Physical Processes of Meso-Scale, Dynamic Auroral Forms

Abstract

Meso-scale auroral forms, such as poleward boundary intensifications, streamers, omega bands, beads and giant undulations, are manifestations of dynamic processes in the magnetosphere driven, to a large part, by plasma instabilities in the magnetotail. New observations from ground-and space-based instrumentation and theoretical treatments are giving us a clearer view of some of the physical processes behind these auroral forms. However, questions remain as to how some of these observations should be interpreted, given uncertainties in mapping auroral features to locations in the magnetotatil and due to the significant overlap in the results from a variety of models of different plasma instabilities. We provide an overview of recent results in the field and seek to clarify some of the remaining questions with regards to what drives some of the largest and most dynamic auroral forms. Keywords Meso-scale aurora • Poleward boundary intensifications • Auroral streamers • Omega bands • Torches • Auroral beads • Giant undulations • Magnetic mapping • Magnetosphere ionosphere coupling • Plasma instabilities • Magnetotail

Are Dawn Storms Jupiter's Auroral Substorms?

“…Many of these auroral forms at Jupiter resemble mesoscale (Forsyth et al, 2020) and large-scale auroral forms observed during substorms at Earth. Furthermore, we found cases of consecutive dawn storms occurring within a few hours, similar to the nonisolated substorms at Earth.…”

“…Substorms are global reconfigurations of the magnetosphere during which the magnetic energy stored in the magnetotail is converted into particle energy, which lead to spectacular auroral brightening in nightside polar regions which generally follow a well‐established sequence of features (Akasofu, 2013). The transient spots observed in Jupiter's aurora share several morphological and temporal characteristics with transient mesoscale features on Earth, sometimes associated with poleward boundary intensifications and sometimes with streamers (Forsyth et al., 2020). Both are often observed before the substorm onset (Nishimura et al., 2011), even if the exact relationship between streamers and substorms is disputed (Miyashita & Ieda, 2018).…”

FTA: A Feature Tracking Empirical Model of Auroral Precipitation

“…Within the aurora, meso‐scale (with scale sizes of 10–100s of kilometers) to small‐scale (with spatial scales down to tens of meters and temporal scales down to fractions of a second) structures appear as arcs, spots, patches, etc. of visual emissions with different luminosities and behaviors, most of which represent complex energy transport between magnetosphere and ionosphere (Borovsky et al., 1991; Frey, 2007; Forsyth et al., 2020; Maggs & Davis, 1968; Nishimura et al., 2020; Paschmann et al., 2012; Sandahl et al., 2008, etc.). The energy flow and structure within the auroral oval are therefore complicated and dynamic under different geomagnetic conditions.…”

Omega Band Magnetospheric Source Location: A Statistical Model‐Based Study

“…Still, all the above hypotheses have some drawbacks. Forsyth et al (2020) argues that the occurrence of a shear flow at the boundary between Region 1 and Region 2 currents, where the omega structures were recently mapped to (Liu et al, 2018), does not appear to be sufficient to generate an omega band, and that the region is generally stable to the shear flow instability. The BBF-associated mechanism allows one to explain the 3D current system associated with an individual omega structure (Amm, 1996;Amm et al, 2005;Opgenoorth et al, 1983), since BBFs have a similar pair of upward and downward field-aligned currents.…”