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 September 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 MHD 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.

The first simulation study of ion (O+ and H+) and electron temperature evolution during equatorial spread F (ESF) is presented. The simulation results are based on the Naval Research Laboratory (NRL) SAMI3/ESF three‐dimensional code. It is found that the ions and electrons undergo both cooling and heating during bubble evolution. The main cause of cooling is adiabatic, associated with the increase of the flux tube volume as the plasma bubble rises. Ion heating is primarily caused by the compression of ions as they stream down the converging magnetic field. The electrons are heated by collisional coupling with the ions. Additionally, it is found that the electrons are heated at high altitudes (≳1200 km) because of thermal conduction, and that hydrogen ions can be heated at relatively low altitudes (≃300 km) because of ion‐neutral frictional heating. We compare the simulation results with observations from the ROCSAT and Hinotori satellites.

A variety of observations have shown strong seasonal variations in a vast array of magnetosphere‐ionosphere parameters, including field‐aligned currents, cross polar cap potential, and precipitating electron energy flux. In this paper we examine how these variations are modeled in the Lyon‐Fedder‐Mobarry (LFM) global‐scale magnetohydrodynamic simulation of the coupled solar wind‐magnetosphere‐ionosphere system. In order to account for changes in the solar wind conditions caused by the seasonal variation of the Earth's dipole tilt we carefully select the solar wind parameters so that the effective driving conditions are the same across the March, June, and December intervals examined. The seasonal variation of the field‐aligned current strengths is in good agreement with observations, with the sunlit hemisphere having more current than the dark hemisphere in the June and December intervals. However, in order to bring the modeled precipitating electron energy flux into better agreement with the observations we need to utilize a modified current‐voltage relationship which includes a proxy for illumination effects. We provide a detailed description of the LFM's magnetosphere‐ionosphere coupling interface including how illumination effects are incorporated into the model. This methodology for including these effects does not allow for determining if changes in conductance or ionospheric density are responsible for the changes. In addition to improving the agreement with observations the new version of the current‐voltage relationship results in enhanced geomagnetic activity in the March interval examined and suppression of activity during the June interval.

We report results from the global circulation model of Lyon, Fedder, and Mobarry with an embedded model of the inner magnetosphere including the plasmasphere. The combination is used to initiate large numbers of representative protons on the geosynchronous orbit L shell, to assign particle weightings, to track their: subsequent trajectories in the 3D fields. This permits us to study the global circulation of plasmaspheric plumes and to compare these with Polar observations from the dayside magnetopause region . A range of events is studied from an isolated period of SBz in the solar wind,to a large storm sequence. We consider effects on circulating plasma reaching the dayside reconnection X-line, the population of the plasma sheet with ionospheric protons and the generation of ring current pressure from this source, compared with solar wind, polar wind, and auroral wind sources. We find that the transient plasmaspheric plume source is large in terms of total fluence, but of modest proportions in terms of contribution to the ring current. Implications of this and other results for improved space weather modeling and prediction will be discussed.

We investigate the fate of a plasmaspheric plume generated by a discrete period of southward interplanetary magnetic field (IMF) to assess its contribution to plasma sheet and ring current pressure and compare with that for other sources. We use test particle motions in Lyon‐Fedder‐Mobarry (LFM) global circulation model fields. The inner magnetosphere is simulated with the Comprehensive Ring Current Model (CRCM) model of Fok and Wolf, driven by the transpolar potential developed by the LFM magnetosphere. A variant of the Ober plasmasphere model is embedded within the models and driven by them. Global circulation is stimulated by a period of southward IMF embedded within a long interval of northward IMF. This leads to the production of a well‐defined plasmaspheric plume, enhancing the plasma density sunward of the plasmasphere. Test particles are launched with the properties of plasmaspheric ions on the L = 6.6 RE shell and weighted with densities as specified by the Ober model, as it responds to convection imposed by CRCM. Particles are tracked until they are lost from the system downstream or into the atmosphere, using the Delcourt full equations of motion, implemented for finite element fields. Results are compared with earlier computations of polar and auroral wind outflows. The plume produces an enhanced flow of plasma ∼10 times the normal polar wind global fluence. However, we find that most of the “plasmaspheric wind” is lost from the magnetosphere such that its contribution to the ring current energy density is comparable to that of the normal polar wind for this type of event.

The refilling of the plasmasphere for 3 <= L <= 4 following a model storm is simulated over long times (days) using the NRL ionosphere code SAMI2 (Sami2 is Another Model of the Ionosphere). Refilling is dependent on the supply of topside H+ and He+ ions with the result that H+ refilling rates decrease and He+ refilling rates generally increase with increasing F10.7 index. Both early- and late-stage refilling are affected by net ion flows from the warmer to the colder geomagnetic hemisphere. When these flows are strong, the ability of the 'winter helium bulge' to increase He+ refilling rates is suppressed. When neutral winds are not included, refilling rates fall, typically by a factor of two. In most cases, late-stage He+ refilling is proportional to H+ refilling, with typical He+/H+ density ratios of 2% for solar minimum and 10% for solar maximum. For high values of F10.7, He+ refilling exhibits a strong diurnal variation so that the He+/H+ density ratio varies by as much as a factor of two during late-stage refilling. Finally if the plasmasphere is left undisturbed, the H+ density can refill for as long as five weeks at L=3 and ten weeks at L=4, with saturation densities nearly an order of magnitude greater than typical observed densities. This confirms that the plasmasphere at these L values rarely obtains saturation.

Recent observations have quantified the auroral wind O+ outflow in response to magnetospheric inputs to the ionosphere, notably Poynting energy flux and precipitating electron density. For moderate to high activity periods, ionospheric O+ is observed to become a significant or dominant component of plasma pressure in the inner plasma sheet and ring current regions. Using a global circulation model of magnetospheric fields and its imposed ionospheric boundary conditions, we evaluate the global ionospheric plasma response to local magnetospheric conditions imposed by the simulation and evaluate magnetospheric circulation of solar wind H+, polar wind H+, and auroral wind O+. We launch and track the motions of millions of test particles in the global fields, launched at randomly distributed positions and times. Each particle is launched with a flux weighting and perpendicular and parallel energies randomly selected from defined thermal ranges appropriate to the launch point. One sequence is driven by a two-hour period of southward interplanetary magnetic field for average solar wind intensity. A second is driven by a 2-h period of enhanced solar wind dynamic pressure for average interplanetary field. We find that the simulated ionospheric O+ becomes a significant plasma pressure component in the inner plasma sheet and outer ring current region, particularly when the solar wind is intense or its magnetic field is southward directed. We infer that the reported empirical scalings of auroral wind O+ outflows are consistent with a substantial pressure contribution to the inner plasma sheet and plasma source surrounding the ring current. This result violates the common assumption that the ionospheric load is entirely confined to the F layer, and shows that the ionosphere is often an important dynamic element throughout the magnetosphere during moderate to large solar wind disturbances.

Riometers monitor the changes in ionospheric onductivity by measuring the absorption of very high frequency radio noise of galactic origin passing through the ionosphere. In this Letter the absorption of radio signals by a thin layer of ionospheric plasma, produced by ionization due to energetic precipitating electrons, is modeled by taking into account strong turbulent heating caused by instabilities. The precipitating electron population is obtained from a global MHD simulation of the magnetosphere, along with the electric fields which excite the Farley-Buneman instability and lead to turbulent electron heating. A comparison, the first of its kind, of the data from polar and sub-auroral riometers for the magnetic cloud event of January 10, 1997 shows good agreement. The ionospheric onductance modified by turbulent electron heating can be used to improve the magnetosphereionosphere coupling in the current global MHD models.

We investigate the global structure and dynamics of plasma circulation produced by prototypical solar wind disturbances of the interplanetary magnetic field and dynamic pressure. We track the global circulation and energization of solar wind, polar wind, and auroral wind plasmas throughout the magnetosphere, until they precipitate or escape into the downstream solar wind. We use the full equations of motion of the plasma ions within fields produced by a global MHD simulation of the dynamic solar wind interaction. We use the dynamic hot plasma density and Poynting energy flux specified at the inner boundary of the MHD simulation as drivers of conjugate ion outflow fluxes using local empirical relations obtained from the FAST and Polar missions. Birkeland currents computed by the MHD code are used to derive a field-parallel potential drop from a Knight-like relation [as modified by Lyons and Evans, 1980]. This potential drop is applied to each ion as an initial bulk energy, added to a thermal heating driven by the locally incident Poynting flux. The solar wind pressure increase case (B(sub Y) = 5; B(sub z) = 0 nT) produces an immediate substorm owing to compression of pre-existing plasmas. The SB(sub z), interval (embedded in NB(sub z)) produces a substorm after about one hour of development. Both disturbances enhance the auroral wind flux and heavy ion pressure of the magnetosphere substantially, with complex dynamic structuring by auroral acceleration vortexes and dynamic reconnection. Comparisons are made with observations during disturbed periods including the Halloween 2003 super-storm and other periods.