Impact of Interplanetary Shocks and Equatorial dB/dt during Quiet Geomagnetic Activity of 23 December 2014

When interplanetary shocks associated to coronal mass ejection (CME) hit the Earth, it will result in intense magnetosphere and ionosphere current, thus generating the induced current on the ground which known as geomagnetically induced currents (GICs). Typically GIC is a special concern in high latitude region because space weather perturbation’s effects are the most intense and most frequent at this region. Nevertheless, during major space weather storms, large geomagnetic disturbances may also occur at much lower latitudes, which indicate the possibility of GIC problems there, too (John G. Kappenman, 2003, Falayi E. O and N. Beloff, 2010). Furthermore, recent studies reveal that magnetosphere and ionosphere current caused by sudden storm commencement (SSC) and sudden impulse (SI) events can pose GIC risk in lower to equatorial region (Watari et al., 2009; Trivedi et al., 2007; Marshall et al., 2011; Pulkkinen at al., 2012; 2012; Carter et al., 2015, 2016, Zhang et al., 2016). So, all this shows that GIC issues have to be taken into account in low-latitude to equatorial networks. Regarding to that, several researches on GIC have been done in mid-low latitude regions such as Brazil, South Africa and China (Nalin. B. Trivedi, Icaro Vitorello et al., 2007, Chigomezyo M. Ngwira, Lee-Anne McKinnell et al., 2011, K. Zheng, L.G. Liu et al., 2012). So far, no severe impacts or problems caused by GIC have been reported in equatorial region. It is, of course, possible that some adverse effects have occurred by GIC in the past but, because of insufficient awareness, they have not been attributed to GIC.

On 23 December 2014, a CME was hurled away from the sun active region 2241 causing sudden increase of solar wind speed of around 180km/sec which first detected by ACE spacecraft at 10:36UT. This event caused unusual phenomena where the interplanetary magnetic field, IMF component Bz pointed northward for long period and produced strong compression at the Earth’s magnetosphere based on solar wind dynamic pressure. While Kp index shows low geomagnetic activity. This event is categorized as Sudden Impulse (SI) by International service on rapid magnetic variations (http://www.obsebre.es/en/) and not causing to any geomagnetic storm. However, Polarlightcenter in Lofoten has reported an induced electrical currents in the soils of Norway associated to this SI event, (http://spaceweather.com/). On the other hand, during the same event, higher increase of ground magnetic field at equatorial region observed in afternoon sector compared to high latitude region (Farah Adilah et. al., 2015), showing the notable ground magnetic impact in lower latitude due to this interplanetary shock occurrence. Therefore, in this study, we extend the previous investigation of this SI impact by calculating the dB/dt from ground magnetic data in order to estimate the level of geomagnetic induced currents (GICs) in function of different latitudes. The different Earth’s currents extracted from different ground magnetic data are also calculated to determine the current involved during this SI event.

In this analysis, two different events; 1) SI event on 23 December 2014 and 2) severe storm on 20 November 2003 which recorded the lowest Dst index in over 10 years are selected in order to compare the level of dB/dt of both events in equatorial region. The dB/dt levels on the ground are determined using 1-min H component of magnetic field collected by the INTERMAGNET and MAGDAS data in three main sectors; American, African and Asian sector over high latitude to dip-equator. The solar wind parameters are then analyzed to study the connection between space events and magnetic ground surface activity. The solar wind parameters, Vsw and interplanetary magnetic field, (IMF) Bz recorded on board the ACE spacecraft and the magnetic indices, SymH, AU and AL are extracted from Data Analysis Center for Geomagnetism and Space Graduate School of Science, Kyoto University database. The magnetic indices, SymH, AU and AL gives estimation of the magnetospheric and auroral electric currents. As the event was caused by sudden increased of solar wind speed which affected to the magnerospheric compression, the analysis on SymH index and are very important to describe the magnetopause current. While AU and AL indices illustrate the auroral electrojets current amplitude and the arrival of magnetospheric particles in the high latitudes ionosphere. To better understand what the Earth current involved for both events, we further study on DP field based on Araki model at different latitudes (Araki, 1994), DP2 enhancement and equatorial electrojet (EEJ).

Based on the results, this local dB/dt level shows higher at equatorial region compared to high latitude station during SI event which opposes to the severe storm event on 20 November 2003 where dB/dt level recorded higher at high latitude region. This finding highlights that SI event can possibly pose GIC in equatorial region as compared to high latitude. The DP2 enhancement is clearly observed during severe storm which consistent with past study by N. M. Mene et al., 2011, which stated that this precess is associated with fluctuations in north to south component in IMF Bz. However, the DP2 enhancement is not clearly observed during SI event, thus showing that ground induced currents in equator might not highly contributed by this process. Moreover, high dB/dt increases in noon sector and decrease in night sector which indicates that the GIC level on the ground due to SI event is influenced by the strength of equatorial electrojet. In overall, this present study indicates that high equatorial induced current observation is not limited to geomagnetic storms but also possible during interplanetary shock arrival with the addition of contribution from the increasing strength of electrojet in this region.