HF coherent scatter radar observations of ionospheric convection during magnetospheric substorms
スポンサーリンク
概要
- 論文の詳細を見る
Observations of ionospheric convection have proven to be extremely valuable in understanding the interaction between the solar wind and the magnetosphere, particularly through the process of magnetic reconnection. In addition, the response of ionospheric convection to substorm activity can provide insight into the mechanisms associated with magnetospheric substorms. In this paper we review observations of ionospheric convection during all phases of the substorm made by HF coherent scatter radars such as those that form the Super Dual Auroral Radar Network (SuperDARN). By concentrating on HF coherent scatter radar observations we stress the importance of ion velocity measurements rather than the conductance controlled ionospheric electrojets. The observations reviewed in this paper demonstrate a number of key results. Following long periods of quiet magnetic activity usually associated with intervals of northward interplanetary magnetic field (IMF), the region of radai backscatter in the dusk local time sector moves equatorward. Based upon this motion of the radar backscatter and a model for the reconnection rate at the dayside magnetopause, it is possible to estimate the length of the reconnection line at the magnetopause, which is found to vary between 12 and 27 R_E. At expansion phase onset, the scatter can often be lost for short periods of time due to absorption of the HF radio wave. There is also evidence that convection vortices in the post noon local time sector relax at the time of expansion phase onset, which hints at a global response to the expansion phase onset. During the latter part of the expansion phase bursts of flow are seen to occur which have repetition rates similar to flux transfer events (FTEs) and current vortices similar to the ionospheric signatures of FTEs. HF coherent scatter radars also play a key role in multi-instrument studies of magnetospheric substorms, for example providing near continuous observations of the convection reversal boundary as a proxy for the polar cap boundary. The recovery phase is the least studied of the various phases but there are key observations of omega bands in the post midnight local time sector, which also hint at the expansion phase being a global phenomenon. The paper concludes with some suggestions of how HF coherent scatter radars will be used in future studies of convection during substorms.
著者
関連論文
- HF coherent scatter radar observations of ionospheric convection during magnetospheric substorms
- A rectified response of daytime radio wave absorption to southward and northward excursions during northward interplanetary magnetic field: A case study
- Interhemispheric differences in the HF radar signature of the cusp region: A review through the study of a case example