SM12A-01
Dynamic Fluid-Kinetic (DyFK) Simulations of Storm-Enhanced Density Supply of Cleft Ion Fountain Outflows
Elevated ionospheric density regions frequently appear to be convected from the subauroral plasmaspheric region toward noon, in association with convection of plasmaspheric tails in the dayside magnetosphere, typically during large geomagnetic storms. In this presentation, we explore the possibility that these Storm Enhanced Density (SED) regions could provide ionospheric plasma source populations for cleft ion fountain outflows. We use our Dynamic Fluid Kinetic (DyFK) code to simulate the entry of a high-density "plasmasphere-like" flux tube entering the cleft region and subjected to an episode of wave-driven transverse ion heating. The results of including different proportions of SED and soft electron precipitation levels, together with transverse ion heating effects on the resulting outflows, will be presented, including the O+ and H+ ion density and related parameter profiles for the simulated SED involved events. We will also compare these modeling results with SED-outflow observations from GPS TEC, and the FAST and IMAGE spacecraft. Foster, J. C., P. J. Erickson, A. J. Coster, J. Goldstein, and F. J. Rich, Ionospheric signatures of plasmaspheric tails, Geophys. Res. Lett., 29(13), 1623, doi:10.1029/2002GL015067, 2002.
SM12A-02
Comparison Between Data-Based and Simulation-Based Ion Outflow Scaling Laws
Previous studies of ionospheric outflows at ~4000 km altitude using data from the Fast Auroral Snapshot Small Explorer (FAST) have shown that the ion flux is correlated with precipitating electron density and quasi- DC Poynting flux. The FAST correlation analysis was purely data-based. In particular the study did not investigate how the energy inputs, including waves, controlled the various parameters of the ionospheric outflow. Such distinct parameters include ion density, ion velocity, and temperature. Physics-based simulation models for ionospheric plasma outflows, such as the UT Arlington Dynamic Fluid Kinetic (DyFK) model, on the other hand, explicitly investigate the outflow properties versus varying wave and precipitation driving agent parameters. Here we present a re-analysis of the FAST data that investigates the dependence of these additional ion parameters on the energy inputs. We find, for example, that the FAST observed ion temperatures are more strongly correlated with electromagnetic energy flux than precipitating electron density, a result which is consistent with the results of the DyFK modeling.
SM12A-03
Ion Upflows in the Polar Magnetosphere During Geomagnetic Storms
We performed a case study of ion upflows enhanced during a geomagnetic storm using data obtained by the Akebono satellite. Based on the location of intense upflows and their velocities, trajectories of the upflowing oxygen ions were traced using the single particle approach. Using these results, the importance of thermal oxygen ions with a large upward flux was discussed. We used electron density data observed by the PWS, and an ion composition ratio and field-aligned velocities observed by the SMS onboard Akebono. A numerical code developed by Ebihara et al. [2006] was used for calculations of oxygen ion trajectories. In the code, the Tsyganenko-89 and Weimer-2K models were used as magnetic and electric field models, under conditions of Kp = 7, nsw = 10 /cc, Vsw = 500 km/s, IMF By = 0 and Bz = -20 nT. We performed a case study for a geomagnetic storm which occurred on March 30, 1990, using data obtained by Akebono in an altitude range of 6000-10000 km in the dayside polar region. During the main phase of the storm, the electron density enhanced 3-30 times larger than the quiet-time level in the auroral zone and polar cap. The SMS instrument measured intense ion upflows in the entire polar cap along the satellite path. Eighty percents of the upflowing ions were composed of oxygen and the upward velocities of oxygen along the field lines ranged 4-10 km/s, which was comparable to the escape velocity. The upflow flux of the oxygen ion mapped to 1000 km altitude corresponded to 1-4×109 /cm2/s. Based on the observations, we calculated trajectories of the upflowing oxygen ions released at 9000 km altitude, which was near the altitude of the ion upflow observed by Akebono. Initial velocities of the oxygen ions were given in a range of 1-12 km/s, directed to the upward field-aligned direction in the electric field (E×B) drifting coordinate. The initial positions were 8, 10, 12, 14, and 16 MLT at 75° ILAT, and 70°, 75°, and 80° ILAT at 12 MLT. At all of the initial positions, the oxygen ions which had initial velocities of 3 km/s or larger, did not fall down to the Earth, but escaped into the magnetosphere. This result indicates that a large portion of the upflowing oxygen ions observed by Akebono in the dayside polar cap during geomagnetic storms flows into the magnetosphere. The ions released from 12 MLT firstly flew into the premidnight magnetotail, and transported to the duskside at L = 3-5, where the storm-time asymmetric ring current developed. In the region, some ions were energized to more than 50 keV. These results indicate that thermal oxygen ions with a large upward flux, which cause the density enhancement in the polar cap during geomagnetic storms, can reach the plasmasheet and contribute to the ring current formation.
SM12A-04
Transport of O+ From the Cusp to the Plasma Sheet: Coordinated CLUSTER/Double Star TC-1 Observations
Using CLUSTER CIS/CODIF data, O+ is clearly observed flowing from the cusp, over the polar cap, and into the plasma sheet at the CLUSTER apogee of 19 Re. This O+ transport to the plasma sheet is predominantly observed during storm times, and may be a dominant source for the storm time ring current. However, due to the polar orbit of CLUSTER, this data set cannot be used to measure the O+ transport to the plasma sheet closer to the earth. Thus we cannot tell if the O+ has direct access via the lobe to the near-earth plasma sheet, or whether it comes from the lobe to the mid-tail plasma sheet, and then is convected inward. The Double Star TC-1 satellite, with a near-equatorial orbit, with 13 Re apogee, is helping to fill this gap. While TC-1 does not have an ion composition instrument, the O+ is often identifiable by its distribution function. In the lobe it appears as a mono-energetic tailward streaming population. In the plasma mantle, it also has a narrow energy distribution, and flows at the same velocity, and therefore at higher energies, than the H+. We have identified a number of events in which tailward streaming O+ is observed both by Double Star and by the CLUSTER spacecraft. In two events, which occurred during storm times, Double Star observed O+ streaming around the dawn-side flank while Cluster observed it entering the plasma sheet at 18 Re. In other events, the tailward streaming O+ distributions just outside the plasma sheet are observed both at Double Star, at 13 Re, and at Cluster, at 18 Re. In other events, Cluster observes the O+ over the polar cap, while Double Star observes it in the lobe inside 13 Re. These observations clearly show that the O+ from the cusp is transported through the lobe to the near-earth (<13 Re ) plasma sheet.
SM12A-05
How Ionospheric Ions Populate the Magnetosphere During a Magnetic Storm
Ionospheric oxygen ions have been observed throughout the magnetosphere, from the plasma sheet to the ring current region. It has been found that the O+/H+ density ratio in the magnetosphere increases with geomagnetic activity and varies with storm phases. During the magnetic storm in late September to early October 2002, Cluster was orbiting in the plasma sheet and ring current regions. At pre-storm time, Cluster observed high H+ density and low O+ density in the plasma sheet and lobes. During the storm main phase, O+ density has increased by 10 times over the pre-storm level. Strong field-aligned beams of O+ were observed in the lobes. O+ fluxes were significantly reduced in the central plasma sheet during the storm recovery. However, O+ was still evident on the boundaries of the plasma sheet and in the lobes. In order to interpret the Cluster observations and to understand how O+ ions populate the magnetosphere during a magnetic storm, we model the storm in early October 2002 using our global ion kinetic simulation (GIK). We use the LFM global simulation model to produce electric and magnetic fields in the outer magnetosphere, the Strangeway outflow scaling with Delcourt ion trajectories to include ionospheric outflows, and the Fok inner magnetospheric model for the plasmaspheric and ring current response to all particle populations. We find that the observed composition features are qualitatively reproduced by the simulations, with some quantitative differences that point to future improvements in the models.
SM12A-06
Simulating the Fate of an Ionospheric Mass Ejection
We report global ion kinetic (GIK) simulations of the 24-25 Sep 1998 storm, with all relevant ionospheric
outflows including polar, auroral, and plasmaspheric winds. This storm included substantial periods of
northward interplanetary magnetic field, but did develop a Dst of -200 nT at its peak. The solar disturbance
resulted form a coronal mass ejection that reached a peak dynamic pressure at the magnetosphere of 6.2
nPa, and produced a substantial enhancement of auroral wind oxygen outflow from the dayside, which has
been termed an "ionospheric mass ejection" in an earlier observational paper. We use the LFM global
simulation model to produce electric and magnetic fields in the outer magnetosphere, the Strangeway-Zheng
outflow scalings with Delcourt ion trajectories to include ionospheric outflows, and the Fok-Ober inner
magnetospheric model for the plasmaspheric and ring current response to all particle populations. We
assess the combined contributions of heliospheric and geospheric plasmas to the ring current for this event.
http://gpl.gsfc.nasa.gov/public/traj
SM12A-07
Effect of Ionospheric Outflow Parameters on Magnetospheric Configuration
Using the newly developed multi-fluid version of the Lyon-Fedder-Mobarry global simulation model we have recently reported that by including Oxygen outflow from the ionosphere into the magnetosphere the simulation produces a sequence of substorms for steady southward IMF instead of a single substorm seen when outflow is not included. We begin with a detailed review of these results, including the specification for the intensity and location of the outflow. Initial results have shown that by increasing the outflow velocity the impact on magnetosphere can be reduced because the majority of the outflow does not enter the magnetospehre. In this presentation we systematically investigate how the location, flux, and velocity of the outflow effects the evolution of the magnetosphere.
SM12A-08
November 7-8, 2004 Superstorm: LFM Simulations with Causally Regulated Ionospheric Outflow
The 7-8 November superstorm has been simulated using the one-fluid LFM global simulation model including ionospheric outflow. The outflow is specified using the empirical relations developed by Strangeway et al. (2005) between ion outflow flux, downward Poynting flux and precipitating electron flux. Results of the simulations with and without outflow are compared to evaluate the effects of the outflow on the global system dynamics. For this storm, the outflow flux varies dynamically with variations in both solar wind dynamic pressure and IMF Bz. We find that outflows regulated in this way: 1) produce a more extended and denser plasmasheet; and 2) increase the density and pressure of the inner magnetosphere, with a resulting increase in the magnetopause standoff distance. The Poynting flux flowing into the more sunlit ionosphere is larger than that in the darker hemisphere, and, therefore, the outflow fluence is larger in that hemisphere. Peak outflow fluxes of a few 1014/m2-s are obtained with peak fluences approaching 1028 ions/s. The outflows also produce the following effects on the magnetosphere-ionosphere interaction: 1) ~30% increase in the power of precipitating electrons, with peak hemispheric power of 600 GW; 2) reduction in the field-aligned current and Joule dissipation; and 3) variable increase and decrease in the transpolar potential during different phases of the storm.