Large-Amplitude Plasma Convection in the High-Latitude Ionosphere

We have investigated ~100 large-amplitude or "fast flow" convection events (> 5 km/s) in the ionosphere measured by the vector electric field double probe on NASA's Dynamics Explorer-2 satellite in years 1981-83. The large E x B velocities can appear at nearly all local time sectors, but are most common in the dawn/morning sector (6-12 MLT). In addition, they appear regularly at dusk (around 18 MLT) and in the pre-midnight sector (21-24 MLT). The fast flows are most common between 70-80° of invariant latitude but are also observed within 60-70° invariant latitude especially in the dusk/pre-midnight sector. For most events, the AE index is above 200 nT but there are also events during quiet intervals (<100 nT). Significant differences in the AE index between dawn/dayside and dusk/nightside events reveal that the dawn/dayside events tend to occur only during active intervals while the dusk/nightside events can occur also during quiet intervals. The strongest events include convection enhancements that last from a second to 10 seconds, so that estimates of their horizontal spatial scales (ignoring temporal variations) typically extend for 10-100 km. Shorter scale variations (below a second or <5 km) are also observed. We examine these fast plasma flows in view of energy transfer between the magnetosphere and ionosphere during active and quiet conditions.