Speaker
Description
The inference of the photospheric magnetic field has, until recently, been limited to one view point: that from Earth. This is especially important when studying the long term evolution of active regions, where they are only close to disc centre for approximately a week. The Polarimetric and Helioseismic Imager (PHI) on board Solar Orbiter (SO) has made it a reality to extend the coverage of an active region in combination with Earth-bound assets, such as SDO/HMI. Due to the highly elliptical orbit, on 6 month intervals, SO/PHI observes the photospheric magnetic field over a wide range of viewpoints away from the Sun-Earth line.
In particular the High Resolution Telescope of PHI (SO/PHI-HRT) has observed active regions mostly when Solar Orbiter is near perihelia and separated from Earth by angles of 40-80+ degrees. This provides the possibility to significantly extend studies of flares and coronal mass ejections that monitor the formation, evolution, and destabilization of coronal structures. Cross-calibrations during Sun-Earth alignment show that SO/PHI-HRT and SDO/HMI are consistent with one another, enabling these types of extended studies.
From spring 2025, SO started to rise significantly above the ecliptic, providing full spectropolarimetric observations of the solar poles for the first time. Such information, of great relevance for solar dynamo studies as well as for coronal heating and solar wind models, will also be crucial for the quantitative constraint of the magnetic field in heliospheric models. Similarly, synoptic maps are widely used as boundary conditions to global models of the magnetic coronal field for space weather applications. The data from these new polar observations can be used for pole-filling in combined SO/PHI and SDO/HMI synoptic maps. Finally, SO/PHI is also the forerunner of the Photospheric Magnetic-field Imager (PMI) onboard the forthcoming L5 mission Vigil, which will provide some of the above applications as routine data products.
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