Abstract:
The St. Patrick’s Day storm of 17 March 2015 has a long-lasting main phase with the Dst reaching
a minimum of 223 nT. During the main phase, two strong prompt penetration electric field (PPEF) phases
took place; first with the southward turning of IMF Bz around ~1200 UT and the second with the onset of a
substorm around ~1725 UT leading to strong equatorial zonal electric field enhancements. The consequent
spatiotemporal disturbances in the ionospheric total electron content and the resultant modifications in the
equatorial ionization anomaly (EIA) over the Brazilian longitudinal sector are investigated in detail. The
simultaneous measurements from a large network of GPS receivers, ionosonde, and magnetometers over the
Brazilian longitudinal sector are used for this study. In the presence of enhanced zonal electric field, the
equatorial F2 layer peak (hmF2) experienced a rapid uplift without any significant change in the base height
(h0F); while the F2 layer is redistributed into F2 and F3 layers. The enhanced zonal electric filed due to PPEF led
to the strong super fountain effect under which the anomaly crest departed poleward to ~40°S latitude. In
the presence of westward and equatorward wind surge over Brazil with the coexisting disturbance dynamo
fields, strong hemispheric asymmetry is seen in the storm time response of EIA during both the PPEF phases.
