SM11B-01 08:00h
Evolution of Plasma Density and ExB drift Near the Plasmapause Region During Disturbed Intervals
We investigate the characteristics of plasma density and ExB drifts in the plasmasphere, plasmapause, and trough regions. We concentrate on the interval of April-June 2001 and use electric field measurements from both Cluster and Polar satellites. The four Cluster satellites, separated by about 600 km and flying in a string-of-pearls formation near the perigee, cross the inner magnetosphere of L = 4-10 every 57 hours and Polar crosses L = 2--10 every 18 hours. During the interval the satellites collect measurements in the 17-23 MLT sector. In addition for every orbit, Polar monitors L = 6--9 shells in the pre-noon sector for nearly 10 hours because of a slow motion of the satellite around the apogee (located close to the equator). The selected interval contains several storms and allows us to investigate density and drift patterns in the inner magnetosphere in variable conditions; in particular we study density profiles and irregularities and how they are correlated with ExB drift observations.
SM11B-02 INVITED 08:15h
Afternoon Subauroral Proton Precipitation Resulting from Ring Current - Plasmasphere Interaction
Although the dominant loss processes for ring current ions are collisional, wave-particle interactions are also believed to play an important role as they provide a mechanism for the rapid decay of the ring current during the early recovery phase of geomagnetic storms. Considerable attention has been given to regions of spatial overlap between energetic, anisotropic ring current ions and cold, dense plasmaspheric material that should be particularly conducive to the growth of electromagnetic ion cyclotron (EMIC) waves. Resonant interaction between ring current ions and EMIC waves results in pitch angle scattering and subsequent precipitation of the energetic ions into the upper atmosphere. Global imaging of the proton aurora by the Far Ultraviolet (FUV) Spectrographic Imager (SI) on-board the IMAGE satellite has led to the identification of arcs of precipitating protons at latitudes equatorward of and separated from the main proton auroral oval in the afternoon local time sector. We investigate the occurrence of these arcs and their relationship with the plasmasphere and electromagnetic ion cyclotron waves. In a four month study interval including sixteen events, we find that the detached proton arcs are more likely to occur during geomagnetically disturbed periods and specifically at times when enhanced energetic ion densities and temperature anisotropies are observed in the equatorial magnetosphere. The disturbance-time arcs tend to be located at lower magnetic latitudes and are consistently associated with plasmaspheric plumes as observed by the IMAGE Extreme Ultraviolet (EUV) instrument. Wave data from the POLAR Magnetic Field Experiment (MFE) available for two of the detached arc events indicate the presence of strong EMIC waves near the equator in the vicinity of the proton precipitation region.
SM11B-03 INVITED 08:35h
The Coupled Response of the Inner Magnetosphere to Substorms and Magnetic Storms as Seen by IMAGE and Other Magnetospheric Spacecraft
Imaging of plasmas and energetic particles throughout the inner magnetosphere along with auroral imaging has revealed new aspects of magnetosphere-ionosphere coupling as well as coupling among different magnetospheric plasma populations. Plasmasphere plumes have been shown to map to the ionosphere where they produce unexpectedly strong space weather effects. Where the plumes intersect the ring current, they have been shown to produce ion precipitation that produces detached proton auroral arcs in the afternoon sector. A significant lag in plasmasphere corotations has been shown to result from auroral heating of the upper atmosphere and the resulting ionospheric disturbance dynamo. These and other strong coupling phenomena, most of which depended uniquely upon magnetospheric imaging for their identification, will be discussed.
SM11B-04 08:55h
Analysis of Plasmaspheric Plumes: CLUSTER and IMAGE Observations and Numerical Simulations
Plasmaspheric plumes have been routinely observed by two recent magnetospheric missions: CLUSTER and IMAGE. The CLUSTER mission provides high time resolution four-point measurements of the plasmasphere crossed at perigee. The total electron density profiles are derived from the plasma frequency (determined from the resonance sounder and wave analyzer WHISPER) and from the spacecraft potential (measured by the electric field instrument EFW). The EUV imager onboard the IMAGE spacecraft provides global images of the plasmasphere with a spatial resolution of 0.1 R$_{E}$ every 10 minutes. EUV images acquired at apogee show a lot of plasmaspheric plumes, and sequences of such 2-D images show the evolution and motion of these structures. The formation of these plumes has been predicted on the basis of a theoretical model based on the interchange instability mechanism. We present several plume events, e.g., during the April-June 2001 and April 2002 time periods. We compare CLUSTER in-situ observations with global images of the plasmasphere obtained from IMAGE, and with numerical simulations. In particular, we track the plasmaspheric plumes and compare their moving path determined by different methods: (i) bulk velocity measured by the ion spectrometer CIS, (ii) plume boundary velocity calculated from time delays of this boundary observed by WHISPER on the four spacecraft, (iii) drift velocity derived from the electron drift instrument EDI and (iv) global velocity determined from successive EUV images.
SM11B-05 09:10h
Acceleration and extreme distortion within the Van Allen radiation belts during the "Halloween" solar storms of 2003
The center of the outer Van Allen radiation belt is usually about 20000 to 25000 km away from Earth. This belt of high-energy electrons that are trapped on magnetic field lines in near-Earth space was enhanced and driven into a highly unusual configuration during the recent solar activity in late October and November - known by scientists as the "Halloween Storm" of 2003. During and following the Halloween Storm, the Van Allen belt electron population was powerfully accelerated and redistributed inward. From November 1 to November 10, the outer belt had its center only about 10000 km from Earth's equatorial surface. As shown here using IMAGE spacecraft data, the Earth's ionized outer atmosphere (plasmasphere) was displaced inward (to an unprecedented degree) in October-November 2003, and concurrently the whole radiation belt structure was transformed. The region between the Van Allen belts, normally devoid of particles, became the location of highest radiation belt particle intensities. Such a remarkable deformation of the entire magnetosphere has not previously been witnessed and implies surprisingly powerful acceleration and loss processes deep within Earth's magnetosphere.
SM11B-06 09:30h
Influence of the thermal plasma distribution on relativistic electron loss during storm conditions
Several distinct classes of plasma waves contribute to relativistic electron loss during storm conditions. Intense bursts of whistler-mode chorus resonate with relativistic electrons in the pre-noon sector at latitudes above 25 degrees leading to microburst precipitation. Such scattering can remove MeV electrons on timescales comparable to the storm duration (~ day). Night-side chorus is ineffective for MeV electron scattering due to the confinement of waves to latitudes below 15 degrees. Intense EMIC waves excited along the night-side plasmapause or within high-density drainage plumes in the post-noon sector can cause rapid loss of MeV electrons during the storm main phase. Since the effective timescale for loss to the atmosphere can be less than a day such waves are a prime candidate to explain observed flux depletions during the main phase of storms. Following the storm, as the plasmapause expands outwards to higher L, injected relativistic electrons can be slowly removed by scattering from plasmaspheric hiss on a timescale of 3-10 days. The distribution of thermal plasma controls such resonant wave-particle scattering and thus provides a natural coupling to the dynamics of the energetic electron population.
SM11B-07 09:45h
Modeling the dynamic plasmapause and plasmaspheric refilling
We have developed a new model that includes both plasmaspheric refilling and the evolution of the plasmapause. The model self-consistently solves the temporal variation of plasma distribution from the ionosphere within the dynamic plasmapause. In the saturated plasmasphere, we found good agreement between the model and previous measurements of electron densities. Furthermore, by imposing a realistic electric potential and depleted flux tubes, the model demonstrates the evolution of a sharp gradient in the plasma density distribution, such as seen at the plasmapause. The model results indicate that the equatorial density profile depends on the degree of flux tube depletion. In this presentation, a detailed analysis of the plasmapause evolution process will be discussed. We will address the impact of the dynamic plasmapause on the refilling time scale, demonstrating the dynamical plasma coupling between plasmasphere and ionosphere.