The sun, the earth, and the space weather

Determining when GPS gives false positioning due to Space Weather consequences has been one of the aims in a study done by Team Nina 2002 during the Alpbach Summer School. For that, TEC maps (Total Electron Contents of the Earth atmosphere at a certain position) must be derived because the precision is invert proportional to the number of particles along the line of sight for satellites. These maps are sensible to the fluctuations day/night but also particles injections coming from the solar corona via Coronal Mass Ejections (CMEs) or Coronal Holes (CHs). Also a 3D prevision of which structures could erupt toward the magnetosphere are needed for these aspects of Space Weather. We first present the SOHO mission and its European data base MEDOC at IAS. SOHO has 12 instruments including a EUV imageur EIT and 3 coronagraphs LASCO. Densities and temperatures can be measured by SOHO/EIT wavelength ratios and the spectroscopic CHIANTI code. SOHO/EIT has observed CMEs evolution in projection. If the GMEs are coming toward the Earth, magnetosphere perturbations can be observed. The understanding and the forecasting need 3D observations and interpretations of such structures. As the solar corona is optically thin, thus the intensity is deduced from the emission measure integrated along the line of sight. This integration creates uncertainties when we want to determine precisely structures morphology and geometrical parameters. Portier-Fozzani [4, 5] has shown that the classical stereo methods do not work directly. Tomography methods would be the most appropriate for optical thin material, but because of the low number of different view angles, these methods cannot be applied easily. Meanwhile, by introducing constraints to stereographics methods such as the geometrical shape of the object (example: loops = circle, plumes = conics....), it is possible to derive some geometrical parameters. Afterward, the physical coherence of this model purely observational is checked. Thus in Aschwanden et al. (APJ. 515-842 (1999)), we could measure from a more sophisticated method the geometrical parameters of loops. Rom the EIT image ratio, physical parameters of potential loops are determined. Considering the possibilities of small deformations, Portier-Fozzani, Demoulin et al. (Sp. Sci. Rev. 97, 51-54 (2001)) took into account that the loops could be twisted. They measured that in an emerging active region, loops appear first twisted and detwist as they expand. This result, if we assume that magnetic helicity has to be conserved [44], gives important stability criteria in function of the size and the twist degrees for coronal loops. Then we describe the future observations that the STEREO/SECCHI Mission will made. It is two satellites separating themselves from 22.5 degrees per year. That will improve stereovision reconstruction that is actually limited to the high temporal dynamic of structures as CMEs involved in Space Weather.