Unusually long lasting multiple penetration of interplanetary electric field to equatorial ionosphere under oscillating IMF B sub(z)

During November 11-16, 2003, the interplanetary magnetic field (IMF) B sub(z) oscillated between northward and southward directions, which suggests discontinuous magnetic reconnection associated with the multiple pulses-like reconnection electric field. The Jicamarca incoherent scatter radar (ISR) measurements of ionospheric zonal electric field showed similar fluctuations during this period. The high correlation coefficient of 0.71 between the reconnection electric field and equatorial zonal electric field during 125 hours suggests that the interplanetary electric field (IEF) pulsively penetrated into the equatorial ionosphere due to the discontinuous magnetic reconnection. It is implied that the short lifetime (-3 hours) dawn-dusk IEF pulses can penetrate into ionosphere without shielding, in other words, they may exhibit the `shielding immunity'. The averaged penetration efficiency is about 0.136 and highly local time-dependent. Furthermore, the intense AU and AL indices imply that the multiple electric field penetration is associated with a `High-Intensity Long-Duration Continuous AE Activity (HILDCAA).'