Incoherent Scatter Radar Estimation of F Region Ionospheric Composition During Frictional Heating Events

A method is developed for estimating F region ion composition from incoherent scatter radar (ISR) measurements during times of frictional ion heating. The technique addresses ion temperature‐mass ambiguities in the IS spectra by self‐consistently modeling ion temperature profiles, including the effects of ion temperature anisotropies and altitude‐independent neutral winds. The modeled temperature profiles are used in a minimization procedure to estimate ion composition consistent with the recorded IS spectra. The proposed method is applicable to short‐integration (min) data sets from either single‐beam or multiple‐beam experiments. Application of the technique to Sondrestrom ISR measurements shows increases in F region molecular ions in response to frictional heating, a result consistent with previous theoretical and observational work. Estimates of ion composition are shown to be relatively insensitive to moderate variations in the neutral atmospheric model, which serves as input to the method. The technique developed in this work is uniquely qualified for studying highly variable ion composition near auroral arcs and associated processes such as molecular ion upflows. It also addresses a systematic source of error in standard ISR analysis methods when they are applied in such situations

High time resolution PFISR and optical observations of naturally enhanced ion acoustic lines

Observations of naturally enhanced ion acoustic lines (NEIALs) taken with the Poker Flat Incoherent Scatter Radar (PFISR) using a mode with very high time resolution are presented. The auroral event took place over Poker Flat, Alaska on 8 February 2007 at 09:35 UT (~22:00 MLT), and the radar data are complemented by common-volume high-resolution auroral imaging. The NEIALs occurred during only one of the standard 15-s integration periods. The raw data of this time show very intermittent NEIALs which occur only during a few very short time intervals (≤1 s) within the 15-s period. The time sampling of the raw data, ~19 ms on average, allows study of the time development of the NEIALs, though there are indications that even finer time resolution would be of interest. The analysis is based on the assumption that the NEIAL returns are the result of Bragg scattering from ion-acoustic waves that have been enhanced significantly above thermal levels. The spectra of the raw data indicate that although the up- and down-shifted shoulders can both become enhanced at the same time, (within 19 ms), they are most often enhanced individually. The overall power in the up-and down-shifted shoulders is approximately equal throughout the event, with the exception of one time, when very large up-shifted power was observed with no corresponding down-shifted power. This indicates that during the 480 μs pulse, the strongly enhanced ion-acoustic waves were only traveling downward and not upward. The exact time that the NEIALs occurred was when the radar beam was on the boundary of a fast-moving (~10 km/s), bright auroral structure, as seen in the high resolution auroral imaging of the magnetic zenith. When viewed with high time resolution, the occurrence of NEIALs is associated with rapid changes in auroral luminosity within the radar field of view due to fast-moving auroral fine structures

Composition dependent electrochemical properties of earth-abundant ternary nitride anodes

Growing energy storage demands on lithium-ion batteries necessitate exploration of new electrochemical materials as next-generation battery electrode materials. In this work, we investigate the previously unexplored electrochemical properties of earth-abundant and tunable Zn1-xSn1+xN2 (x = -0.4 to x = 0.4) thin films, which show high electrical conductivity and high gravimetric capacity for Li insertion. Enhanced cycling performance is achieved compared to previously published end-members Zn3N2 and Sn3N4, showing decreased irreversible loss and increased total capacity and cycle stability. The average reversible capacity observed is > 1050 mAh/g for all compositions and 1220 mAh/g for Zn-poor (x = 0.2) films. Extremely Zn-rich films (x = -0.4) show improved adhesion; however, Zn-rich films undergo a phase transformation on the first cycle. Zn-poor and stoichiometric films do not exhibit significant phase transformations which often plague nitride materials and show no required overpotential at the 0.5 V plateau. Cation composition x is explored as a mechanism for tuning relevant mechanical and electrochemical properties, such as capacity, overpotential, phase transformation, electrical conductivity, and adhesion. The lithiation/delithiation experiments confirm the reversible electrochemical reactions. Without any binding additives, the as-deposited electrodes delaminate resulting in fast capacity degradation. We demonstrate the mechanical nature of this degradation through decreased electrode thinning, resulting in cells with improved cycling stability due to increased mechanical stability. Combining composition and electrochemical analysis, this work demonstrates for the first time composition dependent electrochemical properties for the ternary Zn1-xSn1+xN2 and proposes earth-abundant ternary nitride anodes for increased reversible capacity and cycling stability

PFISR Nightside Observations of Naturally Enhanced Ion Acoustic Lines, and Their Relation to Boundary Auroral Features

We present results from a coordinated camera and radar study of the auroral ionosphere conducted during March of 2006 from Poker Flat, Alaska. The campaign was conducted to coincide with engineering tests of the first quarter installation of the Poker Flat Incoherent Scatter Radar (PFISR). On 31 March 2006, a moderately intense auroral arc, (~10 kR at 557.7 nm), was located in the local magnetic zenith at Poker Flat. During this event the radar observed 7 distinct periods of abnormally large backscattered power from the F-region. These were only observed in the field-aligned radar beam, and radar spectra from these seven times show naturally enhanced ion-acoustic lines (NEIALs), the first observed with PFISR. These times corresponded to (a) when the polar cap boundary of the auroral oval passed through the magnetic zenith, and (b) when small-scale filamentary dark structures were visible in the magnetic zenith. The presence of both (a) and (b) was necessary for their occurrence. Soft electron precipitation occurs near the magnetic zenith during these same times. The electron density in the vicinity where NEIALs have been observed by previous studies is roughly between 5 and 30×1010 m−3. Broad-band extremely low frequency (BBELF) wave activity is observed in situ by satellites and sounding rockets to occur with similar morphology, during active auroral conditions, associated with the poleward edge of the aurora and soft electron precipitation. The observations presented here suggest further investigation of the idea that NEIALs and BBELF wave activity are differently-observed aspects of the same wave phenomenon. If a connection between NEIALs and BBELF can be established with more data, this could provide a link between in situ measurements of downward current regions (DCRs) and dynamic aurora, and ground-based observations of dark auroral structures and NEIALs. Identification of in situ processes, namely wave activity, in ground-based signatures could have many implications. One specific example of interest is identifying and following the temporal and spatial evolution of regions of potential ion outflow over large spatial and temporal scales using ground-based optical observations

Imaging radar observations of Farley Buneman waves during the JOULE II experiment

Vector electric fields and associated <I><B>E</B></I>×<I><B>B</B></I> drifts measured by a sounding rocket in the auroral zone during the NASA JOULE II experiment in January 2007, are compared with coherent scatter spectra measured by a 30 MHz radar imager in a common volume. Radar imaging permits precise collocation of the spectra with the background electric field. The Doppler shifts and spectral widths appear to be governed by the cosine and sine of the convection flow angle, respectively, and also proportional to the presumptive ion acoustic speed. The neutral wind also contributes to the Doppler shifts. These findings are consistent with those from the JOULE I experiment and also with recent numerical simulations of Farley Buneman waves and instabilities carried out by Oppenheim et al. (2008). Simple linear analysis of the waves offers some insights into the spectral moments. A formula relating the spectral width to the flow angle, ion acoustic speed, and other ionospheric parameters is derived

Comparing VHF coherent scatter from the radar aurora with incoherent scatter and all-sky auroral imagery

VHF coherent scatter radar observations of an auroral substorm over Alaska are analyzed in the context of multibeam incoherent scatter plasma density and drifts data and green-line all-sky optical imagery. Coherent scatter arises from Farley Buneman waves which are excited in theEregion whenever the convection electric field is greater than about 20 mV/m. Aperture synthesis radar imaging and other aspects of the methodology facilitate the precise spatial registration of the coherent scatter with coincident optical and incoherent scatter radar measurements. Discrete auroral arcs were found to separate diffuse regions of coherent backscatter and, sometimes, to align with the boundaries of those regions. At other times, auroral arcs and torches lined up adjacent to discrete, structured regions or radar backscatter. Drastic variations in the Doppler shifts of the coherent scatter from one side of the auroral forms to the other suggest the presence of field-aligned currents. An empirical formula based on previous studies but adapted to account approximately for the effects of wave turning was used to estimate the convection electric field from the moments of the coherent scatter Doppler spectra. Line-of-sightF region plasma drift measurements from the Poker Flat Incoherent Scatter Radar (PFISR) were found to be in reasonable agreement with these convection field estimates. Reasons why the empirical formulas may be expected to hold are discussed

Identification of substorm onset location and preonset sequence using Reimei, THEMIS GBO, PFISR, and Geotail

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95307/1/jgra20667.pd

Current Closure in the Auroral Ionosphere: Results from the Auroral Current and Electrodynamics Structure Rocket Mission

The Auroral Current and Electrodynamics Structure (ACES) mission consisted of two sounding rockets launched nearly simultaneously from Poker Flat Research Range, AK on January 29, 2009 into a dynamic multiple-arc aurora. The ACES rocket mission was designed to observe electrodynamic and plasma parameters above and within the current closure region of the auroral ionosphere. Two well instrumented payloads were flown along very similar magnetic field footprints, at different altitudes, with small temporal separation between both payloads. The higher altitude payload (apogee 360 km), obtained in-situ measurements of electrodynamic and plasma parameters above the current closure region to determine the input signature. The low altitude payload (apogee 130 km), made similar observations within the current closure region. Results are presented comparing observations of the electric fields, magnetic components, and the differential electron energy flux at magnetic footpoints common to both payloads. In situ data is compared to the ground based all-sky imager data, which presents the evolution of the auroral event as the payloads traversed through magnetically similar regions. Current measurements derived from the magnetometers on the high altitude payload observed upward and downward field-aligned currents. The effect of collisions with the neutral atmosphere is investigated to determine it is a significant mechanism to explain discrepancies in the low energy electron flux. The high altitude payload also observed time-dispersed arrivals in the electron flux and perturbations in the electric and magnetic field components, which are indicative of Alfven waves

Substorm triggering by new plasma intrusion: Incoherent‐scatter radar observations

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95031/1/jgra20482.pd