R-3 Repository :: Browsing by Author "Toffoletto, Frank R."

Browsing by Author "Toffoletto, Frank R."

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A Dynamic Coupled Magnetosphere-Ionosphere-Ring Current Model
(2013-09-16) Pembroke, Asher; Toffoletto, Frank R.; Warren, Joe; Reiff, Patricia H.
In this thesis we describe a coupled model of Earth's magnetosphere that consists of the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamics (MHD) simulation, the MIX ionosphere solver and the Rice Convection Model (RCM). We report some results of the coupled model using idealized inputs and model parameters. The algorithmic and physical components of the model are described, including the transfer of magnetic field information and plasma boundary conditions to the RCM and the return of ring current plasma properties to the LFM. Crucial aspects of the coupling include the restriction of RCM to regions where field-line averaged plasma-beta <=1, the use of a plasmasphere model, and the MIX ionosphere model. Compared to stand-alone MHD, the coupled model produces a substantial increase in ring current pressure and reduction of the magnetic field near the Earth. In the ionosphere, stronger region-1 and region-2 Birkeland currents are seen in the coupled model but with no significant change in the cross polar cap potential drop, while the region-2 currents shielded the low-latitude convection potential. In addition, oscillations in the magnetic field are produced at geosynchronous orbit with the coupled code. The diagnostics of entropy and mass content indicate that these oscillations are associated with low-entropy flow channels moving in from the tail and may be related to bursty bulk flows and bubbles seen in observations. As with most complex numerical models, there is the ongoing challenge of untangling numerical artifacts and physics, and we find that while there is still much room for improvement, the results presented here are encouraging. Finally, we introduce several new methods for magnetospheric visualization and analysis, including a fluid-spatial volume for RCM and a field-aligned analysis mesh for the LFM. The latter allows us to construct novel visualizations of flux tubes, drift surfaces, topological boundaries, and bursty-bulk flows.
Approximation and computation of the solution to the magnetosphere-ionosphere coupling equation via a mixed formulation
(2004) Wightman, Jennifer Lee; Kloucek, Petr; Toffoletto, Frank R.
This study develops a numerical technique for the approximation of the magnetosphere-ionosphere (MI) coupling equation, which is a crucial step in the Rice Convection Model (RCM), a physical model that treats plasma in Earth's inner and middle magnetosphere via a multi-fluid approximation. The MI coupling equation is a second-order elliptic boundary value problem that describes conservation of current between the magnetosphere and the ionosphere. The current RCM solver is based on a finite difference scheme and produces unphysical results when the ionospheric conductance has large spatial gradients. We develop an alternative finite element approximation of the MI coupling equation, applying the method of fictitious domains to treat the high-latitude boundary condition along the immersed boundary Gamma, a boundary that varies in time and does not align with the computational grid. The result of using fictitious domains is a domain decomposition problem that we solve via a mixed finite element formulation. We compare both a nonconforming and conforming finite element approach within the framework of the mixed formulation. We are able to demonstrate that both the conforming and nonconforming methods generate solutions that are compatible with the current RCM solver when actual RCM data is used. Furthermore, we demonstrate on several analytic test examples that the finite element approximation is more accurate than the finite difference approximation. Therefore, we conclude that the finite element solver is more robust than the finite difference solver. In addition, we provide convergence results for the nonconforming approximation when the conductance coefficients are bounded and measurable, and we use spectral theory from the harmonic Steklov eigenproblem to derive a precise definition of the trace space on the interface Gamma. Our overall approximation technique is generalizable to a class of elliptic boundary value problems in which the boundary varies in time or does not align with a fixed grid. Finally, our numerical solver can be modified for use in the RCM-Jupiter that is currently being developed.
Comparison study of ring current simulations with and without bubble injections
(Wiley, 2016) Yang, Jian; Toffoletto, Frank R.; Wolf, Richard A.
For many years, stand-alone ring current models have been successfully producing storm time ring current enhancements without specifying explicit localized transient injections along their outer boundaries. However, both observations and simulations have suggested that the frequent burst flows or bubble injections can contribute substantially to the storm time ring current energy. In this paper, we investigate the difference in the spatial and temporal development of the ring current distribution with and without bubble injections using the Rice Convection Model-Equilibrium. The comparison study indicates that the simulation with bubble effects smoothed out along geosynchronous orbit can predict approximately the same large-scale ring current pressure distribution and electric potential pattern as the simulation with bubble effects included. Our results suggest that the increase of the hot plasma population along geosynchronous orbit can be envisaged as an integrated effect of bubble injections from the near-Earth plasma sheet. However, the observed fluctuations in the plasma population and electric field can only be captured when the mesoscale injections are included in the simulation. We also confirmed again that adiabatic convection of fully populated flux tubes cannot inject the ring current from the middle plasma sheet. The paper provides a justification for using stand-alone ring current models in the inner magnetosphere to simulate magnetic storms, without explicit consideration of bubbles and magnetic buoyancy effects inside geosynchronous orbit.
Current Sheet Thinning in the Wake of a Bubble Injection
(Wiley, 2022) Wang, Wenrui; Yang, Jian; Toffoletto, Frank R.; Wolf, Richard A.; Nakamura, Rumi; Cui, Jun
A crucial property of the substorm growth phase is the current sheet thinning, which is often attributed to adiabatic convection. Injecting low-entropy bubbles reduce pressure-balance inconsistencies and restore current sheet thickness to its initial value. Recent observations from Cluster and MMS showed additional thinning of the current sheet in the wake of a transitory bubble injection compared with the configuration before the injection. We employ the Rice Convection Model-MHD coupled code to investigate how the transport of bubbles causes the fast thinning. The simulation results reconstructed the observations' most prominent characteristics. We find more earthward transport of the magnetic flux in the bubble than its wake, therefore depleting magnetic flux and stretching the magnetic field lines there. Interestingly, additional R0-sense field-aligned currents close the enhanced dawn-to-dusk current behind the bubble.
Dynamics and Evolution of Solar Eruptive Prominences
(2014-04-24) Zhu, Chunming; Alexander, David; Toffoletto, Frank R.; Niu, Fenglin
Solar eruptive phenomena, including eruptive solar prominences/filaments, solar flares and Coronal Mass Ejections (CMEs), have severe impact on the Earth’s space environment and human activities: so-called Space Weather. The dynamics and evolution of the prominences/filaments are important for our understanding of the initiation processes that drive CMEs and lead to drastic energy release in the solar flares. This thesis focuses on recent progresses on the destabilization and subsequent eruption of the prominences/filaments, via three primary case studies that elucidate the most important activities occurring in the eruptive prominence: eruption of a bifurcated solar filament, interchange reconnection facilitating a filament eruption, and the interaction of two distinct filaments with subsequent production of solar flares. In Chapter 2, we study a partial eruption of a bifurcated filament which exhibited clear and strong kinking motion of the filament axis (∼ 120◦ rotation). Seven mass transfer events are identified and are thought to also transfer magnetic flux from the lower to upper branch, leading to the generation of ideal instabilities, that subsequently triggered the eruption of the upper branch. In Chapter 3, we present evidence of interchange reconnection driven by the interaction of an erupting filament with a nearby coronal hole that leads to the eruption of this filament. Kinking motions in this filament serves to bring the magnetic field of its eastern leg in close contact with the unipolar magnetic field of the coronal hole where it drives the reconnection that governs the subsequent evolution of the fila- ment and coronal hole boundary. The observed EUV brightenings and bi-directional flows in the contact layer formed by this interaction, along with the occurrence of type III radio bursts that are strongly related to escaping electrons along open fields, provide corroborative evidence for the occurrence of reconnection at this location. A consequence of this interaction was the development of a complex CME, that displayed both open and closed features: we believe this is the first time such a CME configuration has been observed directly in association with a filament eruption. In Chapter 4, an interaction between two filaments, rarely reported before, is identified and studied. This complex interaction is responsible for the production of a hard x-ray coronal source as part of a C3.0 class solar flare. The observed hard x-ray coronal source occurring between the two filaments, driven by a convergence of the filaments, and a newly formed hot plasma layer, indicate that magnetic reconnection occurred between the magnetic fields associated with both filaments. The eruption of the filaments later led to the onset of a much larger solar flare, class M2.9, as expected from the standard flare model. It is interesting to note that both loop shrinkage and supra-arcade downflows (SADs) are present during this M2.9 flare.
Inner magnetospheric modeling during geomagnetic active times
(2010) Yang, Jian; Toffoletto, Frank R.
In this thesis we show that the entropy parameter PV5/3 , where P is the pressure and V is the volume of a flux tube with unit magnetic flux, plays a central role in the earthward plasma convection from the near- and middle-Earth plasma sheet to the inner magnetosphere. This work presents a series of numerical simulations, investigating the relationship between the value of PV5/3 and the different features of plasma earthward transport that occur during different types of events in geomagnetic active times. The simulations are conducted using the Rice-Convection-Model (RCM) and the Rice-Convection-Model-Equilibrium (RCM-E) that have carefully designed boundary conditions to simulate the effect of various values of PV 5/3. In Chapter 3 we present results of an RCM simulation of a sawtooth event where it is found that a dramatic reduction of PV5/3 on the boundary along a wide range of local times produces interchange convection in the inner magnetosphere and drives spatially quasi-periodic Birkeland currents that suggest an explanation for the finger-like aurora usually observed during this type of event. In Chapter 4 we present results of an RCM-E simulation of an isolated substorm, which is done by imposing depleted PV5/3 (a bubble) in the expansion phase. The results of this simulation reproduce typical features of a substorm and agree fairly well with multipoint observations. Chapter 6 presents a detailed analysis of the RCM-E expansion phase simulation which indicates that the reconfigurations of PV5/3, plasma pressure and magnetic field in an idealized bubble injection event can be quite complicated. Chapter 7 presents results of a superposed epoch study using Geotail data showing that the time variations of PV 5/3 are different in isolated substorms, pseudo-breakups and convection bay events, suggesting that bubbles have different characteristics in different modes of earthward transport. We follow this up with three corresponding RCM-E simulations by representing a sustained bubble, a transient bubble and sustained low PV5/3 plasma along the boundary. The simulations are roughly consistent with theoretical suggestions, superposed epoch results and some other observations. These simulations provide a systematic description of inner magnetospheric configuration during various active events, suggesting the temporal and spatial characteristics of PV5/3 in the plasma sheet as a key in the magnetospheric convection.
Interaction of Daptomycin with Lipid Bilayers Correlated to Its Action on Cell Membranes
(2013-05-31) Chen, Yen-Fei; Huang, Huey W.; Toffoletto, Frank R.; Killian, Thomas C.
Daptomycin is a lipopeptide antibiotic notably against multidrug-resistant, gram-positive pathogens. Evidence shows that the antibiotic acts neither on DNA nor on the proteins. It has been shown to insert and aggregate in the bacteria membrane; nevertheless, how the molecular interaction leads to cell death is unknown. In this work, the physical properties of interactions between daptomycin and model membranes are studied in order to understand the underlying mechanism of daptomycin. First, daptomycin’s binding affinity to membranes was found to be proportional to Ca++ concentration. The effect of Ca++ cannot be replaced by other divalent ions such as Mg++. After binding, daptomycin was found to form lipid-peptide aggregations on phosphatidylglycerol(PG)-containing vesicles. PG is required for the formation of lipid-peptide aggregates, which eventually lead to membrane ruptures. Cardiolipin, another main component in bacterial membrane, cannot substitute PG to induce the same membrane defect. In addition, with a fixed concentration of Ca++, it requires a minimum concentration of daptomycin to trigger the membrane defect process. The membrane defect results mainly from lipid-peptide aggregations rather than from pores forming in the membrane. Finally, x-ray data imply that daptomycin binds to the headgroup region of the bilayer, which causes membrane thinning. The elastic energy of membrane thinning elevates the energy level of the daptomycin binding state, which explains the transition to the aggregation state.
Modeling electromagnetic fields of the earth's magnetosphere
(1998) Song, Jinwen; Toffoletto, Frank R.
The early version of the Toffoletto - Hill - Ding open magnetosphere model is improved and generalized in this thesis. This model computes the interplanetary magnetic field (IMF) dependent magnetic and electric fields in the Earth's magnetosphere. The magnetospheric magnetic fields contain contributions from the Earth's dipole field, the ring current, the tail field, and the interconnection magnetic field that represents the effect of an open magnetosphere. The solar wind electric field is mapped along open magnetic field lines into the polar cap ionosphere and acts as a driver for magnetospheric convection. We show that the influence of the IMF on the plasma convection in the magnetosphere as given by the new model is consistent with observations. The tail field is modified to be consistent with the interconnection field.
Modeling the Earth's Magnetosphere using Magnetohydrodynamics
(2012) Hu, Bei; Toffoletto, Frank R.
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.
Modeling the Plasma Convection in Saturn's Inner Magnetosphere
(2013-09-16) Liu, Xin; Hill, Thomas W.; Toffoletto, Frank R.; Lenardic, Adrian
Saturn's magnetosphere is unique in the solar system. The rotation-driven convection consists of alternating channels of cool plasma from an interior source moving outward and hot plasma from outside moving inward, making Saturn’s inner magnetosphere a dynamical region. This thesis describes work on developing numerical models to simulate the plasma convection pattern in Saturn's inner magnetosphere. Chapter 2 introduces the numerical Rice Convection Model (RCM), a multi-fluid model that was originally developed for Earth’s magnetosphere. We adapt it for Saturn’s conditions in this thesis. In Chapter 3, we show results of initial RCM simulation runs, in which only cool plasma from the interior source is considered. We also include the Coriolis force and the pickup effect. Because the cool plasma is much denser than the hot plasma and always dominant in determining the convection pattern, it is important and necessary to investigate it first. Chapter 4 compares several cool plasma source models and determines the one that produces the best simulation results when compared to Cassini spacecraft observations. In Chapter 5, we add the finite temperature and associated plasma pressure of the cool plasma. The effect of ionospheric Pedersen conductance is also investigated. Finally in Chapter 6, we add hot plasma at the outer boundary, and simulate the V-shape signatures of the injection-dispersion events, which are considered the most definitive evidence of rotation-driven convection in Saturn's inner magnetosphere. Our simulations conform to the observed fact that wider, slower outflow channels of cooler, denser plasma alternate with narrower, faster inflow channels of hotter, more tenuous plasma. Comparisons between simulated and observed results show great consistency.
On the contribution of plasma sheet bubbles to the storm time ring current
(Wiley, 2015) Yang, Jian; Toffoletto, Frank R.; Wolf, Richard A.; Sazykin, Stanislav
Particle injections occur frequently inside 10 Re during geomagnetic storms. They are commonly associated with bursty bulk flows or plasma sheet bubbles transported from the tail to the inner magnetosphere. Although observations and theoretical arguments have suggested that they may have an important role in storm time dynamics, this assertion has not been addressed quantitatively. In this paper, we investigate which process is dominant for the storm time ring current buildup: large-scale enhanced convection or localized bubble injections. We use the Rice Convection Model-Equilibrium (RCM-E) to model a series of idealized storm main phases. The boundary conditions at 14–15 Re on the nightside are adjusted to randomly inject bubbles to a degree roughly consistent with observed statistical properties. A test particle tracing technique is then used to identify the source of the ring current plasma. We find that the contribution of plasma sheet bubbles to the ring current energy increases from ~20% for weak storms to ~50% for moderate storms and levels off at ~61% for intense storms, while the contribution of trapped particles decreases from ~60% for weak storms to ~30% for moderate and ~21% for intense storms. The contribution of nonbubble plasma sheet flux tubes remains ~20% on average regardless of the storm intensity. Consistent with previous RCM and RCM-E simulations, our results show that the mechanisms for plasma sheet bubbles enhancing the ring current energy are (1) the deep penetration of bubbles and (2) the bulk plasma pushed ahead of bubbles. Both the bubbles and the plasma pushed ahead typically contain larger distribution functions than those in the inner magnetosphere at quiet times. An integrated effect of those individual bubble injections is the gradual enhancement of the storm time ring current. We also make two predictions testable against observations. First, fluctuations over a time scale of 5–20 min in the plasma distributions and electric field can be seen in the central ring current region for the storm main phase. We find that the plasma pressure and the electric field EY there vary over about 10%–30% and 50%–300% of the background values, respectively. Second, the maximum plasma pressure and magnetic field depression in the central ring current region during the main phase are well correlated with the Dst index.
Quantitative modeling of time-dependent phenomena in the magnetospheric magnetic field
(2002) Naehr, Stephen M.; Toffoletto, Frank R.
A series of improvements to the Rice Field Model (RFM) are described, which both increase the accuracy and extend the capabilities of the model. A new ring current parameterization improves the determination of storm-time fields in the inner magnetosphere. Replacement of the tail current module with a more flexible representation also contributes to improved accuracy in the inner magnetosphere, and enables realistic variations in current strength and orientation over the entire magnetotail length. Revision of the tail shielding/interconnection field eliminates inconsistencies in the model magnetotail, and permits variation in the normal component distribution over the tail portion of the magnetopause. The enhanced flexibilities of the interconnection field and cross-tail current module make possible the modeling of variations in the interplanetary magnetic field (IMF) as it propagates downstream, thereby advancing the steady-state RFM an important step toward time-dependent modeling. The modified RFM is used to explore a number of time-dependent magnetospheric phenomena. In simulations of the March 1998 magnetic storm, the new model displays an improved representation of the inner magnetosphere, accurately predicting both storm-induced variations and day-night asymmetry in the field at geosynchronous orbit. The effects of time-dependent interplanetary fields on magnetospheric convection are examined, using a new method to compute ionospheric flow and electric fields in non-steady configurations. This method is applied to simulations of the growth and contraction of the polar cap in Southward and Northward turnings of the IMF. Model convection patterns for Southward turnings are shown to be consistent with theoretical expectations. The RFM is also used to simulate polar cap convection in the particular IMF conditions believed to trigger formation of the theta aurora. The results of the simulation prove to be consistent with several observed properties of the theta aurora, and shed light on the plasma sheet and magnetotail configurations associated with this phenomenon.
RCM-E simulation of a thin arc preceded by a north-south-aligned auroral streamer
(Wiley, 2014) Yang, Jian; Toffoletto, Frank R.; Wolf, Richard A.
The Time History of Events and Macroscale Interactions during Substorms (THEMIS) all-sky imager data have recently revealed a repeatable sequence that occurs during many auroral substorms, in which a newly formed thin arc is preceded by an equatorward propagating streamer. The paper aims at modeling this sequence using the Rice Convection Model–Equilibrium. The simulation shows a thin arc arising when a plasma sheet bubble with its PV5/3 reduced to the transition region value arrives at the magnetic transition region. The modeled thin arc consists of two parts: the one east of the streamer is the result of the bubble pushing high PV5/3 flux tubes ahead of it, strengthening the upward region 2 current, and the one west of the streamer is associated with westward drifting bubble particles, sliding along the transition region. The model predicts that (1) the westward and eastward leading edges of the thin arc propagate azimuthally at a speed of ~0.5–2.7 km/s and (2) the streamer-induced thin arc is accompanied by classic signatures of bubble injections.
RCM-E simulation of bimodal transport in the plasma sheet
(American Geophysical Union, 2014) Yang, Jian; Wolf, Richard A.; Toffoletto, Frank R.; Sazykin, Stanislav; Wang, Chih-Ping
Plasma sheet transport is bimodal, consisting of both large-scale adiabatic convection and intermittent bursty flows in both earthward and tailward directions. We present two comparison simulations with the Rice Convection Model-Equilibrium (RCM-E) to investigate how those high-speed flows affect the average configuration of the magnetosphere and its coupling to the ionosphere. One simulation represents pure large-scale slow-flow convection with time-independent boundary conditions; in addition to the background convection, the other simulation randomly imposes bubbles and blobs through the tailward boundary to a degree consistent with observed statistical properties of flows. Our results show that the bursty flows can significantly alter the magnetic and entropy profiles in the plasma sheet as well as the field-aligned current distributions in the ionosphere, bringing them into much better agreement with average observations.
RCM-E simulation of substorm growth phase arc associated with large-scale adiabatic convection
(Wiley, 2013) Yang, Jian; Wolf, Richard A.; Toffoletto, Frank R.; Sazykin, Stanislav
[1] Substorm auroral breakup often occurs on a longitudinally elongated arc at the end of a growth phase. We present an idealized high-resolution simulation with the Rice Convection Model-Equilibrium (RCM-E) to investigate how large-scale adiabatic convection under equilibrium conditions can give rise to an auroral arc. We find that a thin arc that maps to the magnetic transition region at r ~ 8 RE emerges in the late growth phase. The simulation implies that the arc in the premidnight sector is associated with a sheet of additional region 1 sense field-aligned current (FAC) just poleward of the main region 2 FAC, while the arc in the postmidnight sector is associated with the poleward portion of the main upward region 2 FAC. Explanations for the location and the thickness of the arc are proposed, based on the simulation.
Simulating the driven magnetosphere
(2005) Lemon, Colby Lee; Toffoletto, Frank R.
A significant effort is focused on understanding the behavior of the Earth's magnetosphere during times of southward interplanetary magnetic field, when the magnetosphere is in a driven state. In situ observations of the space environment provide us with real magnetic and electric field and plasma data with which to study magnetospheric processes, yet we lack the ability to experimentally control the parameters that influence these processes. On the other hand, a niche of computational modeling is the ability to experiment with these parameters in a straightforward effort to understand the magnetospheric response. The simulation model employed in this thesis (the Rice Convection Model-Equilibrium, or RCM-E) is unique in its ability to calculate the energy dependent drifts of plasma particles as well as their feedback on both the electric and magnetic fields. Three different RCM-E simulations are presented. First, the magnetospheric response to a moderate level of external driving is modeled, showing that the model reproduces several of the features of steady magnetospheric convection (SMC) events. The simulation is then repeated with a more rigorous calculation of the magnetic field that generally produces a higher quality result but suffers from excessive numerical noise in the important inner plasma sheet region. This simulation produces a more stressed magnetic field, but encounters numerical breakdown due largely to the numerical noise. The proper response to steady driving in the RCM-E is likely to be more stressed than the first simulation, yet more stable than the second simulation. Somewhat counter to conventional wisdom, these simulations suggest that enhanced convection by itself is insufficient to inject a ring current, since the magnetic field response acts to mitigate the injection. In the third simulation, a method for injecting plasma into the ring current without drastically affecting the near-Earth magnetic field configuration is demonstrated: significantly reduce the specific entropy of the injection source. The steady driving simulations apparently failed to produce a realistic ring current injection because the model equations conserve specific entropy as plasma is transported (adiabatic transport). These simulations suggest that a non-adiabatic plasma process---possibly the substorm---plays an important role in the dynamics of geomagnetic storms.
Simulation of Dislocated Flux in Space Plasma Environments: Applications in Geospace Modeling and Ionosphere-Magnetosphere Coupling
(2015-04-23) Schutza, Aaron Moore; Toffoletto, Frank R.; Wolf, Richard A; Ecklund, Karl M
In this study, simulations of a dislocated flux tube are used to model oscillatory flow events and to explore possible ionospheric-magnetospheric coupling mechanisms. A numerical code called the Thin Filament Code (TFC) has been developed using a thin filament approximation to simulate flux tube motion in a stationary 2D background. Previous studies using similar magnetohydrodynamic thin filament models have been used to describe fast flow events and interchange oscillations in the Earth’s plasma sheet. A significantly extended numerical model is employed to explore additional applications. Simulation results include the time evolution of isolated flux tubes with a wide range of stationary background environments and boundary conditions defined by field aligned current systems. Simulations suggest that ionospheric disturbances can introduce waves that propagate to the magnetosphere triggering activity in the magnetotail. Oscillatory motion is simulated on a background model fitted to observation demonstrating new capabilities of the TFC.
Synthetic magnetogram calculations from magnetosphere-ionosphere coupling models
(2009) Ontiveros, Paul Alejandro; Toffoletto, Frank R.
Global MHD models, ring-current models, convection models, and a growing number of coupled models calculate the large-scale currents in the magnetosphere-ionosphere (MI) system. Traditionally, these models have been tested against single-point magnetic field measurements made by individual spacecraft. This often does not provide a clear picture of the pattern of model-data discrepancies. The global network of ground-based magnetograms constitutes a large source of data that is currently being underutilized for validation and analysis of these models. This is primarily due to the fact that a good code does not exist that accurately makes the connection between the models' output and ground magnetometer data. To address this, a numerical code has been developed to compute realistic ground magnetic field perturbations, based upon input from these models, and is described in this thesis. The code includes the effects of all large-scale current systems in the MI system. It also computer the effects from the inner magnetosphere currents by integrating the Biot-Savart integral over a spherical grid centered on the Earth. A scalar potential representation is used for the magnetic field due to the currents in the outer magnetosphere and solar wind. The effects of the ground induction currents are also included with a scalar potential by including the effects of an infinitely conducting sphere below the surface. Aside from the code's ability to compute realistic magnetic field disturbances at individual magnetometers, it is possible to compile synthetic geomagnetic indices and synthetic global disturbance maps. The software is intended as a general-use tool and was built to be flexible so that it can be integrated with a wide variety of large-scale MI coupling models. Initial synthetic magnetogram results are presented based on SWMF and RCM storm simulations. Synthetic Dst was computed for the SWMF simulation results, while synthetic magnetograms, several geomagnetic indices, and an LT-UT map were computed for the RCM simulation results. The magnetogram output is compared to observations to analyze both MI coupling codes.
Tests of the OPEN-GGCM and BATS-R-US global MHD codes
(2005) Li, Yining; Toffoletto, Frank R.
In this thesis, we present the results from tests of two global magnetohydrodynamic (MHD) codes: the University of New Hampshire's OPEN-GGCM model and the University of Michigan's BATS-R-US model. We investigate their consistency with the theory of adiabatic particle drift in the inner and middle magnetosphere. Since the Rice Convection Model (RCM) uses the adiabatic particle drift as one of its basic assumptions, positive results of the tests will help us to establish a better physical model of the magnetosphere and ionosphere by coupling the RCM with one of these global MHD models. An introduction to the two models, the theory for the adiabatic particle drift, and the results from tests of OPEN-GGCM and BATS-R-US models are presented. By tracking individual magnetic tubes and comparing the quantities such as particle number N and theoretical invariant PV5/3 integrated along these flux tubes in different times, we find results of both the OPEN-GGCM and BATS-R-US models suggest that the conservation of the adiabatic invariant is very poor when using low-resolution simulation grid. Another test of the OPEN-GGCM simulation with higher grid resolution shows some improvement in PV5/3 conservation.

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