Ground‐based imaging of detached arcs, ripples in the diffuse aurora, and patches of 6300‐Å emission

Abstract

A period of coordinated, multidiagnostic observations of the subauroral ionosphere conducted in April 1985 resulted in a series of optical and plasma characterizations of three distinct phenomena: arcs detached from the diffuse aurora, undulations in the equatorward edge of the diffuse aurora, and isolated patches of emission in the F region trough. The optical features were observed by the 6300‐Å imaging system in Boston University's Mobile Ionospheric Observatory located at the Millstone Hill observatory; plasma observations were made by the Millstone incoherent scatter radar, Air Force Geophysics Laboratory satellite radio beacon polarimeters, and the Defense Meteorological Satellite Program (DMSP) energetic particle detectors. The detached arc observations showed that strong F region enhancements occured in both 6300‐Å emission and total plasma content, suggesting an electron precipitation source essentially similar to the plasma sheet population that causes the diffuse aurora and the poleward wall of the F region trough. The rippled features along the equatorward edge of the diffuse aurora were associated with strong electric fields and large radial ion temperature gradients, topics discussed in detail in a companion paper. The isolated and long‐lived patches of 6300‐Å emission have no corresponding F region plasma enhancements, but are associated with enhanced radar returns from the E region. Nearly simultaneous DMSP observations point to the importance of ion precipitation effects as a cause for these F region optical and E region plasma enhancements. The entire set of observations (detached arc, ripples, and patches) show that ground‐based imaging and radio techniques can provide detailed spatial and temporal coverage of phenomena hitherto observed by satellite only.