About us

This project aims at developing methods to study the evolution of magnetic activity over several past solar cycles. The project originates from the exploratory work done by some team members (e.g. Pevtsov et al. 2016 and Virtanen et al. 2017). Encouraged by these early results, we have assembled a larger team of experts to pursue this ambitious project.

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First, we will create pseudo-magnetograms using the historical observations of spectroheliograms taken in Ca II K spectral line and the information about the polarity of sunspot magnetic fields. The latter will be inferred from the existing direct measurements (e.g., Mount Wilson Observatory/MWO sunspot field strength measurements, 1917-present), and using the known statistical properties of active region polarity orientation (e.g., Hale polarity rule). Our early work has already identified the most relevant questions that we will address in the framework of this project. First, we will use the magnetic field observations from the SDO/HMI and the plage observations from the SDO/AIA to investigate the distribution of magnetic field inside plages. We will determine the relationship between plages and magnetic field from modern spacecraft observations, and then apply this relationship to scale historical Ca II K data to magnetic field to create a complete set of synoptic (Carrington rotation) pseudo-magnetograms from the early 20th century (start of systematic observations in Kodaikanal in 1907) until present. In addition, we will also compare the measurements of magnetic field strength still continued at MWO with those derived by modern inversions from SDO/HMI to establish the confidence level of the historical measurements of magnetic fields, and to develop a better understanding of the spatial distribution of magnetic field in plages relative to maximum field strength measured by the HMI. Our initial tests indicate the presence of instrumental effects in SDO/AIA (mission calibrated) data. As part of this project, we will assess various approaches to provide an additional calibration to this data. Finally, the magnetic fields outside plages (quiet Sun and high latitude/polar regions) will be modelled using the flux-transport model. The meridional flow, one of the key parameters necessary for successful flux-transport modeling will be determined using the dataset of historical spectroheliograms. We will also explore the properties of the meridional flows using plage observations from the SDO/AIA, and compare these derivations with the other methods. Then the information will be applied to the historical data to derive the meridional flows and their variation over the last 100 years. Finally, we will compare polarities of the coronal magnetic field derived from pseudo magnetograms and PFSS model to satellite observations from 1965 (OMNI data) to evaluate the validity of application of pseudo-magnetograms in representing the polarity of the interplanetary magnetic field over the last 100 years. This part of the project will be based on early works by Mursula & Virtanen (2011) and Koskela et al (2017). The results of this project (pseudo-magnetic field synoptic maps, distribution and evolution of magnetic fields derived from these maps) will useful to various interdisciplinary studies (e.g., solar physics, space climate, Earth’s climate etc). This project is a collaborative effort by the team of scientists from Finland, India, Italy, Russian Federation, United Kingdom, and USA. The team’s work is coordinated by Dr. Alexei Pevtsov (NSO, USA).