Ground-Based Solar Research: An Assessment and Strategy for the Future (1998)

NOTE: The material in this appendix is reprinted from an October 1997 proposal submitted through the Solar Magnetism Initiate Committee and made available on the World Wide Web at <http://www.hao.ucar.edu/smi >.

SYNOPSIS

SOLAR MAGNETISM INITIATIVE

AN INTEGRATED RESEARCH PROGRAM

RECOMMENDATION

TO THE ATMOSPHERIC SCIENCE DIVISION OF THE NATIONAL SCIENCE FOUNDATION

SUBMITTED

OCTOBER 1997

FOR COMPLETE PROPOSAL SEE: http://www.hao.ucar.edu/smi/

The outputs of radiation and magnetized plasma from the Sun are the principal physical agents controlling the Earth's atmosphere and space environment. Because the solar magnetic field ultimately drives the variability of these outputs, a deep understanding of the properties and behavior of the solar magnetic field is required in order to reliably forecast near- and long-term variations in the solar outputs and infer their near-Earth effects. Therefore, comprehensive study of the Sun's magnetic activity cycle is critically important to NSF 's Space Weather Program and Earth System Modeling activities.

The solar physics research community, as represented by the SMI Committee, strongly recommends a broad research initiative to understand solar magnetism. This consensus emerged from two broadly based community workshops totaling five days of discussion among scientists in plenary and focused group sessions. Sixty-eight scientists representing 27 U.S. institutions participated in the process. In addition, nine scientists represented eight institutions abroad. The Attachment lists the organizations that participated in one or both NSF-supported workshops. SMI Committee members are also listed.

An integrated study of solar magnetism and variability is essential because:

• The solar dynamo involves both the convection zone and radiative interior.

• Magnetic buoyancy — under the influence of magnetic tension, gravitational draining, instabilities, and reconnection — is an important process throughout the convection zone, the photosphere, and the corona.

• A systematic organization of magnetic helicity is seen in structures ranging from emerging magnetic flux, to Hα filaments, to the corona and interplanetary space.

• The fibril nature of the magnetic field is important on both very small scales (sub-arcsecond magnetic elements) and global scales (the role of magnetic flux tubes in heating the outer atmosphere and contributing to solar irradiance variations).

The impetus for this Initiative was a series of major advances in both observational and theoretical solar and solar-terrestrial physics over the past decade: the advent of helioseismology, allowing us to “look” into the Sun's interior; the realization of high angular resolution observations of the solar outer atmosphere; the reliable measurement of solar surface vector magnetic fields; the maturity of physical modeling in coronal studies; and the increasing capabilities of large-scale direct numerical simulations, based on the new generation of large parallel computers. Researchers are now in a position to solve some of the fundamental questions of solar magnetism.

The SMI idealized sketch on the cover of this synopsis, depicting a pair of emerging magnetic flux ropes in an active region, illustrates recent observational and theoretical breakthroughs which support the present feasibility of a concerted, integrated research program to understand the Sun's magnetic variability. Precision spectropolarimetry with a SOLIS network affords the possibility of monitoring the evolution of solar surface vector magnetic fields as toroidal flux rope systems, created through dynamo action at the base of the solar convection zone, rise buoyantly through the visible solar surface. Local helioseismology, employing data from ground- and space-based oscillation experiments, may be capable of detecting submerged magnetic flux before it reaches the visible solar surface. The additional impacts of emerging flux on the solar irradiance and the structuring and dynamics of overlying tenuous solar atmosphere will be carefully monitored with the SunRISE PSPT network and the current generation of space-based instrumentation exemplified by TRACE and the proposed Solar-B instrument complex. These new comprehensive observational capabilities have been matched with the recent development of a suite of radiation magnetohydrodynamics simulations capable of treating the complicated interplay between dynamics and thermodynamics in the solar photosphere. Because these numerical codes treat the radiation, plasma, and magnetic fields on an equal footing, they are sophisticated enough to interface with all of the distinct observational data mentioned above.

Scientific understanding of solar magnetism has reached a point where a coordinated community research effort has the capability to produce fundamental answers to the problem of how the Sun's interior magnetically couples to its atmosphere and the interplanetary medium. This central conclusion emerged from two SMI workshops. Representing this consensus, the SMI Committee recommends to the National Science Foundation (NSF) that it establish a national five-year program — the “Solar Magnetism Initiative ” (SMI). An effective initiative requires a balanced strategy and coordination to improve observations, data analysis, theory and modeling through: university grants; postdoctoral fellowships; focus programs and workshops; augmentation of the national center; and instrument development, including replication of the SOLIS vector spectromagnetograph. The programs should be coordinated by a community-based Steering Committee. The recommendation includes provision for the SMI program to be renewable for five more years, depending on the success of the first five years.

The SMI will form an important component of the National Space Weather Program and will advance the development and application of the basic disciplines of plasma physics, fluid dynamics and magnetohydrodynamics, radiative transfer, and computational physics.

The aim of SMI is to establish the feasibility of solar activity forecasting by providing the scientific prerequisites for such forecasting. SMI programs will be designed to:

• identify and understand the physical processes that control how magnetic fields are generated in the solar interior, rise to the surface, and evolve after emergence;

• use this understanding to synthesize a new global paradigm for the operation of the solar cycle; and

• produce quantitative models relevant to the development of science-based forecasting tools for solar activity and space weather.

The SMI Steering Committee would work closely with the solar physics community to determine scientific priorities within the program through the establishment of Focus Programs, observing campaigns, and workshops, and through outreach activities such newsletters and presentations at scientific meetings and workshops. The Initiative would consist of the following components, some of which require one-time capital investments in addition to operating budgets:

• University grants program and SMI postdoctoral fellowships ($2.20M annually for programs).

• Focus programs, workshops, and coordination ($90K annually for programs).

• Support of HAO as the coordinating national center ($220K one-time investment; $500K annually).

• Community instrument development, starting with expansion of SOLIS from one station to a three-station network for continuous measurements of photospheric vector magnetic fields over the full solar disk. The SMI workshops identified a SOLIS network as the highest-priority instrument requirement. ($4.40M one-time investment, $200K annually for operations)

When considering the solar interior and atmosphere with their magnetic fields as a single physical system, the foreseeable scientific challenges are embodied in the following questions:

• What are the processes by which magnetic fields are stored in the base of the convection zone long enough to be regenerated by dynamo action?

• What form does this dynamo action take?

• How are the magnetic fields transported through the convection zone to emerge into the photosphere and above?

• What is the nature of the solar internal rotation and convection so crucial to the above processes?

• What is the nature of the (observationally not yet resolvable) fibril state of the magnetic fields at the level where the fields first become observable?

• What are the contributions to the total unsigned photospheric flux deriving from active regions and from the quiet network?

• What are the fundamental processes of magnetohydrodynamics and energy transport operating at this level and how do these processes relate to the wealth of directly observed phenomena?

• How are the elemental magnetic structures and small-scale turbulent photospheric motions related to the large-scale organized structures, ranging from pores, through sunspots, to active regions, and ultimately to the large “complexes” of multiple active regions?

• How do newly generated magnetic fields emerge through the photosphere to eventually replace the old fields and reverse the global magnetic polarity in a solar cycle?

• Where do the old fields go, given the highly frozen-in state of the magnetic field?

• What is the origin of the weak internetwork magnetic fields?

• How does the internetwork component of the solar magnetic field vary with the solar cycle, and what implications does it carry for the global fields of the Sun?

• How do magnetic fields emerge from below and reverse the polarity of the global magnetic field in this voluminous part of the solar atmosphere?

• How do the many coronal phenomena (helmet-streamers, prominences, coronal holes, active regions; coronal heating; violent eruptions: flares, prominence eruptions, coronal mass ejections; differential rotation of coronal structures; and magnetic flux emergence) relate physically to produce the systematic global evolution of the corona from one activity cycle to the next?

• While it is clear that the corona sets the boundary conditions for the physical state in the heliosphere, does the corona also directly couple onto, and significantly feed back upon the photosphere by influencing the generation of magnetic field through the dispersal of fields from the interior out to the heliosphere as a coupled system?

The SMI's scientific emphases would be organized annually under individual “Focus Programs.” It is expected that a major fraction of the community will contribute, to varying degrees, to each of these Focus Programs in order that the goal of SMI will be addressed. Prospective topics are:

• The Solar Dynamo in the Light of Direct Measurement of Interior Dynamics

• Magnetic Flux Transport Through the Convection Zone

• Emerging Magnetic Flux: An Observational Description

• History of Magnetic Flux: The Solar Magnetic Cycle at the Solar Surface

• The Physics of Coronal Mass Ejections: Cause and Heliospheric Effects

SMI will support observational efforts in two modes: addressing the scientific basis for developing new ground- and space-based instrumentation; and providing support for independent research efforts to explore diagnostic techniques.

In addition to the SOLIS observing network of three stations, which will provide a breakthrough in continuous and precise measurements of the solar vector magnetic field, the SMI will need other elements for the ground-based observational and experimental program:

• Coordinated “Flux Emergence” Observing Campaigns

• Coronal Observations, including magnetic field measurements

• A community Stokes Inversion Program

• Continuing development and refinement of ground-based instruments.

Certain of the SMI science problems involving very high angular resolution and coordinated short-wavelength observations will best be served by observations from a space platform. SMI science is expected to strongly support and strengthen continuing efforts toward such missions.

The proposed SMI program for expansion of data analysis techniques for polarimetry will benefit both ground- and space-based polarimeters. Sophisticated analytic and numerical techniques are required to convert polarimetric observations into quantitative measurements of magnetic and thermodynamic parameters of the solar plasma. Software implementing these techniques (“Stokes Inversion”) is currently dispersed among several research groups and is not widely available to the solar community in a consistent, documented, user-friendly form. The SMI workshops identified a community Stokes inversion code as a high priority requirement for making effective use of state-of-the-art solar polarimeters.

SMI would facilitate community access to the data appropriate to the science goals of the program. Data from new instrumentation, i.e., the SOLIS extended network and space missions like Solar-B, would be included. The databases would be organized around the individual “focus programs” of SMI, and results from theoretical models as well as observational data would become part of the database. SMI would also coordinate with NSSDC to make data accessible through the NASA master directory.

The analysis of SMI data would be carried out both at the national centers and in the university community. To achieve the needed level of collaboration, the SMI program must include all four of the key elements of data analysis: the university grants program, the SMI database, adequate Internet connectivity, and the community inversion code.

The following network of models is proposed for SMI's integrated research. In this listing, each model is indicated to be existing (e) or needed (n):

1. The Solar Dynamo

   • Shear-layer interface at base of convection zone-dynamics & dynamo (e & n).

   • Direct MHD simulation and mean-field dynamo (e).

2. The Solar Convection Zone and Photosphere

   • Hydrodynamic models of stratified convection in rotating systems (e) and their fully MHD extensions (e & n).

3. • Basic physics of turbulent transport of magnetic fields, including the effects of magnetic buoyancy and magnetic reconnection (e & n).

   • Thin-flux-tube models (e) and their extension to finite-flux-tube models (n).

   • Comparison of direct MHD simulation and discrete flux-tube approximation (n).

   • Injection of magnetic flux into the base of the convection zone from below (e & n).

   • Magnetic flux emergence at the top of convection zone and photosphere (n).

   • MHD of the photospheric level with energy and radiative transport (e).

   • Models of transport of photospheric flux (e) and extension to include the effects of flux loss to the corona and to the convection zone (n).

   • Numerical investigations of sub-grid processes. (e & n)

4. The Chromosphere and Corona

   • MHD models of large-scale, long-lived structures in the low-beta atmosphere, including the extrapolation of magnetic fields (e & n).

   • MHD/RT models of the magnetized chromosphere (e & n).

   • MHD modeling of eruptions and flux emergence into the corona (e & n).

   • MHD of quasi-steady evolution, magnetic helicity, global magnetic reversal (n).

   • Time-dependent MHD of Coronal Mass Ejections and Flares (e & n).

5. The Corona and Heliosphere

   • Quasi-steady structure and evolution of the largest-scale corona-coronal holes, hydromagnetic solar wind, and helmet-streamers (e & n).

   • Propagation of the CME from the corona out into the heliosphere (n).

Supercomputing demands for various fluid dynamical and MHD modeling efforts within SMI will increase significantly as the community' s research requires more frequent simulations using coupled models. The scientists conducting the SMI simulations and other data analysis expect to compete for the NCAR and other NSF supercomputer center time as required by the research.

• High resolution MHD models of the type listed above require typically 512³ points, and integration times on the order of 25,000 node hours per realization on a current multi-processor supercomputer (e.g. T3E). Each single output array from such a simulation is about 1 GByte in size. Post-processing both the numerical data and the forthcoming observational data requires a multi-cpu platform (e.g. 10 node SGI Origin 2000) with 1 Gbyte of RAM per processor and significant amounts (250 GBytes) of fast access disk storage.

• The SMI Committee understands that a national effort will be made to restore U.S. competitiveness in supercomputing, under the name “Terascale and Petascale Computing: Digital Reality in the New Millennium. ” Given the need to substantially increase computing capacity for demanding scientific research applications, the SMI Committee strongly advocates this national initiative. We are confident that the scientists carrying out large numerical simulations for SMI can compete successfully for needed supercomputing resources from this source.

ATTACHMENT

SOLAR MAGNETISM INITIATIVE

ORGANIZATIONS REPRESENTED BY PARTICIPANTS IN SMI WORKSHOPS

December, 1995, and/or July, 1996

U.S. ORGANIZATIONS

Harvard-Smithsonian Center for Astrophysics

Helio Research

Helio Synoptics, Inc.

Lockheed Palo Alto Research Laboratory

Michigan State University, Department of Physics and Astronomy

Montana State University, Department of Physics

NASA Goddard Space Flight Center

NASA Marshall Space Flight Center, Space Science Laboratory

National Center for Atmospheric Research, UCAR

High Altitude Observatory

Mesoscale and Microscale Meteorology Division

National Science Foundation, Upper Atmosphere Facilities

National Solar Observatory, Sacramento Peak and NSO-Tucson

Naval Research Laboratory

New Jersey Institute of Technology, Department of Physics

NOAA Space Environment Center

Pennsylvania State University, Department of Astronomy and Astrophysics

Rhodes College, Department of Physics

Science Applications International Corporation

Solar Physics Research Corporation

The Johns Hopkins University, Applied Physics Laboratory

U.S. Air Force, Phillips Laboratory

University of California-Berkeley, Space Sciences Laboratory

University of Chicago, Department of Astronomy and Astrophysics

University of Colorado

Astrophysical and Planetary Sciences Department

Joint Institute for Laboratory Astrophysics

University of Hawaii, Institute for Astronomy

University of Illinois, Department of Astronomy

University of New Hampshire, Space Science Center/EOS Institute

University of Rochester

OTHER INSTITUTIONS

Copenhagen University Observatory

ETH Zurich, Institute of Astronomy

Freie Universitat Berlin

Instituto de Astrofisica de Canarias

Kiepenheuer-Institut fur Sonnenphysik

Observatoire Midi-Pyrenees

University of Oslo

University of Sydney

THE SOLAR MAGNETISM INITIATIVE COMMITTEE

Michael Knoelker, HAO, Co-Chairman

Robert Rosner, U. of Chicago, Co-Chairman

Thomas Bogdan, HAO

Richard Canfield, Montana State University

Fausto Cattaneo, U. of Chicago

Terry Forbes, U. of New Hampshire

Peter Gilman, HAO

John Harvey, NSO

Bruce Lites, HAO

Boon Chye Low, HAO

Douglas Rabin, NSO

John Thomas, U. of Rochester

Aad van Ballegooijen, Harvard-Smithsonian Center