The present paper deals with the transient behavior of MHD perturbations in the inner magnetosphere induced by an impulsive localized eastward current (source current) as a model of Pi2 pulsations in the magnetosphere. The magnetospheric model consists of a dipole magnetic field, plasmasphere, ionosphere with Pedersen conductivity, and a free outer boundary. The source current is an impulsive magnetospheric current at the onset of the substorm current wedge and is distributed around the equatorial plane of L = 10 with ±2 hour longitudinal extent around midnight. The numerical results allow us to track variation in the expected Pi2 pulsation signals in both local time and L. The poloidal-mode wave exhibits plasmasphere virtual resonance, resulting in large amplitudes around midnight, weakening toward dayside. The toroidal-mode wave is excited as a field line resonance immediately after the wave front of the poloidal-mode wave crosses regions ? where the radial gradient of VA is steep. The toroidal-mode wave has largest amplitude at the local time of the east/west edge of the source current. The duration of this wave is ̃5 min. In the middle plasmasphere where the radial gradient of the VA is smaller, the poloidal-mode wave tends to predominate over the toroidal-mode wave. These numerical results are consistent with satellite observations, in so far as the day-night asymmetry of Pi2 pulsations and the observation of transient toroidal waves.
All Science Journal Classification (ASJC) codes
- Space and Planetary Science