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

Browsing by Author "Toffoletto, Frank"

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Large-scale Coupled Models of the Inner Magnetosphere
(2019-12-06) Bao, Shanshan; Toffoletto, Frank
In magnetospheric physics nowadays, the pursuit of realistic numerical simulation of the inner magnetospheric physics of plasma transport, ring current formation and storm-triggered Earth electromagnetic field changes is an ongoing challenge. To this end, we have implemented a large-scale coupled scheme of the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) model with the Rice convection model - equilibrium (RCM-E), the ring current model equipped with a magneto-friction (MF) solver, called LFM-RCM-E. The purpose of the one-way coupling scheme is to allow the RCM-E to continuously update its boundary conditions from the LFM while preserving entropy conservation. It enables a high-resolution self-consistent ring current model with realistic time-dependent outer-magnetospheric magnetic field configurations. Compared with the prior LFM-RCM, the LFM-RCM-E resolves the issue of a restricted simulation region due to a plasma - β constraint that is used to ensure numerical stability. By introducing the MF equilibrium solver, the RCM simulation region expands father out into the plasma sheet where the storm-time plasma transportation takes place. In the ionosphere, the RCM-E replaces the ionospheric electric field solver (MIX) of LFM with the one used by the RCM. The electric potential produced, along with the realistic ionospheric precipitation patterns shows strong consistency with the plasma motion featured with well resolved bubbles and bursty bulk flows. This thesis gives detailed descriptions of the coupling scheme of the model in Chapter 3. A test case of the model is shown in Chapter 4, where results of an idealized event simulation will be presented and discussed. Apart from an idealized event, a robust model should be able to simulate realistic severe space weather events. Chapter 5 presents its application in simulating a real event, the June 1st 2013 storm. The model is run with large solar wind ram pressure and tilted solar wind directions that impact the Earth magnetospheric system on the dayside. A routine of adaptive boundary decision is implemented to ensure a valid RCM simulation region and thus enhances the robustness of the model. Model - data comparisons are conducted, in terms of Dst index, plasma pressure and magnetic field, with Van Allen Probes data. The coupled scheme of LFM-RCM-E is applicable to other global MHD models. Chapter 6 presents the work of a collaborative project with the National Center for Atmospheric Research (NCAR), which is the implementation of a new branch of a coupled MHD code with the aim studying sub-aurora polarization streams (SAPS). Since the RCM ionospheric precipitations are a significant source of diffuse aurora and are responsible for the dynamic change of ionospheric conductivity, feedback channels from RCM to the Coupled Magnetosphere-Ionosphere-Thermosphere model (CMIT), have been established. The fully coupled CMIT-RCM, a.k.a., LFM-RCM-TIEGCM system will be an ideal tool to simulate and analyze SAPS phenomenon comprehensively. The electron average energy has always been underestimated by RCM due to a naïve cold plasmasphere model. Chapter 7 presents the work of integrating a more sophisticated plasmasphere model, modified from the global core plasma model (GCPM), into LFM-RCM-TIEGCM. The geometry of the plasmasphere depends on a measure of the geomagnetic activity, the Kp-index. A set of control experiments shows a substantial increase in the electron average energy and energy flux with the new plasmasphere model.
LFM-RCM: Toward a coupled description of the inner and outer magnetosphere
(2009) Pembroke, Asher; Toffoletto, Frank
Numerical simulations of magnetohydrodynamics (MHD) have led to reasonable descriptions of the general morphology and dynamics of Earth's magnetosphere. However, MHD is invalid in regions close to the Earth where gradient and curvature drifts are comparable to the E × B drift. The Rice Convection Model was designed to take into account such dynamics and provide a more realistic description of the plasma distribution, using an input magnetic field model such as the Lyon Fedder Mobarry (LFM). Recent efforts to couple the RCM and the LFM have led to a more complete picture of magnetospheric processes. This thesis describes the physics of the two regions, our coupling paradigm, and analysis tools for interpreting these results.
Modeling the Space Weather Environment of Terrestrial Exoplanets
(2021-04-28) Sciola, Anthony; Toffoletto, Frank; Alexander, David
The majority of currently known terrestrial exoplanets orbit close to their host stars, on the order of 0.05 AU. Such planets orbiting M Dwarf stars, assuming an Earth-like atmosphere, have the potential to possess liquid water on their surface, a key requirement for habitability of life as we are familiar with. However such close proximity to the star is also likely to result in the planet experiencing stellar wind pressures orders of magnitude greater than that at Earth. An understanding of whether the planet possesses an intrinsic magnetic field, or magnetosphere, and how this interacts with the extreme stellar wind, is necessary in order to constrain other parameters such as atmospheric loss rate. There is a unique radio emission which is expected to be commonly produced by magnetized planets, and is produced by every magnetized Solar System planet. Despite estimates predicting that such emission from Jupiter-sized set of exoplanets should be observable, there have been no confirmed detections thus far. This thesis utilizes magnetohydrodynamic (MHD) models coupled to the Rice Convection Model (RCM), originally developed to simulate Earth’s magnetosphere, to better understand the magnetic environments of terrestrial exoplanets. The first project adapts a coupled MHD+RCM model to simulate the environment of Proxima Centauri b, and estimates the rate of atmospheric loss via charge exchange. The second addresses the calculation of expected radio emission from a given exoplanetary environment, both analytically and numerically, which includes the effects of both ionospheric saturation, and secondary inner magnetosphere currents, on the radio signal’s location of emission and total signal power. This work may be used to better determine which star-planet systems may be more likely to produce observable radio emission, and are therefore better targets for future observation.
Numerical calculation of interaction forces between paramagnetic colloids in two-dimensional systems
(American Physical Society, 2014) Du, Di; Toffoletto, Frank; Biswal, Sibani Lisa
Typically the force between paramagnetic particles in a uniform magnetic field is described using the dipolar model, which is inaccurate when particles are in close proximity to each other. Instead, the exact force between paramagnetic particles can be determined by solving a three-dimensional Laplace's equation for magnetostatics under specified boundary conditions and calculating the Maxwell stress tensor. The analytical solution to this multi-boundary-condition Laplace's equation can be obtained by using a solid harmonics expansion in conjunction with the Hobson formula. However, for a multibody system, finite truncation of the Hobson formula does not lead to convergence of the expansion at all points, which makes the approximation physically unrealistic. Here we present a numerical method for solving this Laplaceﾒs equation for magnetostatics. This method uses a smoothed representation to replace all the boundary conditions. A two-step propagation is used to dramatically accelerate the calculation without losing accuracy. Using this method, we calculate the force between two paramagnetic particles in a uniform and a rotational external field and compare our results with other models. Furthermore, the many-body effects for three-particle, ten-particle, and 24-particle systems are examined using the same method. We also calculate the interaction between particles with different magnetic susceptibilities and particle diameters. The Laplaceﾒs equation solver method described in this article that is used to determine the force between paramagnetic particles is shown to be very useful for dynamic simulations for both two-particle systems and a large cluster of particles.
Origin of Dawnside Subauroral Polarization Streams During Major Geomagnetic Storms
(Wiley, 2022) Lin, Dong; Wang, Wenbin; Merkin, Viacheslav G.; Huang, Chaosong; Oppenheim, Meers; Sorathia, Kareem; Pham, Kevin; Michael, Adam; Bao, Shanshan; Wu, Qian; Zhang, Yongliang; Wiltberger, Michael; Toffoletto, Frank; Lyon, John; Garretson, Jeffrey
Solar eruptions cause geomagnetic storms in the near-Earth environment, creating spectacular aurorae visible to the human eye and invisible dynamic changes permeating all of geospace. Just equatorward of the aurora, radars and satellites often observe intense westward plasma flows called subauroral polarization streams (SAPS) in the dusk-to-midnight ionosphere. SAPS occur across a narrow latitudinal range and lead to intense frictional heating of the ionospheric plasma and atmospheric neutral gas. SAPS also generate small-scale plasma waves and density irregularities that interfere with radio communications. As opposed to the commonly observed duskside SAPS, intense eastward subauroral plasma flows in the morning sector were recently discovered to have occurred during a super storm on 20 November 2003. However, the origin of these flows termed “dawnside SAPS” could not be explained by the same mechanism that causes SAPS on the duskside and has remained a mystery. Through real-event global geospace simulations, here we demonstrate that dawnside SAPS can only occur during major storm conditions. During these times, the magnetospheric plasma convection is so strong as to effectively transport ions to the dawnside, whereas they are typically deflected to the dusk by the energy-dependent drifts. Ring current pressure then builds up on the dawnside and drives field-aligned currents that connect to the subauroral ionosphere, where eastward SAPS are generated. The origin of dawnside SAPS explicated in this study advances our understanding of how the geospace system responds to strongly disturbed solar wind driving conditions that can have severe detrimental impacts on human society and infrastructure.
RCM modeling of bubble injections into the inner magnetosphere: geosynchronous orbit and the ionospheric responses
(Frontiers Media S.A., 2023) Sadeghzadeh, Sina; Yang, Jian; Toffoletto, Frank; Wolf, Richard; Mousavi, Ameneh; Wang, Chih-Ping
Introduction: Accurate characterization of the plasma sheet source population in the ring current region and its outer boundary at geosynchronous orbit is crucial for understanding the dynamics of the Earth’s magnetosphere. The interaction between the ring current and plasma populations from the ionosphere is a focus of extensive research.Methods: We used the Rice Convection Model (RCM) to simulate the transient meso-scale injections of fast flows or plasma sheet bubbles from the outer boundary into the inner magnetosphere and the associated impacts on the ionosphere. We compared our simulation results of the average properties of bulk plasma access to geosynchronous orbit to a number of empirical models. We also examined the role of plasma sheet bubbles in forming field-aligned currents (FACs).Results: Our modeling results show that impulsive plasma sheet injections dramatically alter the average distribution of FACs in the ionosphere. We found both quantitative and qualitative agreements and disagreements when comparing our simulation results to empirical models. Furthermore, we demonstrated that several discrete auroral structures can be identified in the nightside ionosphere in accordance with theupward FACs.Discussion: The significance of plasma sheet bubbles in modifying the averageplasma properties at geosynchronous orbit and FACs in the ionosphere is highlighted by oursimulation findings, offering novel understandings into the dynamics of Earth's magnetosphere,and emphasizing the necessity for further research in this field.
RCM-E and AMIE studies of the Harang reversal formation during a steady magnetospheric convection event
(Wiley, 2014) Yang, Jian; Toffoletto, Frank; Lu, Gang; Wiltberger, Michael
This paper presents the results of a modeling study on the formation of the Harang reversal (HR) during a steady magnetospheric convection event. The Harang reversal is identified as the boundary of the northward and southward electric field in the nightside auroral zone using the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure. We simulate the event with the Rice Convection Model-Equilibrium (RCM-E) by adjusting its boundary conditions to approximately match Time History of Events and Macroscale Interactions during Substorms (THEMIS) and GOES observations in the nightside magnetosphere. Our results show that the HR is collocated with an upward region 1 field-aligned current, where converging ionospheric currents cause a southward/northward electric field on the poleward/equatorward side of the HR. Our results also indicate that the electric field reversal is slightly poleward of the ionospheric east–west current reversal and is to the northeast of the ground magnetic reversal, which is consistent with previous observations. We also test the sensitivity of the HR formation to a variety of parameters in the RCM-E simulations. We find that (1) the reduction of the flux tube entropy parameter PV5/3 near the midnight sector plays a major role in the formation of the HR; (2) a run carried out assuming uniform conductance produced the same major features as the run with more realistic precipitation-enhanced conductance; and (3) the detailed pattern of the polar cap potential distribution plays a minor role, but its dawn-dusk asymmetry significantly controls the location of the HR with respect to midnight. The RCM-E simulations also predict PV5/3 and flow distributions associated with the magnetospheric source of the HR in the plasma sheet, which can be further tested against observations.
Rudolph Jettels’ Der Vollkommene Klarinettist: A Pedagogical Analysis and Suggested Utility
(2015-04-24) Dyachenko, Andriy Valentinovich; Gottschalk, Arthur; Webster, Michael; Toffoletto, Frank
An analysis of each of the fifteen short works found in the first volume of advanced etudes for solo clarinet comprising Rudolph Jettel’s Der Vollkommene Klarinettist, from a pedagogical standpoint, to determine a best application for each etude in the development and encouragement of specific technical and interpretive clarinet competencies. These analyses are discussed, and each etude examined for the specific musical and technical challenges posed by it. Solutions are offered for the instruction necessary to master each such challenge, with a general overview and advice as to how best to prepare and perform each etude in its entirety, once the individual problems have been overcome. Liberal use of examples from the music serve as illustrations, and are annotated by the author.
The role of magnetospheric convection in the formation of ionospheric structuring and irregularities
(2022-07-20) Newheart, Anastasia Michele; Toffoletto, Frank; Fejer, Bela G
In this work, I investigate the effects of magnetospheric convection on ionospheric irregularities. I examine the role of electrodynamics on the equatorial ionization anomaly (EIA), on traveling ionospheric disturbances (TIDs), and on equatorial plasma bubbles. To examine the EIA, we examined the equatorial F-region structure at night using electron density measurements from the ISS Floating Potential Measurement (FPMU) along with Swarm spacecraft electron density measurements and Total Electron Content (TEC) from ground-based GNSS receivers for comparison. During these time periods, the EIA extended to local times late as post-midnight in some cases. To examine the role of high latitude disturbances in TID formation, I utilized spectral analysis of detrended TEC for events with different levels and types of geomagnetic activity to deduce spectral characteristics of observed TIDs and their relationship to the auroral activity at different latitudes and local time sectors. To investigate prompt penetration electric fields and the formation of EPBs, I used numerical simulations with the coupled SAMI3/RCM first-principles model. I used simulation results to examine storm-time electrodynamics and to estimate linear growth rates of the generalized Rayleigh-Taylor instability during major geomagnetic storms. For comparison, I utilized drift velocity measurements from the Jicamarca incoherent scatter radar and observation of plasma bubbles from the FPMU aboard ISS, the Swarm EFI and TEC from GNSS. By comparing calculated growth rates to plasma bubble occurrence, we can examine the role of storm-time electric fields in plasma bubble formation.
Upgrade Studies for the CMS Detector Muon System at the CERN LHC
(2014-10-21) Michlin, Benjamin Ari; Padley, Paul; Ecklund, Karl; Toffoletto, Frank
In the upgraded Large Hadron Collider (LHC) environment the energy and luminosity will approximately double, and the Level-1 trigger (L1) rate will increase six-fold. This increase cannot be accommodated using current methods at the Compact Muon Solenoid (CMS) detector. Also, increased levels of ionizing radiation may interfere with muon endcap electronics. Unreliable performance of the L1 and endcap electronics can compromise physics studies. To determine if the upgraded electronics will function in the improved LHC environment, an irradiation study of the upgraded Muon Port Card (MPC) is performed. Additionally, Global Muon Trigger (GMT) muon isolation using the upgraded Muon Sorter (MS) is presented to reduce the L1 rate. It is determined that the upgraded MPC will operate properly, and that GMT muon isolation alone is not a viable method of rate reduction. Therefore, the MPC upgrade and GMT muon isolation will be implemented in the upgraded CMS detector.

Browsing by Author "Toffoletto, Frank"

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