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Modern Solar Facilities – Advanced Solar Science, 31–38 F. Kneer, K. G. Puschmann, A. D. Wittmann (eds.) c  Universitätsverlag Göttingen 2007 Ground-based solar facilities in the U.S.A. C. Denker1,2,*, D. E. Gary1, and T. R. Rimmele3 1New Jersey Institute of Technology, Newark, NJ, U.S.A. 2Astrophysikalisches Institut Potsdam, Potsdam, Germany 3National Solar Observatory/Sacramento Peak, Sunspot, NM, U.S.A. *Email: cdenker@adm.njit.edu Abstract. In this review, we present the status of new ground-based facilities for optical and radio observations of the Sun in the United States. The 4-meter aperture Advanced Technology Solar Telescope (ATST) under the stewardship of the National Solar Observatory (NSO) has successfully completed its design phase and awaits funding approval. The 1.6-meter aperture New Solar Telescope (NST) at Big Bear Solar Observatory (BBSO) is currently under construction. Complementing these optical telescopes is the Frequency Agile Solar Radiotelescope (FASR) – an instrument for dynamic broadband imaging spectroscopy covering a multitude of radio frequencies from 50 MHz to 20 GHz. Imaging spectroscopy and polarimetry are common features of these telescopes, which will provide new insight regarding the evolution and nature of solar magnetic fields. High-resolution observations of solar activity, bridging the solar atmosphere from the photosphere to the corona, will be obtained with a dedicated suite of instruments. Special emphasis of this review will be put on the interplay between instrumentation and scientific discovery. 1 Introduction Astronomy, astrophysics and solar physics in the United States are periodically evaluated by panels of the National Research Council (Parker 1998; McKee & Taylor 2001; Lanzerotti 2003). In the latest review, the Panel on the Sun and Heliospheric Physics as part of the Solar and Space Physics Decadal Survey (Lanzerotti 2003) identified and prioritized four science questions for new research initiatives in solar and heliospheric physics: (1) What physical processes are responsible for coronal heating and solar wind acceleration, and what controls the development and evolution of the solar wind in the innermost heliosphere. (2) What determines the magnetic structure of the Sun and its evolution in time, and what physical processes determine how and where magnetic flux emerges from beneath the photosphere? (3) What is the physics of explosive energy release in the solar atmosphere, and how do the resulting heliospheric disturbances evolve in space and time? (4) What is the physical nature of the outer heliosphere, and how does the heliosphere interact with the galaxy? The unique combination and research thrusts of the three U.S. ground-based initiatives FASR (Gary 2003; Bastian 2003), NST (Denker et al. 2006), and ATST (Rimmele et al. 2003; Keil et al. 2004a; Oschmann et al. 2004; Rimmele et al. 2005; Wagner et al. 2006) in collaboration with many other national and international programs will undoubtedly advance solar and heliospheric physics across this broad theme in the years to come. These major initiatives are also well-aligned with current and future space missions. 32 C. Denker et al.: Ground-based solar facilities in the U.S.A. Before discussing these major projects in detail, some of the other U.S. ground-based projects should briefly be mentioned. The Global Oscillation Network Group (GONG, Harvey et al. 1996) is a world-wide network of six observing stations to study the internal structure and dynamics of the Sun using helioseismology. In particular, the Sun’s “five minute” oscillations are determined from line shifts due to the Doppler effect, which are measured in the Ni I line at 676.8 nm with a polarizing Michelson interferometer. Synoptic Optical Longterm Investigations of the Sun (SOLIS, Keller et al. 2003) is a synoptic facility to understand the solar activity cycle and monitor solar irradiance changes. The SOLIS instrument suite consists of a Vector Spectromagnetograph (VSM), a Full Disk Patrol (FDP) instrument and an Integrated Sunlight Spectrometer (ISS). Another instrument for synoptic studies of the Sun is the Optical Solar Patrol Network (OSPAN), formerly known as the Improved Solar Observing Optical Network (ISOON, Neidig et al. 1998). OSPAN data products include Hα, He I 1083.0 nm and red continuum full-disk images as well as line-of-sight magnetograms in the Ca I line at 612.2 nm. Future instruments include the Coronal Solar Magnetism Observatory (COSMO), a meter-class coronagraph, which has been proposed by the High Altitude Observatory. COSMO would replace the existing Mauna Loa Solar Observatory operated by the National Center for Atmospheric Research. 2 Frequency Agile Solar Radiotelescope Figure 1. Frequency Agile Solar...

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