Glow discharge excited at low to high radio frequencies around active dipoles in the ionosphere

We present the first space-borne observation of optical emissions of both neutral and ionized argon atoms resulting from a radio-frequency glow discharge (RF-GD) from a sounding rocket payload. The Observations of Electric-field Distributions in the Ionospheric Plasma — a Unique Strategy-C (OEDIPUS-C) payload was designed to separate into two sub-payloads on its up-leg. This separation permitted a number of two-point measurements, including those on radio wave propagation from the active dipole antennas on the upper sub-payload to the synchronized receiving dipoles on the lower sub-payload. A white-light video camera on the lower sub-payload recorded strong luminosity around the active dipoles during the first 15 s after sub-payload separation, when argon gas jets were providing propulsion to separate the two sub-payloads. Parts of the ejected argon appeared as a glowing volume where the large radio-frequency (RF) fields from the two active dipoles excited the optical emission, as the sub-payload separation increased from 2 to 55 m. The shape and intensity of the luminosity were well repeated as a function of the swept frequency (0.025–8.000 MHz), but their frequency dependences were distinctly different from those of sounder-accelerated electrons measured onboard, and deduced to result from the nonlinearity of the glow discharge. The observation is to our knowledge the first of its kind, and is interpreted in terms of a RF-GD energized by the strong near electric fields of the transmitting dipoles.