Tracing magnetic helicity from the solar corona to the interplanetary space

On October 14, 1995, a C1.6 long duration event (LDE) started in active region (AR) NOAA 7912 at approximately 5:00 UT and lasted for about 15 h. On October 18, 1995, the Solar Wind Experiment and the Magnetic Field Instrument (MFI) on board the Wind spacecraft registered a magnetic cloud (MC) at 1 AU, which was followed by a strong geomagnetic storm. We identify the solar source of this phenomenon as AR 7912. We use magnetograms obtained by the Imaging Vector Magnetograph at Mees Solar Observatory, as boundary conditions to the linear force-free model of the coronal field, and, we determine the model in which the field lines best fit the loops observed by the Soft X-ray Telescope on board Yohkoh. The computations are done before and after the ejection accompanying the LDE. We deduce the loss of magnetic helicity from AR 7912. We also estimate the magnetic helicity of the MC from in situ observations and force-free models. We find the same sign of magnetic helicity in the MC and in its solar source. Furthermore, the helicity values turn out to be quite similar considering the large errors that could be present. Our results are a first step towards a quantitative confirmation of the link between solar and interplanetary phenomena through the study of magnetic helicity.