Effect of Disturbance Electric Fields on Equatorial Electrojet Over Indian Longitudes

Prompt penetration (PP) and ionospheric disturbance dynamo (Ddyn) are two expressions of the disturbed electric field developed during a geomagnetic storm in the Earth's ionosphere. Earlier investigations treated these two processes independently over longitudinal separation beyond 20 degrees. In the present study, we investigate the conjunction of these phenomena on equatorial electrojet at 520 degrees longitude separations using daytime magnetic field data from three equatorial sites viz., Minicoy, Vencode, and Campbell Bay and three low-latitude sites viz., Alibag, Hyderabad, and Nabagram, located within 20 degrees longitude over Indian region, during three intense storms (Dst < -150 nT). We propose a statistical method to identify PP signatures from large data set. In addition, we distinguish the signatures of PP and Ddyn during early recovery phase of intense storms and compute pure Ddyn signature in the late recovery phase. It is seen that the effect of PP is similar at the three equatorial sites for each storm. We find that signatures of Ddyn are amplified at Minicoy and Vencode compared to Campbell Bay, and their magnitude decreases toward low-latitude stations, also reflected in the current vector patterns. Our investigations of intense geomagnetic storms show that PP effect dominates the main phase, followed by a combined effect of PP and Ddyn in the early recovery phase. Eventually the Ddyn signature dominates in the late recovery phase with decreasing amplitudes of Ddyn with increasing time. Such investigations can provide new information about variations in ionospheric parameters.