Ionospheric signature of the cusp as seen by incoherent scatter radar

Abstract

Measurements with the Søndre Strømfjord incoherent scatter radar, co‐ordinated with the observations by the Freja satellite, have been performed during three campaigns, April 1993, February 1994, and May–June 1994. Radar signatures of various types of magnetosheath particle injections in the cusp‐cleft region are investigated. The measurement days represent very different geomagnetic conditions, from very quiet to a Kp index of 7+. On three occasions both Freja and the radar detected the cusp. A unique cusp signature is found for a relatively stable cusp, distinguishing it from the many other soft precipitation features seen around noon. The signature includes extremely high electron temperatures in a latitudinally well‐defined region with a sharp equatorward border, some F region electron density enhancement, ion outflow, and mainly poleward plasma flow. Enhanced ion temperatures are also seen in the vicinity of, but not exactly coincident with, the electron temperature enhancements. Other day side precipitation features observed with an intense soft component are narrow arcs, which usually have an accompanying accelerated electron component of several hundred eV to some keV energy. These are typically seen in, or bordering, convection regions where the plasma flow vorticity implies upward field‐aligned currents.

Incoherent scatter radar observations of the cusp acceleration region and cusp field‐aligned currents

“…The radar data (from the S0ndre Str0mfjord radar [Kelly, 1983] and radar mode used here have been reported by Nilsson et al [1996]. In the work of Nilsson et al [1996] we concentrated on F region measurements; here we have also used radar power profiles to study the ionospheric E region and lower F region.…”

“…This appears to be the case in the measurements reported here, obtained on May 28, 1994. Plate I shows the radar power profiles for 16 scans, starting at 1446.52 UT and ending at 1541.12 UT, and obtained in the cusp as identified by Nilsson et al [1996]. The cusp was identified using conjugate Freja satellite observations.…”

An assessment of the role of the centrifugal acceleration mechanism in high altitude polar cap oxygen ion outflow

“…We have also investigated if this mechanism could be an explanation of the so called "overlapping cusp injections" observed for example by the Freja satellite (Norberg et al, 1994;Yamauchi and Lundin, 2001;Nilsson et al, 1996). The overlapping injections are interesting, because if they are caused by processes at the magnetopause they are very difficult to explain using standard reconnection theories of the solar wind magnetosphere interaction (Yamauchi and Lundin, 2001).…”

The structure of high altitude O<sup>+</sup> energization and outflow: a case study

“…The exact relation between ionospheric upflow in the cusp as measured by incoherent scatter radar (e.g. Nilsson et al, 1996;Ogawa et al, 2003) and the more energized ions observed further out in the magnetosphere is still not clear. The further energization of ions of apparently ionospheric cusp origin and subsequent outflow is the subject of several recent studies; Valek et al (2002) used observations of isotropic magnetosheath-like ions in the dayside magnetosphere (i.e.…”