Sound emission due to superfluid vortex reconnections
  By performing numerical simulations of superfluid vortex ring collisions we make direct quantitative measurements of the sound energy released due to vortex reconnections. We show that the energy radiated expressed in terms of the loss of vortex line length is a simple function of the reconnection angle. In addition, we study the temporal and spatial distribution of the radiation and show that energy is emitted in the form of a rarefaction pulse. The pulse evolves into a sound wave with a wavelength of 6-8 healing lengths. 
M. Leadbeater, T. Winiecki, D. C. Samuels, C. F. Barenghi, and C. S.   Adams