Relation between the coronal magnetic helicity to the helicity in interplanetary magnetic clouds

LUONI, M.L.; MANDRINI, C.H.; DÉMOULIN, P.; VAN DRIEL-GESZTELYI, L.; LÓPEZ FUENTES, M.C.

Buenos Aires

Congreso; 45 Reunión Anual de la Asociación Argentina de Astronomía; 2002

Asociación Argentina de Astronomía

On October 18, 1995, the Solar Wind Experiment and the Magnetic Field Instrument on board the WIND spacecraft registered a magnetic cloud at 1 AU, which was followed by a strong geomagnetic storm. The solar source of this phenomenon was located in active region (AR) NOAA 7912. On October 14, 1995, a C1.6 long duration event (LDE) started at approximately 5:00 UT and lasted for around 15 hours. In this work, we compute the variation of the coronal magnetic helicity using a linear force-free model of the field. We use magnetograms obtained at Kitt Peak National Solar Observatory as boundary conditions to extrapolate the photospheric magnetic field to the corona. The magnetic helicity is calculated at three different times, changing the parameters of the magnetic field model to fit the loops observed in soft X-rays by the Soft X-ray Telescope on board of Yohkoh (SXT/Yohkoh). The computations are done before the LDE, during its maximun and its decay phase. The variation of the coronal magnetic helicity is compared to the helicity of the interplanetary magnetic cloud observed by WIND. These values turn out to be quite similar, considering the errors involved. Our results confirm quantitatively the link between solar and interplanetary phenomena.