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

• Published in: Journal of Geophysical Research: Space Physics Vol. 115; no. A5
• Main Authors: Kikuchi, T., Ebihara, Y., Hashimoto, K. K., Kataoka, R., Hori, T., Watari, S., Nishitani, N.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01.05.2010; American Geophysical Union
• Subjects: Atmospheric sciences; DP 2 fluctuations; Earth sciences; Earth, ocean, space; Electric fields; Exact sciences and technology; R1 FACs; R2 FACs; Electric potential; magnetometers; latitude; aluminum; ionosphere; networks; convection; duration; fluctuations; Vortex; flow; Westward electrojet; Interplanetary magnetic field; models; maps; penetration; Birkeland current; cartography; Growth phase magnetic storm; Eastward electrojet; electrical field; intensity; Ring current; radar methods; storms
• ISSN: 0148-0227; 2169-9380; 2156-2202; 2169-9402
• DOI: 10.1029/2008JA013948

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.