Spatial distribution of ionospheric plasma and field structures in the high-latitude F region

Plasma processes are considered to be logical causes for high-latitude plasma irregularities, since there are several sources of free energy available to drive various plasma instabilities. Some of these sources are density gradients, and velocity shears. Kilometer-size ion-density irregularities in high-latitude F region ionosphere are closely related to larger-scale features, such as ionization patches. To study the intermediate-scale (0.1-100 km) structure and its relationship to background conditions in the ionosphere we have formed a reduced database using 16 km segments of the ion density and velocity data obtained from the Dynamics Explorer-2 satellite. The background gradients associated with each segment and the spectral characteristics, such as power at 6 Hz ({dollar}approx{dollar}1.3 km) and spectral index, are among the reduced parameters used in this study. The spectral characteristics of irregularities, seated on large density gradients associated with polar cap ionization patches, are studied. Slightly smaller spectral indices for trailing edges compared to those seen on leading edges support the presence of the {dollar}E times B{dollar} drift instability, but results suggest that stirring by velocity structure may be a more significant contributor to kilometer-size structures in the polar cap. The reduced database is also used to describe the average characteristics of density and velocity structure as a function of magnetic local time and invariant latitude. The relationship between the observed plasma structure and its motion is complex and dependent on the externally applied fields as well as locally generated plasma structure. The evolution of plasma structures also depends critically on the conductivity of the underlying ionosphere. Observations indicate an enhancement of irregularity amplitudes in two spatially isolated regions in both the ion density and the velocity. Convective properties seem to play a more important role in the winter hemisphere where smaller-scale structures are maintained outside the source regions. Velocity irregularity amplitudes are enhanced during northward interplanetary magnetic field regardless of season. The power in velocity is usually higher than that associated with local polarization electric fields suggesting that the observed structure in density is strongly influenced by velocity structure applied to large density gradients.