The structure of flux transfer events recovered from Cluster data

• Published in: Annales geophysicae (1988) Vol. 24; no. 2; pp. 603 - 618
• Main Authors: HASEGAWA, H, SONNERUP, B. U. O, OWEN, C. J, KLECKER, B, PASCHMANN, G, BALOGH, A, REME, H
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau European Geophysical Society 23.03.2006; European Geosciences Union; Copernicus Publications
• Subjects: Earth Sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Ocean, Atmosphere; Physics of the high neutral atmosphere; Physics of the ionosphere; Physics of the magnetosphere; Sciences of the Universe; CLUSTER satellite; Lower bound; Magnetic flux; Multiple X line; Plasma; Magnetic reconnection; magnetic field; Plasma physics; Flux rope; boundary layer; Two dimensional structure; Magnetic rope; Magnetopause; Cross section (collision); solar wind; electrical field; magnetosphere; optimization; Space plasma physics (Magnetic reconnection); High field; two-dimensional models; Magnetospheric physics (Magnetopause, cusp and boundary layers; Solar wind-magnetosphere interactions); Flux transfer; Formation mechanism
• ISSN: 0992-7689; 1432-0576; 1432-0576
• DOI: 10.5194/angeo-24-603-2006

The structure and formation mechanism of a total of five Flux Transfer Events (FTEs), encountered on the equatorward side of the northern cusp by the Cluster spacecraft, with separation of ~5000 km, are studied by applying the Grad-Shafranov (GS) reconstruction technique to the events. The technique generates a magnetic field/plasma map of the FTE cross section, using combined magnetic field and plasma data from all four spacecraft, under the assumption that the structure is two-dimensional (2-D) and time-independent. The reconstructed FTEs consist of one or more magnetic flux ropes embedded in the magnetopause, suggesting that multiple X-line reconnection was involved in generating the observed FTEs. The dimension of the flux ropes in the direction normal to the magnetopause ranges from about 2000 km to more than 1 RE. The orientation of the flux rope axis can be determined through optimization of the GS map, the result being consistent with those from various single-spacecraft methods. Thanks to this, the unambiguous presence of a strong core field is confirmed, providing evidence for component merging. The amount of magnetic flux contained within each flux rope is calculated from the map and, by dividing it by the time interval between the preceding FTE and the one reconstructed, a lower limit of the reconnection electric field during the creation of the flux rope can be estimated; the estimated value ranges from ~0.11 to ~0.26 mV m-1, with an average of 0.19 mV m-1. This can be translated to the reconnection rate of 0.038 to 0.074, with an average of 0.056. Based on the success of the 2-D model in recovering the observed FTEs, the length of the X-lines is estimated to be at least a few RE.