Relationship between ion upflows and suprathermal ions observed with the EISCAT Svalbard radar and Reimei satellite

Ogawa, Y.1, Seki, K.2, Hirahara, M.3, Asamura, K.4, Sakanoi, T.5, Ebihara, Y.6, Obuchi, Y.5, Buchert, S. C.7, Nozawa, S.2 and Fujii, R.2

1 National Institute of Polar Research, Tokyo, Japan
2 Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Japan
3 Department of Physics, College of Science, Rikkyo University, Tokyo, Japan
4 Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Kanagawa, Japan
5 Planetary Plasma and Atmospheric Research Center, Graduate School of Science, Tohoku University, Miyagi, Japan
6 Institute for Advanced Research, Nagoya University, Nagoya, Japan
7 Swedish Institute of Space Physics, Uppsala, Sweden

The relationship between bulk ion upflows and suprathermal ions was investigated using data simultaneously obtained from the European Incoherent Scatter (EISCAT) Svalbard radar (ESR) and the Reimei satellite. Simultaneous observations were conducted in November 2005 and August 2006, and 14 conjunction data have been obtained at approximately 630 km in the dayside ionosphere. In the dayside cusp region, suprathermal ions with energies of a few eV were present, and the ion velocity distribution changed from an isotropic Maxwellian to tail heating at energies above a few eV. The velocity distribution of the suprathermal ions has a peak perpendicular or oblique to the geomagnetic field, and the temperature of the suprathermal ions was 0.9-1.4 eV. An increase in the phase space density (PSD) of the suprathermal ions, measured from Reimei data, was correlated with bulk ion upflow observed at the same altitude using EISCAT, and the energy flux of precipitating electrons with energies of 50-300 eV. The PSD also has a good correlation with the electron temperature, which was increased by precipitation, but not with the ion temperature (0.1-0.3 eV) at the same altitude measured with EISCAT. These results suggest that rather than anisotropic heating due to O+-O resonant charge exchange, plasma waves such as broadband low frequency electric (BBELF) wave fields associated with precipitation are connected to the bulk ion upflows in the cusp and effectively cause the heating of suprathermal ions.