Research on thegeneration mechanisms of ion upflow in the polar cap ionosphere by using ESR.

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By using EISCAT radars together with satellites, we have investigated mainly three aspects of ion upflow phenomena in order to understand the generation mechanisms of ion up flow. The first step was to investigate the relationship between ion upflow and particle precipitation which is different between several magnetospheric regions. The second step was to investigate the relationship between ion upflow and heating, from the macroscopic point of view. The third step was to investigate the characteristics of naturally enhanced ion-acoustic lines (NEIALs), which may be caused by plasma instabilities and are strongly related to ion upflow from the microscopic point of view. We have examined the regions where dayside field-aligned (FA) ion upflows occur, based on a statistical analysis using approximately 170 simultaneous events between the ESR and the DMSP satellites. This systematic analysis for ion upflow has never been examined. We found that ion up flows occur not only in the cusp and … More cleft (the low altitude portion of the low-latitude boundary layer (LLBL)) which have been considered as ion up flow regions, but also in the topside ionosphere connected to the mantle region. Ion upflows seldom occur either in the Boundary Plasma Sheet (EPS) or in the Central Plasma Sheet (CPS) in the dayside high latitudes. Almost all of the events in which the average FA ion velocity is more than 100 m s^<-1> are associated with sufficient soft electron precipitation (differential energy flux of electrons at 100 eV > 10^7 eV cm^<-2> s^<-1> sr^<-1> eV^<-1>). Although soft electron precipitation also sufficiently exists in the EPS, the ion velocities are mostly less than 100 m s^<-1>. The present results indicate that soft particle precipitation is the predominant energy source driving ion up flow in the topside ionosphere, but it works on ion upflow effectively in the higher latitude regions in the dayside and not in the EPS. In addition, plasma heating associated with FA ion upflow in the daysjde topside ionosphere has been examined using data obtained simultaneously with the ESR and the EISCAT VHP radar, and also the wave number (k)-dependence of the received power in high signal-to-noise ratio (SNR) conditions, occurring for NEIALs and for real satellites, has been investigated.The results from these three investigations lead to the conclusion that the energy of soft electron precipitation is considered as the main source of the ion up flow. The energy of soft particle precipitation is supplied to the ions in the topside ionosphere via wave-particle interaction, such as wave-induced transverse ion heating, and upward parallel electric field due to anomalous resistively produced by plasma turbulence. Thus generation mechanisms of ion upflow must have the transversely ion heating and the upward acceleration by wave-particle interaction while the induced plasma waves decay. In addition to direct precipitation effects, namely enhanced ambipolar diffusion and heat flux, wave-particle interaction may hence play an important role in driving ion upflow. Less