Energy Flux Through the Magnetopause During Flux Transfer Events in Hybrid-Vlasov 2D Simulations

Solar wind-magnetosphere coupling drives magnetospheric dynamic phenomena by enabling energy exchange between magnetospheric and solar wind plasmas. In this study, we examine two-dimensional noon-midnight meridional plane simulation runs of the global hybrid-Vlasov code Vlasiator with southward interplanetary magnetic field driving. We compute the energy flux, which consists of the Poynting flux and hydrodynamic energy flux components, through the Earth's magnetopause during flux transfer events (FTEs). The results demonstrate the spatiotemporal variations of the energy flux along the magnetopause during an FTE, associating the FTE leading (trailing) edge with an energy injection into (escape from) the magnetosphere on the dayside. Furthermore, FTEs traveling along the magnetopause transport energy to the nightside magnetosphere. We identify the tail lobes as a primary entry region for solar wind energy into the magnetosphere, consistent with results from global magnetohydrodynamic simulations and observations.Peer reviewe

Comparisons of Three Global Models of Earth\u27s Magnetosphere During Quiet Geomagnetic Times

The Space Weather Modeling Framework (SWMF) at the Center for Space Environment Modeling (CSEM) at the University of Michigan is a powerful tool for modeling space weather and space physics phenomena in the Earth-Sun system. The Block-Adaptive Tree Solarwind Roe-type Upwind Scheme (BATS-R-US), Ionospheric Electrodynamic, and Inner Magnetospheric models within SWMF can be coupled to assess a number of quantities related to the dynamics of the earth\u27s magnetosphere. The basic MHD model—referred in the work as the “Ideal MHD model”—in use is the coupling of BATS-R-US with IE, however IM models are being added to form a global MHD model. Currently, there are two different IM models for this purpose: the Rice Convection Model and the Comprehensive Ring Current Model. This paper assesses the differences between the three couplings and lays a foundation for future comparisons. Cross correlation values between coupling efficiency and cross polar cap potential and polar cap area are carefully considered in the comparison as are time variation plots of each of these values. Contour plots each hemisphere are made for each model and run time and are also considered in the analysis. These plots contain field-aligned currents and Hall and Pedersen conductivities over-plotted on the open-closed field line boundary and electric potential values

Laskennallisten avaruussäämallien kehittäminen, validointi ja käyttö

Currently the majority of space-based assets are located inside the Earth's magnetosphere where they must endure the effects of the near-Earth space environment, i.e. space weather, which is driven by the supersonic flow of plasma from the Sun. Space weather refers to the day-to-day changes in the temperature, magnetic field and other parameters of the near-Earth space, similarly to ordinary weather which refers to changes in the atmosphere above ground level. Space weather can also cause adverse effects on the ground, for example, by inducing large direct currents in power transmission systems. The performance of computers has been growing exponentially for many decades and as a result the importance of numerical modeling in science has also increased rapidly. Numerical modeling is especially important in space plasma physics because there are no in-situ observations of space plasmas outside of the heliosphere and it is not feasible to study all aspects of space plasmas in a terrestrial laboratory. With the increasing number of computational cores in supercomputers, the parallel performance of numerical models on distributed memory hardware is also becoming crucial. This thesis consists of an introduction, four peer reviewed articles and describes the process of developing numerical space environment/weather models and the use of such models to study the near-Earth space. A complete model development chain is presented starting from initial planning and design to distributed memory parallelization and optimization, and finally testing, verification and validation of numerical models. A grid library that provides good parallel scalability on distributed memory hardware and several novel features, the distributed cartesian cell-refinable grid (DCCRG), is designed and developed. DCCRG is presently used in two numerical space weather models being developed at the Finnish Meteorological Institute. The first global magnetospheric test particle simulation based on the Vlasov description of plasma is carried out using the Vlasiator model. The test shows that the Vlasov equation for plasma in six-dimensionsional phase space is solved correctly by Vlasiator, that results are obtained beyond those of the magnetohydrodynamic (MHD) description of plasma and that global magnetospheric simulations using a hybrid-Vlasov model are feasible on current hardware. For the first time four global magnetospheric models using the MHD description of plasma (BATS-R-US, GUMICS, OpenGGCM, LFM) are run with identical solar wind input and the results compared to observations in the ionosphere and outer magnetosphere. Based on the results of the global magnetospheric MHD model GUMICS a hypothesis is formulated for a new mechanism of plasmoid formation in the Earth's magnetotail.Avaruuteen lähetetyistä laitteista suurin osa sijaitsee Maan magnetosfäärissä, missä ne altistuvat avaruussäälle. Avaruussäällä tarkoitetaan Maan lähiavaruuden läpötilan, magneettikentän ja muiden ominaisuuksien päivittäistä vaihtelua auringosta jatkuvasti virtaavan plasman - aurinkotuulen - vuoksi. Avaruussäällä voi olla haitallisia vaikutuksia myön Maan pinnalla, esimerkkinä sähkönsiirtoverkkoihin indusoituvat suuret tasavirrat. Tietokoneiden laskentateho on kasvanut eksponentiaalisesti jo vuosikymmenien ajan, minkä seurauksena myös laskennallisen mallinnuksen merkitys tieteelle on kasvanut huomattavasti. Laskennallinen mallintaminen on erityisen tärkeää avaruusplasmafysiikassa, sillä aurinkokunnan ulkopuolelta ei ole suoria mittauksia, eikä kaikkia avaruusplasman ominaisuuksia voida tutkia maanpäällisissä laboratorioissa. Supertietokoneiden laskentaytimien määrän kasvaessa myös laskennallisten mallien rinnakkaisesta suorituskyvystä on tullut ratkaisevan tärkeää. Väitöskirja koostuu johdannosta ja neljästä vertaisarvioidusta julkaisusta joissa kuvataan laskennallisten avaruussäämallien kehittämistä ja käyttöä Maan lähiavaruuden tutkimiseen. Avaruussäämallien kaikki kehittämisaskeleet käydään läpi alkaen alustavasta suunnittelusta ja toteutuksesta, jaetun muistin rinnakkaistuksesta ja laskentanopeuden optimoinnista aina testaukseen ja validointiin asti. Väitöskirjan yhteydessä on suunniteltu ja toteutettu rinnakkainen hila jota käytetään tällä hetkellä kahdessa Ilmatieteen laitoksella kehitettävässä avaruussäämallissa. Näistä toisen, Vlasovin yhtälöllä plasmaa mallintavan Vlasiatorin, täyden kuusiulotteisen faasiavaruuden (kolme paikka- ja kolme nopeusulottuvuutta) käsittävällä magnetosfääritestillä on osoitettu mallin toimivuus ja soveltuvuus Maapallon koko magnetosfäärin mallintamiseen nykyisillä supertietokoneilla. Ensimmäistä kertaa on myös vertailtu neljän eri avaruussäämallin (BATS-R-US, GUMICS, OpenGGCM, LFM) tuottamia ennusteita Maan lähiavaruudesta käyttäen samaa aurinkotuulisyötettä

The Inertial Range of Turbulence in the Inner Heliosheath and in the Local Interstellar Medium

The governing mechanisms of magnetic field annihilation in the outer heliosphere is an intriguing topic. It is currently believed that the turbulent fluctuations pervade the inner heliosheath (IHS) and the Local Interstellar Medium (LISM). Turbulence, magnetic reconnection, or their reciprocal link may be responsible for magnetic energy conversion in the IHS.   As 1-day averaged data are typically used, the present literature mainly concerns large-scale analysis and does not describe inertial-cascade dynamics of turbulence in the IHS. Moreover, lack of spectral analysis make IHS dynamics remain critically understudied. Our group showed that 48-s MAG data from the Voyager mission are appropriate for a power spectral analysis over a frequency range of five decades, from 5e-8 Hz to 1e-2 Hz [Gallana et al., JGR 121 (2016)]. Special spectral estimation techniques are used to deal with the large amount of missing data (70%). We provide the first clear evidence of an inertial-cascade range of turbulence (spectral index is between -2 and -1.5). A spectral break at about 1e-5 Hz is found to separate the inertial range from the enegy-injection range (1/f energy decay). Instrumental noise bounds our investigation to frequencies lower than 5e-4 Hz. By considering several consecutive periods after 2009 at both V1 and V2, we show that the extension and the spectral energy decay of these two regimes may be indicators of IHS regions governed by different physical processes. We describe fluctuations’ regimes in terms of spectral energy density, anisotropy, compressibility, and statistical analysis of intermittency.   In the LISM, it was theorized that pristine interstellar turbulence may coexist with waves from the IHS, however this is still a debated topic. We observe that the fluctuating magnetic energy cascades as a power law with spectral index in the range [-1.35, -1.65] in the whole range of frequencies unaffected by noise. No spectral break is observed, nor decaying turbulence

20 Years of Cluster Observations: The Magnetopause,

The terrestrial magnetopause forms the boundary between the solar wind plasma with its embedded interplanetary magnetic field on one side, and the terrestrial magnetosphere, dominated by Earth's dipole field, on the other side. It is therefore a key region for the transfer of mass, momentum, and energy from the solar wind to the magnetosphere. The Cluster mission, comprising a constellation of four spacecraft flying in formation was launched more than 20 years ago to study boundaries in space. During its lifetime, Cluster has provided a wealth of new knowledge about the magnetopause. In this paper, we give an overview of Cluster-based studies of this boundary, and highlight a selection of interesting results.publishedVersio

Global Response to Local Ionospheric Mass Ejection

We revisit a reported "Ionospheric Mass Ejection" using prior event observations to guide a global simulation of local ionospheric outflows, global magnetospheric circulation, and plasma sheet pressurization, and comparing our results with the observed global response. Our simulation framework is based on test particle motions in the Lyon-Fedder-Mobarry (LFM) global circulation model electromagnetic fields. The inner magnetosphere is simulated with the Comprehensive Ring Current Model (CRCM) of Fok and Wolf, driven by the transpolar potential developed by the LFM magnetosphere, and includes an embedded plasmaspheric simulation. Global circulation is stimulated using the observed solar wind conditions for the period 24-25 Sept 1998. This period begins with the arrival of a Coronal Mass Ejection, initially with northward, but later with southward interplanetary magnetic field. Test particles are launched from the ionosphere with fluxes specified by local empirical relationships of outflow to electrodynamic and particle precipitation imposed by the MIlD simulation. Particles are tracked until they are lost from the system downstream or into the atmosphere, using the full equations of motion. Results are compared with the observed ring current and a simulation of polar and auroral wind outflows driven globally by solar wind dynamic pressure. We find good quantitative agreement with the observed ring current, and reasonable qualitative agreement with earlier simulation results, suggesting that the solar wind driven global simulation generates realistic energy dissipation in the ionosphere and that the Strangeway relations provide a realistic local outflow description

Two dimensional hybrid simulations of small scale obstacles in the solar wind

The structure and dynamics of the solar wind interaction with two small scale obstacles (of the order of a pickup ion gyroradius) is examined. These are a comet, comparable to Grigg-Skjellerup, and a weakly ionospheric planet. We also perform a pilot study of an intrinsically magnetized planet in such flow, in preparation for a future three-dimensional simulation. Here, we use two-dimensional hybrid simulations (particle ions, fluid electrons) and consider different solar wind Alfven Mach number flow (MA) and interplanetary magnetic field orientation relative to this plane. This allows control of the available wave types. The cometary simulations display magnetosonic "turbulence" as MA is increased, when the field is perpendicular to the simulation plane. If we allow parallel propagating modes by setting the field parallel to the plane, we find the "turbulence" significantly changes in scale and extent, suggesting resonant growth of Alfven ion cyclotron waves in the presence of magnetosonic "turbulence" occurs. Free energy is available from picked up cometary ions. The process depends on the cometary ion density, which strongly varies, and we conclude this explains the broadband nature of the disturbances. In the perpendicular field orientation, the planetary source produces a novel two tail structure which continuously strips the planetary ionosphere. We find these tails have very distinct characteristics, resulting in the wake being filled relatively quickly downstream, by complex structure. At higher MAl magnetosonic "turbulence" again appears. Switching the field parallel to the plane causes massive field line draping and pile-up, and causes instability. A long lasting wake appears, and we conclude that a three-dimensional simulation is required. The magnetized ionospheric planet pilot study proved difficult to scale accurately in two dimensions. The planetary field failed to penetrate the solar wind, however it appears the simulation would be stable and achieve equilibrium in three dimensions

Modeling the Earth's Magnetosphere using Magnetohydrodynamics

This thesis describes work on building numerical models of the Earth's magnetosphere using magnetohydrodynamics (MHD) and other related modeling methods. For many years, models that solve the MHD equations have been the main tool for improving our theoretical understanding of the large-scale dynamics of the Earth's magnetosphere. While the MHD models have been very successful in capturing many large-scale features, they fail to adequately represent the important drift physics in the inner magnetosphere. Consequently, the ring current, which contains most of the particle energy in the inner magnetosphere, is not realistically represented in MHD models. In this thesis, Chapter 2 and 3 will describe in detail our effort to couple the OpenGGCM (Open Geospace General Circulation Model), one of the major MHD models, to the Rice Convection Model (RCM), an inner magnetosphere ring current model, with the goal of including energy dependent drift physics into the MHD model. In Chapter 4, we will describe an initial attempt to use a direct-integration method to calculate Birkeland currents in the MHD code. Another focus of the thesis work, presented in Chapter 5, addresses a longstanding problem on how a geomagnetic substorm can occur within the closed field line region of the tail. We find a scenario of a bubble-blob pair formation in an OpenGGCM simulation just before the expansion phase of the substorm begins and the subsequent separation of the bubble and the blob decreases the normal component of the magnetic field until finally an X-line occurs. Thus the formation of the bubble-blob pair may play an important role in changing the magnetospheric configuration from a stretched field to the X-line formation that is believed to be the major signature of a substorm

Drift Orbit Bifurcation Effects on Earth’s Radiation Belt Electrons

Energetic charged particles trapped in the Earth’s radiation belt form a hazardous space environment for artificial electronic systems and astronauts. The study of Earth\u27s radiation belt is becoming increasingly important with the development of communication technology, which plays a significant role in modern society. Earth’s radiation belt is highly dynamic, and the electron flux can drop by several orders of magnitude within a few hours which is called radiation belt dropout. The fast dropout of energetic electrons in the radiation belt, despite its significance, has not been thoroughly studied. One of the most compelling outstanding questions in Earth\u27s radiation belt studies is: What physical mechanisms cause these rapid and substantial drops of radiation belt electron flux? Apart from well-studied processes like wave-particle interaction, which contribute to the loss of radiation belt electrons through the processes including magnetopause shadowing and atmospheric precipitation, the effects from an anomalous process called drift orbit bifurcation (DOB) have not yet been fully understood. DOB has been suggested to play a major role in the loss and transport of radiation belt electrons since it violates the particles’ second adiabatic invariant and makes the third invariant undefined. In our first study of this dissertation, using guiding-center test particle simulations based on the Tsyganenko-1989c magnetic field model we show that DOB could affect a broad region of the outer radiation belt. It can penetrate inside the geosynchronous orbit at Kp ≥ 3, where Kp is a geomagnetic index that quantifies the general disturbance level of Earth’s magnetosphere. Moreover, DOB effects are more significant further away from Earth, at higher Kp, and for higher electron energies. Specifically, the short-term simulation results after one electron drift show both traditional and nontraditional DOB transport of electrons, with the nontraditional DOB, caused by a third minimum of the magnetic field strength near the equator, reported by us for the first time. Moreover, our results show large ballistic jumps in the second invariant and radial distance for electrons at high equatorial pitch angles after one drift. In addition, long-term DOB transport coefficients of electrons over many drifts are calculated based on our simulation results. We find that the pitch angle and radial diffusion coefficients of electrons due to DOB could be comparable to or even larger than those caused by electron interactions with chorus and Ultra-Low-Frequency waves, respectively. Meanwhile, the last closed drift shell (LCDS) has been identified as a crucial parameter for investigating the magnetopause shadowing loss of radiation belt electrons. However, the DOB effects have not been physically incorporated into the LCDS calculation. In the second study of this dissertation, we calculate the event-specific LCDS using different approaches to dealing with the DOB effects, i.e., tracing field lines ignoring DOB, tracing test particles rejecting DOB, and tracing test particles including DOB, and then incorporate them into a radial diffusion model to simulate the fast electron dropout observed by Van Allen Probes in May 2017. The model effectively captures the fast dropout at high L* (the third adiabatic invariant) and exhibits the best agreement with data when LCDS is calculated by tracing test particles and including DOB effects more realistically. This study represents the first quantitative modeling of the DOB effects on the radiation belt magnetopause shadowing loss via a more physical specification of LCDS. In summary, our results demonstrate that DOB could cause effective loss and transport of radiation belt electrons even in the absence of waves

New perspectives on magnetotail dynamic processes from combined cluster and double star observations

In this thesis, observations of the Earth's magnetotail from ESA's four Cluster and the two Sino-European Double Star spacecraft are presented. The observations are of intervals where data from the combination of Cluster and Double Star provide insights into the dynamics of the magnetotail that are not possible using data from one mission alone. In the �first study, observations of three magnetic flux ropes are presented, two of which were detected near-simultaneously at Cluster and Double Star TC-1, while the third was detected by Cluster, along with a TCR a few minutes later. The observations represent the �first observations of multiple flux ropes existing in the magnetotail simultaneously, providing evidence that flux rope orientation is influenced by neutral sheet tilt and provide further evidence that TCRs in the lobes are caused by the passage of flux ropes in the plasma sheet. In the second study, a detailed analysis of a plasma bubble is presented, including the �first direct observations of the return flows around the flanks of the plasma bubble that are expected from theory and simulation. Furthermore a partially stagnant depleted wake behind the plasma bubble, not predicted by theory or simulation was discovered and the cross-tail extent of the bubble was measured to be 3RE. The fi�rst observations of near-Earth bubble features are also reported. Finally, in the third study, the substorm onset process itself is investigated using a wide array of space- and ground-based instrumentation. A pseudobreakup and later substorm onset are distinguished using both geomagnetic and auroral data and the establishment of the substorm current wedge is observed in-situ using the TC-2 and GOES12 spacecraft. A link between higher latitude geomagnetic activity and the fast flows and plasma sheet expansion related to the reconnection of lobe fi�eld lines is also posited