Location
Yosemite National Park
Start Date
2-12-2014 10:25 AM
End Date
2-12-2014 10:55 AM
Description
The concept behind the Rice Convection Model (RCM) dates back to an attempt, starting in the late 1960s, to mathematize an idea of Schield, Freeman, and Dessler that predicted the pattern of Birkeland currents in Earth's magnetosphere. The original version of the RCM was an elliptic solver that computed the ionospheric potential distribution by assuming a pattern of ionospheric Hall and Pedersen conductances, including day-night asymmetry and auroral enhancement. Ionospheric potential patterns were mapped along equipotential magnetic field lines to predict magnetosphere flow patterns and plasmasphere shapes. A key milestone was the inclusion, a few years later, of a simple mono-energetic plasma sheet and calculation of field-aligned currents resulting from pressure gradients in the magnetosphere. Results exhibited shielding of the inner magnetosphere from the full effects of magnetospheric convection and also predicted most basic characteristics of region-2 currents shortly before the currents were identified observationally. By the late 1970s, the plasma sheet in the RCM had a realistic energy spectrum of both ions and electrons and was exhibiting a number of features that were consistent with observations. Since the 1970s, the RCM has used time-varying magnetic field models, which further improved consistency with observations. A key discrepancy was the tendency for modeled region-2 currents to be too narrow in latitude. Another deep difficulty arose in the late 1970s, when we found that the observed average magnetic field configuration was inconsistent with the idea of simple sunward adiabatic convection in the plasma sheet (pressure balance inconsistency). A milestone, in the early 1980s, was the use of modelcalculated electron precipitation from the plasma sheet to produce an approximation of the diffuse aurora and associated ionospheric conductance enhancement. Better prescriptions of plasma sources on the tailward boundary were shown to produce region-1 and Harang-discontinuity currents flowing on closed field lines. The RCM was adapted to treat interchange-driven transport in the Jovian magnetosphere, and that code was later applied to Saturn. In the late 1990s and early 2000s, we mated the RCM with an MHD-friction code, allowing us to keep the magnetic field in force balance with the RCM-computed particle pressure (RCM-E). A change in numerical methods in the early 2000s made it easy to vary the boundary-condition distribution function in both space and time, allowing investigation of interchange instability for Earth. We present new RCM-E results that include effects of bursty bulk flows as well as first attempts to simulate major discrete auroral features. Initial results suggest that the inclusion of these mesoscale features may help resolve two old conundrums: the pressure-balance inconsistency and latitude distribution of Birkeland currents. We will also address our present code development efforts aimed at including field-aligned electric fields and inertial currents. Forty-five years of work have yielded a numerical model that seems to represent most of the physics involved in large-scale coupling of the inner and middle magnetosphere with the ionosphere.
Forty five years of the Rice Convection Model
Yosemite National Park
The concept behind the Rice Convection Model (RCM) dates back to an attempt, starting in the late 1960s, to mathematize an idea of Schield, Freeman, and Dessler that predicted the pattern of Birkeland currents in Earth's magnetosphere. The original version of the RCM was an elliptic solver that computed the ionospheric potential distribution by assuming a pattern of ionospheric Hall and Pedersen conductances, including day-night asymmetry and auroral enhancement. Ionospheric potential patterns were mapped along equipotential magnetic field lines to predict magnetosphere flow patterns and plasmasphere shapes. A key milestone was the inclusion, a few years later, of a simple mono-energetic plasma sheet and calculation of field-aligned currents resulting from pressure gradients in the magnetosphere. Results exhibited shielding of the inner magnetosphere from the full effects of magnetospheric convection and also predicted most basic characteristics of region-2 currents shortly before the currents were identified observationally. By the late 1970s, the plasma sheet in the RCM had a realistic energy spectrum of both ions and electrons and was exhibiting a number of features that were consistent with observations. Since the 1970s, the RCM has used time-varying magnetic field models, which further improved consistency with observations. A key discrepancy was the tendency for modeled region-2 currents to be too narrow in latitude. Another deep difficulty arose in the late 1970s, when we found that the observed average magnetic field configuration was inconsistent with the idea of simple sunward adiabatic convection in the plasma sheet (pressure balance inconsistency). A milestone, in the early 1980s, was the use of modelcalculated electron precipitation from the plasma sheet to produce an approximation of the diffuse aurora and associated ionospheric conductance enhancement. Better prescriptions of plasma sources on the tailward boundary were shown to produce region-1 and Harang-discontinuity currents flowing on closed field lines. The RCM was adapted to treat interchange-driven transport in the Jovian magnetosphere, and that code was later applied to Saturn. In the late 1990s and early 2000s, we mated the RCM with an MHD-friction code, allowing us to keep the magnetic field in force balance with the RCM-computed particle pressure (RCM-E). A change in numerical methods in the early 2000s made it easy to vary the boundary-condition distribution function in both space and time, allowing investigation of interchange instability for Earth. We present new RCM-E results that include effects of bursty bulk flows as well as first attempts to simulate major discrete auroral features. Initial results suggest that the inclusion of these mesoscale features may help resolve two old conundrums: the pressure-balance inconsistency and latitude distribution of Birkeland currents. We will also address our present code development efforts aimed at including field-aligned electric fields and inertial currents. Forty-five years of work have yielded a numerical model that seems to represent most of the physics involved in large-scale coupling of the inner and middle magnetosphere with the ionosphere.