Chapter 2

Assessment of Current and Approved Ground-based Solar Research Programs

This chapter reviews the principal elements of the current U.S. ground-based solar research program. For convenience, the discussion is organized as follows: (1) major solar observational facilities; (2) data, theory, and modeling; and (3) people, programs, and institutions—the means by which elements 1 and 2 are integrated to advance scientific understanding. After a descriptive summary of existing capabilities, the task group offers a brief assessment of how well these capabilities can respond to the scientific challenges enumerated in Chapter 1.

MAJOR SOLAR OBSERVATIONAL FACILITIES

The National Solar Observatory

The National Solar Observatory (NSO), one of the National Optical Astronomy Observatories (NOAO), is operated by the Association of Universities for Research in Astronomy, under a cooperative agreement with the National Science Foundation (NSF).1 The current responsibilities of NSO include the following:

  1. Continued operation of the Kitt Peak (NSO/KP), Sacramento Peak (NSO/SP, “Sac Peak”), and Tucson facilities;

  2. Operation and upgrade of the multisited telescopes of the Global Oscillations Network Group (GONG) for continuous studies in helioseismology;

  3. Fabrication and operation of the array for the Synoptic Optical Long-term Investigation of the Sun (SOLIS);

  4. Maintainance of data records and providing data distribution; and

  5. Provision of specialist-supported access to national observing facilities.

NSO operates the two largest solar telescopes in the United States for ground-based solar observation—the Vacuum Tower Telescope at Sac Peak (commissioned in 1969) and the McMath-Pierce telescope at Kitt Peak (commissioned in 1961). NSO facilities are available to both local staff and visiting scientists worldwide. To maximize scientific productivity, NSO policy provides for visiting observers to be assisted by experienced NSO staff. This support is unique among solar observatories worldwide and exemplifies the collaborative role of the NSO in the solar physics community.

NSO Sacramento Peak

NSO Sacramento Peak has three solar telescopes: the Vacuum Tower Telescope, which is discussed below; the John W. Evans Solar Facility; and the Hilltop Dome Facility. The Evans facility provides two 40-cm coronagraphs on a common spar, as well as a coelostat. The Evans coronagraphs are the largest in the United States and the best

1  

Information about the NSO can be found on the World Wide Web at <http://www.nso.noao.edu/>.



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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE Chapter 2 Assessment of Current and Approved Ground-based Solar Research Programs This chapter reviews the principal elements of the current U.S. ground-based solar research program. For convenience, the discussion is organized as follows: (1) major solar observational facilities; (2) data, theory, and modeling; and (3) people, programs, and institutions—the means by which elements 1 and 2 are integrated to advance scientific understanding. After a descriptive summary of existing capabilities, the task group offers a brief assessment of how well these capabilities can respond to the scientific challenges enumerated in Chapter 1. MAJOR SOLAR OBSERVATIONAL FACILITIES The National Solar Observatory The National Solar Observatory (NSO), one of the National Optical Astronomy Observatories (NOAO), is operated by the Association of Universities for Research in Astronomy, under a cooperative agreement with the National Science Foundation (NSF).1 The current responsibilities of NSO include the following: Continued operation of the Kitt Peak (NSO/KP), Sacramento Peak (NSO/SP, “Sac Peak”), and Tucson facilities; Operation and upgrade of the multisited telescopes of the Global Oscillations Network Group (GONG) for continuous studies in helioseismology; Fabrication and operation of the array for the Synoptic Optical Long-term Investigation of the Sun (SOLIS); Maintainance of data records and providing data distribution; and Provision of specialist-supported access to national observing facilities. NSO operates the two largest solar telescopes in the United States for ground-based solar observation—the Vacuum Tower Telescope at Sac Peak (commissioned in 1969) and the McMath-Pierce telescope at Kitt Peak (commissioned in 1961). NSO facilities are available to both local staff and visiting scientists worldwide. To maximize scientific productivity, NSO policy provides for visiting observers to be assisted by experienced NSO staff. This support is unique among solar observatories worldwide and exemplifies the collaborative role of the NSO in the solar physics community. NSO Sacramento Peak NSO Sacramento Peak has three solar telescopes: the Vacuum Tower Telescope, which is discussed below; the John W. Evans Solar Facility; and the Hilltop Dome Facility. The Evans facility provides two 40-cm coronagraphs on a common spar, as well as a coelostat. The Evans coronagraphs are the largest in the United States and the best 1   Information about the NSO can be found on the World Wide Web at <http://www.nso.noao.edu/>.

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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE instrumented in the world. In addition, the patrol telescope at the Hilltop Facility provides important diachronic observations of the solar disk. Probing the motions and magnetic fields of the Sun at the smallest scale allowed by atmospheric seeing, the Sacramento Peak Vacuum Tower Telescope (Sac Peak VTT) is the premier U.S. instrument for solar high-resolution imaging and spectroscopy. Put into operation in 1969, the VTT has a telescope aperture of 0.76 m stopped down from the main mirror of 1.6 m in diameter to allow using all the sunlight through a window at the upper end of an evacuated telescopic column. The evacuated interior of the VTT eliminates internal seeing problems, but at the cost of the polarization limitations imposed by a window under fairly heavy stress. The VTT has the largest aperture and best intrinsic resolution of any vacuum telescope in the world: 0.14 arc-seconds (″) at 0.5 microns (µm) and 0.4″ at 1.5 µm.2 However, one should also note that sites such as Big Bear Lake in California and the Canary Islands enjoy more hours of good-quality seeing than Sacramento Peak. For many years, the Sac Peak VTT has been a leading facility in high-resolution studies of small-scale activity. The first pictures of the “filigree,” representing magnetic fibrils, were produced there. The VTT is also host to the High Altitude Observatory (HAO) Advanced Stokes Polarimeter (ASP). The ASP measures the full-vector magnetic field at several heights in the solar atmosphere with high-angular resolution and is the first instrument to deliver quantitative information on the vector magnetic field that is limited primarily by the ability to resolve solar features observed through Earth's atmosphere. Its vector magnetograms and coincident Dopplergrams have a sensitivity that will not be substantially surpassed until the deployment of the recently approved SOLIS instrument (discussed below). The task group believes that the crucial role of the VTT in the immediate future, besides continuing its ongoing studies, will be the development of adaptive optics for an Advanced Solar Telescope (AST). As discussed in Chapter 3, the goal of preliminary adaptive optics work at the VTT would be to demonstrate diffraction-limited operation when the atmospheric seeing is in the 0.5-arc-second range. NSO Kitt Peak NSO/KP is the site for the Vacuum Telescope and the McMath-Pierce telescope. As discussed below, NSO/KP has unique capabilities to conduct high-resolution observations in the infrared (IR). Vacuum Telescope: The Vacuum Telescope at Kitt Peak is dedicated to obtaining daily full-disk, seeing-limited observations of solar magnetic fields (magnetograms) and daily full-disk observations of the helium chromosphere (He I 1083 nm spectroheliograms), which are widely distributed in near-real time and archived in a permanent record. McMath-Pierce Telescope: The McMath-Pierce Telescope at Kitt Peak, put into operation in 1961, is the world's largest solar telescope, with an aperture of 1.5 m. Its 2   In terms of operational vacuum telescopes, the Sac Peak/VTT is the largest and best high-resolution telescope in the world. THEMIS, on the Canary Islands, is a 90-cm vacuum telescope, but its current image quality is poor as something is apparently wrong with the figure of the mirror.

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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE working resolution in visible light is not often outstanding because it is not a vacuum telescope, but the absence of a vacuum window allows it to function well into the IR. For that reason, the McMath-Pierce telescope is currently the premier instrument for IR studies, which offer several advantages over those made at visible wavelengths. For example, taking advantage of the rapid increase of the Zeeman effect with increasing wavelength facilitates the study of the structure of magnetic fields.3 In addition, as IR spectral lines come from a broad range of heights in the solar atmosphere, one can carry out studies of vector magnetic fields, temperature, and atomic abundances from the visible surface to the base of the corona. For example, it has come to light in recent years that abundances of such elements as C, N, and O, as well as such molecules as CO and OH, are most accurately determined from IR spectra extending to roughly 15 µm. Temperatures as a function of height are obtained relatively easily and without dependence on atmospheric models by taking advantage of the fact that the excitation of molecules is in local thermodynamic equilibrium. Hence, the patches of chromosphere are more easily analyzed in the IR, whereas visible light reveals relatively little of their structure. Technology has made IR observations effective only recently, and much of the IR spectrum remains unexplored. The large aperture of the McMath telescope is particularly advantageous in the IR where the atmospheric seeing is much better than at visible wavelengths, while the diffraction limit decreases in inverse proportion to the wavelength. Furthermore, in the near term, IR observations at high spatial resolution will not be feasible from spaceborne telescopes because of the large aperture required. The Global Oscillations Network Group GONG is a community-based project to conduct a detailed study of solar internal structure and dynamics using helioseismology.4 In order to exploit this new technique, six extremely sensitive and stable velocity imagers located around Earth5 have been linked to obtain nearly continuous observations of the Sun's “five-minute” oscillations, or pulsations. The GONG system has provided long sequences of solar surface oscillations (without the day-night interruptions) for probing the interior of the Sun through 3   The Zeeman splitting of spectral lines is proportional to the square of the wavelength, which results in a factor of ten more sensitivity at-IR wavelengths compared to typical visible observations. 4   Helioseismology uses waves that propagate throughout the Sun to measure, for the first time, the internal structure and dynamics of a star. See D.O. Gough et al., “Perspectives in Helioseismology,” Science, 272: 1281-1283, May 31, 1996. Also see “GONG Helioseismology, ” Science, vol. 272, May 31, 1996, (special issue); also available online at <http://helios.tuc.noao.edu/helioseismology.html/>. 5   Each of the six sites represents one of the six longitudinal bands that allow the network to make 24-hour-a-day observations of the Sun. The six sites composing the GONG network are the Big Bear Solar Observatory in California, the High Altitude Observatory at Mauna Loa in Hawaii, the Learmonth Solar Observatory in Western Australia, the Udaipur Solar Observatory in India, and the Observatorio del Teide in the Canary Islands.

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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE helioseismology. The quite different rotation of the central regions compared to the surface rotation rate is of particular interest. 6 GONG was established with support from the NSF and completed in October 1995. On December 2, 1995, the Solar and Heliospheric Observatory (SOHO) spacecraft was successfully launched. A project of the European Space Agency and NASA, SOHO's sensors include three different helioseismological experiments (MDI, GOLF, and VIRGO) to observe the Sun continuously from the spacecraft's halo orbit near the Sun-Earth Lagrangian point. Recent helioseismic data from the MDI, GOLF, and VIRGO instruments on SOHO and the ground-based instruments7 provide complementary insights into the nonuniform rotation and global flows beneath the visible surface of the Sun, with implications for the solar dynamo. SOHO was originally designed for a lifetime of 2 years but was equipped with sufficient onboard consumables for at least an extra 4 years of operation. Even though the spacecraft's consumables should allow for operation considerably longer than 4 years, it is prudent to plan for either MDI, the key instrument for helioseismology, or an essential spacecraft subsystem, to fail before observations of the present 11-year magnetic activity cycle are completed. Synoptic Optical Long-term Investigation of the Sun NSO/Kitt Peak full-disk magnetograms have been, and remain today, the cornerstone of modern solar physics. The magnetograms (with a sensitivity of about 4 Gauss per square arc-second) are crucial for studies of the global aspects of the magnetic cycle as well as for the magnetic structure of active and quiet regions on all scales down to a few thousand kilometers. Analysis of the magnetograms has led to fundamental discoveries related to the processes underlying these phenomena. The Synoptic Optical Long-term Investigation of the Sun (SOLIS) will continue this key synoptic record of the Sun's magnetism with at least the same spatial resolution and with substantially increased sensitivity (~ 1 G) for the line-of-sight component of the magnetic field.8 SOLIS will have the important capability to measure the transverse magnetic field component in all active regions, ephemeral regions, and in parts of the 6   The surface rotation period is 25 days at the equator and more than 35 days at the poles. To first order, however, the solar radiative zone rotates rigidly. There is a gradient at the top of the zone where it is thought that the main solar dynamo resides. In the early stages of helioseismology, there was controversy about the solar core. Some expected, guided by theory, that the core would rotate rapidly. Although the data still are uncertain below 0.2 R, the data do show that there is not a large store of angular momentum hiding in the core. See special issue, “GONG Helioseismology,” Science, 272, May 31, 1996; R. Howe, “Solar Dynamics: Internal rotation, Jets, and the Tachocline; Implications for the Solar Dynamo” and, A. Eff-Darwich and S. G. Korzennik, “Rotation of the Solar Core: Compatability of the Different Data Sets,” in A. Wilson (ed.), Structure and Dynamics of the Interior of the Sun and Sun-Like Stars, ESA SP-418, in press. 7   In addition to GONG, these include LOWL (an instrument in Mauna Loa, Hawaii, that observes deeply penetrating low-degree 1 modes), International Research on the Interior of the Sun (IRIS), and Experiment for Coordinated Helioseismic Observations (ECHO)—instruments whose observations complement and correlate those of GONG. 8   SOLIS became an approved and funded NSF project during the course of the task group's study. SOLIS is expected to be completed in February 2001 at a cost of approximately $6 million. A technical description of the project can be found online at <http://www.nso.noao.edu>.

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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE magnetic network wherever this component is 20 G or stronger (the present sensitivity is 100 to 200 gauss with the HAO Advanced Stokes Polarimeter). Using SOLIS, vector magnetic fields will be mapped in 15 minutes over the entire solar disk with spatial elements of 1″. These carefully calibrated magnetic field observations will be made and reduced using a technique similar to that developed for the ASP and will also provide measures of the full-disk intensity and Doppler velocity maps. No existing instrument has these capabilities, which will greatly enhance the usefulness of the magnetograms for studies of the nonpotential field configurations that explode into flare and coronal mass ejections, including small events such as the larger microflares and the macrospicules in quiet regions. The full-disk magnetograms and Dopplergrams will be the centerpiece of the SOLIS data, which will also include two additional instruments: the Full-Disk Patrol providing images in H-alpha, He I 10830 A, Ca II K, and other spectral lines, showing the atmospheric structure and chromospheric heating associated with the magnetic fields; and the Integrated Solar Spectrometer that will measure and monitor Sun-as-a-star high-spectral-resolution, dispersed spectra at many wavelength bands. This will open a new and timely window for studying the intricacies of the active phenomena on the Sun and of the Sun within the context of other stars, complemented (should funding be available) by coronagrams. The SOLIS instruments will provide the primary means for searching out the weak, but presumably very active, interfibril magnetic fields, as well as studying the slow circulation of gas across the surface of the Sun at high spatial resolution. The deployment of SOLIS will provide better full-disk synoptic magnetograms, chromospheric images, and whole Sun spectra at more rapid cadence with less manpower and cost than at present. Other Major Solar Optical Observatories The task group's assessment of U.S. observatories focused on facilities at the National Solar Observatory. However, important solar facilities exist elsewhere and support both synoptic and research programs. For example, active region vector magnetograms are recorded by several observatories outside the NSO, notably Mees Solar Observatory, San Fernando Observatory, Marshall Space Flight Center, and Big Bear Solar Observatory. In addition, the Wilcox Observatory specializes in low-resolution magnetograms that show the current sheet separating the northern and southern magnetic hemispheres of the Sun and large-scale surface velocity patterns. Facilities outside the NSO also provide data that are essential to support ongoing NSO programs. For example, GONG is complemented by instruments deployed on the 60-foot and 150-foot towers on Mt. Wilson. Brief sketches of some of these facilities are given below. Big Bear Solar Observatory In addition to the vector magnetograms noted above, the Big Bear Solar Observatory (BBSO) also specializes in high-resolution observations of magnetic fields, motions, and line intensities. BBSO was responsible for some of the first high-precision

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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE studies of helioseismology. It appears that the excellent seeing at BBSO is owing to its being a lake site—Big Bear Lake, California. High Altitude Observatory-Mauna Loa Solar Observatory The High Altitude Observatory (HAO) is dedicated to the study of the Sun and of the response of Earth's upper atmosphere to the Sun 's output. HAO is a division of the National Center for Atmospheric Research, which is managed by the University Corporation for Atmospheric Research, under contract with NSF. HAO operates the Mauna Loa Solar Observatory (MLSO) in Hawaii. Instruments at MLSO currently include these: Digital Prominence Monitor (DPM), Mark 3 K-Coronameter (MK3), Low-degree (LOWL) solar oscillation experiment, and Chromospheric Helium I Imaging Photometer (CHIP). These instruments collect the following: H-alpha disk and limb images, collected with the DPM or the (pics) instrument, a telescope with a removable occulting disk used to make observations of the limb or disk in hydrogen-alpha (wavelength 656.3 nm); Coronal images in white-light polarization brightness, collected with the MK3-coronameter, a 23-cm objective coronameter-polarimeter; Solar oscillation data collected with the LOWL instrument; Helium I 1083 nm images, collected with CHIP, installed with the MkIII white-light coronagraph and digital prominence monitor at MLSO in 1996. CHIP was built by the HAO instrumentation group and is the first increment of the Advanced Coronal Observing System (ACOS). CHIP is unique compared with other Helium I imagers, in that it obtains images every 3 minutes, the high cadence crucial to study the rapid evolution of coronal mass ejections. MLSO and HAO are also host to one of the three currently planned Precision Solar Photometric Telescopes (PSPT).9 The PSPT is the centerpiece of the NSF Radiative Inputs from Sun to Earth (RISE) program, a community-based activity whose aim is to measure and understand variability in the solar radiative output. HAO and NSO/SP also collaborate on the operation of the HAO-developed Advanced Stokes Polarimeter (see discussion of NSO/Sac Peak VTT, above). 9   The PSPT produces seeing-limited full disk digital (2048 × 2048) images in CaIIK (393 nm +/− 0.3 nm), and blue (408-412 nm) and red (605-610 nm) continuum, at an unprecedented 0.1% photometric precision per pixel. It was designed and built by the National Solar Observatory. The minimal PSPT network configuration is planned for sites at the Rome Astronomical Observatory, MLSO, and Sac Peak. The PSPT at MLSO was installed in September 1997.

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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE Lockheed Martin Solar and Astrophysics Laboratory Lockheed Martin Solar and Astrophysics Laboratory (LMSAL) is a department of the Lockheed Martin Advanced Technology Center in Palo Alto, California, whose scientists and engineers design, build, and operate solar and astrophysical observing instruments. LMSAL staff make use of the Swedish Vacuum Solar Tower, one of many telescopes on the island of La Palma in the Canary Islands, in addition to a variety of space-based instruments, notably the Soft X-Ray Telescope, currently flying aboard the Japanese Yohkoh spacecraft; Michelson Doppler Imager, currently flying on the NASA/European Space Agency SOHO satellite; and sensors on the Transition Region and Coronal Explorer, a NASA Small Explorer, launched April 1, 1998. LSMAL also operates the ground-based Solar Optical Universal Polarimeter, a solar observation filter that is now working at the La Palma observatory. Marshall Space Flight Center Marshall Space Flight Center (MSFC) has a solar observatory that has been operating since the early 1970s. The observatory is located west of Huntsville, Alabama, and specializes in vector magnetography. The MSFC Vector Magnetograph Facility, housed at the top of a 40-foot tower, was assembled in 1973 to support the Skylab. Improvements to the vector magnetograph were made in 1976, and the facility added a co-aligned H-alpha telescope in 1989. Images from this telescope provide a view of chromospheric structures, flare activity, and additional information on the orientation of the magnetic field in active regions. Mees Solar Observatory Located on the island of Maui in Hawaii, Mees Solar Observatory (MSO) is operated by the Institute for Astronomy of the University of Hawaii. MSO instruments study solar flares, magnetic fields on the Sun, and solar oscillations. Currently operating instruments at MSO are these: Imaging Vector Magnetograph: maps the vector magnetic field in the solar photosphere. The IVM observes a region about 203,000 km2 on the Sun; Haleakala Stokes Polarimeter: maps the vector magnetic field in the solar photosphere; Mees Imaging Spectrograph: H-alpha imaging spectroscopy; Mees White Light Telescope: acquires digital full-disk white-light images with a high-resolution charge coupled device (CCD) camera; K-line Telescope: records images of the full disk of the Sun in the Ca II K line at 393.3 nm with a CCD camera; P-mode Oscillations Imager: observes the Sun in the Ca K spectral line; and H-alpha Video Coronagraph.

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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE Mt. Wilson Observatory—University of California at Los Angeles The Mt. Wilson Observatory (MWO) is the oldest solar observatory in the United States and the site for the 150-foot tower telescope. Instruments at the tower are currently used to study oscillations of the magnetic fields in the photosphere, as well as chromospheric oscillations in conjunction with the SOHO/GOLF experiment. In addition, the tower hosts instruments for daily full-disk magnetograms and Dopplergrams. The observatory was built by the Carnegie Institution of Washington in 1917 and is currently operated by the University of California, Los Angeles. Mt. Wilson Observatory—University of Southern California Mt. Wilson's 60-foot tower telescope was built early in this century. The facility is currently used mostly for helioseismology; however, under a joint program with UCLA, full-disk white-light photographs are made daily to continue the long series of such images started at Mt. Wilson nearly 100 years ago. The tower is one of the two sites in the High Degree Helioseismology Network (HiDHN), the other being the Crimean Astrophysical Observatory in the Ukraine. The HiDHN is designed to study the high-order oscillations of the Sun. Maintaining two observing sites at opposite sides of the Earth allows for nearly continuous coverage of the Sun during the summer months. San Fernando Solar Observatory This facility is operated by the Department of Physics and Astronomy of the California State University at Northridge (CSUN). It was built by the Aerospace Corporation in 1969 and was donated to CSUN in 1976. The ongoing research programs at the San Fernando Observatory fall into two main categories: the study of the evolution of magnetic fields in solar active regions and the study of the energy balance of active regions and its effect on solar irradiance. In contrast to the sites for other major solar observatories, the best observing weather in the San Fernando Valley comes in the summer months. Researchers at the observatory note that long observing days, stable air, and little prospect of rain make their facility well suited to monitor solar activity. U.S. Air Force Solar Optical Observing Network The Solar Optical Observing Network (SOON), designed and deployed in the 1970s, is a network of five identical telescopes at selected sites around the world providing real-time solar activity information for prediction of space weather to support the Air Force mission. Data from these telescopes flows in real time to the National Oceanic and Atmospheric Administration's (NOAA) Space Environment Center (SEC) in Boulder, Colorado. A joint civilian and Air Force forecast center uses the data to make publicly available space weather forecasts. Improved SOON (ISOON) will replace the existing SOON system in the year 2000. ISOON will deliver near-real-time, rapid-cadence solar images to the Air Force Space Command and NOAA/SEC. The ISOON network will consist of four sites and will be operated autonomously and remotely controlled from Schriever Air Force Base,

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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE Colorado. The ISOON instrument will have a 1.15-solar-diameter (37') field of view with 1.1″ pixels and will nominally deliver Ha images at a 1-minute cadence, a continuum image every hour, and a line-of-sight magnetogram every 3 hours. A high-resolution imaging mode at 0.3″ pixels will also be incorporated into the prototype. It is the announced intention that data from ISOON will be publicly available. At present the main data set is H-alpha images of selected active regions. Wilcox Solar Observatory—Stanford University The Wilcox Solar Observatory (WSO) is located in the foothills west of the Stanford University campus. Established in May 1975, it is supported mainly by grants to Stanford University. WSO produces low-angular-resolution synoptic magnetograms and Sun-as-a-star magnetic field measurements. It is also a site in the IRIS helioseismology network Major Solar Radio Observatories Solar radio observations are carried out at three facilities in the United States: The frequency-agile solar array at Owens Valley,10 which has good frequency coverage, but with limited imaging; the Very Large Array,11 which, when available for solar observations, has good imaging but limited frequency coverage; and the Berkeley Illinois Maryland Association's millimeter-wave array.12 Owens Valley Radio Observatory The Owens Valley Radio Observatory (OVRO) is located near Bishop, California. Its solar array, a solar-dedicated 5-element radio synthesis instrument, typically takes data at 45 frequencies in the range of 1 to 18 GHz. OVRO has a large database of solar flare and active region data, which are used for research in the structure and phenomena of the active solar corona. Very Large Array The Very Large Array (VLA), in Socorro, New Mexico, consists of 27 antennas arranged in a huge Y pattern up to 36 km across. The VLA is operated by the National Radio Astronomy Observatory, an NSF facility, operated under cooperative agreement by Associated Universities, Inc. At its highest frequency of operation (43 GHz), the array has a resolution of 0.04 arc-seconds. 10   Information about the Owens Valley Radio Observatory (OVRO) can be found online at <http://www.ovro.caltech.edu/>. 11   Information about the VLA is available online at <http://www.nrao.edu/vla/html/VLAhome.shtml>. 12   Technical information about the BIMA array can be found online at <http://astro.berkeley.edu/~plambeck/technical.html>.

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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE Berkeley Illinois Maryland Association The Berkeley Illinois Maryland Association (BIMA) Millimeter Array is a 10-antenna aperture synthesis telescope that operates at wavelengths of 3 mm (70 to 116 GHz) and 1 mm (210 to 270 GHz). The array is located at the Hat Creek Radio Observatory, 250 miles north of Berkeley, California. It is operated by the BIMA consortium, consisting of the Radio Astronomy Laboratory of the University of California at Berkeley, the Laboratory for Astronomical Imaging of the University of Illinois, and the Laboratory for Millimeter Astronomy of the University of Maryland, with support from NSF. Use of these facilities has demonstrated the potential for using radio observations for flare diagnostics and mapping of magnetic fields, leading to the development of plans for a Frequency-Agile Solar Radio telescope (see Appendix E). The unique ability of radio observations to detect individual small (<1024 ergs) flare events is of central importance for probing the heating of the solar corona. High spatial resolution is essential for distinguishing the individual small event from the background sea of unresolved small events. Solar Optical Observatories Outside the United States Many excellent solar observing facilities exist outside the United States. Distributed worldwide, they illustrate a widespread interest in the active Sun and suggest the possibility of a vigorous international collaborative effort should the United States choose to go forward with plans for the Advanced Solar Telescope discussed in Chapter 3. Among the most important international facilities and institutions are the following: Huairou Solar Station This facility is operated by the Beijing Astronomical Observatory (BAO) of the Chinese Academy of Sciences and is located on the north bank of the Huairou reservoir where the atmosphere is stable. Instruments at this facility include the Multi-Channel Solar Magnetic Field Telescope (4 telescopes on one mounting, the largest of which is a 60-cm Gregorian). The solar vector magnetic field and the radial velocity field are the main observation targets. Meter-class telescopes are under development at Huairou. Hida Observatory Hida Observatory is operated by the University of Kyoto and is located not far from Kyoto. The facility hosts a major 65-cm research telescope and a new synoptic telescope. The 65-cm instrument is the largest refracting telescope in Asia. In 1979, the Domeless Solar Telescope was completed; it is the highest-resolution multiple solar telescope in Japan.

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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE Hiraiso Solar Terrestrial Research Center Located north of Tokyo, the Hiraiso Solar Terrestrial Research Center (HSTRC) is a facility operated by the Communications Research Laboratory of the Ministry of Posts and Telecommunications of Japan. The center 's organization is similar to the NOAA Space Environment Center; however, HSTRC operates its own observing facilities. Scientists using the HSTRC conduct research in space weather forecasting, solar physics, and solar terrestrial physics. Alerts and forecasts of space disturbances are issued from the HSTRC on a daily basis with solar optical observations from an H-alpha solar telescope and solar radio observations from fixed frequency observations at 200, 500 and 2800 MHz. Kanzelhöhe Solar Observatory The only solar observatory in Austria, the Kanzelhöhe Solar Observatory has been in operation since 1943. It is currently operated by the Institute of Astronomy of the Karl Franzens University of Graz and is located in the mountains near Vienna. In addition to synoptic equipment for routine optical monitoring of the Sun, a very modern 40-cm vacuum telescope with CCD processing of spectra recently started operations. Kiepenheuer Institute for Solar Physics The Kiepenheuer Institute for Solar Physics (KIS) is a research institute of the German state Baden-Württemberg and is supported by various federal and state sources. It was founded in 1943 and produces synoptic H-alpha images daily from its facilities at the Observatorio del Teide on Tenerife, Canary Islands. KIS also operates a Vacuum Tower Telescope, which has an aperture of 70 cm and can be operated with an image-stabilizing system. Lomnicky Stit Observatory This is a high-altitude observing site long used for coronal observations. Instruments at the site include a 20-cm double chronograph, with Fe X-XV and Ca XV photometry. The observatory is operated by the Department of Astronomy of the Astronomical Institute of Slovakia of the Slovak Academy of Sciences. The home base is located at Tatranska Lomnica in Slovakia. Observatoire de Meudon Located in the southeast suburbs of Paris, the Observatoire de Meudon has a number of solar synoptic instruments and a database that is one of the oldest in the world. The observatory itself has been in operation since 1667, and includes a heliograph and spectroheliograph, producing both full-disk H-alpha and Ca II K 393.3 nm images.

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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE National Astronomical Observatory of Japan The National Astronomical Observatory of Japan (NAOJ) has two solar observing sites: Mitaka near Tokyo, with several solar telescopes (started in 1938), and Norikura in the Japanese Alps, with three coronagraphs (started in 1950). A third site at Okayama was recently closed. The Norikura site is used only in the summer due to access difficulties in heavy snow. A new vector magnetograph is planned for operation at Mikaka. Pic-du-Midi Pic-du-Midi is the site of the first coronagraph and is located in southwest France high in the Pyrenees. Synoptic observations have been taken at Pic-du-Midi since the 1940s. Recently the organization of this observatory has been in a state of flux, and the continuation of synoptic observations is not certain. Rome Astronomical Observatory The Rome Astronomical Observatory (OAR) has a long tradition of synoptic observations. Currently, OAR operates one of the RISE/PSPT instruments, as well as H-alpha and K-line filtergraphs. Teide Observatory This is a premier solar observing site on Tenerife in the Canary Islands, operated by the Instituto de Astrofisica de Canarias. The observatory has attracted some of the best European solar telescopes and instruments, among them the Franco-Italian THEMIS (see below), the German/KIS VTT (see above), as well as nodes of the GONG (United States of America), IRIS (France), and BiSON (United Kingdom) helioseismology networks. Télescope Héliographique pour l'Etude du Magnétisme et des Instabilités Solaires Télescope Héliographique pour l'Etude du Magnétisme et des Instabilités Solaires (THEMIS-Heliographic Telescope for the Study of Solar Magnetism and Atmospheric Instabilities) is a Franco-Italian project nearing completion at the Teide Observatory in the Canary Islands. This 90-cm aperture telescope is mainly a research instrument but will also produce daily full-disk magnetograms in the NaI D1 line. Selected Solar Radio Telescopes Outside the United States Nançay Radioheliograph The Nançay radioheliograph, a French facility, is currently the only instrument to provide the astronomical community with daily radio observations of the solar corona, 8 hours per day, all year round. The radiograph consists of a cross-shaped multiantenna

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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE array, comprising an east-west branch with 19 antennas along a 3200 meter baseline and a north-south branch of 24 antennas over a total length of 1250 meters. The radiograph can obtain true two-dimensional imaging of the solar corona, using all possible baselines of the cross-shaped array, at a rate of five images per second in each of five fixed wavelengths between 60 cm and 2 meters. Observations at different wavelengths probe different heights in the corona; the Nançay radioheliograph probes regions between 0.1 and 0.5 solar radius above the visible surface. Nobeyama Solar Radio Telescope The Nobeyama radioheliograph in Japan is a dedicated solar radio telescope that operates at two frequencies, 17 and 34 GHz. Operation at these frequencies probes the solar atmosphere much closer to the visible surface than the Nançay facility. Discussion Several of the facilities described above have research capabilities in a class similar to that of the U.S. National Solar Observatory. Particularly noteworthy are observatories on the islands of Tenerife and La Palma in the Canary Islands, which have attracted some of the best European solar telescopes and instruments, among them the Franco-Italian THEMIS, the German VTT, the Swedish VTT, and eight international instruments for solar seismology, with nodes of the most important helioseismological networks of all the world: GONG (United States of America), IRIS (France), and BiSON (United Kingdom). The Canary Island sites, especially La Palma, site of the Swedish VTT, have exceptional seeing for relatively long periods. The THEMIS telescope, although not yet fully operational, has a 1-meter aperture. However, this telescope is available only to French and Italian scientists; furthermore, it is experiencing problems that may prevent it from reaching its design objectives. The German National Facility has a number of telescopes, the largest of which is the 0.7-m German VTT. However, this VTT is oversubscribed and priority is given to German nationals. The Swedish VTT has a 48-cm aperture and accepts an international community of scientists. Although the instrumentation of the telescope is limited, it produces the very highest quality images of the Sun. It is currently planned for an upgrade to a 1-meter aperture to be complete in about 2 years. Both the German and Swedish telescope facilities are run as remote sites with a minimal resident staff. To use either of these telescopes, it is necessary to establish a collaboration with the appropriate scientific staff member. Other important optical observatories are located in China and Japan; however, these are seldom used by U.S. observers because of the lack of unique instrumentation and the cost of a visit. Nevertheless, these observatories often make important contributions during campaigns to observe the Sun 24 hours a day; BAO and BBSO collaborations have been especially productive. In summary, the task group believes that there is no solar observatory outside the United States that operates a wide range of well-documented instruments with resident observers to aid in their operation and, furthermore, that meeting the scientific challenges enumerated in Chapter 1 cannot be accomplished with existing U.S. or international solar

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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE facilities. Understanding many of the questions at the frontiers of solar physics requires resolving the interaction of magnetic fields and convective flows on the scales at which they occur, which the last decade of solar research has shown to require spatial resolutions of fractions of an arc-second and temporal resolutions of a few seconds. Further, the need for high sensitivity to magnetic fields also makes desirable an IR capability out to 15 µm. Operating at such long wavelengths with even minimally acceptable resolution requires a larger-aperture telescope than currently exists. Finally, the task group notes that upgrades to the capabilities of existing solar radio facilities would also be required to enable addressing several of the fundamental solar science questions mentioned in Chapter 1. DATA, THEORY, AND MODELING Studies of the Sun and its influence on the interplanetary and Earth environment often involve correlations between various observed physical parameters. Easy and efficient access to a variety of current and future data sets serves several important functions: It improves knowledge of solar and related phenomena through comparisons of data taken in campaign and synoptic modes at a multitude of wavelengths, spatial resolutions, and time scales. It is essential to the development of theoretical models. It offers a valuable educational tool, informational resource, and research opportunity for students, teachers, the general public, and scientists. Achieving a readily usable and accessible data archive requires an easily searchable catalog of data, access to data through user-friendly software, and the ability to handle the large quantities of data now available and that are planned for the future. Such data archiving is important to maintaining existing, ongoing, and future data sets. Several centers and institutions in the United States have, or will soon have, online images and other data available through the Internet. These include, for example, NASA/Solar Data Analysis Center, NOAA/Space Environment Center, NOAA/National Geophysical Data Center, High Altitude Observatory, National Solar Observatory (which is now placing its entire synoptic database spanning the last three decades online), and the Stanford SOHO helioseismology data center. These data, as well as data from other observatories around the world, are available via Web sites, electronic request, and anonymous ftp. The NSO SOLIS Telescope and the HAO Solar Magnetism Initiative (see Chapter 3) include data archiving as an integral and essential part of their programs. For example, efforts are already underway at NSO to assess the data requirements of the scientific and educational community for SOLIS, based in part on the current users of NSO's present synoptic database. However, it is often a formidable task to sift through the vast quantities of data for observations of specific solar phenomena without an intimate knowledge of the institution's archive structure or a catalog that goes beyond merely a list of the available data. As a result, several efforts are being advanced to provide a mechanism to identify and retrieve data from a large number of sources. For example, NASA is developing the

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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE Space Science Data System to provide a common or uniform catalog and access protocol for data access.13 Within the framework of this proposed program, a Solar Physics Data Service would provide access to both ground- and space-based solar data, insitu heliospheric observations, and relevant stellar data (e.g., activity and variability). The data itself would continue to reside at the home facilities or centers, where the characteristics of the data are best known, and users could interact directly with staff. The Whole-Sun Catalog14 reflects a similar approach and is being developed in conjunction with the ARTHEMIS15 and BASS 200016 archives. Using a commercial database application, it will provide robust storage of data catalogs and allow a search of data based on a broad list of parameters and solar phenomena. Common to these two approaches is an effort to encourage cooperation and participation in the archiving of databases spanning many relevant disciplines and to provide a common interface protocol to search and access the vast quantities of past, current, and future solar data sets. It is crucial in any data archive program, however, to be sensitive to and understand the requirements of the community using data archives, whether at institutions or through a common archiving and access protocol procedure (as well as to the cost-effectiveness of such efforts). Acknowledging the importance of providing data to the community, the task group encourages the cooperation and participation of observatories and institutions in efforts to archive and ensure access to their data. Indeed, the task group believes that cooperation and participation in data archiving and access programs should be an integral part of the planning of future telescopes and facilities. PEOPLE, PROGRAMS, AND INSTITUTIONS The critical ingredients that enable the capacity of state-of-the-art observing systems and the potential of richly populated data collections to be translated into scientific understanding are people, programs, and institutions. That is, science depends on being able to draw on a critical-mass-size research community (people) who, in turn, 13   The NASA Space Science Enterprise plans to establish a unified Space Science Data System (SSDS) to improve the quality, accessibility, and usability of NASA's space science data holdings for scientists, educators, and the general public. This will build on and evolve in phases from the current configuration of distributed data systems closely associated with the science community. The formulation and implementation of the SSDS will be led by the science community. See “The NASA Space Science Data System: A White Paper,” online at <http://rick.stanford.edu/ssds/wp.html/>. 14   The Whole-Sun Catalog aims to maintain a complete list of all solar observations made around the world each day. In addition, an interactive solar ephemeris is available for computing heliocentric and geocentric coordinates. 15   ARTHEMIS is an archive for solar data coming from the THEMIS telescope, the RISE/PSPT instrument in Rome, and the Whole-Sun Catalog. The archive has RISE/PSPT data beginning with July 1996 and running through the current date. The THEMIS data will be available once the telescope enters full operation. 16   BASS 2000 (BAse Solaire Sol 2000) is a French national database for solar observations, created to support THEMIS data and complement the MEDOC (Multi-Experiment Data Operations Center) database of space observations for SOHO. (MEDOC is designed to meet the needs of European SOHO investigators who wish to work together on data analysis and preparation of joint observations using SOHO instruments and European solar ground-based observatories.) Information about BASS 2000 is available online at <http://bass2000.bagn.obs-mip.fr/ows-doc-eng/presentation_generale_eng.html/ >.

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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE are supported by adequate intellectual and physical infrastructure (institutions). Specific programs can serve to integrate the contributions of various kinds of research (e.g., observations, theory, modeling) and promote the synthesis of new perspectives about critical scientific problems. The task group examines several aspects of these ingredients below, particularly as they relate to the size of the research community and the institutional base for U.S. solar research and the funding for that research. A strong and successful national program of solar research requires vigorous complementary research programs through programs for universities and institutes funded by NASA and NSF. NASA funding is typically mission related, focusing attention on specific research methods and tools developed by consortia of institutes and universities, while NSF funding is often topical, aiding and stimulating the freely inquiring initiatives of researchers. At present, there is a strong space-based solar observational program that is adequately funded to analyze and interpret the observations. Solar space research is carried out in university space science groups, NASA centers, Department of Defense research laboratories, and some corporate research facilities. However, historically strong, university-based research centers that carry on ground-based solar research (for example, those at the California Institute of Technology, Stanford University, the University of Maryland, and the University of Colorado) are losing or have lost tenured solar faculty. Although institutions such as the New Jersey Institute of Technology and Montana State University have stepped in with new faculty hires, the task group remains concerned about the loss of faculty at older research centers and its likely effect on training the next generation of graduate students. The task group is also concerned with the state of university-based instrumentation programs, as they are widely seen as essential to future instrument development, as well as the training of new researchers with hands-on experience. Existing programs are few in number and rely on precarious grant-based funding. The Demographics of Ground-based Solar Research It is difficult to identify “solar astronomers” or “solar researchers” from the larger pool of scientists engaged in work with a solar connection. For example, the once sharply separated interplanetary (solar wind, energetic particles) and solar communities now show considerable overlap. There now also are more stellar astronomers and high-energy physicists who make use of solar observations. In addition, the current interest in space weather has also led to an even greater blurring of boundaries as scientists in a variety of disiplines strive to trace the effects of solar events on Earth. With these trends and limitations in mind, the task group asked the Solar Physics Division (SPD) of the American Astronomical Society to provide a snapshot of the demographics of U.S. ground-based solar research based on membership data (see Appendix F). At the end of 1997, the SPD had 379 full-time members, 51 student members, and 74 affiliate members. From these data, the task group makes the following observations:

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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE The large number of universities involved (220) in solar research is indicative of a robust core community. Further, the numbers from the SPD are conservative and likely undercount the actual population of solar researchers. With only a few exceptions, there are only a few faculty members (typically, three or fewer) at each institution, and often only one. The task group believes that those institutions with large numbers of SPD faculty are all involved in space programs. The implication is that when there is an opportunity for state-of-the-art observations with cutting-edge instruments, the field attracts ample numbers of strong researchers. The number of students is small—even allowing for the likely undercounting—and is consistent with the task group's belief that a more promising observational future will be necessary to attract students to the field. Not linked to the SPD numbers, but relevant, is the observation that there is a second vigorous feeder community—the space physics community —that will move to solar astronomy if the facilities are there to do cutting-edge work. An estimate of the size of that community can be made by looking at the Space Physics and Aeronomy Section of the American Geophysical Union. Within that section (which had about 3,100 total members as of September 1, 1998), the Solar and Heliospheric Physics Section had 736 members. The Fiscal Context for Ground-based Solar Research The charge to the task group included consideration of the fiscal context in which ground-based solar research is now and might be pursued in the coming decade. A summary of funding trends for the NSO over the period from 1992 to 1999, derived from data provided by the NSF and the NOAO, is presented in Table 2.1. Box 2.1 provides an overall summary of NSF funding for solar and solar-related research in FY 1998. More detail is provided in Appendix G. There was a general decline in the NSO budget from $9.1 million in FY 1992 to less than $8 million in FY 1997, followed by a substantial increase to $9.7 million and $9.9 million in FY 1998 and FY 1999, respectively. That represents an 8.7% net growth over the 7-year interval, not counting for inflation. Over the same period the total NSF budget has increased by 42%. The increases for FY 1998 and FY 1999 compared to the earlier years are more than accounted for by additional funding for SOLIS, a 3-year project slated to be completed in February 2001. NSF funding for NSO came primarily from the Astronomy Division. The Atmospheric Sciences Division funded the other major national facility, the High Altitude Observatory, at a level of $5.4 million in FY 1998. To examine other portions of NSF funding for solar research the task group used NSF data to create a snapshot for FY 1998. The total funding awarded for grants for solar research was $11.3 million. When awards by NSF to support solar-related research (i.e., solar-terrestrial, solar wind, and solar wind/magnetosphere/ionosphere interaction studies and studies of solar influences on climate, oceans, and/or the biosphere) are included, the total funding was $17.5 million. There were 163 solar research grants awarded over the period, of which 84% (137) representing 90% of the funds went to

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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE university investigators or university-affiliated solar observatories. Of the larger pool of solar plus solar-related grants, 87% (222 of 255) representing 88% of the funds went to university investigators or observatories. The NSF Atmospheric Sciences and Physics divisions provided the largest portion of grant funding (nearly 80% of the total). Box 2.1 shows that the total funding for the two major national solar research facilities or centers sponsored by the NSF received funding at a level above the funding for grants specifically focused on solar research but below the total NSF grant funding for solar and solar-related research. Box 2.1 also shows that the total NSF investment is on the order of $32 million. For comparison, NASA officials indicated that funding for research and analysis grants in the Sun-Earth Connections program has been running at about $24 million per year. TABLE 2.1 Trends in NSF Funding for the National Solar Observatory, FY 1992 to FY 1999   Fiscal Year   1992 1993 1994 1995 1996 1997 1998 1999 Centers and Initiatives                 NOAO/NSO                 NSO/KP 2174 1926 2105 2240 2334 2418 2232 2305 NSO/SP 2986 2616 2635 2376 2325 2210 2367 2395 NSO 5778 5075 5311 5189 5245 5220 5119 5287 GONG 3278 2684 3272 3140 2380 2107 2217 2216 RISE 52 142 197 274 456 439     SOLIS             2396 2396 TOTAL 9108 7868 8780 8603 8051 7766 9731 9900 NOTE: The numbers shown represent actual-year figures in thousands of dollars. They are not adjusted for inflation. Overhead is included in the totals, calculated on the basis of 19.8% for NSO/KP and 9.6% for NSO/Sac Peak. SOURCE: Data are taken from 1993, 1995, 1997, and 1998 annual programplans prepared by NOAO, NSO, and from NSF.

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GROUND-BASED SOLAR RESEARCH: AN ASSESSMENT AND STRATEGY FOR THE FUTURE BOX 2.1 Summary of NSF Solar Research Funding for FY 1998 (in $ millions) NSO Kitt Peak and Tucson facilities 2.5 NSO Sacramento Peak facilities 2.0 GONG 2.2 SOLIS 2.4 Total NSO 9.1 HAO 5.4 NSF solar research grants 11.3 NSF solar-related research grants 6.2 Total NSF research grants 17.5 Total NSF funding 32.0 Research Bases Historically, many of the innovations that have led to new observational facilities have had their origins in small-scale university and institutional research. Theoretical concepts originating from studies of solar activity, include, for example, coronal expansion and the solar wind and the heliosphere, the solar dynamo, rapid reconnection of magnetic fields, radio emission from plasma oscillations, and the negative hydrogen ion. Much of the current solar data analysis and theory is carried out in universities and in national institutes (e.g., HAO and NSO) with NSF funding, or in institutes and universities that focus more on space-based projects, with only indirect attention to ground-based studies, through supporting research and technology contracts from NASA. Thus, for example, the Big Bear Solar Observatory, the Lockheed Martin Solar Research Laboratory, the Marshall Space Flight Center, and others reflect the changing funding patterns away from traditional NSF support, now significantly oriented to exploit and support space observations of the Sun. New university groups at Michigan State University, California State University at Northridge, Montana State University, and the New Jersey Institute of Technology are part of this same trend.