Ionospheric and Magnetic Changes Induced by Space Weather at Low- and Mid-Latitudes

Abstract

Space weather activities poses a major threat to terrestrial environment and under standing their impact to ionosphere is a significant scientific and technological challenge of our era. Particularly at low- and mid-latitudes, the horizontal geomagnetic field and its closed field-lines support the existence of distinct electric current systems, abrupt electric field variations and the development of plasma irregularities. Space weather can result in the ionospheric disturbances which are responsible for the disruption of trans-ionospheric radio waves used for navigation, communication, and terrestrial ob servations. In this regard, the rapid increase of satellite missions facilitate the study of ionospheric variations, especially the phenomena that are expected to harm space instruments and thus disrupt the respective signals. We have investigated the ionospheric variations during the disturbed and quiet geo magnetic conditions to discuss the following scientific problems; 1. How ionospheric plasma density and regular oscillation varies with a solar cycle? 2. Temporal and longitudinal features of ionospheric disturbance dynamo during coro nal mass ejection (CME) and high speed solar wind streams (HSSWs) generated storms? 3. Temporal variations of thermospheric O/N2 changes at low- and mid-latitudes and its impact on plasma density. The results indicate: 1. Existence of saturation effect in ionospheric plasma density at high solar activity, and phase of annual variations is found to be strongly affected by the solar cycle. The semi annual variations dominate in the northern hemisphere, whereas annual variations are prominent in the southern counterpart. The amplitude of annual variations in southern hemisphere is found to be higher than northern side at all latitudes. This asymmetry in the amplitude of annual variations is maximum at low-latitudes, followed by mid and high-latitudes, respectively. Whereas, the semi-annual variations are in-phase for both hemispheres and follow the solar cycle. The northern hemisphere depicts rela i DRSML QAU tively large amplitude of semi-annual variations and exhibit the maximum effect at high-latitudes. 2. The ionospheric disturbance dynamo – depending on the strength of CME generated storms – may be observed at one, two or three longitudinal sectors. Whereas, during HSSW events, disturbance dynamo is observed globally due to oscillatory z-component of interplanetary magnetic field (IMF). The Ddyn duration is found to be maximum for the storms occurring during equinox seasons. Moreover, the HSSWs events are more likely to cause – because of the oscillatory IMF Bz – long lasting Ddyn as compared to CME generated counterparts. 3. We observe a decrease in thermospheric O/N2 at mid-latitudes corresponding to negative storm effect at the respective zones. Depending on the storm intensity, the de crease in O/N2 may also be observed at low-latitudes. During the early recovery phase, there is enhancement of the said ratio at low-latitudes and contribute to the positive storm effect. Strong hemispheric asymmetries, in O/N2 variation, have been observed at the mid-latitudes sector, and can be associated with the asymmetric energy input. The HSSWs, during the recovery phases, have caused a significant reduction in O/N2 at mid-latitudes, which could not be reproduced by the coupled thermosphere-ionosphere plasmasphere electrodynamics (CTIPe) model. On the other hand, the low-latitudes region depict an enhancement in O/N2 and can be related with positive storm effect. In this regard, the CTIPe model showed discrepancies, especially during the recovery phases, in reproducing the satellite data. In the broader context, this dissertation shows that dedicated ground observatories along with satellite missions improve the specification of the low-latitudes ionospheric electrodynamics and expand the knowledge which is valuable for current and future communication, navigation, and Earth-observing missions. The contributions of this investigation represent several “firsts” in the study of ionosphere, e.g., (1) the obser vational evidence of magnetic signatures of disturbance dynamo; (2) the spatial and temporal characterization of disturbance dynamo during CME and HSSWs generated storms; (3) the quantification of thermospheric composition changes at low- and mid latitudes using TIMED/GUVI satellite data. These findings provide an insights that promise to advance our current knowledge of low- and mid-latitudes ionospheric envi ron