SOI Investigation Proposal Title: Are Photospheric Magnetic and Kinetic Helicity Related? Lead Investigator: Louis H Strous, New Jersey Institute of Technology, University Heights, Newark, NJ 07102 Other Team Members: Richard C Canfield & Alexei A Pevtsov, Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 SOI Coordinator: ? SSSC Programmer: ? Abstract: For one or more active regions, we plan to compare magnetic helicity maps derived from vector magnetograms made at ground-based observatories with kinetic helicity maps derived from three-dimensional velocity measurements based on high-resolution MDI Dopplergrams to determine if the distribution of the vertical component of magnetic helicity density is in any observable way related to the distribution of the vertical component of the kinetic helicity density (i.e. flows) in the photosphere. The vertical velocities are derived directly from the Dopplergrams, and the horizontal velocities at the same photospheric heights are derived from the same Dopplergrams by correlation and/or feature tracking on the granulation visible in the Dopplergrams. The Dopplergrams need to be recorded at a sampling rate that sufficiently covers the granular lifetime if granulation is to be used to derive horizontal velocities. Investigation Plan: Helicity is a fundamental attribute of magnetic fields in laboratory and astrophysical plasmas. In the Sun, magnetic helicity is observed on scales ranging from the smallest to the largest observable scales. Previous work [ref 1] has shown that the magnetic helicity density within active regions is structured on scales from 5 arcseconds to several arcminutes, with substantial stability (at least 27 hours timescale). In [ref 5] we argue that this structure is determined in part in a shear layer at the base of the convection zone and in part by turbulence within the convection zone itself, but there is no evidence that photospheric motions are involved. Hence, the goal of this proposal is to determine whether patterns of the vertical component of the magnetic helicity density are related in any observable way to the patterns of vertical component of the kinetic helicity density in the photosphere. The approach is observational and has two aspects: (1) magnetic helicity observations, based on vector magnetograms made at Sacramento Peak Observatory (the Advanced Stokes Polarimeter) and Mees Observatory, through which the pattern of photospheric magnetic helicity density will be determined; (2) photospheric 3D flow observations, based on high-resolution MDI Dopplergrams from which horizontal flows are determined by feature or correlation tracking on granulation visible in Dopplergrams. The pattern of photospheric kinetic helicity will be determined from the 3D velocity patterns. The magnetic helicity measurements require spectrograph-based Stokes polarimeter observations; typical filter-based vector magnetographs cannot correct for well-known under-resolution and magneto-optical effects that distort helicity density determinations. Data reduction techniques for the spectroscopic polarimetric observations and local helicity density calculations [ref 1] have already been developed. The comparison can only be made within active regions, since the magnetic helicity density can be determined only when the measured flux is above a few hundred Gauss. In the quiet sun, the magnetic helicity signal is lost in noise, at the spatial resolution routinely obtained on the ground. High-resolution MDI Dopplergrams recorded at an interval significantly shorter than the granular lifetime yield both vertical flows and, at the same height levels in the photosphere, horizontal flows (through feature or correlation tracking of the granules visible in Dopplergrams). High-resolution continuum observations would yield only horizontal flows. Correlation tracking and feature tracking techniques [ref 6, Chapter 8; ref 7] for determining the motion of granules and magnetic footpoints from the observations are available. Horizontal velocities can be determined with correlation techniques only somewhat beyond the length scale of a granule. At such length scales, typical horizontal (in the solar reference frame) velocities far exceed typical vertical velocities (about 60 vs. 6 m/s at a scale of 8 Mm), so special care must be taken in the disentanglement of both solar-frame velocity components from the MDI-frame (line-of-sight/plane-of-sight) velocity measurements, and high accuracy is required of the Dopplergrams both per pixel and across the field of view. The more accurate the Dopplergram values are, the further away from disk center can a meaningful disentanglement of velocity components be made. Scheduling This project requires cotemporal magnetic helicity and photospheric dynamics observations lasting a few hours, for a period of several successive days. An active region must be present within a day or two of the central meridian. Of course, the schedule also needs to be adapted to SOHO mission operations constraints, with which we are not sufficiently familiar at this time. The magnetic helicity observations will be based on vector magnetograms obtained at Mees Solar Observatory and (more significantly) the Advanced Stokes Polarimeter at NSO/SP. The former are gathered on a daily basis, and therefore require no scheduling. We have proposed to do so on a bumping basis, for which observations can be made within one to two days after a "go" decision is made. A proposal for ASP observing time has been submitted for two weeks per quarter for the next year, starting in the fourth quarter of 1995. No time is required for development of analysis tools. The analysis of a week's data from Mees is only a few days' work; the analysis of a week's data from NSO is a few weeks' work. The MDI dynamics observations and the ground-based ASP/MSO observations need to be coordinated to overlap in both time period and field of view. No time is needed for development of analysis tools. The analysis of a week's calibrated MDI data should take a few weeks or less, depending on the state in which it is made available to us. References: 1. Pevtsov, A.A., Canfield, R.C., & Metcalf, T.R. 1994, ``Patterns of Helicity in Solar Active Regions'' ApJ, 425, L117. 2. Pevtsov, A.A., Canfield, R.C., & Metcalf, T.R. 1995, ``Latitudinal Variation of Helicity of Photospheric Fields'' ApJ, 440, L109. 3. Canfield, R.C., Pevtsov, A.A., Acton, L.W. 1995, ``Helicity of Active Regions in the Photosphere and Corona'' Eos Trans. AGU, 76(17), Spring Meet. Suppl., S235. 4. Pevtsov, A.A., Canfield, R.C., & Metcalf, T.R. 1995, ``Helicity of Photospheric Magnetic Fields'' Eos Trans. AGU, 76(17), Spring Meet. Suppl., S228. 5. Pevtsov, A.A., Canfield, R.C., & Glatzmaier, G.A 1995, ``Signatures of Convection in Solar Magnetic Helicity'' in Geophysical and Astrophysical Convection Workshop, October 10-13, National Center for Atmospheric Research, Boulder. 6. Strous, L.H. 1994, ``Dynamics in Solar Active Regions: Patterns in Magnetic-Flux Emergence'' Ph.D. thesis, Utrecht University 7, Strous, L.H., Scharmer, G., Tarbell, T.D., Title, A.M., Zwaan, C. 1995 ``Phenomena in an emerging active region. I. Horizontal dynamics'' A&A (accepted)