We use APEX mapping observations of ^ { 13 } CO , and C ^ { 18 } O ( 2-1 ) to investigate the internal gas kinematics of the filamentary cloud G350.54 + 0.69 , composed of the two distinct filaments G350.5-N and G350.5-S. G350.54 + 0.69 as a whole is supersonic and gravitationally bound .
We find a large-scale periodic velocity oscillation along the entire G350.5-N filament with a wavelength of \sim 1.3 pc and an amplitude of \sim 0.12 km s ^ { -1 } .
Comparing with gravitational-instability induced core formation models , we conjecture that this periodic velocity oscillation could be driven by a combination of longitudinal gravitational instability and a large-scale periodic physical oscillation along the filament .
The latter may be an example of an MHD transverse wave .
This hypothesis can be tested with Zeeman and dust polarization measurements .