Characteristics of Poker Flat Incoherent Scatter Radar (PFISR) naturally enhanced ion-acoustic lines (NEIALs) in relation to auroral forms

Abstract

Abstract. Naturally enhanced ion-acoustic lines (NEIALs) have been observed with the Poker Flat Incoherent Scatter Radar (PFISR) ever since it began operating in 2006. The nearly continuous operation of PFISR since then has led to a large number of NEIAL observations from there, where common-volume, high-resolution auroral imaging data are available. We aim to systematically distinguish the different types of auroral forms that are associated with different NEIAL features, including spectral shape and altitude extent. We believe that NEIALs occur with a continuum of morphological characteristics, although we find that most NEIALs observed with PFISR fall into two general categories. The first group occurs at fairly low altitudes -F region or below -and have power at, and spread between, the ion-acoustic peaks. The second group contains the type of NEIALs that have previously been observed with the EIS-CAT radars, those that extend to high altitudes (600 km or more) and often have large asymmetries in the power enhancements between the two ion-acoustic shoulders. We find that there is a correlation between the auroral structures and the type of NEIALs observed, and that the auroral structures present during NEIAL events are consistent with the likely NEIAL generation mechanisms inferred in each case. The first type of NEIAL -low altitude -is the most commonly observed with PFISR and is most often associated with active, structured auroral arcs, such as substorm growth phase, and onset arcs and are likely generated by Langmuir turbulence. The second type of NEIAL -high altitude -occurs less frequently in the PFISR radar and is associated with aurora that contains large fluxes of low-energy electrons, as can happen in poleward boundary intensifications as well as at substorm onset and is likely the result of current-driven instabilities and in some cases Langmuir turbulence as well. In addition, a preliminary auroral photometry analysis revealed that there is an anticorrelation between the altitude of the NEIALs and the calculated energy of the electrons, which is consistent with the hypotheses presented here regarding generation mechanisms.

First optical observations of interhemispheric electron reflections within pulsating aurora

“…The pulsating auroral event was observed with several imagers (Andor Ixon DU‐888 EMCCD) Electron Multiplying Charge Coupled Device using different fields of view and filters. More detailed descriptions of the Multispectral Observatory Of Sensitive EMCCDs imager suite can be found in Michell et al [] and Michell and Samara []. An all‐sky imager was used with a 557.7 nm narrowband filter and was operated at 3.3 frames per second (300 ms exposure time).…”

Diffuse and Pulsating Aurora

“…The Multispectral Observatory Of Sensitive EMCCDs (MOOSE) suite of imagers was deployed in Poker Flat, AK as a pathfinder for future larger arrays for exploring the electrodynamics of the aurora from ground multi-spectral imaging. It consists of five Andor Ixon DU-888 EMCCD imagers that have a 1024×1024 pixel chip each, with internal binning and sub-framing capabilities that allow trade-offs between temporal and spatial resolution (details in Michell et al, 2014). These imagers are well suited to high spatial and temporal resolution auroral morphology studies (such as, Michell et al, 2012).…”

Correlated Pc4–5 ULF waves, whistler‐mode chorus, and pulsating aurora observed by the Van Allen Probes and ground‐based systems

“…For a full examination of this event, we bring together ground-based data from the THEMIS all-sky imager array [Donovan et al, 2006] and MOOSE (Multi-spectral Observatory Of Sensitive EMCCDs) imager [see Michell et al, 2014], in situ wave and particle data from the Van Allen Probes satellites [Mauk et al, 2012], and contextual data of solar wind and geomagnetic indices from OMNI Web. The instrumentation used from the Van Allen Probes includes the EMFISIS (Electric and Magnetic Field Instrument Suite and Integrated Science) fields experiment [Kletzing et al, 2013], the EFW (Electric Field and Waves) fields experiment [Wygant et al, 2013], and the MagEIS (Magnetic Electron Ion Spectrometer) particle detector [Blake et al, 2013] from the ECT (Energetic particle, Composition, and Thermal plasma) instrument suite [Spence et al, 2013].…”