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SOOP Coordinator

Vincenzo Andretta


Simultaneous observations of the resonantly scattered component of He+ emission by EUI/FSI 30.4 nm, and neutral hydrogen by Metis Lyα (121.6 nm) to examine helium abundances in the corona / inner solar wind. These can be compared with SWA.

Full Description

Compared to its value in the solar convective envelope, the helium abundance in the in-situ measurements of the fast and slow solar wind has long been known to be depleted relative to hydrogen, with occasional transient exceptions (Bochsler 1998, SSRv 85, 291). In the slow solar wind, the degree of depletion has more recently been shown to depend upon the wind speed and the level of solar activity (Aellig et al. 2001, GeoRL 28, 2767). Measurements of the helium abundance in the corona, associated to measurements of the coronal outflow velocity, will provide evidence for the degree of correlation between wind speed and helium abundance and allow identification of the source regions of the slow wind streams with different helium abundance. During quasi-corotation the intrinsic evolution of magnetic topology will be observed and thus its influence on the wind parameters (such wind outflow velocity and helium abundance) will be directly assessed. The abundance can be derived from simultaneous observations of the resonantly scattered component of singly ionized helium by EUI/FSI in its 30.4 nm channel and of that of neutral hydrogen by Metis in Lyα (121.6 nm).

Useful contributions can be given by SPICE, mapping the near-surface elemental abundances, including that of helium (TBC), which constitutes a reference for establishing abundance variations in the wind. PHI can also contribute, providing data suitable for coronal magnetic field extrapolations.

Note: this is essentially an EUI/Metis sub-objective, but in-situ may be interested also. For instance, SWA/HIS will measure the α/p density ratio.

EUIFSI Synoptic mode (S), 20-min cadence Occultor likely to be used in conjunction with this mode


MAGTOP, 20-min cadence, duration ≥ 2 hours

WIND, 20-min cadence, duration ≥ 2 hours

Global maps of:

  • neutral hydrogen Lyα intensity
  • electron density
  • outflow velocity in corona
PHIPHI_synoptic_FDT_4: FDT, 6-hour cadenceData suitable for coronal magnetic field extrapolation
Measure solar wind speed above potential source region in co-ordination with Metis
SPICESPICE Composition Mapping

EPDNormal Mode
MAGNormal Mode
RPWDetection ModeBurst Triggers Active
SWANormal Mode

SAP objectiveTargetDurationOpportunity
(e.g., orbital requirements, solar cycle phase, quadrature ...)

Operational constraints 

Additional comments

1.1.2 Source regions of the slow solar wind Abundance of helium as a function of height and latitude in the corona as a tracer of the source regions of the slow solar wind

Inner corona within EUI/FSI and Metis FOVsfew hours per day
  • Inside 0.45–0.5 AU (optimised distance for EUI/FSI's occulter)
  • or perihelion, for quasi-corotation measurements.
Disc-centre pointingEarth view beneficial before RSW to estimate the global solar magnetic field. Is this because another view than PHI/FDT is needed, e.g., to get front- and back-side measurements?
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  1. This SOOP would also benefit from coordination with DKIST (Cryo-NIRSP instrument) when Solar orbiter is in conjunction or opposition with Earth. A DKIST Science Use Case has been filed already ( - only accessible with DKIST JIRA account). The SOOP page should be updated with this information.

    1. Added a paragraph mentioning this at the end of the description (see comment)

  2. SOOP ID in SOOP Kitchen = LF4