Ionospheric effects of the solar eclipse of September 23, 1987, around the equatorial anomaly crest region

Abstract

The ionospheric responses to the solar eclipse of September 23, 1987, in the equatorial anomaly crest region have been investigated by using ionospheric vertical sounding, VLF propagation delay time, and differential Doppler shift data observed at Chungli, which is located near the northern equatorial anomaly crest region. It has been found that temporal variations of the F1 layer and D region are mainly controlled by local solar radiation. Quantitative analysis of the variations of the F1 layer critical frequency, ƒ0F1, shows that electrons are removed from the F1 layer through ionic recombination. However, the temporal variations of ƒ>0F2 and electron density above 200 km show that the variations of the F2 layer around the equatorial anomaly region are controlled not by local solar radiation but by solar radiation at the equator. The fountain effect plays an important role even during the solar eclipse. The VLF propagation time delay is controlled by the variations of average path obscuration. Atmospheric gravity waves produced by the moving bow wave front of the solar eclipse are found with a period around 17‐23 min and wavelength about 293 km.

Ionospheric response over Europe during the solar eclipse of March 20, 2015

“…TEC is an integral measure and delayed response is expected since the topside ionosphere is less prone to radiation and is rather influenced by plasma redistribution, while the bottomside ionosphere is mainly controlled by local solar radiation (Cheng et al 1992). It can be seen that the delay practically vanishes when the maximum obscuration is about less than 30%.…”

“…Due to the eclipse-induced reduction of photoionization, the D layer slowly disappears and the bottomside of the ionosphere moves upward, causing significant changes in signal strength and phase of VLF measurements. It is expected that the bottomside ionosphere moves upward causing an enlargement of the VLF ray path or time delay that has been reported in the literature (e.g., Cheng et al 1992;Clilverd et al 2001;Pal et al 2012).…”

“…The observations indicate that a number of competitive processes are initiated by an eclipse often enhanced by dynamic forces associated with large-scale geophysical conditions not directly impacted by the solar eclipse. Thus, the ionospheric depletion signatures may be heavily disturbed by electrodynamic forces in equatorial regions (e.g., Cheng et al 1992;Tsai & Liu 1999) and by space weather effects, such as particle precipitation, at high latitudes (e.g., Rashid et al 2006;Pitout et al 2013). As reported by Chimonas & Hines (1970) and others, the rapidly moving cooling spot can act as a continuous source of travelling ionospheric disturbance (TID) like gravity waves (e.g., Liu et al 1998;Altadill et al 2001;Jakowski et al 2008).…”

“…However, above 40°N latitude, the eclipse effect decreases with increasing latitude. Whereas the analysis of low-latitude eclipses is affected by dynamic processes related to the equatorial anomaly (e.g., Cheng et al 1992; Le et al 2010), high-latitude eclipses are affected by a strong coupling with the magnetosphere, in particular during geomagnetic storms (e.g., Rashid et al 2006;Pitout et al 2013). The analysis of the solar eclipse on March 20, 2015 presented here will contribute to comparing solar eclipse effects at different latitudes.…”

“…Since most solar eclipses occur in mid-and low latitudes (e.g., Jakowski et al 1983Jakowski et al , 2001Jakowski et al , 2008Cheng et al 1992;Fritts & Luo 1993;Mueller-Wodarg et al 1998;Krankowski et al 2008;Le et al 2008Le et al , 2009Le et al , 2010, the number of publications considering high-latitude eclipses is rather low (e.g., Rashid et al 2006;Pitout et al 2013). Le et al (2009) investigated the latitudinal dependence of the ionospheric response to solar eclipses and found that eclipse effects are larger at middle latitudes than at low latitudes.…”