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(All of the following objectives require simultaneous measurements from another satellite or from the ground.)

5.5.1 How strongly does the solar luminosity vary and what is the source of these variations?  Provide magnetic field and continuum brightness data in order to determine Sun’s irradiance at different heliospheric latitudes and phases of the solar cycle (Krivova et al., 2003). (Requires simultaneous observations from PHI and an instrument on the ground or another satellite.)  Comparison with Sun-like stars’ larger irradiance variations (Schatten et al., 1993; Knaack et al., 2001):

    • Is it a line of sight effect relative to their rotation axes or
    • Will the Sun also display larger variations in the future?

5.5.2 Miscellaneous Science Objectives of PHI Effect of granulation and oscillations, i.e. interaction of modes and convection (stereoscopic helioseismology). Two components of velocity. What is the relationship between the components of the velocities in granulation? Supergranulation? Various modes in quiet Sun? (stereoscopic helioseismology) Shape of the Sun. Extend oblateness study of (Emilio et al., 2007; Kuhn et al., 2012).


Other remarks:

Martínez González & Bellot Rubio, 2009 raise the question whether the emerging loops identified in the magnetograms reach the upper chromosphere or even the corona. EUI HRI Ly-alpha and 174, respectively, can contribute with joint observations to answer this question. Closest matching mode: Q. Min obs time: several hours. But cadence can probable be lowered to 60 s or more. Other instruments: PHI, SPICE.