Zhengwei Cheng

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.

Distribution of field-aligned electron events in the high-altitude polar region: Cluster observations

Field Aligned Electrons (FAEs) are important for the energy transport in the solar wind-magnetosphere-ionosphere coupling. However, the distribution of FAEs and the concerning physical mechanism in different altitudes of the polar region are still unclear. In this paper, data from the Cluster spacecraft were used to study the characteristics of FAEs in high altitude polar region. We selected FAE events with a flux higher than 3×108(cm2﹒s)-1 for our analysis. Their distribution was double peaked around the auroral oval. The main peak occurred around the cusp region (MLT 0700-1500) which leaned to the dawnside. The other peak appeared in the evening sector with MLT 2100-2300 just before midnight. The durations of the FAE events covered a wide range from 4 to 475 seconds, with most of the FAE events lasting less than 40 seconds. The possible physical mechanisms are discussed, namely that the downward FAEs may consist of decelerated solar wind and reflected up-flowing ionospheric electrons in the potential drops, whereas the upward ones may be mirrored solar wind electrons and accelerated ionospheric up-flowing electrons.

Some properties of field-aligned electron events in high-altitude polar regions

Using data from the Cluster spacecraft from January 2003 to December 2004, we perform a statistical study on some properties of the field-aligned electron (FAE) events and interplanetary magnetic field (IMF) By dependence of FAE events with different durations in high-altitude polar regions. A total of 1335 FAE events were observed by the C3 spacecraft. More down-flowing events were observed in the Southern Hemisphere, and more up-flowing events were observed in the Northern Hemisphere. It proves that down-flowing events mainly originate from magnetosphere or solar wind and up-flowing events are mainly derived from ionosphere. Short-lifetime events showed a morning concentration in the magnetic local time distribution, and long-lifetime events were concentrated both before and after noon. For the IMF By dependence of the FAE events, short-lifetime events were much affected by IMF By and resulted in a morning concentration, while the long-lifetime events were almost unaffected by IMF By. With further analysis, we determined that the short-lifetime and long-lifetime events had different sources.