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We present the low-latitude ionospheric electric field during the main impulse (MI) phase of two geomagnetic sudden commencements (SCs), observed for the first time by an FM-CW radar. From our observation, the direction of the ionospheric electric field is eastward in the daytime and westward in the nighttime sectors. This difference indicates the penetration of the dawn-to-dusk polar electric field associated with the SCs into the low-latitude ionosphere.
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Ikeda et al. (2008) studied this question.
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