磁暴期间高纬顶部电离层离子上行特征——DMSP卫星观测

本文利用DMSP F13和F15卫星观测数据,对2001—2005年58个磁暴(-472 nT≤Min.Dst≤-71 nT)期间高纬顶部电离层离子整体上行特征进行了统计研究.观测表明,磁暴期间,顶部电离层离子上行主要发生在极尖区和夜间极光椭圆区.在北半球,磁正午前,高速的离子上行(≥500 m·s-1)多集中在65° MLat以上;午后,高速离子上行区向低纬度扩展,上行速度要略高于午前;在南半球,磁午夜前,DMSP卫星在考察区域内几乎所有的纬度上都观测到了高速上行的离子;午夜后,各纬度上观测到上行离子的速度明显降低.离子上行期间,DMSP卫星在极区顶部电离层高度上也频繁地观测到电子/离子增温,且电子增温发生的频率要远高于离子增温.O+密度变化分析显示,DMSP卫星磁暴期间观测到的上行离子更多地源于顶部电离层高度.这些结果表明电子增温在驱动暴时电离层离子整体上行过程中起着重要作用.

Feature of ion up-flow at high-latitude topside ionosphere during geomagnetic storms from the Defense Meteorological Satellite Program

A statistical study was carried out on the characteristics of storm-time bulk ion upflows at high-latitude topside ionosphere, with observations from DMSP F13 and F15 spacecraft during 58 geomagnetic storms (-472 nT≤Min.Dst≤-71 nT)in the period of 2001—2005. Analysis shows that, during the geomagnetic storms, topside ionospheric ion upflows were primarily detected in the cusp and night-time auroral region. In the northern hemisphere, high-speed (≥500 m·s^-1) up-flowing ions were frequently observed at altitudes above 65° MLat before magnetic noon, and high-speed ion up-flowing region was extended to lower latitude with slightly higher velocity after magnetic noon. In the southern hemisphere, however, high-speed up-flowing ions could be detected everywhere before midnight. It was found that storm-time ion upflows at high-latitude topside ionosphere are usually accompanied by electron/ion heating, during which electron heating predominated. Analysis of O⁺ density variation indicates that up-flowing ions observed by DMSP spacecrafts during storms are mainly from topside ionosphere. It is suggested that electron heating is an important driving force for storm-time ionospheric up-flowing ions.