SM52A-01 11:15h
Relativistic electron flux enhancement during SEP event observed on October 28, 2003
Abrupt enhancement of Rrelativistic electron (E>2MeV) flux abrupt enhancement was observed by geosynchronous and polar orbit satellites at$\sim$11:50 UT on Oct. 28, 2003 after an intense X17 solar x-ray burst on at 11:10 UTOct. 28, 2003. The relativistic electron enhancement of relativistic electron occurred before the magnetic storm starting at 6:00 UT on the next day and was directly correlated with the Solar Energetic Particles (SEP) events in the upstream solar wind. Observations at theby SAMPEX (E>1MeV) and NOAA/POES (E>0.3MeV) polar satellites show that the abrupt electron enhancements extend across all high L-values (L>6) at the same timewith no notable time difference. The increase of electron flux will lasted for more than one several day,s and with its peak was being clearly associated in conjunction with the arrival of an interplanetary shock arriving at the Eearth and the onset of the storm main phase. Obviously, this these relativistic electrons were not accelerated by the varying electric fields in geospace associated with development of the stormgeneration couldn't be explained by the other two mechanism have been proposed before for the variations of these relativistic electrons related to magnetic storm. It has been known that relativistic electrons can be generated in SEP events. The measurement Measurements of energetic electron from ACE/EPAM and SOHO/COSTEP experiments showindicateds that the enhancement of energetic electron with energy being a few hundreds keV in the solar wind is was synchronous seen simultaneously with the increase of relativistic electron flux increase at high L-values in the Earth. Therefore us, Thesethe observations presented in this paper results strongly suggest that the MeV electrons in the solar wind may bprovidee an additional the source forof the relativistic electron in the magnetosphere. It is perhaps a new mechanism for the relativistic electron events.
SM52A-02 11:30h
Plasmoid in the High Latitude Boundary /Cusp Region Observed by Cluster II
Plasmoid-like structure without a core field has been observed in the high latitude region when Cluster was travelling outbound on April 21, 2001. Bursty electrons and ions are well confined in this plasmoid-like structure and associated with a rotational local Bz component (Bi-polar signature) when IMF has a northward Bz and a dominate positive By component. The structure is associated with a dramatic change of plasma flow from tailward to dawnward. The thermal plasma velocity in the structure (Vx -20, Vz 50, Vy -120 km/s) is significantly different from the ambient, it is flowing dawnward away. Electrons are found to be confined in a smaller spatial extent than ions. These observations suggested the observed plasmoid is formed by multi X lines reconnection in dusk (or dawn) side of the cusp region when IMF has northward Bz and a dominate positive (or negative) By component.
SM52A-03 11:45h
Magnetic reconnection in space plasmas, collisionless and multi-scales
Magnetic reconnection in space plasmas is investigated, particularly its collisionless and multi-scale features. In the ion inertial region, the reconnection rate scaling is discussed and structures of Hall MHD and Alfven-whistler waves are demonstrated. In the electron dynamic region, a fast mode in an electron Alfvenic regime is found.
SM52A-04 12:00h
High-latitude Magnetopause Boundary Observed by Cluster II on 26 January, 2001
On January 26, 2001 from 10:14 to about 11:24 UT, after passing over the high-altitude cusp, the Cluster constellation was traversing the high-latitude duskside magnetopause boundary. In the first part of this time interval (10:14-11:04), the constellation met a magnetospheric region mixed with thermal plasma of solar wind origin. In close conjunction with multiple magnetopause crossing, four spacecraft saw several times of Alfvenic accelerated flows, FTE-like flux ropes, and rotational discontinuity-type structure. In the second part of the time interval, Cluster encountered with an energetic ion layer beyond and adjacent to the magnetopause. Multiple (in total 8) energetic ion flux bursts were observed quasi-periodically with repeating time period being ~ 72 second. The observed energetic ions are of magnetospheric character. Each energetic ion burst is closely related to a magnetic flux rope structure. We have performed the minimum variance analysis (MVA), deHffmann-Teller (DHT) analysis and Walen test to study this magnetopause boundary crossing event. It is found that the energetic ions were moving along the axes of flux ropes (both outside and inside the magnetopause) on the whole from the magnetosphere toward the magnetosheath. While the velocity of the thermal plasma in the HT frame of reference was basically along the magnetic field lines from the magnetosheath towards the magnetosphere. All flux ropes (both outside and inside the magnetopause) are shown to move from the same direction (southward and dawnward of Cluster) towards the spacecraft location. These observations further indicate that the high-latitude magnetopause is a source region, as well as a loss region, for the magnetospheric plasmas and that the reconnected open flux ropes provide a mechanism for the plasma entry and escape across the magnetopause.
SM52A-05 12:15h
Energetic Particles Observed in the Earth Plasmasheet by ClusterII
Based on the energetic particle measurement obtained by CLUSTER/RAPID, ion composition information in the plasmasheet has been investigated. All of the center plasmasheet crossing events, together with several storm cases, and a few energetic particle events in the year 2001 and 2002, have been sampled for the study. Dawn-dusk asymmetry has been found for almost all of the ion species, which direct to a possible current sheet acceleration scenario. By comparing ion composition during different storm phases, it is found that, in addition to the enhanced energy density of all ion species, the ratio of oxygen ions to protons shows an increase during geomagnetic active times in the near Earth plasmasheet (X=-7 to $-14R_E$). It is noteworthy that the ratio shows a decrease in the distant plasmasheet (X=$-16 R_E$). This observation result has also been confirmed by a statistical study of all the plasmasheet crossings. Observations also show that the energetic particles embedded in the earthward moving magnetic structures (such as plasmoids or magnetic bubbles) and in the earthward high-speed streams observed in the plasmasheet have an obvious low abundance of heavy ions. These structures are most likely formed in the distant region down the tail and the composition information where they formed could be preserved during the earthward moving. It is implied that much less ionosphere origin particles could reach the region of X<$-16R_E$ than the near Earth plasmasheet.