SM12A-01 INVITED 10:20h
Heavy Ions in the Magnetosphere: Results from CLUSTER/CIS
The CLUSTER spacecraft have now been operating for 3.5 years. The large geometric factor and fast energy sweeping of the CIS ion composition instrument on CLUSTER, combined with the multispacecraft capabilities, have allowed unprecedented measurements of heavy ions in the magnetosphere. In this talk we will review recent results on heavy ions in the magnetosphere from the CLUSTER/CIS instrument. We have found that there are time periods throughout the magnetosphere where heavy ions are a dominant species, effecting the dynamics. In addition, the heavy ions are always important as a tracer to determine the sources and transport paths of the ions. We will discuss the impact of heavy ions on substorm dynamics and reconnection in the magnetotail. Measurements in the plasmasphere have shown that the density profiles are different for the main plasma species, and that at CLUSTER altitudes, H+ and He+ are mainly trapped, while O+ is upwelling. Finally, comparisons between the in situ measurements of heavy ions from CLUSTER and remote sensing from IMAGE neutral imagers and EUV measurements have helped to understand the dynamics of the plasmasphere and ring current.
SM12A-02 10:40h
The role of Dayside O$^+$ ions in the magnetosphere during the September 24-25, 1998 Magnetic Storm
We have used a global time-dependent magnetohydrodynamic (MHD) simulation of the magnetosphere and particle tracing calculations to determine the access of dayside ionospheric O$^+$ ions to the storm-time near-Earth plasma sheet and ring current during the September 24-25, 1998 magnetic storm. The September 24 - 25, 1998 magnetic storm began with the arrival of a sudden impulse at 23:45 UT on September 24th which abruptly increased the solar wind dynamic pressure on the nose of the magnetosphere from 2 nPa to 15 nPa. Dst reached a minimum of -207 at ~1000 UT on September 25th. During this event, the TIDE instrument on board the POLAR spacecraft observed large-scale dayside ionospheric outflows in direct response to the impact of the pressure pulse on the magnetosphere. The MHD simulation was initiated with solar wind data obtained from the WIND spacecraft for this event. We traced a large number of particle orbits from the dayside ion fountain throughout the main and recovery phases of the magnetic storm. Particle launches were carried out at five minute intervals, and the ion outflow rates were normalized with empirical models as well as in-situ observations from POLAR/TIDE. This allowed us to assess the time-dependent access of ionospheric O$^+$ ions to the magnetosphere during the storm, their energization in the magnetotail current sheet, their contribution, both in mass and energy density, to the inner magnetosphere, and their subsequent loss from the magnetosphere. Doing so also allows us to calculate the time-dependent contribution of O$^+$ ions to Dst.
SM12A-03 INVITED 11:00h
Mass Density Inferred From Toroidal Wave Frequencies And its Comparison to Electron Density
The frequency of standing Alfven waves depends on the plasma mass density and this fact has been used since the late 1950s to infer the mass density from observed ULF waves. The technique is valuable in magnetospheric physics because particle experiments usually cannot determine the total ion mass density. The ULF technique was revitalized in the early 1990s when the cross phase technique was developed to provide accurate standing wave frequencies from observations on the ground. It is important to note that reliable conversion from the frequency to the density depends on a number of factors. First, the field line configuration needs to be known. Second, a functional form needs to be given for the variation of the mass density along the field line. Third, the harmonic number of the observed waves needs to be determined. Concerning these factors, spacecraft observations have several advantages: the local magnetic field can be measured (although at a single point), multiharmonic toroidal waves are routinely detected to allow modeling of the mass density distribution along the field line, and the harmonic mode can be unambiguously determined using combined electric and magnetic field observations. In this presentation we use data from the CRRES satellite to illustrate the ULF technique during a period of high geomagnetic activity. We discuss the contribution of heavy ions to the storm time ring current by comparing inferred values of the mass density from the ULF technique with values of the electron number density inferred from plasma wave data.
SM12A-04 INVITED 11:20h
Heavy Ionospheric Ion Effects on Reconnection in the Magnetotail
Heavy ionospheric ions such as $O^+$ can produce significant mass loading to the magnetotail and because of their gyro-radius can be substantially different from ionospheric or solar wind protons, the heavy ions can modify both the timing and structure of the magnetotail. Multi-fluid simulations are used to examine the changing structure of the tail under the influence of such heavy ionospheric ions. It is shown that for isolated substorms, the arrival of $O^+$ tends to be late relative to the onset of reconnection and therefore is only a minor player substorm initiation. However, if there are repeated north/south turnings of the IMF even on an hourly basis, the magnetosphere becomes loaded with heavy ions and the reconnection tail dynamics becomes substantially modified. These same IMF turning are shown to produce modifications of the plasma profile to the plasmaspheric/plasma sheet boundary.
SM12A-05 INVITED 11:40h
The Role of the Heavy Ions in the Wave Magnetospheric Phenomena
This talk will emphasize the role of the heavy ions in the number of wave-particle interaction magnetospheric processes. In particular, we will discuss some of the experimental and theoretical studies that have investigated the role of the heavy ions (mainly He+ and O+) in generation and propagation of electromagnetic ion cyclotron waves and their contribution to the heating of magnetospheric electrons and ions. The more recent studies have also shown that the heavy ions can greatly contribute to a generation of lower hybrid waves, ring current precipitation phenomena, and the overall energy redistribution in the inner magnetosphere. Using newly developed 2.5-dimentional particle-in-cell simulations, we study the energization and nonlinear coupling of different plasma waves in the presence of the heavy ions. We have shown that the high frequency wave modes critically depend on the heavy ion density and irrespective of the driven wave modes, both the light and heavy ions undergo significant transverse acceleration. But for the large heavy-ion densities, even the electrons are significantly accelerated in the parallel direction by the waves below the LH frequency.
SM12A-06 12:00h
Simulations of MHD waves in the 3-D dipole model with a realistic magnetospheric density profile
In a realistic magnetosphere, the density profile becomes asymmetric in local time. The location of the plasmapause and the density distribution significantly vary with respect to local time, and this asymmetry effect has been neglected in previous magnetospheric ULF wave studies. In this study, we numerically examine the MHD wave properties of field line resonances (FLRs) and Pi2 pulsations when the realistic 3-D density model is assumed. We use the dipole magnetic field model, but our density model is based on observational data from the IMAGE satellite. We assume an impulsive input in the magnetotail, and investigate i) how local FLRs appear in both the radial and azimuthal oscillations owing to the asymmetry and ii) how plasmaspheric Pi2 signals appear in this case. Our results show that the polarization of FLRs becomes mixed owing to the asymmetry and Pi2 pulsation are strongly affected by ambient plasmaspheric structure for different local times. We compare our results with the observational data of Pi2 events.