A "Mission-Class" Ground-Based Geospace Observing Program

Coupling between regions, and across spatio-temporal scales and between energy ranges is of fundamental importance in geospace dynamics. This is perhaps most interesting in Earth's ionosphere, where the neutral atmosphere and vast magnetosphere overlap. On small scales, in situ space-based observations have explored the mechanisms that accomplish transport and coupling. Similarly, observatory-class ground-based installations (e.g., EISCAT, RISR, Sondrestrom, Arecibo, etc.) provide comprehensive observations of upper-atmospheric parameters such as convection, particle precipitation, neutral winds, and more, but only in relatively small regions above those facilities. At the far-end of the scale-spectrum, satellite-borne imagers and extensive ground-based networks provide effectively global but much lower fidelity information. Combining such in situ and global remote sensing observations was the strategy of ISTP, a program which highlighted the importance of simultaneous observations of the small-scale processes and their system-level consequences. It turns out that for system-level science, there is a critical range of scales within which we have done a poor job of observing. The questions at the forefront of our field demand that observations with higher resolution than can be achieved globally be made over larger regions than can be observed from one location (either on the ground or in space). In auroral observations, we have bridged this scale-gap with the continent-wide THEMIS-ASI network. Having the ability to image mesoscale processes such as the substorm onset with spatial and temporal resolution allowing for tracking key dynamic aurora such as arcs and streamers has been truly revolutionary. However, THEMIS-ASI gives us only the aurora, and only in white-light. In this paper, I will present what I argue is the logical and achievable observational "next step" for geospace research at the system level. I imagine a true mission class ground-based observing program, where an extensive sensor web would provide 3D imaging of convection, multi-wavelength auroral intensities, composition, neutral winds, charge densities, and more, all in a region large enough to span key mesoscale processes. By "mission class", I mean we should dare to spend as much on this as we spend on a typical satellite mission. For "large enough", I imagine a combined field of view extending from deep in the polar cap to mid-latitudes, and spanning several hours of MLT. This project would fuel the science of both GEM and CEDAR, and would pave the way for profound steps forward in our understanding of the multi-scale geospace dynamics.