Abstract:
Before the onset of a geomagnetic storm on 22 January 2012 (Ap =24), an enhancement in
solar wind number density from 10/cm3 to 22/cm3 during 0440–0510 UT under northward interplanetary
magnetic field (IMF Bz) condition is shown to have enhanced the high-latitude ionospheric convection and
also caused variations in the geomagnetic field globally. Conspicuous changes in ΔX are observed not
only at longitudinally separated low-latitude stations over Indian (prenoon), South American (midnight),
Japanese (afternoon), Pacific (afternoon) and African (morning) sectors but also at latitudinally separated
stations located over high and middle latitudes. The latitudinal variation of the amplitude of the ΔX
during 0440–0510 UT is shown to be consistent with the characteristics of prompt penetration
electric field disturbances. Most importantly, the density pulse event caused enhancements in the
equatorial electrojet strength and the peak height of the F layer (hmF2) over the Indian dip equatorial sector.
Further, the concomitant enhancements in electrojet current and F layer movement over the dip equator
observed during this space weather event suggest a common driver of prompt electric field disturbance at
this time. Such simultaneous variations are found to be absent during magnetically quiet days. In absence
of significant change in solar wind velocity and magnetospheric substorm activity, these observations point
toward perceptible prompt electric field disturbance over the dip equator driven by the overcompression of
the magnetosphere by solar wind density enhancement.
