Penetration of the convection and overshielding electric fields to the equatorial ionosphere during a quasiperiodic DP 2 geomagnetic fluctuation event

Abstract

[1] The convection electric field penetrates to the equatorial ionosphere with no significant shielding during DP 2 fluctuation events with periods of 30-60 min (Nishida, 1968) and even during the main phase of a storm that continues over several hours (Huang et al., 2007). On the other hand, shielding becomes effective in 20 min during the substorm growth phase (Somayajulu et al., 1987), and in 1 h during the main phase of a storm (Kikuchi et al., 2008a). To clarify the relative contributions of the convection and shielding electric fields at middle to equatorial latitudes, we analyzed an equatorial DP 2 fluctuation event of 30 min duration, using magnetometer data, Super Dual Auroral Radar Network (SuperDARN) convection maps, and electric potentials calculated with the comprehensive ring current model (CRCM). The equatorial DP 2 fluctuations were found to be caused by alternating eastward electrojets (e-EJ) and westward electrojets (w-EJ) in the equatorial ionosphere, which were caused by the southward and northward interplanetary magnetic field, respectively. Using the SuperDARN convection map, we further show that the e-EJ is associated with large-scale two-cell convection vortices, while the w-EJ accompanies reverse flow vortices equatorward of the two-cell vortices. With the aid of the CRCM, we suggest that the reverse flow vortices were associated with the region 2 field-aligned currents (R2 FACs) that caused overshielding at the equator. We think it reasonable that the overshielding electric field could appear at middle to equatorial latitudes irrespective of the period of fluctuations as the region 1 FACs decrease their intensity. This scenario well explains both DP 2 fluctuations with periods of 30-60 min and continuous penetration for several hours during the main phase of storms.Citation: Kikuchi, T., Y. Ebihara, K. K. Hashimoto, R. Kataoka, T. Hori, S. Watari, and N. Nishitani (2010), Penetration of the convection and overshielding electric fields to the equatorial ionosphere during a quasiperiodic DP 2 geomagnetic fluctuation event,

Magnetic latitude and local time distributions of ionospheric currents during a geomagnetic storm

“…Here we note that the electric field at low latitude is determined by a sum of the convection and shielding electric fields. Therefore, the overshielding could appear whenever the convection electric field decreases compared with the developed shielding electric field even during the DP2 fluctuation events [ Kikuchi et al , 2010] and even during the storm main phase [ Fejer et al , 2007; Veenadhari et al , 2010].…”

Long-duration positive ionospheric storm during the December 2006 geomagnetic storm: Ionizing effect of forbidden electrons

“…However, the observations showed a strong increase in VTEC as clearly seen in Figure 4 (right). At that time, magnetic measurements showed a quiet level of the ionospheric electric fields (Lei et al, 2008b;Kikuchi et al, 2010;Wei et al, 2010).…”

“…Extreme solar and space weather events of 13-16 December 2006 have comprehensively studied earlier (Dmitriev et al, , 2010Lei et al, 2008aLei et al, , 2008bEbihara et al, 2009;Myagkova et al, 2009;Pedatella et al, 2009;de Jesus et al, 2010;Kikuchi et al, 2010;Wang et al, 2010;Wei et al, 2011;Dahlgren et al, 2012;Klimenko and Klimenko, 2012) and still attract much attention, particularly in studies of the upper atmosphere and ionosphere (Koshiishi, 2014;Zigman et al, 2014;Kumar et al, 2015). Also, the positive ionospheric storm and FEE enhancement during the main phase and maximum of the 15 December geomagnetic storm were analyzed in our previous works (Suvorova et al, 2012(Suvorova et al, , 2013.…”

Effects of ionizing energetic electrons and plasma transport in the ionosphere during the initial phase of the December 2006 magnetic storm

“…Ionospheric effects during the 14–16 December 2006 storm were considered in numerous studies [ Lei et al , ; Pedatella et al , ; Wang et al , ; de Jesus et al , ; Kikuchi et al , ; Leonovich et al , ; Wei et al , ; Klimenko and Klimenko , ; Suvorova et al , , , ; Wu et al , ]. In particular, Suvorova et al [] emphasized that the positive ionospheric storm was unusually long and was accompanied by several FEE enhancements that occurred from the initial to late recovery phases.…”