What is airflow vibrato?

Vocal vibrato has a number of manifestations. Typically vibrato is first thought of as a variation in fundamental frequency (fo), and secondarily as a variation in intensity and sound quality. Other variations that accompany these three types of vibrato include movement of throat structures (changes in larynx height, alterations in arytenoid adduction, pharyngeal wall movement, tongue movement, etc.), and especially muscle contraction variations that accompany all mentioned vibrato types.