SM21A-0441 0800h
Survey of oxygen ions and mass density in the dayside near-magnetopause region
Since december 2000, The Cluster spacecraft have been conducting detailed measurements of the magnetospheric boundaries and confirmed the unambiguous presence of ions of terrestrial origin (e.g. O+) in regions adjacent to the dayside, mid-latitude magnetopause. The present paper focusses on the statistical properties of the O+ ion component at energies ranging from 30 eV up to 40 keV using three years of ion data at solar maximum from the Cluster Ion Spectrometry (CIS) experiment aboard two Cluster spacecraft. The O+ density decreases on average by a factor of 6 when crossing the magnetopause from the magnetosphere to the magnetosheath, but depends on several parameters such as the geomagnetic activity or the disturbed storm time index, and on their location. The O+ density is significantly higher in the duskside than in the dawnside region, which is consistent with the view that they originate mainly from the plasma sheet. A remarkable finding is that inward of the magnetopause, O+ is the dominant contributor to the mass density 30% of the time on the duskside as against 3% in the dawnside and 4% near noon. The O+ ion density in the adjacent magnetosheath is found to be slightly higher when the interplanetary magnetic field (IMF) is northward rather than southward, indicating that energetic ions are always escaping whether or not conditions support dayside reconnection. This result can also be explained in terms of convection drift paths; the presence of sunward drift velocities under northward IMF helps ions from dayside sources to leak out across the dayside magnetopause while in contrast, antisunward drift velocities under southward IMF would prevent such ions from escaping. We also discuss the role of a substantial O+ ion component in affecting physical processes such as the Kelvin-Helmholtz instability or magnetic reconnection.
SM21A-0442 0800h
Multipoint Observations of Magnetospheric Oxygen Ions at the Dusk Flank Magnetopause: a Case Study with Cluster
We present Cluster CIS observations along the dusk flank magnetopause during an outbound orbit on November 20, 2001. Cluster detects magnetospheric oxygen ions both in the boundary layer inside the magnetopause and in the adjacent magnetosheath. Oxygen presence lasts for several hours while the spacecraft move from 22 to -2 degree GSM latitude at approximately 19 MLT. Just inside the magnetopause two different oxygen populations seem to coexist, a high energy population and a tailward flowing population which is detected also outside the magnetopause. The plasma three dimensional distribution functions measured by the three spacecraft are studied in detail and under variable interplanetary magnetic field orientation.
SM21A-0443 0800h
Cluster Observations of Cusp Population by Solar Wind Compression
The Cluster spacecrafts crossed through the southern magnetosheric cusp several times during the geomagnetic storm period 24 October - 03 November 2003. Analysis of the CIS, FGM and STAFF data during these stormtime and previous quiettime cusp crossings provide evidence for the cusp population by solar wind compression during the onset and early main phase of the storms on 24 and 29 October. The crossing on 24 October occurred during the onset of a moderate geomagnetic activity. The prevailing solar wind, as observed by ACE, became strong (pressure over 10 nPa, density up to 80 cm$^{-3}$, speed exceeding 600 km s$^{-1}$) and IMF Bz turned strongly northward at around 15:00 UT. About 30 min later, when Cluster was entering the cusp through the entry layer, the ion density (H$^{+}$ and He$^{++}$) increased suddenly over 50 times and ion velocity turned strongly southward. The cusp crossing on 29th October occurred during the early main phase of a severe geomagnetic storm. The prevailing solar wind became very strong (speed exceeded 1500 km s$^{-1}$; pressure and density not available) and IMF Bx, By and Bz started fluctuating around zero starting at around 05:45 UT. About 20 min later, the Cluster, which was entering the cusp through the entry layer, started detecting over 20 times increase in ion density (H$^{+}$, He$^{++}$ and O$^{+}$), and ion velocity turned strongly southward. These observations of large ion density with strong southward ion flows in the southern magnetospheric cusp, following strong solar wind, indicate cusp population by solar wind compression. The magnetic field components Bx, By and Bz show large fluctuations during both crossings, consistent with the ion velocity fluctuations. Magnetic wave activity also became strong at the time of sudden increase in ion density during both crossings.
SM21A-0444 0800h
Ionospheric Ion Beam Accelerations Above the Polar Cap
We present a Cluster multi-experiment study of near mono-energetic ion beams inside the polar cap. Data are taken at altitudes of 4 - 7 Re. Using the Cluster mass spectrometers a clear distinction is made between ion beams ejected from the polar cusp and those ejected along the local magnetic field line passing by the spacecraft. Polar cusp beams are characterized by the encounter of field aligned proton and oxygen ions with energies differing by a factor of about 4, as expected from the velocity filter effect. Polar cap local outflowing beams are characterized by a series of nearly monoenergetic ion inverted V structures in the 100 eV to ~ 3 keV range. Ions are field aligned and in many occasions the structures are associated with a converging electric field. The field aligned potential drop fits quite well the ion energy profile. No ion precipitation is recorded. In several cases comparisons of ion and electron distributions show that the parallel electric field is weak and can extend to altitudes higher than that of the satellite. Detailed analysis of the ion energy distribution show that oxygen ions are more energetic than protons and that outflowing ions are heated during their parallel acceleration. As for the auroral region, these observations could be due to an ion two-stream instability. We present the correlation of these events with the IMF orientation and use DMSP data to show the simultaneous occurrence of polar rain over the polar cap.
SM21A-0445 0800h
Charge States of O Ions Injected at Substorm Onset and Estimation of the O+/O6+ Flux Ratio: Geotail/EPIC Observation
Oxygen ions in the Earth's magnetosphere are supplied from two sources, that is, the ionosphere and the solar wind. The charge states of oxygen from the ionosphere are generally low such as O+, while those from the solar wind are highly charged (mainly O6+). Investigating the amount of oxygen with each charge state in various energy ranges in the magnetosphere and its source region gives us information how it is energized during travel from its origin to the magnetosphere. This would be a clue to know the acceleration mechanisms of oxygen in the magnetosphere. However, only a few satellites carried instruments which can measure the ions' charge states. Furthermore, they are not sensitive enough in the high energy range (more than 100 keV) because the number of ions in this energy range is small. It is also difficult to analyze a phenomenon in a short time scale such as ion injection from the near-Earth tail into the inner magnetosphere at substorm onset. In this study, we estimate the charge state of injected oxygen in various energy ranges by using the method of Sibeck et al. [Geophys. Res. Lett., 15, 1287 - 1290, 1988] with the flux data from the EPIC/ICS instrument on Geotail; it can measure mass of ion in the energy range of 50 keV - 3 MeV but not charge state. This method uses the energy dispersion of flux enhancements of injected ions, which is dependent on the charge state of them. This dispersion is responsible for the drift velocity of ions in the inner magnetosphere depending on their energy and charge state. We analyzed the ICS data statistically to estimate charge state of oxygen ions for the period of 1996 and October 2000 to September 2001. We also used data from the Geotail/EPIC STICS sensor, which can measure charge state and ion mass, so that the O+/O6+ ratios were given for a few cases where STICS provided enough ion flux to be analyzed for these events. From the analysis we found that (1)In the 50 to 150 keV energy range, the amount of injected O+ ions was much larger than that of injected O6+; (2)In the 150 to 250 keV energy range, the amount of injected O+ ions was comparable with that of injected O6+; (3)In higher than 250 keV energy range, the amount of injected O6+ ions was much larger than that of injected O+; and (4)The amount of injected O+ during the solar maximum period was larger than those during the solar minimum period. Results 1 - 3 would mean that the energy of solar wind oxygen in the magnetosphere would be generally higher than that of ionospheric oxygen, though solar wind oxygen might be energized more effectively only at substorm injection. Result 4 confirms the well-known fact that the amount of O+ ions of ionospheric origin become larger during the solar maximum period [Young, D.T., H. Balsiger, and J. Geiss, J. Geophys. Res., 87, 9077-9096, 1982].
SM21A-0446 0800h
OBSERVATIONS AND MODELING OF GLOBAL O$^+$ SUBSTORM INJECTIONS
The High Energy Neutral Atom (HENA) camera on board IMAGE has revealed significant increases in the Oxygen energetic neutral atom (ENA) in the 50-200 keV range, coincident with storm-time substorm onsets. Preliminary analysis shows that at the time of auroral onset there is an $\leq$2 min enhancement of ENA emissions originating from high altitudes. 5-10 min after, low-altitude ENA emissions increase dramatically. Neither of these signatures are present in the hydrogen ENA images. One scenario that may explain these observation relates to the different gyroperiods of oxygen ions and protons. When a geomagnetic storm commences, O$^+$ flows out from the polar and auroral ionosphere and reaches the plasmasheet with roughly $\sim$1 keV energy. As the geomagnetic field dipolarizes at substorm onset, the duration of the induced electric field is of the same order as the O$^+$ gyroperiod as ($\sim$min), while the proton gyroperiod is sixteen times shorter. Therefore, O$^+$ ions behave non-adiabatically in the dipolarization process and can be shown to reach high energies. This scenario would explain the sudden occurence of high-energy oxygen ENAs. However, high-energy O$^+$ ions have been observed at in the auroral region at ionospheric heights by the FAST satellite in relation to substorm onsets. A 3D particle code has been developed with a time-varying model magnetic field obtained from an MHD model during a substorm dipolarization. We will present and discuss the analysis of the ENA images and the {\it in-situ} data in light of the new model results.
http://sd-www.jhuapl.edu/IMAGE/
SM21A-0447 0800h
Occurrence statistics of cold, streaming ions in the near-Earth magnetotail
Results are presented from a survey of cold ion observations in the near-Earth magnetotail using data from the Polar Thermal Ion Dynamics Experiment (TIDE). During the interval from July to December of 2001, Polar had its apogee ($\sim$ 9.5 RE) near the equatorial plane in the tail region of the magnetosphere. It is shown that a lobal wind is ubiquitous in the inner tail, with low-energy ($<$ 300 eV) ions streaming from the ionosphere downtail. In addition to the results of a survey of the occurrence statistics of these streaming ions, several example case studies of moments and distribution functions are presented. These lobal winds often pass through the plasma sheet, forming bi-directional streams, in addition to the uni-directional beams seen at higher magnetic latitudes. The observance of bi-directional streams is inversely correlated with geomagnetic activity. It is inferred from the universality of these observations during Polar's passage through the inner tail region that the ionosphere is a continuous supplier of plasma to the near-Earth magnetosphere.
SM21A-0448 0800h
Ionospheric and Solar Plasmas in Geospace Storms
We consider the formation of ring current plasmas in the inner magnetosphere in moderately active conditions that precondition the plasma sheet and ring current-like region for full fledged geospace storms. We seek to better understand recent IMAGE energetic neutral atom observations of the ring current, showing that proton injection is relatively smooth and continuous, while O+ injection is episodic in close association with multiple substorms. We use a modeling framework of collisionless test particle motions in magnetospheric fields from a magnetohydrodynamic simulation. The simulation is used to generate bulk properties and detailed velocity distributions at key locations, for comparison with observations. Particles are initiated in regions representative of the solar wind proton source upstream of the bow shock, the polar wind proton source, and the auroral zone enhanced outflows of O+, or uroral wind. Trajectories are run up to 24 hours to assure a complete circumnavigation of the Earth. Results reflect steady growth phase conditions after 45 minutes of southward interplanetary field, Bz = -5 nT (By=0). Solar wind protons enter the ring current principally through the dawn low latitude boundary layer, while polar wind protons and auroral wind O+ enter the ring current through the midnight plasma sheet. Thus, solar wind and ionospheric plasmas take very different transport paths to the ring current region. Accordingly, they should be expected to respond differently to substorm dynamics of the magnetotail, as recently observed. Polar wind protons make a minor contribution to ring current pressure under steady conditions, but auroral wind O+ has the potential to dominate the ring current, when dayside outflow is strongly enhanced as it is observed to be during periods of enhanced solar wind dynamic pressure fluctuations.
http://tem692.gsfc.nasa.gov/public/AGUFM04
SM21A-0449 0800h
Ion Acceleration in the Plasma Sheet Boundary Layers
We present a study of ion acceleration and heating inside the plasma sheet boundary layers. Two components can generally be detected there, high energy plasma sheet ions streaming earthward and ionospheric protons and oxygen ions flowing tailward. Alfven waves with large and variable amplitude are found to control at times the perpendicular motion of these ions. Inside the PSBL, both the ion parallel and perpendicular velocities increase. The temperature of the ions is also enhanced. Using the four Cluster spacecraft, we test if centrifugal accelerations could be responsible for an exchange between perpendicular and parallel energies and if the observed low frequency waves are able to locally heat efficiently the ionospheric ions.
SM21A-0450 0800h
Upstreaming Ion Acceleration by Alfven Waves
Spacecraft observations of the upper (~4 Earth radii) regions of auroral flux tubes have shown that the energy flux incident on the ionosphere in the form of Alfven waves is larger than the energy deposited in the aurora. Simulataneously, large fluxes of upward-moving ions are observed. Standard fluid approximations cannot explain these observations, since ion gryomotion is not included in MHD-like models. In order to study the energy transfer, a 2D auroral simulation code has been modified to include ion motion for both hydrogen and oxygen. The effect of the ions on the fields was not included. The simuations predict the observed ion energy flux and distribution. An ionospheric density cavity similar to those observed is also produced. These results suggest that the non-MHD mechanism of acceleration by parallel and perpendicular electric fields produces upward-streaming ions on auroral field lines.
SM21A-0451 0800h
Thermal N+ in the Inner Magnetosphere
There has been much interest in O+ in the magnetosphere since it was first reported in 1971. However, relatively little has been done with N+ even though it is the second most abundant ion in the ionosphere at the F2 peak. What observations there are show that there is a large range in the magnitude of the ratio of the N+ density to the O+ density, that N+ is a significant ion in the ionosphere, and that the concentration of this ion varies with season, time of day, solar cycle, latitude, and geomagnetic conditions. Most observational studies have not been used with a large database, nor have they been of a statistical nature. We use the DE1 RIMS observations to survey where N+ is found, in what concentrations relative to O+, and how this concentration varies with changes in the solar input, season, and time of day. We also gauge our understanding of N+ in the ionosphere and plasmasphere by comparing Field Line Inter-hemispheric Plasma (FLIP) model results with the observations.
SM21A-0452 0800h
The Origin and Evolution of Deep Plasmaspheric Notches
Deep plasmaspheric notches can extend over more than 2 RE in radial distance and 3 hours MLT in the magnetic equatorial plane. They appear to be among the largest evacuated features in the exterior plasmaspheric boundary. They can last for days and exhibit varying structure. It appears the origin of notches is shared by low-density channels that result from entrainment of the plasmaspheric convection plume during storm-time recovery. Notches rather than channels result from differences in the location and population of the plume due to differences in the strength of the storm-time convection electric field. Strong convection tends to result in low-density channels, while weaker convection and limited erosion results in notches. Over the 18 events in 2000 have been analyzed. Among these events, notches were found to drift as slowly as 72% of corotation. In only one case was a notch found to drift at the corotation rate with measurement error. On average, notches drift at about 21.5 hours per day or 90% of the corotational rate. Notches also sometimes exhibit interior structures, in particular what appears to be an extended "finger" of dense plasma that forms a W-like feature in IMAGE/EUV images when viewed from Earth-center. Evidence exists such features may be caused by localized, small-scale potential structures caused by injected ring current plasma.
SM21A-0453 0800h
IMAGE - POLAR Concurrent Plasmapause Observations
Two critical issues that influence the quantitative scientific value of the IMAGE Ultraviolet Camera (EUV) are: (1) the accuracy with which EUV imaging can be used to determine the position/location of the plasmapause; and (2) the sensitivity threshold of the EUV instrument. Previous studies have addressed these issues via correlation of EUV-extracted plasmapause locations with steep density gradient plasmapause encounters detected by the IMAGE Radio Plasma Imager (PRI) pre-/post-EUV observation, employing the caveat of corotation. Here, these issues are addressed through analysis of concurrent remote observations of the plasmasphere/plasmapause made by IMAGE EUV with simultaneous in-situ observations acquired by the Polar/TIDE/EFI instruments. Preliminary results are presented with regards to the validity of the extraction of the plasmapause using EUV and initial in-flight, in-situ estimates of the EUV sensitivity threshold. Early estimates suggest a sensitivity threshold for EUV of 25 $\pm$ 15 cm$^{-3}.
SM21A-0454 0800h
Electromagnetic Ion Cyclotron Waves as a Diagnostic for Heavy Ion Mass Density
Conjugate observations of electromagnetic ion cyclotron (EMIC) waves by satellites, rockets, and ground based magnetometers have the potential to identify mass concentrations along magnetic field lines. EMIC wave tend to propagate along magnetic field lines so measurements made in conjunction along a field line can be used to infer conditions along that field line. Moreover, because wave propagation through heavy ion resonances is strongly dependent on the heavy ion concentration near the resonance location, it is possible to deduce localized information about the heavy ion mass concentration from a comparison between wave measurements and theoretical calculations of wave propagation that include wave dissipation near the heavy ion resonances. When a spectrum of wave measurements is available, the spread of frequency maps to an altitude range along the field line for which mass concentrations can be inferred. Because wave measurements are available in the range 1-200 Hz, it is possible to induce information about mass concentration from the topside ionosphere to beyond geosynchronous orbit. To obtain accurate wave solutions we solve a set of electromagnetic wave equations relevant to wave propagation through the magnetosphere and topside ionosphere. These solutions include the possibility of mode conversion among the propagating wave modes, dissipation at the cyclotron resonance, and collisional dissipation and reflection of the wave in the ionosphere. The model predicts observables such as Poynting flux, wave polarization, and wave amplitude that constrain the heavy ion concentrations along the field line. The wave solutions could also be the basis for a control experiment by emitting EMIC waves from a satellite and detecting them using other satellites or ground based instruments.
http://w3.pppl.gov/~jrj/icw.html
SM21A-0455 0800h
Conjugate Observations of Field-Line Resonances in the Inner Magnetosphere from the MEASURE and SAMBA Magnetometer Chains
The newly installed SAMBA (South American Meridional B-field Array) chain is a low latitude meridional chain of 11 magnetometers at L=1.1 to L=2.5 along the coast of Chile and in the Antarctica peninsula. Five of the SAMBA magnetometers at L=1.7 to L=2.5 are directly conjugate to an equivalent number of northern hemisphere magnetometers of the MEASURE (Magnetometers Along the Eastern Atlantic Seaboard for Undergraduate Research and Education) chain. A unique characteristic is that both the SAMBA and the MEASURE magnetometers are set up as pairs of stations making it possible to determine the local Field-Line Resonance (FLR) from conjugate points and thus testing the accuracy of the technique and the models used. An initial study of the local FLR from conjugate pairs of stations at L=1.6 and L=1.7 was done during the moderate storm of July 11, 2003. The frequency of the local resonance can be used to determine the equatorial mass density of the resonating flux tube. From our two conjugate pairs we found, surprisingly, that the difference between the derived mass density between these two very close L values does not agree with densities predicted by any of the existing models or from past observations. If this result is general and not an isolated or rare occurrence it indicates that our understanding of the inversion of FLRs to determine the equatorial mass density is not complete and existing models could be constrained by our observations. We have now isolated a period of approximately 60 days during 2003 with complete coverage from conjugate pairs of stations and we are extending the study of conjugate FLRs to a large amount of days in order to determine the generality, or not, of the results from the July 11, 2003 storm. Initial analysis indicates quite a number of asymmetries in the ULF wave power between the two hemispheres, which might be a contributing factor to the difference in the mass density derived from the conjugate pairs. We plan to investigate these asymmetries more and determine their source and cause.
SM21A-0456 0800h
Co-ordinated IMAGE satellite and ground-magnetometer observations of a cross-phase reversal at a steep plasmapause.
For a few hours during the local morning of the 14th May 2001 the cross-phase peak observed using European sector ground-based magnetometer station pairs with mid-points at L = 3.16 and L = 3.34 changed polarity from positive to negative. All other BGS, SAMNET and IMAGE station pairs examined showed a positive cross-phase peak throughout the day. The IMAGE satellite made an excellent close conjunction with these ground-based magnetometer arrays on this day, and data from the RPI instrument shows a very steep plasmapause in this region during this UT. IMAGE EUV results show that the plasmapause moved outward through the day, passing through the region of observed negative cross-phase peak. The observed negative cross-phase peak is theoretically expected at a plasmapause with a gradient steeper than r$^{-8}$, but is rarely observed. The observations also infer the presence of an enhanced heavy ion population outside the plasmapause in the inner plasmatrough on this day. We discuss the possibility that refilling through the day reduced the gradient of the initially steep plasmapause, eventually removing the negative cross-phase peak.
SM21A-0457 0800h
Estimating magnetospheric densities using observations of the Alfven continuum
Modern data analysis techniques allow the frequencies of standing shear Alfven waves (Alfven continuum) in the magnetosphere to be estimated almost routinely. These frequencies are primarily determined by two factors: the magnetic field intensity and density distribution along the length of geomagnetic magnetic field lines. We solve an eigenvalue problem to obtain the frequency of shear waves based on a general magnetic topology provided by the Tsyganenko magnetic field model and the global MHD model BATS- R-US. Together with the measured Alfven continuum frequencies, this technique is used to infer the magnetospheric plasma density over a range of local time. Our estimates are based on observations made under "typical" solar wind conditions when the empirical Tsyganenko model likely provides a good approximation for the magnetic field, as well as for extreme solar wind conditions (May 12, 1999, "the day Solar Wind disappeared") when global models may be expected to provide a more accurate representation of the magnetic field.
SM21A-0458 0800h
Field Line Dependence of the Mass Density and Electron Density
Based on the harmonic frequencies of the field line resonance mode, the typical field line dependence of the mass density is locally peaked at the magnetic equator. In situ measurements of the electron density by the Polar spacecraft have not yet shown such a local peak. Rather they indicate that the electron density decreases as the magnetic equator is approached. On the other hand, there is a considerable uncertainty in the inferred mass density, and most of the electron density values at large $L$ measured by Polar are at high latitude. Here we examine the uncertainties in the field line dependence based on these two approaches in order to see if the results could be consistent, or if it is necessary to hypothesize a population of heavy ions localized to the magnetic equator.
SM21A-0459 0800h
Lower Limit Of Plasma Densities At The Beginning Of Plasmaspheric Flux Tube Refilling
In this study we estimate the lower limit of the ion densities at the beginning of the flux tube refilling in the plasmasphere. We first calculate the densities of ions passing through the newly closed flux tubes in the magnetotail, i.e., the densities of the ions within the loss cone. The newly closed flux tubes drift earthward to the inner magnetosphere, where they may start to corotate with the earth and are subjected to the plasma refilling from the underlying ionosphere. Because of adiabatic compression, a portion of the passing ions become trapped, resulting in the increased ion densities within the flux tube. It is shown that the equatorial densities at the beginning of the refilling can not be zero but are at least several to several hundreds cm$^{-3}$, depending on how close the flux tubes drift toward the earth and how large the ion density at the topside ionosphere is. The finite plasmaspheric flux tube densities are consistent with the measurements from the Radio Plasma Imager (RPI) on the IMAGE spacecraft, which suggest that the depleted flux tubes maintain equatorial densities of tens to hundreds cm$^{-3}$ at $L = 3.7-2.2$. This estimated lower limit of the densities has important implication to the early stage refilling of the plasmaspheric flux tubes.
SM21A-0460 0800h
Relative Abundance and Escape Flux Composition During Storm Time: 3-D Model
The dynamic behavior of the "generalized" polar wind is investigated using a 3-D dynamic model. In this study, we simulate the behavior of a large number (~100 to 1000) of plasma-filled geomagnetic tubes. The model is composed of two components. The high-altitude component is based on a macroscopic particle-in-cell (mac-PIC) approach that extends from an altitude of 1200 km to several Earth radii. The lower boundary conditions of the mac-PIC model are provided by a 3-D fluid-like model (low-altitude component) that extends down to 100 km in altitude. The total number of simulation particles in the mac-PIC component is more than 10$^{8}$. The generalized polar wind is followed for about 12 hours with a time step of 2.5 seconds. The model properly accounts for many physical mechanisms such as: ion-ion collisions, wave-particle interactions, magnetospheric enegetic electrons, and low-altitude ion energization. The computing-intensive nature of the model requires utilization of super computers with ~100 to 1000 processors. A 3-D picture is assembled from the temporal evolution of the individual flux tubes by keeping track of their locations. The resulting 3-D dynamic picture is investigated with special emphasis difference between the behaviors of the O$^{+}$ and H$^{+}$ ions. In particular, we address questions such as: (1) what is the relative abundance of the different ion species and (2) what is the composition of the ion escape flux, and how this varies with location and storm phase. These, and other results, are presented.
SM21A-0461 0800h
The Effect of Heavy Ions and Mass Density on Magnetic Reconnection
Reconnection plays an integral role in magnetospheric dynamics, but currently there is no clear understanding of when and how heavy ions will impact the reconnection process. Understanding the effect of heavy ions is important because the mass density of O+ in the magnetotail often exceeds that of the protons. Using theoretical arguments and three-fluid simulations, we examine reconnection in a three-species plasma. Besides the usual two length scales present in two-species reconnection, there are two additional larger length scales in the system: one associated with a "heavy whistler'' which produces a large scale quadrupolar out-of-plane magnetic field, and one associated with the "heavy Alfven" wave which can slow the outflow speed and thus the reconnection rate. The consequences for magnetotail reconnection and satellite signatures will be discussed.
SM21A-0462 0800h
On the role of O+ on Magnetic Reconnection in the Earth's Magnetotail: a comparison between CLUSTER observations and simulation results
The CLUSTER mission has provided a considerable number of in-situ observations of the formation of an X-line in the mid-tail region of the Earth's magnetotail. From these observations it has become evident that there are time periods where heavy ion density (mainly O+ of ionospheric origin) exceeds that of the protons. How does the higher mass density of O+ affect the reconnection process in the Earth's magnetotail? In this study we use observations from the CLUSTER/CIS ion composition instrument and we compare those with results from three-fluid simulations in order to identify the observational signatures of the role of O+ in the reconnection process.
SM21A-0463 0800h
Effects of heavy ions on ULF waves in the magnetosphere
We present a simulation study of the propagation of ULF waves in the magnetosphere when multi-ions such as helium and oxygen ions are present. Since the inclusion of multi-ions facilitates the propagation of waves for the band of frequency below each ion gyro-frequency, a multi-fluid treatment is required. We adopt a three-dimensional multi-fluid model, which can fully include the effects of multi-ions and electron. In a box model of an inhomogeneous plasma, we examine the resonant absorption through mode conversion when the MHD approximations break down. The wave spectra and energy relations are presented for ion cyclotron waves of helium and oxygen ions. In addition, the role of plasma composition in the wave coupling problem is investigated in detail. We discuss and compare our results with the previous theoretical and numerical studies.