LESIA - Observatoire de Paris

Dynamical evolution of interplanetary flux ropes

Thursday 17 September 2009, by A. M. Gulisano (Instituto de Astronomia y Fisica del Espacio, Buenos Aires, Argentina)

Tuesday 13 October 2009 à 11h00 , Lieu : Salle de conférence du bât. 17

Magnetic Clouds (MCs) are a subset of Interplanetary Coronal Mass Ejections (ICMEs) that present to an heliospheric observer distinctive characteristics: enhanced magnetic field intensity with respect to the surrounding Solar Wind (SW), low proton temperature, and a coherent rotation of the magnetic field during about one day. During their travel from the Sun, these structures evolve and interact with the SW. These structures can be geoeffective and are believed to trigger the most important geomagnetic storms.

To characterize MCs near Earth, it is useful to compute invariants such as the magnetic helicity and magnetic fluxes, which are also useful to link them with their solar source regions. In this work we present results addressing to test the robustness of these invariants under different cylindrical models for their magnetic structure.

These invariants depend strongly on the correct determination of the MC axis orientation. Thus, to improve their estimations, we perform a simultaneous fit with several models, and we also use the minimum variance technique (that does not assume any physical model).

Finally, we present an analysis of the dynamical evolution of MCs in the inner heliosphere (from 0.3 to 1 AU). We introduce and study a dimensionless expansion coefficient, zeta, from an heuristic point of view. This expansion parameter is in agreement with previous theoretical approaches. For MCs perturbed by the surrounding SW, we found different local behavior for zeta from the expected global expansion