  This white paper advocates the importance of multi-height measurements of the
vector magnetic field in the solar atmosphere. As briefly described in this
document, these measurements are critical for addressing some of the most
fundamental questions in solar and heliospheric physics today, including: (1)
What is the origin of the magnetic field observed in the solar atmosphere? (2)
What is the coupling between magnetic fields and flows throughout the solar
atmosphere? Accurate measurements of the photospheric and chromospheric
three-dimensional magnetic fields are required for a precise determination of
the emergence and evolution of active regions. Newly emerging magnetic flux in
pre-existing magnetic regions causes an increase in the topological complexity
of the magnetic field, which leads to flares and coronal mass ejections.
Measurements of the vector magnetic field constitute also the primary product
for space weather operations, research, and modeling of the solar atmosphere
and heliosphere. The proposed next generation Ground-based solar Observing
Network Group (ngGONG), a coordinated system of multi-platform instruments,
will address these questions and provide large datasets for statistical
investigations of solar feature behavior and evolution and continuity in
monitoring for space-weather focused endeavors both research and operational.
It will also enable sun-as-a-star investigations, crucial as we look toward
understanding other planet-hosting stars.
