Multispacecraft observation of magnetic cloud erosion by magnetic reconnection during propagation

A. Ruffenach (1) , B. Lavraud (1) , M. J. Owens (2) , J.-A. Sauvaud (1) , N. P. Savani (3) , A. P. Rouillard (1) , P. Démoulin (4) , C. Foullon (5) , A. Opitz (1) , A. Fedorov (1) , C. J. Jacquey (1) , Vincent Génot (1) , P. Louarn (1) , J. G. Luhmann (6) , C. T. Russell (7) , C. J. Farrugia (8) , A. B. Galvin (8)

1 IRAP - Institut de recherche en astrophysique et planétologie
2 UOR - University of Reading
3 UCAR - University Corporation for Atmospheric Research
4 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
5 CFSA - Centre for Fusion, Space and Astrophysics
6 SSL - Space Sciences Laboratory [Berkeley]
7 IGPP - Institute of Geophysics and Planetary Physics [Los Angeles]
8 SSC - UNH Space Science Center [Durham]

During propagation, Magnetic Clouds (MC) interact with their environment and, in particular, may reconnect with the solar wind around it, eroding away part of its initial magnetic flux. Here we quantitatively analyze such an interaction using combined, multipoint observations of the same MC flux rope by STEREO A, B, ACE, WIND and THEMIS on November 19-20, 2007. Observation of azimuthal magnetic flux imbalance inside a MC flux rope has been argued to stem from erosion due to magnetic reconnection at its front boundary. The present study adds to such analysis a large set of signatures expected from this erosion process. (1) Comparison of azimuthal flux imbalance for the same MC at widely separated points precludes the crossing of the MC leg as a source of bias in flux imbalance estimates. (2) The use of different methods, associated errors and parametric analyses show that only an unexpectedly large error in MC axis orientation could explain the azimuthal flux imbalance. (3) Reconnection signatures are observed at the MC front at all spacecraft, consistent with an ongoing erosion process. (4) Signatures in suprathermal electrons suggest that the trailing part of the MC has a different large-scale magnetic topology, as expected. The azimuthal magnetic flux erosion estimated at ACE and STEREO A corresponds respectively to 44% and 49% of the inferred initial azimuthal magnetic flux before MC erosion upon propagation. The corresponding average reconnection rate during transit is estimated to be in the range 0.12-0.22 mV/m, suggesting most of the erosion occurs in the inner parts of the heliosphere. Future studies ought to quantify the influence of such an erosion process on geo-effectiveness.

Mots clés: Interplanetary Physics: Coronal mass ejections (4305; 7513); Interplanetary Physics: Ejecta; driver gases; and magnetic clouds; Interplanetary Physics: Solar wind plasma; Interplanetary Physics: Solar wind sources; Solar Physics; Astrophysics; and Astronomy: Magnetic reconnection (2723; 7835)

Domaines: Planétologie et astrophysique de la terre [astro-ph.EP]; Planétologie et astrophysique de la terre [astro-ph.EP]

A. Ruffenach, B. Lavraud, M. J. Owens, J.-A. Sauvaud, N. P. Savani, et al.. Multispacecraft observation of magnetic cloud erosion by magnetic reconnection during propagation. Journal of Geophysical Research, 2012, 117, pp.09101. ⟨10.1029/2012JA017624⟩. ⟨hal-00736700⟩