Impact of Oscillating IMF <i>B</i> _<i>z</i> During 17 March 2013 Storm on the Distribution of Plasma Over Indian Low-Latitude and Mid-Latitude Ionospheric Regions

We show evidence of a positive ionospheric storm occurring simultaneously at the equatorial, low-latitude and mid-latitude ionospheric regions in the Indian sector in response to an intense geomagnetic storm on 17 March 2013. The storm had its onset time coinciding with the local noon. An on-site digisonde at Trivandrum (dip equator) recorded a sharp decrease in the height of F\ region peak in the afternoon, which is a signature of westward electric field associated with a counter electrojet (CEJ). Coupled with it was a simultaneous increase in total electron content (TEC) in the entire Indian region. The magnitude of increase in TEC decreased slowly northward of the dip equator and had almost no change near the anomaly crest. Farther northward of the anomaly crest, the TEC started increasing again and at Shimla, a mid-latitude station, it had a value close to 2 times its monthly mean. We surmise that the westward electric field resulting from the CEJ pushed the F\ layer at the dip equator down to the altitude regions where recombination and diffusion played minimal roles. No loss of plasma due to diffusion while photoproduction of ions was still taking place, led to an enhancement in the electron density near the equatorial/low-latitude region. The Joule heating of the thermosphere, on the other hand, gave rise to the traveling atmospheric disturbances which pushed the plasma up in altitude at the equatorial anomaly region. It supplemented the loss of plasma at the anomaly crest region resulting in no change in the TEC thereat and a marked increase in the TEC in the mid-latitude ionosphere.