ABSTRACT The Rice Convection Model (RCM) is an established physical model of the inner and middle... more ABSTRACT The Rice Convection Model (RCM) is an established physical model of the inner and middle magnetosphere that includes coupling to the ionosphere. It uses a many-fluid formalism to describe adiabatically drifting isotropic particle distributions in a self-consistently computed electric field and specified magnetic field. We will describe a computational model, the RCM-E (Rice Convection Model – Equilibrium), that self-consistently calculates the inner magnetosphere plasma, electric, and magnetic field distributions by coupling the RCM to a magnetic field equilibrium solver. Recent results using the coupled code are presented and discussed. Simulations of storm-time ring current injection suggest that a non-adiabatic reduction of PV γ in a portion of the near-Earth tail is required in order to produce a significant injection.
ABSTRACT This study is an extension of our previous high-performance storm simulation with the co... more ABSTRACT This study is an extension of our previous high-performance storm simulation with the coupled BATS-R-US (Block Adaptive Tree Solar-wind Roe-type Upwind Scheme) global magnetohydrodynamics (MHD) model, Rice Convection Model (RCM), and Ridley Ionosphere Model (RIM). In this work, the superposed epoch recovery phase of 34 moderate storms at solar maximum (July, 1999 -- June, 2002) is simulated for averaged upstream solar wind conditions with the standalone RCM and also with the coupled codes. Superposed epoch averages of Dst, Sym-H, and the Los Alamos Magnetospheric Plasma Analyzer (MPA) observations at geosynchronous orbit are used to validate the modeling results. In addition, parameters in the standalone RCM and the coupled codes are adjusted to systematically study the effects of interchange instability, charge exchange rate, particle drift intensity, and particle energy levels on the ring current decay. Computer experiments will also explore how magnetic field changes and time-dependent plasma-sheet density affect the recovery phase.
In order to understand the evolution of protons and magnetic fields in the inner plasma sheet as ... more In order to understand the evolution of protons and magnetic fields in the inner plasma sheet as increasing convection electric field brings protons earthward to regions of strong dipole field, we use a modified version of the Magnetospheric Specification Model to simulate proton electric and magnetic drifts and obtain proton distributions. The magnetic field is provided by a modified version of the Tsyganenko 96 model with two-dimensional force balance maintained along the midnight meridian. The convection electric field is determined mainly by the cross polar-cap potential drop (Delta Phi ) and the equatorward edge of the convection electric field (shielding latitude theta ). The local-time dependent proton differential fluxes assigned to the model boundary are a mixture of hot plasma from the mantle and cooler plasma from the low latitude boundary layer. We previously used this model to simulate the inner plasma sheet under weak convection corresponding to Delta Phi and theta equal to 26 kV and 66° , and obtained two-dimensional quiet time equilibrium that agrees well with observations. In the current simulation, we start with the quiet time equilibrium and boundary particle sources and enhance convection by increasing Delta Phi steadily from 26 to 146 kV and lowering theta from 66° to 52° in 5 hours while keeping the boundary sources time independent. The inner edge of the plasma sheet at midnight, mapped to the equatorial plane using the self-consistent magnetic field, moves from ~ 10 RE for Delta Phi = 26 kV to ~ 4 RE for 146 kV. This earthward penetration to regions of dipole field results in strong plasma pressure increase, which significantly stretches the original dipole field lines. Proton pressure at r = 6.6 RE increases from ~1 to 6 nPa as Delta Phi increases from 26 to 146 kV, while the magnetic field strength decreases from ~80 to 10 nT. The simulated pressure and magnetic field strength, their radial variations at midnight, and their changes with convection strength in the inner plasma sheet in general agree with observations. Protons undergo enhanced earthward electric drift but are significantly diverted toward dusk by azimuthal magnetic drift around midnight. The enhanced magnetic drift, responding to enhanced particle energy, changes particles' trajectories and magnetic field configuration in a way that restrains particle energization, thus plays an important role in plasma sheet dynamics. Simulations are also run to a steady state under constant Delta Phi = 98 kV and theta = 57.6° , which indicates the inner plasma sheet can remain steady under moderate and constant convection. A scale analysis of our results suggests that using the frozen-in condition E = -vxB in MHD can lead to an inconsistency with Faraday's law in the inner plasma sheet because of neglect of the Hall term in the generalized term.
Global MHD simulations of resonant ULF mode coupling in the inner magnetosphere and plasmasphere*... more Global MHD simulations of resonant ULF mode coupling in the inner magnetosphere and plasmasphere* S. G. Claudepierre1, F. Toffoletto2, J. G. Lyon3, M. Wiltberger4, R. Denton3 1The Aerospace Corporation, Los Angeles, CA, USA 2Rice University, Houston, TX, USA 3Dartmouth College, Hanover, NH, USA 4NCAR/HAO, Boulder, CO, USA *Originally titled: Initial results from global MHD simulations of magnetospheric ULF pulsations driven by IMF fluctuations SM31B-2307
This textbook gives a perspective of heliophysics in a way that emphasizes universal processes fr... more This textbook gives a perspective of heliophysics in a way that emphasizes universal processes from a perspective that draws attention to what provides Earth (and similar (exo-)planets) with a relatively stable setting in which life as we know it can thrive. The book is intended for students in physical sciences in later years of their university training and for beginning graduate students in fields of solar, stellar, (exo-)planetary, and planetary-system sciences.
We present results from a modified MHD code that is used to compute global three-dimensional forc... more We present results from a modified MHD code that is used to compute global three-dimensional force equilibria in the Earth's magnetosphere. A nonuniform rectilinear grid is used along with initial conditions supplied by empirical magnetic field and pressure models. These initial conditions do not, in general, satisfy the force balance condition J × B = p. The MagnetoFriction code solves the equations of ideal MHD, modified to include a frictional dissipation term, allowing the system to relax into an equilibrium state. 1 Background Computing solutions to the force balance equation J × B = p (1) in magnetospheric plasmas is a task which continues to receive attention in the space plasma physics community. Not only are magnetospheric equilibria theoretically interesting, but a magnetospheric model such as the Rice Convection Model (RCM) requires the calculation of plasma equilibria in order to maintain self-consistentcy between the particle pressure and the magnetic field. Cheng (1995) has developed a numerical scheme to calculate three-dimensional magnetic fields that are in force equilibrium with a specified isotropic pressure distribution, but no procedure has been developed to couple the Cheng code to a code such as the RCM. Hesse and Birn (1993) modified an MHD code to include a frictional dissipation term in the momentum equation which allowed them to calculate three-dimensional equilibria in the magnetotail. This MagnetoFriction code also employs a ballistic method to remove kinetic energy from the system once the kinetic energy peaks. The MagnetoFriction code has since been enhanced to calculate global magnetospheric equilibria, extending down to 1RE geocentric distance and to the dayside magnetopause, and is used with the RCM to model magnetospheric convection.
We present recent results of coupling the Rice Convection Model to a magnetofriction equilibrium ... more We present recent results of coupling the Rice Convection Model to a magnetofriction equilibrium solver in order to examine the effect on the pressure in the inner and middle plasma sheet during substorm growth and expansion phases. The coupled model represents a set of partial differential equations that describes the tail and inner plasma sheet and their coupling to the
The initial results of a model of inner magnetospheric convection are presented. The model employ... more The initial results of a model of inner magnetospheric convection are presented. The model employs the Rice convection model with a magnetic field computed with the constraint of magnetostatic equilibrium. The approach computes equilibria from a magnetofriction code which is a modified version of the Hesse-Birn equilibrium code adopted for use in the inner magnetosphere. The code uses the pressure distribution computed from the Rice convection model to update the magnetic field. The algorithm used to compute the inner magnetospheric equilibria is outlined, and the coupling of the equilibrium code with the convection model is described.
ABSTRACT The Rice Convection Model (RCM) is an established physical model of the inner and middle... more ABSTRACT The Rice Convection Model (RCM) is an established physical model of the inner and middle magnetosphere that includes coupling to the ionosphere. It uses a many-fluid formalism to describe adiabatically drifting isotropic particle distributions in a self-consistently computed electric field and specified magnetic field. We will describe a computational model, the RCM-E (Rice Convection Model – Equilibrium), that self-consistently calculates the inner magnetosphere plasma, electric, and magnetic field distributions by coupling the RCM to a magnetic field equilibrium solver. Recent results using the coupled code are presented and discussed. Simulations of storm-time ring current injection suggest that a non-adiabatic reduction of PV γ in a portion of the near-Earth tail is required in order to produce a significant injection.
ABSTRACT This study is an extension of our previous high-performance storm simulation with the co... more ABSTRACT This study is an extension of our previous high-performance storm simulation with the coupled BATS-R-US (Block Adaptive Tree Solar-wind Roe-type Upwind Scheme) global magnetohydrodynamics (MHD) model, Rice Convection Model (RCM), and Ridley Ionosphere Model (RIM). In this work, the superposed epoch recovery phase of 34 moderate storms at solar maximum (July, 1999 -- June, 2002) is simulated for averaged upstream solar wind conditions with the standalone RCM and also with the coupled codes. Superposed epoch averages of Dst, Sym-H, and the Los Alamos Magnetospheric Plasma Analyzer (MPA) observations at geosynchronous orbit are used to validate the modeling results. In addition, parameters in the standalone RCM and the coupled codes are adjusted to systematically study the effects of interchange instability, charge exchange rate, particle drift intensity, and particle energy levels on the ring current decay. Computer experiments will also explore how magnetic field changes and time-dependent plasma-sheet density affect the recovery phase.
In order to understand the evolution of protons and magnetic fields in the inner plasma sheet as ... more In order to understand the evolution of protons and magnetic fields in the inner plasma sheet as increasing convection electric field brings protons earthward to regions of strong dipole field, we use a modified version of the Magnetospheric Specification Model to simulate proton electric and magnetic drifts and obtain proton distributions. The magnetic field is provided by a modified version of the Tsyganenko 96 model with two-dimensional force balance maintained along the midnight meridian. The convection electric field is determined mainly by the cross polar-cap potential drop (Delta Phi ) and the equatorward edge of the convection electric field (shielding latitude theta ). The local-time dependent proton differential fluxes assigned to the model boundary are a mixture of hot plasma from the mantle and cooler plasma from the low latitude boundary layer. We previously used this model to simulate the inner plasma sheet under weak convection corresponding to Delta Phi and theta equal to 26 kV and 66° , and obtained two-dimensional quiet time equilibrium that agrees well with observations. In the current simulation, we start with the quiet time equilibrium and boundary particle sources and enhance convection by increasing Delta Phi steadily from 26 to 146 kV and lowering theta from 66° to 52° in 5 hours while keeping the boundary sources time independent. The inner edge of the plasma sheet at midnight, mapped to the equatorial plane using the self-consistent magnetic field, moves from ~ 10 RE for Delta Phi = 26 kV to ~ 4 RE for 146 kV. This earthward penetration to regions of dipole field results in strong plasma pressure increase, which significantly stretches the original dipole field lines. Proton pressure at r = 6.6 RE increases from ~1 to 6 nPa as Delta Phi increases from 26 to 146 kV, while the magnetic field strength decreases from ~80 to 10 nT. The simulated pressure and magnetic field strength, their radial variations at midnight, and their changes with convection strength in the inner plasma sheet in general agree with observations. Protons undergo enhanced earthward electric drift but are significantly diverted toward dusk by azimuthal magnetic drift around midnight. The enhanced magnetic drift, responding to enhanced particle energy, changes particles' trajectories and magnetic field configuration in a way that restrains particle energization, thus plays an important role in plasma sheet dynamics. Simulations are also run to a steady state under constant Delta Phi = 98 kV and theta = 57.6° , which indicates the inner plasma sheet can remain steady under moderate and constant convection. A scale analysis of our results suggests that using the frozen-in condition E = -vxB in MHD can lead to an inconsistency with Faraday's law in the inner plasma sheet because of neglect of the Hall term in the generalized term.
Global MHD simulations of resonant ULF mode coupling in the inner magnetosphere and plasmasphere*... more Global MHD simulations of resonant ULF mode coupling in the inner magnetosphere and plasmasphere* S. G. Claudepierre1, F. Toffoletto2, J. G. Lyon3, M. Wiltberger4, R. Denton3 1The Aerospace Corporation, Los Angeles, CA, USA 2Rice University, Houston, TX, USA 3Dartmouth College, Hanover, NH, USA 4NCAR/HAO, Boulder, CO, USA *Originally titled: Initial results from global MHD simulations of magnetospheric ULF pulsations driven by IMF fluctuations SM31B-2307
This textbook gives a perspective of heliophysics in a way that emphasizes universal processes fr... more This textbook gives a perspective of heliophysics in a way that emphasizes universal processes from a perspective that draws attention to what provides Earth (and similar (exo-)planets) with a relatively stable setting in which life as we know it can thrive. The book is intended for students in physical sciences in later years of their university training and for beginning graduate students in fields of solar, stellar, (exo-)planetary, and planetary-system sciences.
We present results from a modified MHD code that is used to compute global three-dimensional forc... more We present results from a modified MHD code that is used to compute global three-dimensional force equilibria in the Earth's magnetosphere. A nonuniform rectilinear grid is used along with initial conditions supplied by empirical magnetic field and pressure models. These initial conditions do not, in general, satisfy the force balance condition J × B = p. The MagnetoFriction code solves the equations of ideal MHD, modified to include a frictional dissipation term, allowing the system to relax into an equilibrium state. 1 Background Computing solutions to the force balance equation J × B = p (1) in magnetospheric plasmas is a task which continues to receive attention in the space plasma physics community. Not only are magnetospheric equilibria theoretically interesting, but a magnetospheric model such as the Rice Convection Model (RCM) requires the calculation of plasma equilibria in order to maintain self-consistentcy between the particle pressure and the magnetic field. Cheng (1995) has developed a numerical scheme to calculate three-dimensional magnetic fields that are in force equilibrium with a specified isotropic pressure distribution, but no procedure has been developed to couple the Cheng code to a code such as the RCM. Hesse and Birn (1993) modified an MHD code to include a frictional dissipation term in the momentum equation which allowed them to calculate three-dimensional equilibria in the magnetotail. This MagnetoFriction code also employs a ballistic method to remove kinetic energy from the system once the kinetic energy peaks. The MagnetoFriction code has since been enhanced to calculate global magnetospheric equilibria, extending down to 1RE geocentric distance and to the dayside magnetopause, and is used with the RCM to model magnetospheric convection.
We present recent results of coupling the Rice Convection Model to a magnetofriction equilibrium ... more We present recent results of coupling the Rice Convection Model to a magnetofriction equilibrium solver in order to examine the effect on the pressure in the inner and middle plasma sheet during substorm growth and expansion phases. The coupled model represents a set of partial differential equations that describes the tail and inner plasma sheet and their coupling to the
The initial results of a model of inner magnetospheric convection are presented. The model employ... more The initial results of a model of inner magnetospheric convection are presented. The model employs the Rice convection model with a magnetic field computed with the constraint of magnetostatic equilibrium. The approach computes equilibria from a magnetofriction code which is a modified version of the Hesse-Birn equilibrium code adopted for use in the inner magnetosphere. The code uses the pressure distribution computed from the Rice convection model to update the magnetic field. The algorithm used to compute the inner magnetospheric equilibria is outlined, and the coupling of the equilibrium code with the convection model is described.
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Papers by Frank Toffoletto