13:45 〜 14:00
[PEM14-13] Two Types of Plasma Flow Oscillations Observed at Midlatitude Topside Ionosphere
キーワード：Two types of plasma flow oscillations are observed at midlatitude topside ionosphere., Type I oscillation has three plasma flows oscillating together with the density. , Type II oscillation in the two perpendicular components without density oscillation., Type I oscillation comes lower ionosphere and Type II is originated from the magnetosphere.
Two types of plasma flow oscillations with different characteristics are observed by The Republic of China Satellite-1 (ROCSAT-1) at 600 km midlatitude topside ionosphere. The plasma flows perpendicular to the background geomagnetic field line oscillate in the outward and zonal directions in both types of flow oscillations. For the Type I oscillation, it further indicates that the field-aligned plasma flow and the density are oscillating. On the other hand, these two ion parameters are not oscillating in the Type II oscillation. The perpendicular plasma flow components in these two types of oscillations have different wave form characteristics (linear vs. circularly left-handed polarization; half cycle vs. full cycle) that reveal different origins of the observed plasma flow oscillations. As Type II oscillations (full cycle with circular/elliptical polarization) are observed at the onset of a substorm/storm, the cause is related to the magnetospheric fast mode that is generated during the substorm/storm period. The inward propagating fast wave then resonate interacts with the magnetic field lines in the topside ionosphere near Earth to convert into a transverse Alfven wave observed as the Type II plasma flow oscillation. On the other hand, Type I oscillation (half cycle with linear polarization) that occurs without the substorm/storm onset can be theoretically connected to the Perkins instability process in the nighttime midlatitude bottomside ionosphere.