Scintillation and EISCAT investigations of gradient-drift irregularities in the high latitude ionosphere

Scintillation observations of vhf satellite transmissions provide information on the occurrence of ionospheric irregularities with horizontal scale sizes in the sub-kilometre regime. Although incapable of sufficient resolution to observe such irregularities, incoherent scatter radar yields measurements of ionospheric plasma parameters on a larger scale. Thus, coordinated observations using both techniques allow a study of the mechanisms responsible for the production and growth of the small scale irregularities. Results are presented of scintillation measurements made at Kiruna in northern Sweden using transmissions from satellites in the Navy Navigational Satellite System (NNSS) at times when the European incoherent scatter radar facility (EISCAT) was operating in a meridional scan common programme mode. Two satellite passes are discussed in which scintillation-producing irregularities were found in the vicinity of larger scale long-lived gradients in F-region electron density. Radar measurements of plasma drift velocity indicate that the small scale structures could have originated from destabilization of the electron density gradients by the E sx B gradient-drift instability mechanism.