SM31B-0452
Ion Outflow in the Auroral Downward-Current Region: Moving Double Layers (DLs) vs. the Static Extended Potential Drop, and Parametric Studies for the DL-associated ion outflow
Test particle simulations of ion outflow in the auroral downward-current region are performed to compare the effect of a series of localized, moving double layers (DLs) and a static, altitudinally extended parallel electric field ( E\parallel). The profiles of DL potential, extended E\parallel, and heating rates are based on in- situ observations and dynamic simulations. Moving DLs give rise to intermittent ion out-fluxes along the flux tube with time, supporting the observations that physical processes of the ion outflow might be intermittent. DL evacuates the downward-current-region flux tube via ion outflow effectively compared to the time scale of a convecting flux tube. The out-flowing ions in the DL run do not necessarily have to pass through the retarding potential of the DL, and appear to be "plowed" in front of the DL. The pressure-cooker ions that flow anti- earthward above the extended E\parallel have to overcome the upper boundary of the extended E\parallel which acts as a high-energy "filter" for ions appoaching from below. Ion density profile and distribution functions of the DL run dynamically change as a function of the relative distance to the DL and time, while those in the extended E\parallel run are maintained stationary throughout the run. Parametric studies of the DL-associated heating profile, DL velocity, and DL starting alitude indicate that both H+ and O+ ions are observed to respond more efficiently for an intense, localized heating profile, rather than a moderate, wider heating along the flux tube. A faster DL greatly reduces number fluxes of both outflowing ions, and a slower DL retards H+ outflow a bit due to a limited source population in the lower ionosphere, but promotes O+ outflows by increasing the exposure time of ion heating.
SM31B-0453
Fluid-kinetic simulations of the passage of Storm Enhanced Density (SED) plasma flux tubes through the dayside cleft auroral processes region
Foster et al. [2002] and others have reported on elevated ionospheric density regions being convected from the subauroral plasmaspheric region toward noon, in association with convection of plasmaspheric tails in the dayside magnetosphere. It has been suggested that these so-called Storm Enhanced Density (SED) regions could serve as ionospheric plasma source populations for cleft ion fountain outflows. To investigate this scenario, we have used our Dynamic Fluid Kinetic (DyFK) model 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. We find that the O+ ion density at higher altitudes increases and the density at lower altitudes decreases, following this heating episode, indicating increased numbers of O+ ions from the ionospheric source gain sufficient energy to reach higher altitudes after the effects of transverse wave heating. We also find that O+- H+ crossing point in topside ionosphere moves upward as the wave heating continues. 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.
SM31B-0454
Multi-Instrument Observations of Pc 3-4 Pulsations at Cusp Latitudes in Svalbard, Norway
It has been generally accepted that Pc 3-4 pulsations (~ 10-100 mHz) originate in the ion foreshock upstream of the bow shock due to the interaction between reflected ions and the solar wind, but it is not clear how these waves propagate to the high-latitude ionosphere. Many early studies noted increased power in the vicinity of the dayside cusp. In this study, we compared signal power at Pc 3-4 frequencies from searchcoil magnetometers at three closely-spaced stations on Svalbard: Ny Alesund (76.31o Magnetic Latitude), Longyearbyen (75.26o Magnetic Latitude) and Hornsund (74.24o Magnetic Latitude). Data from the SuperDARN Finland HF radar and DMSP satellites were used to accurately locate the cusp latitudes. We found several events where magnetometers showed strong, narrow-band Pc 3-4 signals, while during the same period the SuperDARN radar saw a clear-edged cusp and a DMSP satellite passing overhead observed the typical cusp signature. We found that often the wave packets were localized and linearly polorized. Also most of the time, the signals were strongest equatorward of the cusp, consistent not with entry via the cusp proper but along field lines equatorward of the cusp which map to the boundary layer or outer magnetosphere.
SM31B-0455
Seasonal and Solar Cycle Variations in High-Probability Reconnection Regions on the Dayside Magnetopause
Future satellite missions like NASA's upcoming Magnetospheric Multiscale (MMS) mission are targeting reconnection diffusion regions at the Earth's magnetopause. These diffusion regions are small compared to the total surface area of the magnetopause. Furthermore, the location of the diffusion region depends on external parameters such as the current state of the Earth's magnetic field and the interplanetary magnetic field (IMF), which is frozen into the solar wind. Even given a complete set of these initial conditions, the location of the diffusion region is still the subject of ongoing research and has yielded several competing models. Our objective is to locate areas on the magnetopause where the diffusion region may be found with a higher probability at a given time. Since the principal temporal variation in the Earth's magnetic field is governed by the Earth's seasonal dipole tilt and because solar conditions are roughly periodic over an eleven-year cycle, the external parameters on which the location of the diffusion region depends can be inferred from past data. Using this technique we will explore possible relationships between the terrestrial season and solar cycle and locations where the diffusion region may be found with higher probability. Several of the most popular reconnection models will be used in this analysis, including the tilted neutral line model of component reconnection, anti- parallel reconnection, and a hybrid scheme developed by the present authors which utilizes elements from each of these.
SM31B-0456
Energetic Particles Observed by ISEE-1 and ISEE-2 in a Cusp Diamagnetic Cavity on September 29, 1978
Observations by the ISEE-1 and ISEE-2 spacecraft on September 29, 1978 show large CEP (Cusp Energetic Particle) fluxes while passing through the dayside magnetospheric cusp in near coincident orbits. The event was observed around 11 MLT between roughly 12:30 and 13:00 UT by ISEE-1 and 12:00 and 13:00 UT by ISEE-2. During these periods, both electron and ion fluxes increased by more than two orders of magnitude. A boundary sounding technique was used to probe the location and orientation of a cusp boundary as the spacecraft approached. Inside this cusp cavity, pitch angle distributions of the electrons showed a strong peak at a pitch angle of 90°. During this period, the solar wind was ~710 km/s and the Dst was ~-200 nT, suggesting the occurrence of a strong geomagnetic storm. The ISEE-1 and ISEE-2 observations, however, show no time-energy dispersion of the CEPs, leading us to believe that these particles could not be the result of substorm processes in the magnetotail. Inside the cavity, the local magnetic field was depressed and extremely turbulent. These changes in the local magnetic field strength anticorrelate closely to variations of the electron flux. The observations of electron flux peaking at 90° and the close anticorrelation between strength of the local magnetic field and electron flux are unique and provide evidence of a potential local source for these energetic particles.
SM31B-0457
Anatomy of Diamagnetic Cusp Cavities - Cluster observations
We present a systematic study of the diamagnetic cavities and adjacent regions in the vicinity of the high-altitude cusp. We are utilizing various Cluster spacecraft separations in order to identify the size and overal structure of these cavities and will compare with 3-D high-resolution MHD simulations. Our initial simulation results indicate that the diamagnetic cavities can play an important role in the particle acceleration, therefore it is important to understand their formation mechanism, overal dynamics and structure.
SM31B-0458
Particle Acceleration in Cusp Diamagnetic Cavities
The acceleration of charged particles is a topic of fundamental importance in may space and astrophysics plasma systems. A particularly controversial topic is the observation of a accelerated ion populations associated with cusp diamagnetic cavities. While there are some indications that the acceleration of these particles occurs locally other observations seem to indicate the quasi-parallel bow shock as the source region for these particles. Here we will address this issue in the framework of testparticle simulations using electric and magnetic field from MHD simulations of diamagnetic cavities. The results demonstrate that particle acceleration can be highly efficient in the cavity geometry. We will review the properties of this acceleration process and compare the results to typical observations.
SM31B-0459
A New List of Flux Transfer Events in the CLUSTER Data by Use of an Automated Technique
We have used our newly developed data mining software called MineTool for automated detection of flux transfer events (FTEs) in the CLUSTER data. Data mining techniques can be divided into two types, supervised and unsupervised. In supervised algorithms like MineTool, one teaches the algorithm using examples from labeled data. Considering the case of FTEs, the user would provide examples of FTEs as well as examples of non-FTEs and label (as FTE or non-FTE) the data. We used a list of FTEs compiled by Y. Wang to create the labeled data. We then used MineTool on this data set to develop an automated detection model for FTEs. Finally we applied this model to CLUSTER data to search for new FTEs. We have compiled a list of new FTEs which are made publicly available.
SM31B-0460
Simulations of the formation of O+ trough zones in the polar cap ionosphere-magnetosphere coupling region
Thermal ion measurements by the Thermal Ion Dynamics Experiment(TIDE) on the POLAR spacecraft show that the O+ densities in the polar cap near 6000 km altitude display structured variations featuring low-density trough regions. We use the UT Arlington Dynamic Fluid-Kinetic (DyFK) model to model such O+ density profiles. Treating different cases of TIDE observations near polar perigee by using available measured solar wind parameters to drive a time-varying high-latitude convection model and incorporating auroral processes of soft electron precipitation and wave-driven ion heating, we simulate the evolving high-latitude ionospheric plasma transport and associated parameter profiles for several convecting flux tubes in the high-latitude ionosphere- magnetosphere system, incorporating estimated locations of the auroral processes regions from HYDRA and the Ovation auroral oval model. This auroral oval model has as inputs auroral precipitation measurements from DSMP. For the convection patterns thus computed, these flux tubes nominally intersected the POLAR trajectory where the density measurements were made. It is found that, owing chiefly to F-region recombination processes during trajectory segments when the low altitude portions of such flux tubes in darkness, as well as incorporating auroral fountain effects in the auroral region, normal and low trough-like densities at higher altitudes developed along these flux tubes. The modeled densities near 6000 km altitudes will be compared with multiple trough events featuring POLAR/TIDE-measured O+ densities for inside and outside of such trough regions.
SM31B-0461
Solar Wind Speed as a Driver of Magnetospheric Activity
Statistical analysis of sawtooth events and steady magnetospheric convection (SMC) periods show that the solar wind speed is much higher during sawtooth events than it is during SMC periods even for a set of cases with similar driving solar wind electric field values. Thus, high solar wind speed seems to induce periodic activity while low speed and larger IMF tend to produce a steadily convecting, rather stable magnetosphere. Further statistics of all activity conditions shows that during southward IMF, for the same solar wind electric field value larger speed and smaller Bz magnitude drive higher activity than smaller speed and larger Bz magnitude. These results are confirmed by results from three LFM global MHD simulation runs, which show that originally stable magnetosphere remains stable if IMF Bz magnitude is increased, while stronger activity and localized flows appear if the solar wind speed is increased. All these results point out the key role of the solar wind speed in determining the global state of the magnetosphere.
SM31B-0462
On the generation and topology of Flux Transfer Events
We investigate the generation and topology of Flux Transfer Events (FTEs) under generic southward IMF conditions. Previous research with the OpenGGCM code (Raeder, 2007) concluded that FTEs form only when the dipole tilt is nonvanishing. The Raeder FTE generation mechanism invokes a two-dimensional reconnection scenario in which the location of the stagnation point differs from that of the magnetic neutral point (owing to the dipole tilt). In the Raeder scenario, magnetosheath flow drives the formation of a new X line, producing a magnetic island which propagates northward or southward, depending on the dipole tilt. The topology of the resulting FTE is simple, consisting of a flux rope bounded by two X lines. In this work, we use the OpenGGCM code to demonstrate that in the high Lundquist number limit (i.e., when the plasma resistivity is uniformly small), FTEs can form under vanishing dipole tilt conditions. Flux ropes form spontaneously in two stages: 1) resistive tearing modifies the initially stable stagnation point flow, causing it to become unstable; 2) the stagnation point flow instability (an ideal MHD instability) results in the formation of large scale vortices which drive the formation of multiple magnetic separators. The resulting magnetic field topology becomes significantly more complex than the double X line model of Raeder (2007). We discuss some possible reasons for the discrepancy.