Magnetic helicity analysis of an interplanetary flux tube

DASSO, S.; MANDRINI, C.H.; DÉMOULIN, P.; FARRUGIA, C.J.

JOURNAL OF GEOPHYSICAL RESEARCH

American Geophysical Union

Año: 2003 vol. 108 p. 1362 - 1368

0148-0227

We compute the magnetic flux and helicity of an interplanetary flux tube observedby the spacecraft Wind on 24–25 October 1995. We investigate how model-dependent arethe results by determining the flux-tube orientation using two different methods (minimumvariance and a simultaneous fit), and three different models: a linear force-free field, auniformly twisted field, and a nonforce-free field with constant current. We have fittedthe set of free parameters for the six cases and have found that the two force-freemodels fit the data with very similar quality for both methods. Then, both the comparablecomputed parameters and global quantities, magnetic flux and helicity per unit length,agree to within 10% for the two force-free models. These results imply that the magneticflux and helicity of the tube are well-determined quantities, nearly independent of themodel used, provided that the fit to the data is good enough.