Energetic electron dynamics in the outer Van Allen radiation belt during sheath regions driven by interplanetary coronal mass ejections

Phenomena originating in the Sun are the main drivers of activity in the near-Earth space environment. Plasma and magnetic fields constantly flow out of the solar atmosphere, including eruptions of large magnetized plasma clouds. These clouds propagate away from the Sun to large distances, and when detected directly, they are called interplanetary coronal mass ejections (ICMEs). When ICMEs impact the Earth, they compress the magnetosphere and fill it with different plasma waves, which further affect the charged particles trapped in the geomagnetic field. These energetic particles in the Earth’s radiation belts are important to understand because they pose a significant threat for satellites. However, which physical processes – such as acceleration, scattering loss or radial diffusion – dominate the radiation belt response to a given solar wind driver structure cannot yet be predicted accurately. The dynamics remain elusive especially on short timescales of less than an hour due to the demanding level of the required data density. This thesis performs the first comprehensive and detailed statistical study on how turbulent sheath regions ahead of ICMEs affect plasma waves in the inner magnetosphere and outer radiation belt electrons. With high quality multi-point satellite measurements, the outer belt response to sheaths as a function of electron energy and radial location has been revealed. The studied sheath events were also divided based on their capability to drive geomagnetic activity, and computational tools were employed to separate adiabatic and nonadiabatic effects. Statistical analysis presented in this thesis shows that wave activity is elevated during sheaths which provides favorable conditions for wave-particle interactions. The high dynamic pressure of the sheaths also pushes the magnetopause inward facilitating significant electron losses. Flux measurements from both the Van Allen Probes and the Global Positioning System (GPS) satellite missions evidence that sheaths tend to enhance the fluxes of low energy (10s to 100s keV) electrons but deplete the high energy (> MeV) electrons. The larger number of satellites in the GPS constellation was crucial in confirming that the obtained results were due to the sheath and not influenced significantly by the following ejecta. Additionally, computation of phase space density showed that all sheaths can cause permanent loss, either by loss at the magnetopause or scattering to the atmosphere, but energization of electrons requires a sheath than can also drive storm conditions in the magnetosphere. This thesis shows that by utilizing multi-point and multi-satellite observations, assessing the overall geospace conditions from waves, geomagnetic activity and radiation belt electron variability, the impact of sheath regions could be determined. This thesis also demonstrates that sheaths which do not generate geomagnetic storms are able to drive significant changes in the outer belt electron populations, which should be noted in the event selection that often focuses on storm periods. Furthermore, the work presented in this thesis highlights the high data density of GPS satellites, which enables studying electron dynamics on timescales of a few tens of minutes, and its good synergy with Van Allen Probes measurements.Maapallon magneettikenttä vangitsee sähköisesti varattuja hiukkasia muodostaen planeetan ympärille niin kutsutut säteilyvyöt. Ulompi säteilyvyö koostuu pääosin elektroneista, joiden määrä ja energiat vaihtelevat niin minuuttien kuin päivien aikaskaaloilla johtuen vuorovaikutuksista esimerkiksi sähkömagneettisten aaltojen kanssa. Tutkimuksia elektronivuon muutoksista tarvitaan, jotta voidaan selvittää säteilyvyön olosuhteita kulloinkin hallitsevat mekanismit. Tämä tieto on tärkeää, sillä useat navigaatio- ja telekommunikaatiosatelliitit kiertävät Maata ulommassa säteilyvyössä, jossa ne ovat alttiita korkeaenergisten elektronien aiheuttamille häiriöille ja vahingoille. Säteilyvöiden olosuhteita muovaa aurinkotuuli, joka koostuu Auringosta alati virtaavista varatuista hiukkasista ja kuljettaa mukanaan Auringon magneettikenttää. Lisäksi tähtemme koronassa tapahtuu ajoittain voimakkaita purkauksia, joissa planeettainväliseen avaruuteen sinkoutuu valtavia kaasupilviä. Nämä koronan massapurkaukset saavat aikaan erityisen voimakkaita muutoksia säteilyvöissä niihin törmätessään. Purkaukset ovat yleensä niin nopeita, että niiden eteen muodostuu shokkiaalto. Shokin ja itse purkauksen välissä aurinkotuuli pakkautuu purkauksen eteen, ja tätä pyörteistä aluetta, jossa magneettikentän suunnassa ja voimakkuudessa on suurta heilahtelua, kutsutaan välivyöhykkeeksi. Tässä väitöskirjassa tutkitaan nimenomaan välivyöhykkeiden aikaansaamia muutoksia ulomman säteilyvyön olosuhteissa. Tutkimuksessa tarkasteltiin huomattavasti lyhyempiä aikaskaaloja kuin aiemmin, jotta välivyöhykkeen aiheuttamat muutokset voitiin erottaa heti sen jälkeen Maan lähiavaruuteen iskeytyvän massapurkauksen aiheuttamista muutoksista. Käyttämällä ulommassa säteilyvyössä sijaitsevien satelliittien tieteellisiä mittauksia, työssä määritettiin erityyppisten sähkömagneettisten aaltojen aktiivisuus Maan magnetosfäärissä sekä elektronivuon muutos verraten vuon arvoja välittömästi ennen ja jälkeen välivyöhykkeen vaikutusta. Aaltoaktiivisuus on korkea välivyöhykkeiden aikana, minkä ansiosta monet vuorovaikutukset ovat mahdollisia, joko antaen elektroneille energiaa tai poistamalla niitä säteilyvöistä. Elektronivuon muutokset riippuvat energiasta ja etäisyydestä Maasta. Elektronivuon arvoista ja Maan magneettikentän mallinnuksesta johdettua suuretta, faasiavaruustiheyttä, tarkastelemalla selvitettiin, että useimpien välivyöhykkeiden vaikutuksesta elektroneita poistuu systeemistä, joko planeettainväliseen avaruuteen tai Maan ilmakehään. Sen sijaan vain sellaiset välivyöhykkeet, jotka aikaansaavat magneettisen myrskyn, voivat energisoida elektroneita pysyvästi

”sumu oli haihtunut ja sisään lankesi kesän kirkkaus” : Haavoittuvuuden tuottamat merkitykset väkivallalle Iida Rauman romaanissa Seksistä ja matematiikasta

Tarkastelen pro gradu -tutkielmassani Iida Rauman Seksistä ja matematiikasta -romaanin (2015) väkivaltakuvauksia ja haavoittuvuutta. Romaanin alussa kuvataan, kuinka Tom raiskaa Erikan. Alun väkivallan kuvaus ei jää ainoaksi, vaan Erikan lapsuutta ja nuoruutta värittää väkivaltaiset kohtaamiset. Nämä väkivallanteot tekevät Erikasta entistä haavoittuvaisemman ja häiritsevät hahmon kykyä rakentaa tarinaa itsestään. Selvitän, miten erityisesti Erikan autismikirjo ja sukupuoli altistavat hahmon kerrostuvalle haavoittuvuudelle. Tarkastelen haavoittuvuutta aktiivisena ja merkityksiä purkavana, kaikkia ihmisiä yhdistävänä piirteenä. Tavoitteeni on selvittää, mitä merkityksiä vammaisen naisen haavoittuvuus tuottaa väkivallalle. Representaatioissa autismikirjo kiinnittyy maskuliinisina pidettyihin piirteisiin, kuten rationaalisuuteen tai matemaattiseen lahjakkuuteen. Esittelen, miten tämä narratiivi on mahdollisesti syntynyt ja miten Erikan hahmo häiritsee sitä. Teoreettinen viitekehys rakentuu Irmtraud Huberin metamodernismin kehikkoon. Metamodernismin palauttaa maailman tekstin taakse, mikä mahdollistaa romaanin kiinnittämisen suomalaiseen kulttuuriin. Metamodernismi muovaa metafiktiota, jonka avulla tarkastelen romaanin fantastisia aineksia ja kummituksen allegoriaa. Metanarratiivisuuden avulla esittelen romaanin kerronnallista tietoisuutta kahdella kerronnan tasolla. Luen romaanin kommentoivan suomalaista kulttuuria, jossa väkivallasta ja pärjäämisen eetoksesta tulisi irtautua. Väkivalta rakentuu pahaksi ja elämän raiteilta syökseväksi voimaksi, joka osuu kipeästi jo ennestään haavoittuvaisiin. Osoitan, miten haavoittuvuus aktiivisena toimintana muuntuu emansipatoriseksi. Näin haavoittuvuus on ihmisiä yhdistävää, jolloin rakkaus ja riippuvuus muista mahdollistaa oman tarinan uudelleen kirjoittamisen

Radial Transport in the Earth’s Radiation Belts: Linear, Quasi-linear, and Higher-order Processes

Observational studies of the Earth’s radiation belts indicate that Alfvénic fluctuations in the frequency range of 2–25 mHz accelerate electrons to relativistic energies. For decades, statistical models of radiation belts have quantified the impact of Alfvénic waves in terms of quasi-linear diffusion. However, quasi-linear models are inadequate to quantify Alfvénic radial transport occurring on timescales comparable to the azimuthal drift period of 0.1–10 MeV electrons. With recent advances in observational methodologies offering coverage of the Earth’s radiation belts on fast timescales, a theoretical framework that distinguishes between fast and diffusive radial transport can be tested for the first time in situ. In this report, we present a drift-kinetic description of radial transport for planetary radiation belts. We characterize fast linear processes and determine the conditions under which higher-order effects become dynamically significant. In the linear regime, wave–particle interactions are categorized in terms of resonant and nonresonant responses. We demonstrate that the phenomenon of zebra stripes is nonresonant and can originate from injection events in the inner radiation belts. We derive a radial diffusion coefficient for a field model that satisfies Faraday’s law and that contains two terms: one scaling as L ^10 independent of the azimuthal number m , and a second scaling as m ^2 L ^6 . In the higher-order regime, azimuthally symmetric waves with properties consistent with in situ measurements can energize 10–100 keV electrons in less than a drift period. This process provides new evidence that acceleration by Alfvénic waves in radiation belts cannot be fully contained within diffusive models

Quantifying the non-linear dependence of energetic electron fluxes in the Earth's radiation belts with radial diffusion drivers

In this study, we use mutual information to characterise statistical dependencies of seed and relativistic electron fluxes in the Earth's radiation belts on ultra-low-frequency (ULF) wave power measured on the ground and at geostationary orbit. The benefit of mutual information, in comparison to measures such as the Pearson correlation, lies in the capacity to distinguish non-linear dependencies from linear ones. After reviewing the property of mutual information and its relationship with the Pearson correlation for Gaussian bivariates, we present a methodology to quantify and distinguish linear and non-linear statistical dependencies that can be generalised to a wide range of solar wind drivers and magnetospheric responses. We present an application of the methodology by revisiting the case events studied by Rostoker et al. (1998). Our results corroborate the conclusions of Rostoker et al. (1998) that ULF wave power and relativistic electron fluxes are statistically dependent upon one another. We also estimate that the Pearson correlation is missing between 20 % and 30 % of the statistical dependency between ULF wave power and relativistic electron fluxes. Thus, the Pearson correlation underestimates the impact of ULF waves on energetic electron fluxes. However, we find that observed enhancements in relativistic electron fluxes correlate modestly, both linearly and non-linearly, with the ULF power spectrum when compared with values found in previous studies (Simms et al., 2014) and with correlational values found between seed electrons and ULF wave power for the same case events. Our results are indicative of the importance of incorporating data analysis tools that can quantify linear and non-linear interdependencies of various solar wind drivers.In this study, we use mutual information to characterise statistical dependencies of seed and relativistic electron fluxes in the Earth's radiation belts on ultra-low-frequency (ULF) wave power measured on the ground and at geostationary orbit. The benefit of mutual information, in comparison to measures such as the Pearson correlation, lies in the capacity to distinguish non-linear dependencies from linear ones. After reviewing the property of mutual information and its relationship with the Pearson correlation for Gaussian bivariates, we present a methodology to quantify and distinguish linear and non-linear statistical dependencies that can be generalised to a wide range of solar wind drivers and magnetospheric responses. We present an application of the methodology by revisiting the case events studied by Rostoker et al. (1998). Our results corroborate the conclusions of Rostoker et al. (1998) that ULF wave power and relativistic electron fluxes are statistically dependent upon one another. We also estimate that the Pearson correlation is missing between 20 % and 30 % of the statistical dependency between ULF wave power and relativistic electron fluxes. Thus, the Pearson correlation underestimates the impact of ULF waves on energetic electron fluxes. However, we find that observed enhancements in relativistic electron fluxes correlate modestly, both linearly and non-linearly, with the ULF power spectrum when compared with values found in previous studies (Simms et al., 2014) and with correlational values found between seed electrons and ULF wave power for the same case events. Our results are indicative of the importance of incorporating data analysis tools that can quantify linear and non-linear interdependencies of various solar wind drivers.Peer reviewe

Phase space density analysis of outer radiation belt electron energization and loss during geoeffective and nongeoeffective sheath regions

Coronal mass ejection driven sheath regions are one of the key drivers of drastic outer radiation belt responses. The response can however be significantly different based on the sheath properties and the associated inner magnetospheric wave activity. We performed two case studies on the effects of sheaths on outer belt electrons of various energies using data from the Van Allen Probes. One sheath caused a major geomagnetic disturbance and the other had only a minor impact. We especially investigated the phase space density (PSD) of seed, core, and ultrarelativistic electrons to determine the dominant energization and loss processes taking place during the events. Both sheaths produced substantial variation in the electron fluxes from tens of kiloelectronvolts up to ultrarelativistic energies. The responses were however the opposite: the geoeffective sheath mainly led to enhancement, while the nongeoeffective one caused a depletion throughout most of the outer belt. The case studies highlight that both inward and outward radial transport driven by ultra-low frequency waves played an important role in both electron energization and loss. Additionally, PSD radial profiles revealed a local peak that indicated significant acceleration to core energies by chorus waves during the geoeffective event. The distinct responses and different mechanisms in action during these events were related to the timing of the peaked solar wind dynamic pressure causing magnetopause compression, and the differing levels of substorm activity. The most remarkable changes in the radiation belt system occurred in key sheath sub-regions near the shock and the ejecta leading edge.Peer reviewe

Using mutual information to investigate non-linear correlation between AE index, ULF Pc5 wave activity and electron precipitation

In this study, we use mutual information from information theory to investigate non-linear correlation between geomagnetic activity indicated by auroral electrojet (AE) index with both the global ultra low frequency (ULF) Pc5 wave power and medium energy (>= 30 keV) electron precipitation at the central outer radiation belt. To investigate the energy and magnetic local time (MLT) dependence of the non-linearity, we calculate the mutual information and Pearson correlation coefficient separately for three different energy ranges (30-100 keV, 100-300 keV and >= 300 keV) and four different MLT sectors (0-6, 6-12, 12-18, 18-24). We compare results from 2 years 2004 and 2007 representing geomagnetically more active and less active years, respectively. The correlation analysis between the AE index and electron precipitation shows a clear MLT and energy dependence in both active and quiet conditions. In the two lowest energy ranges of the medium energy electrons (30-100 keV and 100-300 keV) both non-linear correlation and Pearson correlation indicate strong dependence with the AE index in the dawn sector. The linear dependence indicated by the Pearson correlation coefficient decreases from dawn to dusk while the change in the non-linear correlation is smaller indicating an increase in the non-linearity from dawn to dusk. The non-linearity between the AE index and electron precipitation is larger at all MLT sectors except MLTs 6-12 during geomagnetically more active year when larger amount of the activity is driven by interplanetary coronal mass ejections (ICMEs) compared to lower activity year with high speed stream (HSS) and stream interaction region (SIR) driven activity. These results indicate that the processes leading to electron precipitation become more non-linear in the dusk and during geomagnetically more active times when the activity is driven by ICMEs. The non-linearity between the AE index and global ULF Pc5 activity is relatively low and seems not to be affected by the difference in the geomagnetic activity during the 2 years studied.Peer reviewe

Outer Van Allen belt trapped and precipitating electron flux responses to two interplanetary magnetic clouds of opposite polarity

Recently, it has been established that interplanetary coronal mass ejections (ICMEs) can dramatically affect both trapped electron fluxes in the outer radiation belt and precipitating electron fluxes lost from the belt into the atmosphere. Precipitating electron fluxes and energies can vary over a range of timescales during these events. These variations depend on the initial energy and location of the electron population and the ICME characteristics and structures. One important factor controlling electron dynamics is the magnetic field orientation within the ejecta that is an integral part of the ICME. In this study, we examine Van Allen Probes (RBSPs) and Polar Orbiting Environmental Satellites (POESs) data to explore trapped and precipitating electron fluxes during two ICMEs. The ejecta in the selected ICMEs have magnetic cloud characteristics that exhibit the opposite sense of the rotation of the north-south magnetic field component (B-Z). RBSP data are used to study trapped electron fluxes in situ, while POES data are used for electron fluxes precipitating into the upper atmosphere. The trapped and precipitating electron fluxes are qualitatively analysed to understand their variation in relation to each other and to the magnetic cloud rotation during these events. Inner magnetospheric wave activity was also estimated using RBSP and Geostationary Operational Environmental Satellite (GOES) data. In each event, the largest changes in the location and magnitude of both the trapped and precipitating electron fluxes occurred during the southward portion of the magnetic cloud. Significant changes also occurred during the end of the sheath and at the sheath-ejecta boundary for the cloud with south to north magnetic field rotation, while the ICME with north to south rotation had significant changes at the end boundary of the cloud. The sense of rotation of B-Z and its profile also clearly affects the coherence of the trapped and/or precipitating flux changes, timing of variations with respect to the ICME structures, and flux magnitude of different electron populations. The differing electron responses could therefore imply partly different dominant acceleration mechanisms acting on the outer radiation belt electron populations as a result of opposite magnetic cloud rotation.Peer reviewe

Outer radiation belt and inner magnetospheric response to sheath regions of coronal mass ejections : a statistical analysis

The energetic electron content in the Van Allen radiation belts surrounding the Earth can vary dramatically at several timescales, and these strong electron fluxes present a hazard for spacecraft traversing the belts. The belt response to solar wind driving is, however, largely unpredictable, and the direct response to specific large-scale heliospheric structures has not been considered previously. We investigate the immediate response of electron fluxes in the outer belt that are driven by sheath regions preceding interplanetary coronal mass ejections and the associated wave activity in the inner magnetosphere. We consider the events recorded from 2012 to 2018 in the Van Allen Probes era to utilise the energy- and radial-distance-resolved electron flux observations of the twin spacecraft mission. We perform a statistical study of the events by using the superposed epoch analysis in which the sheaths are superposed separately from the ejecta and resampled to the same average duration. Our results show that the wave power of ultra-low frequency Pc5 and electromagnetic ion cyclotron waves, as measured by a Geostationary Operational Environmental Satellite (GOES), is higher during the sheath than during the ejecta. However, the level of chorus wave power, as measured by the Van Allen Probes, remains approximately the same due to similar substorm activity during the sheath and ejecta. Electron flux enhancements are common at low energies ( 4). It is distinctive that the depletion extends to lower energies at larger distances. We suggest that this L-shell and energy-dependent depletion results from the magnetopause shadowing that dominates the losses at large distances, while the wave-particle interactions dominate closer to the Earth. We also show that non-geoeffective sheaths cause significant changes in the outer belt electron fluxes.Peer reviewe

Large-Scale Dune Aurora Event Investigation Combining Citizen Scientists' Photographs and Spacecraft Observations

Recently, citizen scientist photographs led to the discovery of a new auroral form called "the dune aurora" which exhibits parallel stripes of brighter emission in the green diffuse aurora at about 100 km altitude. This discovery raised several questions, such as (i) whether the dunes are associated with particle precipitation, (ii) whether their structure arises from spatial inhomogeneities in the precipitating fluxes or in the underlying neutral atmosphere, and (iii) whether they are the auroral manifestation of an atmospheric wave called a mesospheric bore. This study investigates a large-scale dune aurora event on 20 January 2016 above Northern Europe. The dunes were observed from Finland to Scotland, spanning over 1,500 km for at least 4 h. Spacecraft observations indicate that the dunes are associated with particle precipitation and reveal the presence of a temperature inversion layer below the mesopause during the event, creating suitable conditions for mesospheric bore formation. The analysis of a time lapse of pictures by a citizen scientist from Scotland leads to the estimate that, during this event, the dunes propagate toward the west-southwest direction at about 200 m s(-1), presumably indicating strong horizontal winds near the mesopause. These results show that citizen science and dune aurora studies can fill observational gaps and be powerful tools to investigate the least-known region of near-Earth space at altitudes near 100 km.Peer reviewe