Pi2 pulsations observed around the dawn terminator

<jats:title>Abstract</jats:title> <jats:p> We examined Pi2 pulsations observed simultaneously at low‐latitude stations ( <jats:italic>L</jats:italic> = 1.15 − 2.33) around the dawn terminator. Those Pi2 pulsations observed in the sunlit region were polarized in the azimuthal ( <jats:italic>D</jats:italic> , positive eastward) direction. We found that the <jats:italic>D</jats:italic> component oscillations in the dark and sunlit regions were in antiphase, whereas the <jats:italic>H</jats:italic> component oscillated in phase. A statistical analysis indicates that these <jats:italic>D</jats:italic> component phase reversals occurred about 0.5 h sunward of the dawn terminator at 100 km in altitude, corresponding to the highly conducting <jats:italic>E</jats:italic> layer. The azimuthal polarization and <jats:italic>D</jats:italic> component phase reversals related to the dawn terminator cannot be explained by the existing models of low‐latitude Pi2s (e.g., cavity resonance or substorm current wedge oscillations). Similar <jats:italic>D</jats:italic> component phase reversals were also found on the dusk side although the amplitude of the <jats:italic>D</jats:italic> component is smaller than that of the <jats:italic>H</jats:italic> component. We suggest that the meridional ionospheric current in the sunlit region adjacent to the dawn terminator drives the <jats:italic>D</jats:italic> component oscillations in antiphase with those <jats:italic>D</jats:italic> oscillations produced by the oscillatory field‐aligned current (FAC) on the postmidnight side. The meridional current is expected to form a part of a current system that extends from the postmidnight FAC to the equatorial Cowling current. The <jats:italic>D</jats:italic> component oscillations in the Northern and Southern Hemispheres are also in antiphase, indicating that the current system is symmetric with respect to the equator. </jats:p>