formation of higher altitude layers (the F2 region) in the mid-latitude ionosphere is predominantly determined by plasma diffusion, and the F2 region has behaved quite differently in each eclipse event.…”

What are the influences of solar eclipses on the equatorial electrojet?

“…Among the various ionospheric effects reported, the reduction of the E region electron density is one of the most frequently confirmed (Rishbeth, 2000;Korte et al, 2001). At this low altitude ionospheric layer the amount of charged particles is closely related to the amount of incident short wavelength radiation.…”

“…In particular, the ionosphere is known to experience significant changes in response to the blocking of the sun. Although quite a number of studies have been published on solar eclipses effects (Beynon and Brown, 1956;Salah et al, 1986;Cheng et al, 1992;Korte et al, 2001) there is still no consensus on the typical response of the current systems. The infrequent occurrence of solar eclipses and the sparse distribution of suitable observatories have largely hampered the clear identification of cause and effect relations.…”

Mid-latitude solar eclipses and their influence on ionospheric current systems

“…The work of Korte et al (2001) showed that although the E-region electron density was markedly reduced during the 11 August 1999 eclipse, no significant change in S q current strength was detected. The authors suggest that the missing effect could be explained by considering a bypass of the current by field-aligned currents (FAC) to the Southern Hemisphere during the eclipse.…”