Alouette observations taken during a middle-latitude red arc

A comparison of 6300 Å airglow data obtained at the Fritz Peak Airglow Observatory with topside ionosonde data obtained with the Alouette satellites on September 29, 1967, indicates the presence of a field-aligned depression of electron density associated with middle-latitude auroral red arcs. The Alouette data also indicate that the plasma temperature along field lines intersecting the arc may be somewhat higher than in neighboring regions. Furthermore, the transition from dominant O⁺to dominant H⁺occurs at much higher altitudes on the field lines intersecting the arc.