Ionospheric Alfvén resonator and aurora: Modeling of MICA observations

Abstract

We present results from a numerical study of small‐scale, intense magnetic field‐aligned currents observed in the vicinity of the discrete auroral arc by the Magnetosphere‐Ionosphere Coupling in the Alfvén Resonator (MICA) sounding rocket launched from Poker Flat, Alaska, on 19 February 2012. The goal of the MICA project was to investigate the hypothesis that such currents can be produced inside the ionospheric Alfvén resonator by the ionospheric feedback instability (IFI) driven by the system of large‐scale magnetic field‐aligned currents interacting with the ionosphere. The trajectory of the MICA rocket crossed two discrete auroral arcs and detected packages of intense, small‐scale currents at the edges of these arcs, in the most favorable location for the development of the ionospheric feedback instability, predicted by the IFI theory. Simulations of the reduced MHD model derived in the dipole magnetic field geometry with realistic background parameters confirm that IFI indeed generates small‐scale ULF waves inside the ionospheric Alfvén resonator with frequency, scale size, and amplitude showing a good, quantitative agreement with the observations. The comparison between numerical results and observations was performed by “flying” a virtual MICA rocket through the computational domain, and this comparison shows that, for example, the waves generated in the numerical model have frequencies in the range from 0.30 to 0.45 Hz, and the waves detected by the MICA rocket have frequencies in the range from 0.18 to 0.50 Hz.

Morphology of the Auroral Tail of Io, Europa, and Ganymede From JIRAM L‐Band Imager

“…At the ionosphere, these currents can affect the Hall and Pedersen currents, hence the evolution of the IFI ultimately depends on the relative direction between the ionospheric electric field and the perpendicular wavevector of the incident shear Alfven wave. Most of the theoretical studies of the IFI focused on a 2D geometry in which : in this case, the feedback process could lead to the formation of parallel arcs at different latitudes (see for example the theoretical results by Atkinson, 1970; Miura & Sato, 1980; Pokhotelov, 2003 and the measurements reported by Lynch et al., 2015; Tulegenov & Streltsov, 2017), reminiscent of the Io tail splitting observed by Mura et al. (2018) far down the tail.…”

“…k E : in this case, the feedback process could lead to the formation of parallel arcs at different latitudes (see for example the theoretical results by Atkinson, 1970;Miura & Sato, 1980;Pokhotelov, 2003 and the measurements reported by Lynch et al, 2015;Tulegenov & Streltsov, 2017), reminiscent of the Io tail splitting observed by Mura et al (2018) far down the tail. In order to include an arbitrary direction of   E k a full 3D geometry have to be considered.…”

Resonant Alfvén Waves in the Lower Auroral Ionosphere: Evidence for the Nonlinear Evolution of the Ionospheric Feedback Instability

“…The resonator can trap Alfvén waves by partial reflection at its boundaries, forming a standing wave pattern. Under favorable conditions, the trapped waves may become unstable to the Ionospheric Feedback Instability (IFI; Atkinson, 1970; Lysak & Song, 2002; Sato, 1978; Streltsov & Lotko, 2004; Tulegenov & Streltsov, 2017) and grow to large amplitudes where they can further modify the ionosphere via the current they carry or via the Ponderomotive force of their electric fields (Streltsov & Lotko, 2008).…”

On the Existence of Ionospheric Feedback Instability in the Earth's Magnetosphere‐Ionosphere System

“…A special, dedicated sounding rocket experiment, Magnetosphere‐Ionosphere Coupling in the Alfvén resonator, was conducted to verify that prediction in 2012. Results from the Magnetosphere‐Ionosphere Coupling in the Alfvén resonator experiment and numerical modeling are in a good quantitative agreement (Figure d; Tulegenov & Streltsov, ).…”

“…(C) Prediction of the frequencies of ULF waves used in active experiments at High frequency Active Auroral Research Program to initiate a substorm (from Streltsov et al ). (D) Prediction of the structure and location of small‐scale ULF waves observed in the vicinity of discrete arcs by the MICA sounding rocket flight (from; Tulegenov & Streltsov, ).…”