NSWP: Synoptic Solar Magnetic Field Measurements at the Mt. Wilson 150-foot Tower Telescope in Support of Heliospheric Predictions and Modeling

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The solar surface magnetic field is the anchor point for the structure of the heliospheric magnetic field. This proposed effort will improve the PI's ability to predict the state of the near-earth heliospheric environment through a continuation and enhancement of the synoptic program of observations at the 150-foot solar tower on Mt. Wilson. Each clear day, the Mt. Wilson Observatory (MWO) program contributes up to twenty full disk magnetograms, and its daily measurements of the photospheric field are used operationally by the Space Environment Center of NOAA (National Oceanic and Atmospheric Administration) to predict the state of the near-earth heliosphere. The MWO provides a unique combination of good spatial resolution with a well-calibrated magnetic field zero point and a temporal coverage extending back to 1967. This proposal will enable the continuation of this project and the distribution of new data products to the community through a user-initiated, web-based retrieval process.The proposer plans to investigate the commonly used potential theory model as the method of representing the magnetic field between the Sun and solar wind, and to investigate the possibility of estimating electric currents from line-of-sight magnetograms. He plans to use a method he developed for measuring the field's transverse component, after he compared observed transverse fields with fields derived from the potential field theory and found substantial disagreements. He discovered that if a different spectral line pair near the core of the sodium D line is used to make the basic magnetic field measurement, the problems with the potential field theory are reduced. This spectral line pair is formed at the base of the chromosphere instead of in the middle of the photosphere. The PI will investigate the advantages of using this new line pair on a regular basis as an augmentation of MWO's regular data products. The combination of two or more spectral sampling pairs for the basic magnetic field measurement permits an estimation of vertical gradients in the field strength. By using his estimation of the transverse field components at different altitudes, the PI will estimate the component of the curl of the magnetic field in the north-south direction. This in turn will provide an estimate of photospheric electric currents, which have been found to be a predictor of coronal instability. The PI will investigate the locations of enhanced magnetic curl to learn about the magnetic configurations that lead to these currents.