GROUND-BASED SOLAR MEASUREMENTS
Significant science results of the past decade were accomplished at ground-based facilities—probing solar processes from the interior through the solar surface to the chromosphere and corona. Existing ground-based optical platforms include the Mauna Loa Solar Observatory (operated by HAO), the Sacramento Peak Observatory, Kitt Peak Observatory, GONG, and SOLIS (operated by the National Solar Observatory), the Mees Solar Observatory (University of Hawaii), the Big Bear Solar Observatory (New Jersey Institute of Technology), the San Fernando Observatory (CSUN), and the Mt. Wilson 60-foot tower (USC) and Mt. Wilson 150-foot tower (UCLA). Existing ground-based radio platforms include the Owens Valley Radio Observatory (OVSA; operated by NJIT), the Long-Wavelength Array (New Mexico State University), and the Haystack Mountain Observatory (MIT).
The Advanced Technology Solar Telescope (ATST) will provide U.S. leadership in large-aperture, high-resolution, ground-based solar observations and will be a unique complement to space-borne and existing ground-based observations. Full-Sun measurements by existing synoptic facilities (e.g., GONG, SOLIS, and ISOON), and new initiatives such as the Coronal Solar Magnetism Observatory (COSMO) and the Frequency-Agile Solar Radiotelescope (FASR), have the potential to balance the narrow field of view captured by ATST and are essential for the study of transient phenomena.
A major science goal is to continue comparison of highly resolved observations with numerical models in order to critically define the physical nature of photospheric features such as sunspots, faculae, and cool molecular clouds. Another goal is to better understand the physical behavior of magnetic fields in the chromosphere and corona—both on small and large scales—in order to study the flow, storage, and eruption of energy and mass in these poorly understood regions. The recent, mostly unexpected, behavior of the solar cycle and solar scientists’ inability to predict its future course makes synoptic studies of the magnetic field and surface and interior mass flows that are related to the solar dynamo a high-priority goal. Ground-based observations are increasingly used in near-real-time data-driven models of the heliosphere and space weather. A goal is to improve the quality of these measurements and to extend them upward into the chromosphere and corona.
Compared with space missions, ground-based facilities can be far larger, more flexible and exploratory, and longer-lived. Accordingly, emphasis is on achieving high spatial resolution (e.g., NST, ATST), making unique measurements of physical processes at long wavelengths (e.g., OVSA, FASR), and collecting sufficient light flux to make high-time-resolution, high-precision measurements of magnetic and velocity fields, long-term synoptic observations, and novel frontier observations of various kinds (e.g., COSMO).
GROUND-BASED ATMOSPHERE-IONOSPHERE MEASUREMENTS
Ionospheric modification is an incisive tool for probing the upper atmosphere from the ground and offers a means of performing repeatable experiments and obtaining reproducible results. Ionospheric modifications use powerful high-frequency transmitters to induce phenomena in ionospheric plasmas. Some of these phenomena give insights into complicated plasma physics processes that may occur elsewhere in nature but that are difficult or impossible to explore in the laboratory or numerically. Other processes provide diagnostics of naturally occurring ionospheric phenomena and of natural rate constants that are otherwise hard to quantify. Ionospheric modification experiments affect the propagation of radio signals passing through the modified volume, which is how the phenomenon was first discovered (i.e,. the radio Luxembourg effect). These experiments generate airglow and radio emissions, which can be observed from the ground; create field-aligned plasma density irregularities that can be interrogated by small coherent scatter radars; generate low-frequency radio signals, which have practical societal utility; accelerate