We present small and meso‐scale properties of a substorm onset arc observed simultaneously by the Reimei THEMIS satellites together with ground‐based observations GBO system. The optical revealed slow equatorward motion growth‐phase development much brighter poleward it. Both arcs showed typical particle signature electrostatic acceleration in an inverted‐V structure strong Alfvén wave at edge arc. Two spacecraft encountered earthward flow bursts around times expanding aurora reached their...

ABSTRACT The path, eye and body movements of a teleost fish (the leatherjacket Acanthaluteres spilomelanurus) approaching taking food were measured by cinematography. Fixation the movement eyes is an invariable feature approach. then remain aligned with target while moves forward round to bring mouth food. When pursuing pieces moving vertically at constant velocity through water these normally trace out pathway that can be calculated assuming aims constantly Predictive pathways imply...

Abstract. Two discrete auroral arc filaments, with widths of less than 1 km, have been analysed using multi-station, multi-monochromatic optical observations from small and medium field-of-view imagers the EISCAT radar. The energy flux precipitating electrons, volume emission rates local electric fields in ionosphere determined at high temporal (up to 30 Hz) spatial (down tens metres) resolution. A new time-dependent inversion model is used derive spectra electron density profiles. are also...

A large increase in electron temperature measured filamentary aurora with the European incoherent scatter radar has been modeled a one‐dimensional transport and ion chemistry code. To account for observed changes temperature, while also reproducing E region density profiles, source of heating is required addition to local from energy degradation precipitating electrons. We show that ohmic strong field‐aligned current can heat source.

Abstract. The ASK instrument (Auroral Structure and Kinetics) is a narrow field auroral imager, providing simultaneous images of aurora in three different spectral bands at multiple frames per second resolution. emission species studied are O2+ (5620 Å), O+ (7319 Å) O (7774 Å). was installed operated for the first time an observational campaign on Svalbard, from December 2005 to March 2006. measurements were supported by data Spectrographic Imaging Facility (SIF). relation between morphology...

High time resolution optical measurements in the magnetic zenith are compared with European Incoherent Scatter (EISCAT) field‐aligned of electron density at 0.2‐s and horizontal electric field made 278 km 9 s. In one event, 20 min after a spectacular auroral breakup, system narrow active arc elements moved southward into zenith, where it remained for several minutes. During 30‐s interval activity element very close to radar beam, vectors 3‐s were found be extremely large (up 400 mV m −1 )...

The combination of high time and space resolution measurements in the magnetic zenith (optical radar) detailed modeling ionospheric response to auroral particle precipitation has produced new result that most energy density a bright arc resides an extremely narrow filament, embedded broader feature. We are able show filaments, order 100 m width, by monoenergetic beams electrons, whereas surrounding emissions lower broad spectral distributions. is achieved combining different spectra as input...

Abstract. Simultaneous images of the aurora in three emissions, N21P (673.0 nm), OII (732.0 nm) and OI (777.4 have been analysed; ratio atomic oxygen to molecular nitrogen has used provide estimates changes energy flux precipitation within scale sizes 100 m, with temporal resolution 32 frames per second. The choice filters for imagers is discussed, particular emphasis on line at 777.4 nm as one emissions measured. optical measurements combined radar compared results an auroral model, hence...

We present an analysis of flickering (2–10 Hz) auroras observed with a state‐of‐the‐art multispectral imaging system, Auroral Structure and Kinetics, located in Tromsø, Norway. Short (1–2 s) periods aurora have been identified which the frequency brightness oscillations decreases or increases smoothly over time. To authors' knowledge this is first detailed such “chirps” field‐aligned bursts. found that electron precipitation energy strongly anticorrelated during all chirps. This result...

This work presents first results and the numerical methods of a highly improved two‐dimensional three‐fluid simulation model ionosphere‐magnetosphere system. The considers ionization recombination, ion‐neutral friction, Hall term in Ohm's law, various heat sources energy equations. electrodynamic response evolution collision frequencies are treated self‐consistently height‐resolved ionosphere. is to our knowledge only that can resolve dynamic nonlinear electromagnetic interaction between...

Abstract. We study a brightening of the Lyman-a emission in cusp which occurred response to short-lived south-ward turning interplanetary magnetic field (IMF) during period strongly enhanced solar wind plasma concentration. The proton is detected using SI-12 channel FUV imager on IMAGE spacecraft. Analysis IMF observations recorded by ACE and Wind spacecraft reveals that assumption constant propagation lag from upstream Earth not adequate for these high time-resolution studies. variations...

Abstract. The generation mechanism for naturally enhanced ion-acoustic echoes is still debated. One important issue how these enhancements are related to auroral activity. All events of observed simultaneously with the EISCAT Svalbard Radar (ESR) and high-resolution narrow field-of-view imagers have been collected studied. Characteristic all appearance very dynamic rayed aurora, some intrinsic features displays identified. Several identified directly presence low energy (10-100eV)...

Abstract Optical measurements from three selected wavelengths have been combined with modeling of emissions an auroral event to estimate the magnitude and direction small‐scale electric fields on either side arc. The temporal resolution estimates is 0.1 s, which much higher than Super Dual Auroral Radar Network (SuperDARN) in same region, we compare our estimates. Additionally, used Scanning Doppler Imager instrument measure neutral wind during order calculate height integrated Joule...

We apply a numerical model of time‐dependent ionospheric convection to two directly driven reconnection pulses during 15‐min interval southward IMF on 26 November 2000. The requires an input magnetopause rate variation, which is here derived from the observed variation in upstream clock angle, θ. mapped merging gap, MLT extent inferred Doppler‐shifted Lyman‐α emission newly opened field lines, as by FUV instrument IMAGE spacecraft. used reproduce variety features this event: SuperDARN...

Abstract This study investigates the interhemispheric nature of polar cap auroras via ultraviolet imaging, combined with particle data, to determine whether they occur on open or closed field lines. Data from SSUSI (Special Sensor Ultraviolet Spectrographic Imager) instrument board DMSP (Defence Meteorological Satellite Program) spacecraft are examined. The in 90‐min orbits; hence, images each hemisphere separated by 45 min providing a good opportunity for study. 21 arc (PCA) events recorded...

Two cases of discrete aurora are presented, in which auroral curls and rays, respectively, were seen. The was imaged by two spatially separated imagers with a long‐pass filter (mainly sensitive to N 2 + emissions), another imager narrow‐band 7325 Å (sensitive forbidden O doublet). Also, spectra the recorded. Using multispectral imaging we find that occurred caused precipitation energetic electrons lack low‐energy population, while rays both high low energy present simultaneously. These...

An imaging Echelle spectrograph designed for high‐resolution studies of selected spectral features located in the visible spectrum was deployed from November 2001 until April 2003 Tromsø, Norway. For moderately disturbed magnetic conditions, Tromsø is on equatorial edge evening auroral oval several hours. Energetic protons are frequently dominant particle energy source this region. experiment, four windows were selected, each around different emission features: H α (656.3 nm), β (486.1 N 2 +...

Abstract This paper presents observations of polar cap auroral features on 19 January 2008, evaluated using multiple instruments with near‐simultaneous in both hemispheres. Analysis the indicates that there are at least two formation mechanisms/types aurora occurring simultaneously different magnetic field topologies (one open and other closed magnetospheric lines). Two high‐latitude structures were observed opposing sides northern hemisphere same time interval. The structure duskside was...

Abstract Technological advances leading to improved sensitivity of optical detectors have revealed that aurora contains a richness dynamic and thin filamentary structures, but the source structured emissions is not fully understood. In addition, high‐resolution radar data indicated auroral arcs can be correlated with highly varying large electric fields, detailed picture electrodynamics filaments yet incomplete. The Auroral Structure Kinetics (ASK) instrument state‐of‐the‐art ground‐based...

Electron density profiles acquired with the EISCAT radar at 0.2 s time resolution, together TV images and photometric intensities, were used to study characteristics of thin (< 1 km) auroral arc structures that drifted through field view instruments. It is demonstrated both high space resolution are essential for deriving input parameters electron flux responsible elemental structures. One such structure required a 400 mW m −2 (erg cm −1 ) downward energy carried by an 8 keV monochromatic...

A state‐of‐the‐art multispectral imager has been used to study the flickering component of an auroral event at high spatial (40 m) and temporal (32 fps) resolution. Scale sizes for patches were found be regularly smaller than 1 km. The typical frequency observed was in range 6–8 Hz, although both lower higher frequencies identified. structure correlated with coincident non‐flickering aurora, showing that there is a relationship between two, no correlation. These results support theory caused...