• magnetic structure
• magnetopause
• multi-fluid model
• non-stationarity
• numerical simulation
• plasma mixing

New methods are presented which are able to obtain a "realistic" multi-fluid analysis of the Earth’s magnetopause. The goal is reached in three steps. The analysis of spacecraft data acquired across the magnetopause is done by means of new techniques which relax most of the hypotheses usually assumed about the observed plasmas. These techniques help in disentangling the principal causes of misunderstanding in data interpretations by discerning whether the observed variations are due to the magnetopause motion in the spacecraft frame or due to the purely temporal variations of the magnetopause structure. Optimization techniques help in determining automatically the parameters the methods are dependent by. The spatial profiles feed a new 3fluid analytical model (two ion and one electron populations) able to confine the magnetospheric and magnetosheath plasmas in their own regions and letting them to partially overlap close to the contact boundary. This model determines the two ions contributions to the total ion population ratio in case it is not provided by the distribution functions. A 3fluid equilibrium is then perturbed and evolved in time by means of a new 3fluid numerical code, coded to take the 3fluid model outputs as inputs. The numerical model of the magnetopause develops a magnetic reconnection instability, in agreement to what is observed close to the analyzed magnetopause crossing and leads to conclusions about the spatial distribution of the mixing processes.