Abstract:
The relative contributions of the composition disturbances and the disturbance electric fields
in the redistribution of ionospheric plasma is investigated in detail by taking the case of a long-duration
positive ionospheric storm that occurred during 18–21 February 2014. GPS total electron content (TEC)
data from the Indian Antarctic station, Bharti (69.4∘S, 76.2∘E geographic), the northern midlatitude station
Hanle (32.8∘N, 78.9∘E geographic), northern low-latitude station lying in the vicinity of the anomaly crest,
Ahmedabad (23.04∘N, 72.54∘E geographic, dip latitude 17∘N), and the geomagnetic equatorial station,
Trivandrum (8.5∘N, 77∘E geographic, dip latitude 0.01∘S) are used in the study. These are the first
simultaneous observations of TEC from Bharti and Hanle during a geomagnetic storm. The impact of the
intense geomagnetic storm (Dst ∼−130 nT) on the southern hemisphere high-latitude station was a
drastic reduction in the TEC (negative ionospheric storm) starting from around 0330 Indian standard time
(IST) on 19 February which continued till 21 February, the maximum reduction in TEC at Bharti being
∼35 TEC units on 19 February. In the northern hemisphere midlatitude and equatorial stations, a positive
ionospheric storm started on 19 February at around 0900 IST and lasted for 3 days. The maximum
enhancement in TEC at Hanle was about ∼25 TECU on 19 February while over Trivandrum it was ∼10 TECU.
This long-duration positive ionospheric storm provided an opportunity to assess the relative contributions
of disturbance electric fields and composition changes latitudinally. The results indicate that the negative
ionospheric storm over Bharti and the positive ionospheric storm over Hanle are the effect of the changes
in the global wind system and the storm-induced composition changes. At the equatorial latitudes, the
positive ionospheric storm was due to the interplay of prompt penetration electric field and disturbance
dynamo electric field.
