Temporal and spatial scales of a high‐flux electron disturbance in the cusp region: Cluster observations

Using the Cluster multispacecraft observations, we analyze a long-duration field-aligned high-flux electron disturbance in the cusp region on 30 September 2001. All four Cluster spacecraft observed the same disturbance in which both the upward and downward electrons are observed and the electron flux was 1 order of magnitude higher than usual in the cusp. The temporal scale of the field-aligned electron disturbance was at least 50 min. The spatial scale was about 540 km in the direction along the orbit and at least 1800 km in local time extent in the midaltitude cusp region. It was the longest duration and the largest spatial scale of any field-aligned electron disturbance observed in the polar region up to date, and its observation would not have been possible with a single satellite. Both upward and downward electrons are the main contributors to the field-aligned currents in the electron disturbance. During this electron disturbance, the solar wind dynamic pressure increased, and the interplanetary magnetic field (IMF) kept being southward. It is likely that the field-aligned high-flux electron disturbance with its long temporal and large spatial scales was caused by high dynamic pressure of the solar wind during a permanently southward IMF. This enables us to learn more about electron disturbances in the cusp and is important to understand the physical mechanism, especially for the solar wind-magnetosphere-ionosphere coupling.