Astro2020 Science White Paper: Dynamical Processes in the Planet-Forming
  Environment
  The transfer of circumstellar disk mass and momentum onto the protostar and
out into the environment occurs via a variety of mechanisms including
magnetospheric accretion, jets, outflows, and disk winds. The interplay of
these processes determine both the conditions under which planet formation
occurs and the lifetime of the disk. Metallic emission lines, along with the
Balmer series of hydrogen, probe the kinematics of gas within the
planet-forming and central regions of circumstellar disks. High-spectral
resolution study of these emission lines provides critical information on mass
and momentum loss, turbulence, and disk wind origins.
