  The paper describes the occurrence of a pair of oppositely directed sudden
impulses (SI), in the geomagnetic field ($\Delta$X), at ground stations, called
SI${^{+}}$ -- SI${^{-}}$ pairs, that occurred between 1835 UT and 2300 UT on 23
April 1998. The SI${^{+}}$ -- SI${^{-}}$ pair, was closely correlated with
corresponding variations in the solar wind density, while solar wind velocity
and the southward component of the interplanetary magnetic field (Bz) did not
show any correspondence. Further, this event had no source on the visible solar
disk. However, a rear-side partial halo coronal mass ejection (CME) and an M1.4
class solar flare behind the west limb, took place on 20 April 1998, the date
corresponding to the traceback location of the solar wind flows. This event
presents empirical evidence, which to our knowledge, is the best convincing
evidence for the association of specific solar events to the observations of an
SI${^{+}}$ -- SI${^{-}}$ pair. In addition, it shows that it is possible for a
rear side solar flare to propagate a shock towards the earth.
