Title:

Magnetoatmospheric Effects in Helioseismology

Proposer:

Margarita Ryutova

Lawrence Livermore National Laboratory
Institute of Geophysics and Planetary Physics, L-413
Livermore, CA 94550

Potential collaborators:

Alan Title, Ted Tarbell, Tom Berger, Dick Shine, Neal Hurlburt (Lockheed), Tom Duvall and Todd Hoeksema (Stanford).

SOI Coordinator: Ted Tarbell

Abstract

Strong inhomogeneity of solar atmosphere with respect to distribution of magnetic flux makes magnetic effects the efficient means for understanding the basic plasma processes in Sun and for development of the adequate diagnostic appliance. To analyze the observational data and provide the appropriate diagnostic procedure for photospheric and chromospheric manifestation of solar oscillations it is necessary to take into account these inhomogeneities. The objective of this research is to address this problem and to study the interaction of the random ensembles of magnetic flux tubes with the convective and wave motions, which includes as an important part, the investigation of the collective phenomena in the propagation of the acoustic waves through quiet regions, sunspots and plages. We intend to analyze and compare the observed differences in the p-mode propagation through these differently magnetized regions. Such complementary studies will allow us to develop the reliable basis for "magnetoacoustic" spectroscopy, on one hand, and, on the other hand, to understand the coupling of photospheric dynamics with the processes in chromosphere and predict their possible observed signatures.

Investigation Plan:

The proposed investigation plan consists of three main directions:
(1) the dynamics of the emerging magnetic flux;
(2) the collective phenomena in the ensembles of magnetic flux tubes - magnetic effects in the dynamics of quiet regions, sunspots and plages, the special attention will be placed on the analysis and comparison of theoretical and the observed differences in the p-mode propagation through these differently magnetized regions;
(3) the magnetic and mechanical coupling of photospheric dynamics with the processes in chromosphere and transition region.

Based on the observational data, in all three directions of the proposed investigation the analytical theory will be used to establish the model dependence on parameters and for its predictive abilities.

(1) We intend to develop the dynamic model of a magnetic flux emerging from the convective zone and interacting with the convective and wave motions;

The emerged magnetic flux interacting with the convective motions and acoustic waves shows some specific macroscopic features that can be observed. Depending on the physical parameters of the medium (convective flows, lifetime of granules, radius of emerging flux, latitude, etc), a single magnetic flux tube may be either split into thinner flux tubes or dissolved diffusively into the ambient plasma. If in the splitting regime the same conditions are fulfilled for the newborn flux tubes, each of a newborn flux tube experiences further spitting. This process of filamentation of magnetic structure proceeds until fragmented magnetic tubes meet conditions corresponding to diffusive dissolution. The lifetime of flux tubes which is determined by these processes is expressed through parameters among which one is a free parameter (say, the coefficient of turbulent viscosity) and others can be inferred from observational data. The fragmentation process is accompanied by the generation of mass flows and current drive: the complex topology of generated currents and the distortion of magnetic field may meet the conditions of the local reconnection. This process may be identified as observed bright points.

(2) The overall dynamics of solar atmosphere, the mechanisms of the energy transfer and its release in the upper layers are, however, governed by the collective phenomena in the ensembles of magnetic flux tubes randomly distributed in space and over their physical parameters. In particular, the response of differently magnetized regions of solar atmosphere to the propagation of the acoustic waves is completely different. The farther evolution of a system, the redistribution of the absorbed or scattered acoustic power strongly depends on the magnetic filling factor of a large areas and the actual distribution and topology of magnetic fluxes, as well as on the variation of the background physical parameters ( the density, the temperature, mass flow velocities, etc.). Obviously, the observed signatures of the collective phenomena in the ensembles of widely spaced flux tubes (quiet regions) and closely packed domains (active regions) are also significantly different. The goal here is to address these problems, to analyze and compare the observed and theoretical differences in the dynamics of quiet regions, sunspots and plages, to develop an adequate diagnostic procedure and prophecy algorithm.

For example, in the ensembles of widely spaced flux tubes (quiet regions and enhanced network) the energy of the acoustic oscillations is resonantly absorbed and accumulated in a system of random flux tubes remaining for a long time in a form of flux tube oscillations which, obviously, have a random phases. Oscillating flux tubes then radiate accumulated energy as secondary acoustic waves in the upper layers of atmosphere. In the near-plage regions and magnetically enhanced network this process results in the spreading of the energy input region and specific frequency shift of the emitted waves. These effects may identified as the observed acoustic halos. The localization of an efficient energy input, and, respectively, the secondary emission of acoustic waves and their intensity depend on the distribution of magnetic structures. The results (the frequency shift, specific properties and location of acoustic halos, and others) are represented mainly in terms of the observed parameters. Free parameters in theory can be tested from alternative data.

In sunspot and plage regions which we model as a dense conglomerate of a random flux tubes and magnetic domains we address the problem of an acoustic power deficit, and as a next step, we will answer the question where the energy of the acoustic oscillations and suppressed convection goes, what are the atmospheric manifestation of this energy supply, how the mass flows in penumbra and superpenumbra affect the observed properties of active region dynamics.

(3) Collective phenomena in the ensembles of magnetic fluxes include also the coupling processes between the lower and upper layers of atmosphere. We intend to investigate the magnetic and mechanical coupling of photospheric dynamics with the processes in chromosphere and transition region. The emphasis will be placed on the difference between the quiet and active region characteristics: it is precisely this difference which makes the magnetic effects the most efficient diagnostic means.

Data Requested:

The images of photospheric magnetic and velocity fields; time series of these images in quite regions and enhanced magnetic network; flows and magnetic fields at different heights; intensity fluctuations in photosphere, temperature minimum and low chromosphere in different active regins, in regions of isolated sunspots and pore, as well as in quite regions, latitude dependence is also important.

Data on the magnetic elements and bright points seen in intergranular lanes - their size, lifetimes, actual motions, their number (as a conglomerate along the granule, histograms of numbers), surface velocities, electric currents, all possible signatures of exploding granules; latitude dependence of these parameters.

References related to proposed research:

LaBonte, B. and Ryutova, R. 1993, ApJ, 419, 388: "A Possible Mechanism for Enhanced Absorption of p-modes in Sunspot and Plage Regions."
Ryutov, D.D. and Ryutova, M.P. 1976, JETP, Sov. Phys. 43, 491: "Sound Oscillations in a Plasma with "Magnetic Filaments."
Ryutova, M. and Persson, M. 1984, Physica Scripta, 29, 353: "Dispersion Properties and Enhanced Dissipation of MHD-Oscillations in a Plasma with Random Inhomogeneities".
Ryutov D.D. and Ryutova M.P. 1989, Sov.Phys. JETP, 69, 965: "Magnetic Field Generation by Sound Waves in the Solar Atmosphere".
Ryutova M.P., 1988, Sov. Phys. JETP, 67, 1594: "Negative-Energy Waves in a Plasma with Structured Magnetic Field."
Ryutova, M., Kaisig, M. and Tajima, T. 1991, ApJ, 380, 268: "Propagation of Magnetoacoustic Waves in the Solar Atmosphere with Random Inhomogeneities of Density and Magnetic Fields."
Ryutova, M.P. and Priest, E.R. 1993 a , ApJ , 419, 349: "The Propagation of Sound Waves in Randomly Magnetized Solar Atmosphere. I. General Consideration."
Ryutova, M.P. and Priest, E.R. 1993 b , ApJ , 419, 371: "The Propagation of Sound Waves in II. The Interaction of Unsteady Wave-packets with the Ensembles of Magnetic Flux Tubes. Randomly Magnetized Solar Atmosphere."
Ryutova, M.P. and Priest, E.R. 1993 c, 1993, in The Magnetic and Velocity Fields of Solar Active Regions, ASP Conf. Series, Vol. 46, 554: "Unsteady Wave-Packets in the Random Ensembles of Magnetic Flux Tubes: Acoustic Halos."
Ryutova, M.P., 1993, in The Magnetic and Velocity Fields of Solar Active Regions, ASP Conf. Series, Vol. 46, 549: "Generation of Plasma Flows and Filamentation of Magnetic Fields in the Solar Atmosphere."
Ryutova, M., Kaisig, M. and Tajima, T. 1995, submitted to ApJ: "The Evolution of Magnetic Structures due to "Magnetosonic Streaming."
Ryutova, M. and Habbal, S., 1995, to be appeared in ApJ, Vol. 451: "The Effects of Mass Flows on the Dissipation of Alfven Waves in Upper Layers of Atmosphere."