Mapping the coronal hydrogen temperature in view of the forthcoming coronagraph observations by Solar Orbiter

Context. Synergistic visible light and ultraviolet coronagraphic observations are essential to investigate the link of the Sun to the inner heliosphere through the study of the dynamic properties of the solar wind. Aims. We perform spectroscopic mapping of the outer solar corona to constitute a statistically significant database of neutral hydrogen coronal temperatures, which is suitable for overcoming the lack of spectrometric information in observations performed by coronagraphs that are solely equipped for visible light and ultraviolet imaging; these include the forthcoming Metis instrument on board Solar Orbiter. Methods. We systematically analysed neutral hydrogen Ly alpha line data that was obtained by UVCS/SOHO observations of the extended solar corona relevant to a lot of polar, mid-latitude and equatorial structures at different phases of solar activity, and collected far longer than a whole solar cycle (1996 2012). Results. We created a database consisting in both the neutral hydrogen temperature components, which are perpendicular and parallel to the radially symmetric coronal magnetic field lines, as a function of the heliocentric distance and polar angle and for different phases of the solar activity cycle. We validated the reliability of the constituted neutral hydrogen temperature database, investigating a new set of UVCS Ly alpha data with the Doppler dimming technique. The solar wind outflow velocities obtained by adopting both the neutral hydrogen temperature distribution directly derived from the observed Ly alpha profiles and those taken from our database well agree within the uncertainties.