Variation of surface electric field during geomagnetic disturbed period at Maitri, Antarctica N Jeni Victor, C Panneerselvam∗ and C P Anil Kumar Equatorial Geophysical Research Laboratory, Indian Institute of Geomagnetism, Krishnapuram, Tirunelveli 627 011, India. ∗Corresponding author. e-mail: [email protected] The paper discusses on the variations of the atmospheric vertical electric field measured at sub-auroral station Maitri (70◦75′S, 11◦75′E), and polar station Vostok (78.5◦S, 107◦E) during the geomagnetic disturbances on 25–26 January 2006. Diurnal variation of surface electric field measured at Maitri shows a similar variation with worldwide thunderstorm activity, whereas the departure of the field is observed during disturbed periods. This part of the field corresponds to the magnetospheric/ionospheric (an additional generator in the polar regions) voltage generators. Solar wind parameters and planetary indices represent the temporal variation of the disturbances, and digital fluxgate magnetometer variation continuously monitored to trace the auroral movement at Maitri. We have observed that the electrojet movement leaves its signature on vertical and horizontal components of the DFM in addition; the study infers the position of auroral current wedge with respect to Maitri. To exhibit the auroral oval, OVATION model is obtained with the aid of DMSP satellite and UV measurements. It is noted that the Maitri is almost within the auroral oval during the periods of disturbances. To examine the simultaneous changes in the vertical electric field associated with this magnetic disturbance, the dawn–dusk potential is studied for every UT hours; the potential was obtained from Weimer model and SuperDARN radar. The comparison reveals the plausible situation for the superposition of dawn–dusk potential on surface electric field over Maitri. This observation also shows that the superposition may not be consistent with the phase of the electrojet. Comparison of surface electric field at Maitri and Vostok shows that the parallel variation exhibits with each other, but during the period of geomagnetic disturbances, the influence is not much discerned at Vostok. 1. Introduction of understanding fully the electrical environment of the Earth. Further, since the global electric cir- The atmospheric global electric circuit is a current cuit links the lower troposphere, the ionosphere system in which currents flow upward from thunder- and the magnetosphere, the measurement of atmo- storm current generators, through the ionosphere, spheric electrical parameters will be useful in any and down to the Earth’s surface in the fair weather integrated approach that involves all these regions regions. Continuous measurements of atmospheric (Bering 1995; Rycroft et al. 2000). Long term electrical parameters, namely, the vertical electric measurements from various sites would be consid- field, the conductivity, and the air–Earth current, ered useful for addressing some of the problems that characterize the global electric circuit (GEC) associated with the global change. Despite a long are considered useful in any study with the aim history and good number of observations carried Keywords. Atmospheric electric field; magnetic storm; magnetosphere; ionosphere; global electrical circuit. J. Earth Syst. Sci. 124, No. 8, December 2015, pp. 1721–1733 c Indian Academy of Sciences 1721 1722 N Jeni Victor et al. out for more than four decades (Kasemir 1955; 1986; Roble and Tzur 1986; Burns et al. 2005; Anil Byrne et al. 1993; Burns et al. 1995; Bering Kumar et al. 2009). This dawn-to-dusk horizontal et al. 1998; Deshpande and Kamra 2001; Virkkula potential difference due to the interaction of the et al. 2005; Panneerselvam et al. 2007a, b, 2010; solar wind with the Earth’s magnetosphere (V × B) Anil Kumar et al. 2008, 2009, 2013), knowledge of causes the two-cell convection pattern in the polar the relations between atmospheric electricity, solar region. In this part, the principal component analy- cycle, climate and air pollution is insufficient for sis was carried out by Panneerselvam et al. (2007a), extensive applications. Hence, the non-linear effect using surface electric field data at Maitri, and they may be important in the real atmospheric electrical stated that the first eigen value gives information processes because the thunderstorms are non-steady, about the thunderstorm contribution to the global and the electric charges may play an important electric circuit. The second and third components role in the thunderstorm electrification (Chiu 1978; will give the information about the E-region iono- Mathpal et al. 1980; Kuettner et al. 1981; Mathpal sphere dynamo and the solar wind-magnetosphere and Varshneya 1982). Many studies suggested that dynamo, respectively. The currents and electric fields the solar activity influences due to ionospheric produced by the ionospheric wind dynamo are rela- electric field disturbances may significantly control tively weak in comparison with those of solar wind- the global electric circuit state (Sao 1967; Apsen magnetosphere dynamo at high latitude during et al. 1988; Michnowski 1998; Bering et al. 1998; solar active time, since cross-polar cap potential has Rycroft et al. 2000; Frank-Kamenetsky et al. 2001; a significant influence in high-latitude region and Nikiforova et al. 2003). extended up to 40◦ magnetic co-latitudes (Hairston Measurements over polar regions are of great and Heelis 1990; Tinsley 2008). The extended hori- importance in understanding GEC as these regions zontal electric field is (dawn–dusk potential) gra- are practically free from anthropogenic pollution. dually downward to the lower atmosphere. The Since maximum parts of the continent are covered clockwise cell would map to increase the upward by ice, the ionization produced by the radioactiv- vertical electric field and current at the ground. ity element at ground surface is almost absent. The The anti-clockwise convection would map down to electrical conductivity of the ice surface is in sev- decrease to the measured atmospheric electric field eral orders of magnitude higher than that of air and current (Park 1976). The nature of the convec- (Cobb 1977). The atmospheric electrical studies at tive cell depends on the relative position of the Antarctica are useful for investigating the large- station with respect to magnetic dawn to dusk. scale electrical process which is unique at high Solar wind induced changes can be involved by latitudes (Byrne et al. 1993; Panneerselvam et al. more direct effects of the deep penetration of the 2007a, b, 2010; Anil Kumar et al. 2009; Kleimenova interplanetary electric field into middle- and low- et al. 2012). The global electric circuit involves latitude ionosphere. The strongest manifestations of lower atmosphere generators (mostly controlled by the solar wind interactions with the magnetosphere the thunderstorm) and upper atmosphere genera- and ionosphere processes are especially evident at tors (ionosphere/magnetosphere), the most impor- the auroral and polar latitudes. Many studies of tant of which are at the high latitude (polar caps) surface electric field associated with these effects (Richmond 1986; Roble and Tzur 1986). The influ- have been carried out at high and polar Arctic and ence of this external generator on surface electric Antarctic areas (Reddell et al. 2004; Kleimenova field is dependent on magnetic coordinates of the et al. 2008 and references therein) but the magne- measuring site. Atmospheric electrical parameters tospheric/ionospheric contribution to atmospheric have been measured at Maitri and reported by electricity at sub-auroral stations is discussed by few many authors, local summer (Panneerselvam et al. researchers (Anil Kumar et al. 2009; Panneerselvam 2007a, b), influence on coronal mass ejection (Anil et al. 2010; Minamoto and Kadokara 2011; Odzimek Kumar et al. 2008), electrodynamic coupling func- et al. 2011; Frank-Kamenetsky et al. 2012; Luk’ tion (Anil Kumar et al. 2009), etc. Panneerselvam yanova et al. 2011). Frank-Kamenetsky et al. (2012) et al. (2007a) reported that the surface electric field noted that the correlation between variation in measurement at Maitri is similar like ‘Carnegie the surface electric field at high latitude and the curve’, the so-called thunderstorm generated elec- calculated horizontal electric potential (Weimer 05 tric field pattern. He further stated that the classic model) are insignificant, and the correlation is rela- diurnal variation is not regularly seen on individ- tively linked with the occurrence of auroral electro- ual days but it only emerged when many days are jet. However, no consistent results were drawn from averaged (Anil Kumar et al. 2008, 2009). earlier studies and a similar approach was not used An additional problem while trying to study the at the equatorward auroral boundary stations. global electric circuit at the high latitude-polar-cap In this paper, we have attempted to discuss the region is that horizontal ionospheric electric fields temporal variation of surface electric field measured map downward to the Earth’s surface (Richmond at Maitri (70◦45′52′′S, 11◦44′03′′E, 117 m amsl) and Variation of surface electric field at Maitri, Antarctica 1723 Vostok (78◦27′52′′S, 106◦50′14′′E, 3488 m amsl) and 1.25 its departure during the geomagnetic disturbed periods. 2. Experimental technique 1.00 Widely used ground-based sensors for the measure- ment of air–Earth current are the Wilson plate (Israel 1973), the horizontal long-wire antenna (Kasemir 1955; Ruhnke 1969; Panneerselvam et al. Normalized Electric field 2010). The atmospheric electric field has been mea- 0.75 sured at Maitri with the field mill made out of non- 0 2 4 6 8 10121416182022 magnetic stainless steel to reduce the contact Time (hrs) UT potentials. The sensor plates and rotor in the field mill are of 8.5 cm diameter. The shaft of the ac Figure 1. Diurnal variation of normalized atmospheric elec- motor (220 V, 50 Hz, 1500 rpm) is grounded with a tric field (ENZQ) averaged over 69 fair weather days at et al. carbon bush. The signal from the field mill is ampli- Maitri, Antarctica (Panneerselvam 2007a).