A STUDY OF LOW-LATITUDE VHF SCINTILLATIONS IN RELATION TO ELECTRIC-FIELDS DURING MAGNETIC STORMS

Nighttime VHF scintillations observed at Lunping (magnetic latitude 14 .7-degrees-N) during four specific seasonal storms showed four differe nt types of behaviour: Scintillation activity was found to be either i nhibited or triggered during magnetic storms depending on the phase of the storm and its local time. A qualitative explanation for this beha viour is attempted in terms of storm time electric fields. The trigger ing of postmidnight scintillation activity during the recovery phase s eems to be a result of penetration of the dusk-dawn electric fields du e to shielding charges developed in the ring current region,while inhi bition 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 w as triggered seems to be a result of penetration of dawn-dusk convecti on electric field which developed following the main phase onset.