Nighttime VHF scintillations observed at Lunping (magnetic latitude 14.7¿N) during four specific seasonal storms showed four different types of behavior: Scintillation activity was found to be either inhibited or triggered during magnetic storms depending on the phase of the storm and its local time. A qualitative explanation for this behavior is attempted in terms of storm time electric fields. The triggering of postmidnight scintillation activity during the recovery phase seems to be a result of penetration of the dusk-dawn electric fields due to shielding charges developed in the ring current region, while inhibition of usual premidnight scintillation activity seems to be related to the ionospheric disturbance dynamo electric fields acting opposite to normal fields. One case where post-sunset scintillation activity was triggered seems to be a result of penetration of dawn-dusk convection electric field which developed following the main phase onset. ¿ American Geophysical Union 1993