On the latitudinal changes in ionospheric electrodynamics and composition based on observations over the 76-77\textdegreeE meridian from both hemispheres during a geomagnetic storm

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\textendash21 February 2014. GPS total electron content (TEC) data from the Indian Antarctic station, Bharti (69.4\textdegreeS, 76.2\textdegreeE geographic), the northern midlatitude station Hanle (32.8\textdegreeN, 78.9\textdegreeE geographic), northern low-latitude station lying in the vicinity of the anomaly crest, Ahmedabad (23.04\textdegreeN, 72.54\textdegreeE geographic, dip latitude 17\textdegreeN), and the geomagnetic equatorial station, Trivandrum (8.5\textdegreeN, 77\textdegreeE geographic, dip latitude 0.01\textdegreeS) 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.