No description available.

The Earth's polar ionosphere is a highly dynamic region of the upper atmosphere, and acts as the closure of the greater magnetospheric current system. This region plays host to many electrodynamic effects that impact terrestrial systems, such as power grids, railroads, and pipelines. These effects are fundamentally related to the currents, electric fields, and conductivity present in the polar ionosphere. Understanding and predicting the electrodynamics of this region is vital to being able to determine the physical impacts on terrestrial systems and provide predictions to government and commercial entities. Empirical models play a key role in the research and forecasting of the solar wind and interplanetary magnetic field's impact on the polar ionosphere, and is an active area of development and research. Recent interest in polar ionospheric conductivity has led to a community-wide campaign to develop our understanding of this portion of the electrodynamic system. Characterizing the interactions between the solar wind and the polar ionosphere is a difficult task, as the region of interest is highly data starved in many respects. In particular, satellite based data products are scarce due to being costly and logistically difficult. Recent advancements in data sources (such as the Swarm and CHAMP satellite missions) as well as continued research into the physical relationships between solar wind and interplanetary magnetic field drivers have provided the opportunity to develop new, novel tools to study this region of interest. In this dissertation, two polar ionosphere models are described in Chapters 3 and 4, along with the original research that their construction has produced in Chapter 1. These two models are combined to provide a foundation for future research in this area, which is described in Chapter 5. / Doctor of Philosophy / The Earth is subjected to a constant bombardment of solar particles and magnetic fields, known as the solar wind. Our planet’s geomagnetic field protects the atmosphere from this bombardment, and directs the plasma from the solar wind into the magnetic poles of the earth. This plasma flows through a region of the atmosphere called the ionosphere, where its energy is then dissipated. This energy has many impacts on the surface of the planet, including driving currents in power grids and generating auroral displays. The polar ionosphere is the fundamental connection between the solar wind and the planet, and being able to predict how and where this connection occurs is vital to studying its nature. This work describes two models of the plasma properties in the polar ionosphere, and provides some description of the original research that these models have garnered.

The electrodynamic interaction of Ganymede’s mini-magnetosphere with Jupiter’s corotating magnetospheric plasma has been shown to give rise to strong current systems closing through the moon and its ionosphere as well as through its magnetopause and magnetotail current sheet. This interaction is strongly evidenced by the presence of aurorae at Ganymede and of a bright Ganymede footprint on Jupiter’s ionosphere. This footprint is located equatorward of the main auroral emissions, at the magnetic longitude of the field line threading Ganymede. The brightness of Ganymede’s auroral footprint at Jupiter along with its latitudinal position have been shown to depend on the position of Ganymede relative to the center of the Jovian plasma sheet. Additionally, observations using the Hubble Space Telescope showed that Ganymede’s auroral footprint brightness is characterized by variations of three different timescales: 5 hours, 10-40 minutes, and ~100 seconds. The goal of the present study is to examine the relationship between the longest and the shortest timescale periodicities of Ganymede’s auroral footprint brightness and the local processes occurring at Ganymede. This is done by coupling a specifically developed brightness model to a three-dimensional multifluid model which tracks the energies and fluxes of the various sources of charged particles that precipitate into Ganymede’s ionosphere to generate the aurora. It is shown that the predicted auroral brightnesses and morphologies agree well with observations of Ganymede’s aurora from the Hubble Space Telescope. Our results also suggest the presence of short- and long-period variabilities in the auroral emissions at Ganymede due to magnetic reconnections on the magnetopause and in the magnetotail, and support the hypothesis of a correlation between the variability of Ganymede’s auroral footprint on Jupiter’s ionosphere and the variability in the brightness and morphology of the aurora at Ganymede. Finally, the modeled aurora at Ganymede reveals that the periodicities in the morphology and brightness of the auroral emissions are produced by two different dynamic reconnection mechanisms. The Jovian flow facing side aurora is generated by electrons sourced in the Jovian plasma and penetrating into Ganymede’s ionosphere through the cusps above the separatrix region. In this case, the reconnection processes responsible for the auroral emissions occur on Ganymede’s magnetopause between the Jovian magnetic field lines and the open magnetic field lines threading Ganymede’s Polar Regions. As for the magnetotail side aurora, it is generated by electrons originating from Ganymede’s magnetospheric flow. These electrons are accelerated along closed magnetic field lines created by magnetic reconnection in Ganymede’s magnetotail, and precipitate into Ganymede’s ionosphere at much lower latitudes, below the separatrix region.

We use electric and magnetic field data from MMS spacecraft between 2016 and 2017 tostatistically investigate earthward propagating plasma flow bursts and field-aligned currents(FACs) inside the plasma sheet of the geomagnetic tail. We observe that the occurrence rateof flow burst peaks around the midnight region with decreasing trend towards Earth and theplasma sheet flanks. Further, we distinguish between long and short FACs. Long FACs laston average 6 sec and have a magnitude of 5-20 nA/m 2 . Short FACs last on average 10 timesshorter and have an magnitude of 10-50 nA/m 2 . Both, long and short FACs occur on averageone time per flow burst, on minimum 0 times and on maximum 4 times per flow burst. Intotal, 43 % of the observed FACs are located in a flow burst, 40 % before and 17 % right after aflow burst.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20183号 / 理博第4268号 / 新制||理||1613(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 家森 俊彦, 教授 田口 聡, 教授 塩谷 雅人 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The bow shock is formed due to the abrupt deceleration of the supersonic solar wind in front of the terrestrial magnetic field. The solar wind plasma and the Interplanetary Magnetic Field (IMF) are both compressed across the shock, and according to Ampère's law a current thus flows on the bow shock at all times. The Bow Shock Current (BSC) is suggested to play an important role in solar wind-magnetosphere coupling, but there is still an open debate about its closure path. For predominantly east-west IMF, the BSC has been suggested to close to Earth's high latitude ionosphere as Field-Aligned Currents (FACs). Since the bow shock is magnetically connected to the solar wind, it must do so via open field lines through the magnetosheath. For southwards IMF with a significant east-west component, the R0 FAC flows into the ionosphere in one hemisphere, and out of it in the other. The R0 current flows on open field lines, and is thus a potential candidate to close the BSC. While a few studies have already found evidence in favour of this idea, the majority have been based on simulations. Additional observational evidence is required to confirm these findings. We used OMNI data for the IMF at the bow shock, and Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) data for the FACs, to make simultaneous observations of the IMF at the bow shock and the northern hemisphere FACs, including the R0 current. We successfully identified 15 events of southwards but predominantly east-west IMF (Bz<0, |By|>|Bz|) at the bow shock, for which the northern hemisphere R0 current could be observed both in the AMPERE and DMSP data. In each of these events, the R0 current was of the correct polarity to connect to the BSC. Moreover, using Defense Meteorological Satellite Program (DMSP) and Super Dual Auroral Radar Network (SuperDARN) data, we were able to verify that part of the R0 current was flowing on open field lines. Collectively, the 15 events presented here constitute an argument in favour of at least a partial BSC closure to Earth's high latitude ionosphere as R0 FACs, for predominantly east-west IMF. Additional investigation is required to reveal the details of BSC closure.

Idag finns det omkring 5 000 operativa satelliter i omloppsbana runt jorden. Bland dessa finns MATS, DMSP-17/18 och Swarm-A/B/C. De tre satellitprogrammen ger olika data från jordens övre atmosfär där MATS bland annat observerar infraröd emission, DMSP mäter elektron- och jonnedfall från rymden och Swarm bland annat mäter variationer i jordens geomagnetiska fält. Dessa data ger möjlighet att analysera aurora. Aurora, även känt som polarsken, är ett fantastiskt ljusfenomen som kan urskiljas i olika färger och som har forskats på under flera decennier. Till följd av detta finns även möjligheten att göra gymnasieelever mer intresserade av rymden. När elever deltar i autentiskt lärande kan det bidra till ökat intresse inom naturvetenskap. Studien syftar till att undersöka auroraregionerna och jämföra data mellan MATS, DMSP och Swarm för att skapa en helhetsbild av fenomenet. Dessutom utvecklas ett lektionsmaterial som syftar till att öka intresset för rymden och fysik i allmänhet bland gymnasieelever. Metoden för den tekniska delen innefattade att finna konjunktioner mellan MATS och en annan satellit eftersom satelliterna ska ge data för samma fenomen. Under en konjunktion behövde banorna stämma överens samtidigt som satelliterna skulle ha tillgänglig data vid tidpunkten. För den pedagogiska delen har en enkätstudie använts för att samla in lärares åsikter om utveckling och utvärdering av lektionsmaterialet. Fem konjunktioner undersöktes och resultaten visade på en ökning av elektron och jonenergi samt flöde i auroraregioner. Ett fall visade en svag uppåtriktad ström som en potentiell förklaring till den ökade energin, vilket möjligtvis tillåter elektronerna att accelerera mot jorden och därav ökar flödet. Enkätstudien visade att det fanns ett intresse för ett lektionsmaterial. Fokus skulle ligga på att skapa ett autentiskt material där eleverna fick en genomgång om hur polarsken uppstår och därefter diskutera frågor kopplade till materialet. Utvärderingen visade att syftet och lärandemålen för lektionen hade uppfyllts. Eleverna deltog aktivt i diskussioner, ställde följdfrågor och ansågs vara intresserade av materialet. / Today there are around 5 000 operative satellites currently in orbit. MATS,DMSP-17/18 and Swarm-A/B/C are just a few among them. These three satellite programs produce different data from Earth’s upper atmosphere. MATS observe infrared emission, DMSP measure electron- and ion precipitation and Swarm measure variations in Earth’s geomagnetic field. This data provides the opportunity to analyze aurora. Aurora, also known as polar lights, is a fantasticlight phenomenon that can be observed in different colors and has been researched for decades. As a result, there is also a possibility to increase the interest among high school students to learn about space. A contribution to their interest can be seen when the students are allowed to participate in authentic learning.The study aimed to investigate aurora regions and compare data between MATS, DMSP and Swarm in order to create a comprehensive picture of the phenomenon. Additionally, an educational material was developed with the aim of increasing interest in space and physics in general among high school students. The methodology for the technical part consisted of finding conjunctions between MATS and one other satellite. This was because of the fact that the satellites were required to give data from the same phenomenon. During a conjunction the orbits of the satellites had to correspond and the satellites also needed to have available data from the time period. A survey study was conducted for the pedagogical part in order to collect opinions from teachers about the development and evaluation of the educational material. Five conjunctions were examined, and the results indicated an increase in electron and ion energy as well as flux in auroral regions. One case showed a weak upward current as a potential explanation for the increase in energy, possibly allowing electrons to accelerate towards the Earth and thus increasing the flux. The survey study showed that there was an interest in the educational material. The focus would be to create an authentic material where students were given an overview of how aurora occur followed by questions to discuss related to the material. The evaluation showed that the purpose and learning objectives of the lesson had been fulfilled. Students actively participated in discussions, asked follow-up questions and were considered to be interested in the material.