Abstract:
On 13 April 2013, the ACE spacecraft detected arrival of an interplanetary shock at 2250 UT,
which is followed by the passage of the sheath region of an interplanetary coronal mass ejection (ICME)
for a prolonged (18-hr) period. The polarity of interplanetary magnetic field Bz was northward inside the
magnetic cloud region of the ICME. The ring current (SYM-H) index did not go below −7 nT during this event
suggesting the absence of a typical geomagnetic storm. The responses of the global ionospheric electric
field associated with the passage of the ICME sheath region have been investigated using incoherent scatter
radar measurements of Jicamarca and Arecibo (postmidnight sector) along with the variations of equatorial
electrojet strength over India (day sector). It is found that westward and eastward prompt penetration
(PP) electric fields affected ionosphere over Jicamarca/Arecibo and Indian sectors, respectively, during
0545–0800 UT. The polarities of the PP electric field perturbations over the day/night sectors are consistent
with model predictions. In fact, DP2-type electric field perturbations with ∼40-min periodicity are found to
affect the ionosphere over both the sectors for about 2.25 hr during the passage of the ICME sheath region.
This result shows that SYM-H index may not capture the full geoeffectivenss of the ICME sheath-driven
storms and suggests that the PP electric field perturbations should be evaluated for geoeffectiveness of
ICME when the polarity of interplanetary magnetic field Bz is northward inside the magnetic cloud region
of the ICME.
