Tomography of solar photospheric magnetic fields using Solar Orbiter
IAA-CSIC offers a four years PhD contract in the framework of the Project “Severo Ochoa”. Candidates are expected to carry out their activity in the research line of solar physics. Supervisor: J.C. Del Toro Iniesta (firstname.lastname@example.org).
Solar photospheric magnetic fields are currently being monitored from the Earth point of view using ground-based and space-borne observatories. The Polarimetric and Helioseismic Imager (PHI), a vector magnetograph on board the Solar Orbiter (SO) ESA mission whose launch is scheduled for February 2020, will be the first-ever instrument to provide measurements of solar magnetic fields at different angular spacings from Earth. SO/PHI, therefore, opens up a window of opportunity for unique science. With its two telescopes, a Full Disk Telescope (FDT) and a High Resolution Telescope (HRT), PHI will achieve 2 and 0.3 arcseconds spatial resolution at perihelion (0.3 AU) while providing high sensitivity, full spectropolarimetric measurements. Such vantage points will allow to perform stereoscopic measurements of solar magnetic fields. Stereoscopy is nothing but the three dimensional reconstruction of -in our particular case- magnetic fields, by combining SO/PHI measurements with those from other instruments on or orbiting Earth. The main goal of the study is to investigate the nature of magnetoconvection in the Sun by analyzing the three-dimensional temporal evolution of magnetic fields in different solar scenarios (quiet Sun, active regions and, for the very first time, the solar poles).
The investigations will mainly concentrate in the emergence and disappearance of flux structures on the solar surface. Data from the Helioseismic and Magnetic Imager (HMI) of the NASA’s Solar Dynamics Observatory and the Spectropolarimeter (SP) onboard the JAXA’s Hinode satellite will be mainly used for stereoscopy since these two instruments reach comparable resolutions to the FDT (HMI; 0.5 arcseconds) and HRT telescopes (SP; 0.16 arseconds). The work will tackle new problems for efficiently combining data from different instrumental point of views such as projection effects, slightly different spectral and spatial resolutions, different sensitivities to magnetic fields, the so-called 180 degree ambiguity of the Zeeman effect, or the influence of different line-of-sight flows. The use of facilities on the ground such as the German GREGOR telescope or DKIST will also be encouraged although it adds severe complications in the data analysis such as the influence of the atmospheric seeing in stereoscopy. Getting ready for this new challenge is of paramount importance for both improving our current knowledge of solar magnetism and for successfully exploiting the capabilities of SO/PHI, an instrument for which the IAA has a high degree of responsibility because it is the co-PI institution. The geometrical problem will be studied and the algorithms for the correct interpretation of the results will be developed during the thesis. Very specifically, the disambiguation of the 180º degree azimuth ambiguity will be addressed with the help of the results from the different lines of sight. Data from SO/PHI will be available soon after launch that are suitable for the analysis although still far from the scientific orbits (Year 2022).