Flow-aligned jets in the magnetospheric cusp: Results from the Geospace Environment Modeling Pilot program
- Rice Univ., Houston, TX (United States)
- Hanscom Air Force Base, MA (United States); and others
The extended flight of the Airborne Ionospheric Observatory during the Geospace Environment Modeling (GEM) Pilot program on January 16, 1990, allowed continuous all-sky monitoring of the two-dimensional ionospheric footprint of the northward interplanetary magnetic field (IMF) cusp in several wavelengths. Especially important in determining the locus of magnetosheath electron precipitation was the 630.0-nm red line emission. The most striking morphological change in the images was the transient appearance of zonally elongated regions of enhanced 630.0-nm emission which resembled {open_quotes}rays{close_quotes} emanating from the centroid of the precipitation. The appearance of these rays was strongly correlated with the Y component of the IMF: when the magnitude of B{sub Y} was large compared to B{sub Z}, the rays appeared; otherwise, the distribution was relatively unstructured. Late in the flight the field of view of the imager included the field of view of flow measurements from the European incoherent scatter radar (EISCAT). The rays visible in 630.0-nm emission exactly aligned with the position of strong flow jets observed by EISCAT. The authors attribute this correspondence to the requirement of quasi-neutrality; namely, the soft electrons have their largest precipitating fluxes where the bulk of the ions precipitate. The ions, in regions of strong convective flow, are spread out farther along the flow path than in regions of weaker flow. The occurrence and direction of these flow bursts are controlled by the IMF in a manner consistent with newly opened flux tubes; i.e., when {vert_bar}By{vert_bar}>{vert_bar}B{sub z}{vert_bar}. The length of the reconnection pulse is difficult to determine, however, since strong zonal flows would be expected to persist until the tension force in the field line has decayed, even if the duration of the enhanced reconnection was relatively short. 88 refs., 7 figs.
- OSTI ID:
- 207219
- Journal Information:
- Journal of Geophysical Research, Vol. 100, Issue A5; Other Information: PBD: 1 May 1995
- Country of Publication:
- United States
- Language:
- English
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