Κατεύθυνση Αστροφυσική
Library of the School of Science

2020-09-17

2020

Moutsiana Georgia

Ιωάννης Α. Δαγκλής, Καθηγητής, Τμήμα Φυσικής, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών

Ο ρόλος ιονοσφαιρικών ιόντων Οξυγόνου στη δυναμική εξέλιξη του δακτυλιοειδούς ρεύματος

Greek

The role of ionospheric Oxygen ions in ring current dynamics

The terrestrial ring current is a toroidal electric current flowing westward around our planet. It is located at an equatorial distance between ~ 2RΕ and ~ 7RΕ, while it is dominated by ions with energies from ~ 1 keV to a few hundred keV. The main carriers of the ring current during quiet time (geomagnetic) conditions are protons originating mainly from the solar wind. However, during geomagnetically active times, both in situ satellite measurements and modeling work have confirmed the significant contribution of ionospheric Oxygen ions to the ring current energy density. The enhanced Oxygen presence in the inner magnetosphere affects various processes, such as wave propagation and their consequent interaction with ring current particles, as well as the charge exchange process, which constitutes one of the most important decay mechanisms of the ring current, depending on particle species and energy. Therefore, studying Oxygen ions behaviour is considered important in understanding ring current dynamics during geomagnetic activity variations.

In the present thesis we describe and investigate H - ions and O - ions injection events in the inner magnetosphere, as well as their decay characteristics in comparison with geomagnetic activity variations. We study the above parameters during the entire year 2015 with special reference in June because of its interesting geomagnetic activity. In particular, we use data from the WDC for Geomagnetism, Kyoto for the Dst-index or SYMH-index regarding the monitor of geomagnetic storms, and for the AL-index regarding the monitor of magnetospheric substorms. Furthermore, we use omnidirectional and integral flux data for H - ions and O - ions from the RBSPICE-B instrument of the Van Allen Probes Mission. The energy range of measured particles is ~ 45 keV - ~ 600 keV for H - ions and ~ 142 keV - ~ 1127 keV for O - ions, which means that only higher energy O - ions are taken into consideration. At first, we examine the temporal and spatial evolution of the Integral Flux for both particle species and each entire energy range, as well as the ratio of O-ions flux / H-ions flux according to geomagnetic activity variations. Then, we repeat the above calculations and study, but this time we are using fluxes for the common energy range of the aforementioned particle species. These fluxes are acquired using three distinct integration methods over the omnidirectional flux for both ion species and across the common energy range. After comparing the results of the two above cases for common periods of time, we discuss the contribution of higher energy O - ions to the injection and decay events of the ionospheric component of the ring current along various L shells. Finally, we discuss the contribution of magnetospheric substorms in O - ions injection events in the inner magnetosphere.

Science

terrestrial ring current, Oxygen ions, ion fluxes, terrestrial magnetosphere, geomagnetic storms, magnetospheric substorms, RBSPICE instrument, Van Allen Probes mission

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https://pergamos.lib.uoa.gr/uoa/dl/object/2922690