Some existing auroral data products are insufficient for ionospheric simulation input on subkilometer spatial scales and high (second) time resolution near the boundaries of arc structures. Ideally, two-dimensional data maps of the relevant parameters over these small scales would provide models with constraining inputs. Available in situ data have the time and spatial resolution for small-scale features but only provide a 1-D cut through the structure. Ground-based data can provide 2-D maps but have lower resolution in time and space than is required to accurately interpret the small-scale structure near an arc. This paper provides a method to construct two-dimensional maps of auroral parameters from the combination of one-dimensional in situ data cuts with two-dimensional ground-based (and time dependent) camera imagery. Arc boundaries for each image are defined, and the available 1-D ionospheric flow data are replicated into many 1-D cuts at different points along the arc, yielding an irregularly sampled 2-D flow map. These mapped data are fitted to a regular grid via a divergence minimization routine to generate a regularly sampled flow field that is enforced as divergence free. Comparison of the generated 2-D data maps to available information from camera inversions and other data products is shown, as are assumptions made through the replication process and alternative strategies. Reconstructed flow maps are shown to maintain the small-scale features near arc boundaries while increasing the dimensionality to 2-D and to follow the time evolution of the arc structure by comparisons to imagery. The average electric field magnitudes per unit area of the reconstructed and divergence-minimized flow fields are also calculated and compared between different data sources.

A new anisotropic fluid model is developed to describe ionospheric upflow responses to magnetospheric forcing by electric fields and broadband ELF waves at altitudes of 90–2500 km. This model is based on a bi‐Maxwellian ion distribution and solves time‐dependent, nonlinear equations of conservation of mass, momentum, parallel energy, and perpendicular energy for six ion species important to E, F, and topside ionospheric regions. It includes chemical and collisional interactions with the neutral atmosphere, photoionization, and electron impact ionization. This model is used to examine differences between isotropic and anisotropic descriptions of ionospheric upflow driven by DC electric fields, possible effects of low‐altitude (<500 km) wave heating, and impacts of neutral winds on ion upflow. Results indicate that isotropic models may overestimate field‐aligned ion velocity responses by as much as ∼48%. Simulations also show significant ionospheric responses at low altitudes to wave heating for very large power spectral densities, but ion temperature anisotropies below the F region peak are dominated by frictional heating from DC electric fields. Neutral winds are shown to play an important role regulating ion upflow. Thermospheric winds can enhance or suppress upward fluxes driven by DC and BBELF fields by 10–20% for the cases examined. The time history of the neutral winds also affects the amount of ionization transported to higher altitudes by DC electric fields.

Reported observations of picket fence signatures associated with subauroral Strong Thermal Emission Velocity Enhancement (STEVE) emission events look strikingly similar to rayed auroral curtains. Rayed auroral curtains are often the visible signatures of tearing‐mode‐unstable current sheets with precipitating auroral electron current carriers. Picket fence signatures are not located where auroral precipitation explanations apply, and are closely collocated with STEVE emission events. A similar tearing‐mode‐instability explanation can be invoked with a different source for the originating field‐aligned current (FAC) sheet. In this explanation, the FAC sheet is sourced by ionospheric conductance gradients adjacent to the localized flows of the STEVE event. Geospace Environment Model of Ion‐Neutral Interactions (GEMINI) models of the 3D ionosphere near counterstreaming STEVE‐associated flow structures show the development of sufficiently strong current sheets for tearing mode instabilities to take hold. These instabilities can locally accelerate ambient ionospheric thermal electrons to the few eV needed for the reported observed green picket fence signatures.

High-latitude precipitation of charged particles is a crucial driver of ionospheric electrodynamics (e.g., Kivelson & Russell, 1995). These particles precipitate from the near-Earth plasma environment to form the aurora, and enhance the electrical conductance in the polar regions (e.g., Schunk & Nagy, 2009). Auroral precipitation is broadly defined into two types: diffuse and discrete aurora. Particles scattered into the loss cone by plasma waves create the diffuse aurora (Nishimura et al., 2020a and references therein). Diffuse particles precipitate into the upper atmosphere without the need of acceleration, and can consist of both electrons (e.g., Evans & Moore, 1979) and ions (e.g., Sergeev et al., 1983). Conversely, the discrete aurora is generated by particles that are accelerated into the ionosphere (e.g., Korth et al., 2014). These particles can be accelerated by geomagnetic field-aligned electric fields (monoenergetic; e.g., Evans, 1974;Knight, 1973) or by dispersive Alfvén waves (broadband; e.g., Chaston et al., 2003;Ergun et al., 1998). The conductance enhancements caused by auroral precipitation are important to investigative studies of magnetosphere-ionosphere coupling (e.g., Öztürk et al., 2020), since it regulates the closure of field-aligned currents (FACs;Iijima & Potemra, 1976) and maintain the nonlinear feedback

This study examines how thermospheric motions due to gravity waves (GWs) drive ion upflow in the F region, modulating the topside ionosphere in a way that can contribute to ion outflow. We present incoherent scatter radar data from Sondrestrom, from 31 May 2003 which showed upflow/downflow motions, having a downward phase progression, in the field‐aligned velocity, indicating forcing by a thermospheric GW. The GW‐upflow coupling dynamics are investigated through the use of a coupled atmosphere‐ionosphere model to examine potential impacts on topside ionospheric upflow. Specifically, a sequence of simulations with varying wave amplitude is conducted to determine responses to a range of transient forcing reminiscent of the incoherent scatter radar data. Nonlinear wave effects, resulting from increases in amplitude of the modeled GW, are shown to critically impact the ionospheric response. GW breaking deposits energy into smaller scale wave modes, drives periods of large field‐aligned ion velocities, while also modulating ion densities. Complementary momentum transfer increases the mean flow and, through ion‐neutral drag, can increase ion densities above 300 km. Ionospheric collision frequency (cooling) and photoionization effects (heating), both dependent on ionospheric density, modify the electron temperature; these changes conduct quickly up geomagnetic field lines driving ion upflow at altitudes well above initial disturbances. This flow alters ion populations available for high‐altitude acceleration processes that may lead to outflow into the magnetosphere. We have included a representative source of transverse wave heating which, when supplemented by our GWs, illustrates strengthened upward fluxes in the topside ionosphere.