Auroral ionospheric F region density cavity formation and evolution: MICA campaign results

Abstract

Scatter Radar) during the MICA (Magnetosphere-Ionosphere Coupling in the Alfvén Resonator) sounding rocket campaign are critically examined alongside complementary numerical simulations. Particular processes of interest include cavity formation due to intense frictional heating and Pedersen drifts, evolution in the presence of structured precipitation, and refilling due to impact ionization and downflows. Our analysis uses an ionospheric fluid model which solves conservation of mass, momentum, and energy equations for all major ionospheric species. These fluid equations are coupled to an electrostatic current continuity equation to self-consistently describe auroral electric fields. Energetic electron precipitation inputs for the model are specified by inverting optical data, and electric field boundary conditions are obtained from direct PFISR measurements. Thus, the model is driven in as realistic a manner as possible. Both incoherent scatter radar (ISR) data and simulations indicate that the conversion of the F region plasma to molecular ions and subsequent recombination is the dominant process contributing to the formation of the observed cavities, all of which occur in conjunction with electric fields exceeding ∼90 mV/m. Furthermore, the cavities often persist several minutes past the point when the frictional heating stops. Impact ionization and field-aligned plasma flows modulate the cavity depth in a significant way but are of secondary importance to the molecular generation process. Informal comparisons of the ISR density and temperature fits to the model verify that the simulations reproduce most of the observed cavity features to a reasonable level of detail.

Ionospheric response to infrasonic‐acoustic waves generated by natural hazard events

“…The 2-D ionospheric model (described in detail in section A2) used in this study is based on the model developed in Zettergren and Semeter [2012] and later extended in Zettergren and Snively [2013] and Zettergren et al [2014]. This model comprises a fluid system of equations [Schunk, 1977;Blelly and Schunk, 1993;Huba et al, 2000a], describing dynamics of the ionospheric plasma, self-consistently coupled to an electrostatic treatment of auroral and neutral dynamo currents.…”

Measuring the seeds of ion outflow: Auroral sounding rocket observations of low‐altitude ion heating and circulation

“…PFISR was run in a 15‐beam mode allowing observations of plasma density and large‐scale electric fields. (See Zettergren et al [] for a detailed description of the PFISR experiment and data from the MICA campaign.) A Scanning Doppler Imager (SDI, a Fabry‐Perot interferometer) at Poker Flat monitored E and F region neutral winds and temperatures [ Conde and Smith , ; Anderson et al , , ].…”

VISIONS remote observations of a spatially-structured filamentary source of energetic neutral atoms near the polar cap boundary during an auroral substorm

“…4 is that the accelerated ions are coincident with a region where DC electric fields are high enough ($90 mV/m, see panel (c)) to elicit a fairly strong ionospheric response in terms of type-1 upflows (e.g., Wahlund et al (1992)) and substantial increases in molecular ion concentrations (e.g., Zettergren et al (2011Zettergren et al ( , 2014). Both the upflows and molecular ion enhancements are initiated by strong frictional heating due to the ExB drifts of the ionosphere through the background neutral atmosphere.…”