spaceweb@oulu.fi - last update: 30 April 1997, 1000 UT (RR) . In the magnetospheric physics, the ballooning mode instability (BMI) is a disturbance of the equilibrium between outward directed forces caused by the particle pressure and the curvature drift on one hand and inward directed forces exerted by the tangential stress of the field lines on the other hand (e.g., Hameiri et al., ... For recent references on ballooning instability, see, e.g., Liu (1997). ... 102 , 4927-4931, 1997. ...