Atmospheric electric field variations and lower ionosphere disturbance during the total solar eclipse of 2010 July 11
Introduction
The atmospheric electric field persists in fair weather1 regions mainly due to thunderstorms occurring at remote locations. This is part of the current knowledge of the global atmospheric electric circuit (GAEC). In short, the GAEC relates the charge separation in regions of disturbed weather to electrical current flowing in fair weather regions. Recent advances on study of the GAEC are reviewed in Williams and Mareev (2014).
The atmospheric electric field in fair weather regions is affected by several phenomena, such as for example, solar and seismic activities (see references in Tacza et al., 2014). Investigations of the effects of solar eclipses on the atmospheric electric field have also been reported for a long time. Previous studies showed an increase of the atmospheric electric field (Anderson and Dolezalek, 1972, Dhanorkar et al., 1989, De et al., 2009), while other reports mention a decrease (Jones and Giesecke, 1944, Markson and Kamra, 1971, Kamra and Varshneya, 1967, Retalis, 1981, Kamra et al., 1982, Manohar et al., 1995, Babakhanov et al., 2013, De et al., 2013, Kumar et al., 2013). Finally, few studies do report no change at all (Freier, 1960). Inconsistency of the effects of a solar eclipse on atmospheric electricity may occur because of different instrumentations and local meteorological conditions during observations (Babakhanov et al., 2013).
Two factors have been proposed to explain the effect of the eclipse on atmospheric electrical parameters. These are, changes in upper atmosphere processes (e.g. Koenigsfeld, 1953, Dhanorkar et al., 1989, De et al., 2009, Kumar et al., 2013, Babakhanov et al., 2013) or changes in atmospheric boundary layer processes close to ground surface (e.g. Jones and Giesecke, 1944, Gish, 1944, Anderson, 1972, Anderson and Dolezalek, 1972, Kamra et al., 1982).
With respect to processes in the upper atmosphere, Koenigsfeld (1953) suggests that variations in the amount and height of ozone influence the amount of ultraviolet radiation absorbed and reduce the electrical conductivity of the atmosphere. In addition, the author mentions that the ionization of ice crystals by ultraviolet photons should result in change of the electrical conductivity. De et al. (2009) suggest that the removal of electrons from the lower ionosphere due to recombination during the solar eclipse may give rise to an increase in the electrical field.
With respect to changes in atmospheric boundary layer, Anderson and Dolezalek (1972) propose a mechanism to determine the variation of the electric field intensity. The attenuation of solar radiation due to an eclipse causes a reduction in the turbulent activity (or eddies) starting at the lowest levels of the atmosphere and propagating upward. After a series of processes, a downward convection current of heavy positive ions is established. The latter, causes a reduction in electrical conductivity and therefore produces an increase in the atmospheric electric field. Jones and Giesecke (1944) also proposed a similar mechanism.
In this paper, we study the variations of atmospheric electric field during the total solar eclipse (TSE) on July 11, 2010 at Complejo Astronómico El Leoncito (CASLEO), Argentina (Lat. 31.798°S, Long. 69.295°W, Altitude: 2550 masl). Section 2 presents the instrumentation and data treatment. In Section 3 we present our results by comparing the effects of the TSE on both electric field records, and VLF phase measurements. Section 4 is devoted to the discussion of our findings, and in Section 5 we give our concluding remarks.
Section snippets
Instrumentation
Continuous measurements of atmospheric electric field are being recorded with two sensors located in CASLEO (CAS1 and CAS2), ∼0.4 km apart. Each sensor consists of a commercially manufactured (Boltek Corporation EFM100-1000120-050205) electric field mill (EFM) and is part of a network of electric field sensors installed in South America. The dynamic range of the EFM is ±20 kV/m and the response time 0.1 s. The principle of EFM operation is based on the fundamental laws of electromagnetism. When a
Observations
The path of the TSE on July 11, 2010 over the Earth’s surface is illustrated in Fig. 1. The trajectory of the umbra and penumbra are represented by a sequence of filled circles and by solid lines, respectively. The TSE has is first contact on the Earth’s surface at 17:10 UT and ended at 21:58 UT. The percentage of maximum obscurity over CASLEO was of 41.73%. The end of the eclipse coincides with the sunset in CASLEO (21:50 UT). The local circumstances of the eclipse were obtained from //xjubier.free.fr/en/site_pages/SolarEclipseCalculator.html
Discussion
The similarity shown in Fig. 3, Fig. 5, and mentioned in the previous section, may indicate the independent responses to a single phenomenon, i.e. the TSE of 2010, July 11. Indeed, the TSE gradually blocks the solar Lyman-α photon flux, and free electrons in the lower ionospheric D-region progressively recombine. This leads to a rise-up of the reflection height, which is observed as a phase (delay) change (Raulin et al., 2010).
On the other hand, as we mentioned in the introduction, the TSE
Conclusions
The present study examines the evolution of the atmospheric electric field under the influence of the TSE of July 11, 2010. The results show an increase of electric field during the eclipse period, closely related to similar time variations of the phase of VLF signals. This may indicate two independent manifestations of the effects of the TSE. However, we cannot exclude a causal relationship between electrical conductivity changes in the lower ionosphere, and electric field variations at 2550
Acknowledgments
Observational electric field and VLF data from this study are available upon request. The work of JT was supported by CAPESP funding agency. JPR thanks CNPq funding agency (Proc. 482000/2011-2 and 312788/2013-4). Authors are grateful to anonymous reviewers for their constructive comments and suggestions, which helped to improve the quality of the paper.
References (24)
Atmospheric electricity, turbulence and a pseudo-sunrise effect resulting from a solar eclipse
J. Atmos. Terr. Phys.
(1972)- et al.
Atmospheric electricity measurements at Waldorf, Maryland during the 7 March 1970 solar eclipse
J. Atmos. Terr. Phys.
(1972) - et al.
The geophysical disturbances during the total solar eclipse of 1 August 2008 in Novosibirsk, Russia
J. Atmos. Sol. Terr. Phys.
(2013) - et al.
Atmospheric electricity measurements at Pune during the solar eclipse of 18 March 1988
J. Atmos. Terr. Phys.
(1989) - et al.
The effect of a solar eclipse on atmospheric potential gradients
J. Atmos. Terr. Phys.
(1967) - et al.
Airborne and ground measurements of the atmospheric potential gradiente during a solar eclipse
J. Atmos. Terr. Phys.
(1971) Atmospheric electrical potential gradient measurements during the annular solar eclipse of 29 April 1976
J. Atmos. Terr. Phys.
(1981)- et al.
A new South American network to study the atmospheric electric field and its variations related to geophysical phenomena
J. Atmos. Sol. Terr. Phys.
(2014) - et al.
Recent progress on the global electric circuit
Atmos. Res.
(2014) - et al.
Electrification in the Earth’s atmosphere for altitude between 0 and 100 kilometers
J. Geophys. Res.
(1965)