Global quantities in expanding magnetic clouds

NAKWACKI, M.S.; DASSO, S.; MANDRINI, C.H.; DÉMOULIN, P.,

Pucón

Congreso; 11th Latin-American Regional Meeting, IAU Meeting, (LARIM-2005); 2005

IAU

We use magnetic (Magnetic Field Instrument, MFI) and plasma(Solar Wind Experiment, SWE) data.We analyze here two cylindrical models: (1) a staticmodel that considers the cloud magnetic structure as alinear force free field (i.e., the Lundquist's solution),and (2) a radial expanding selfsimilar model (Farrugia et al.,JGR 98, 7621, 1993). In both cases, we derive expressionsfor magnetic fluxes, helicity, and energy.We apply the minimun variance method to find the cloud orientation and compute the cloud radius for the staticmodel ($R_s$).For the dynamic model, we fit the initialradius for the expandingmodel ($R_0$) and the age of the cloud ($T_0$) fromthe observed velocity profile. We also fit the free parameters of each magnetic modelusing the magnetic observations, and find thatthe dynamical modelbetter represents the data, since it fits theassymetry caused by the expansion in the cloud. Finally, for both models, we quantify the magnetic fluxes,helicity and energy, as done in Nakwacki et al.(Proc. Solar Wind 11 - SOHO 16, ESA SP-592, 629, 2005).We find a change in the computed helicity and fluxes ofless than $30\%$ (comparing static and dynamic models).%From the fitted parameters of the dynamic model, andConsidering the range of time in which Wind observesthe cloud, and the dynamic model, we find a magneticenergy decay of less than $\approx 12\%$ and a radialexpansion of $17\%$.