1,721,070 research outputs found
Variations in energy, flux, and brightness of pulsating aurora measured at high time resolution
No full textHigh-resolution multispectral optical and incoherent scatter radar data are used to study the variability of pulsating aurora. Two events have been analysed, and the data combined with electron transport and ion chemistry modelling provide estimates of the energy and energy flux during both the ON and OFF periods of the pulsations. Both the energy and energy flux are found to be reduced during each OFF period compared with the ON period, and the estimates indicate that it is the number flux of foremost higher-energy electrons that is reduced. The energies are found never to drop below a few kilo-electronvolts during the OFF periods for these events. The high-resolution optical data show the occurrence of dips in brightness below the diffuse background level immediately after the ON period has ended. Each dip lasts for about a second, with a reduction in brightness of up to 70 % before the intensity increases to a steady background level again. A different kind of variation is also detected in the OFF period emissions during the second event, where a slower decrease in the background diffuse emission is seen with its brightness minimum just before the ON period, for a series of pulsations. Since the dips in the emission level during OFF are dependent on the switching between ON and OFF, this could indicate a common mechanism for the precipitation during the ON and OFF phases. A statistical analysis of brightness rise, fall, and ON times for the pulsations is also performed. It is found that the pulsations are often asymmetric, with either a slower increase of brightness or a slower fall
Electrodynamics and energy characteristics of aurora at high resolution by optical methods
Full text linkTechnological advances leading to improved sensitivity of optical detectors have revealed that aurora contains a richness of dynamic and thin filamentary structures, but the source of the structured emissions is not fully understood. In addition, high resolution radar data have indicated that thin auroral arcs can be correlated with highly varying and large electric fields, but the detailed picture of the electrodynamics of auroral filaments is yet incomplete. The ASK instrument is a state-of-the-art ground-based instrument designed to investigate these smallest auroral features at very high spatial and temporal resolution, by using three EMCCDs in parallel for three different narrow spectral regions. ASK is specifically designed to utilize a new optical techique to determine the ionospheric electric fields. By imaging the long-lived O+ line at 732~nm, the plasma flow in the region can be traced, and since the plasma motion is controlled by the electric field, the field strength and direction can be estimated at unprecedented resolution. The method is a powerful tool to investigate the detailed electrodynamics and current systems around the thin auroral filaments. The two other ASK cameras provide information on the precipitation by imaging prompt emissions, and the emission brightness ratio of the two emissions, together with ion chemistry modeling, is used to give information on the energy and energy flux of the precipitating electrons. In this paper, we discuss these measuring techniques, and give a few examples of how they are used to reveal the nature and source of fine scale structuring in the auror
Dataset for Horizontal electric fields from flow of auroral O+(2P) ions at sub-second temporal resolution
No full textAuroral Structure and Kinetics (ASK) data for
Tuttle, et al. (2020), Horizontal electric fields from flow of auroral O+(2P) ions at sub-second resolution Ann. Geophys., doi:10.5194/angeo-38-845-2020
ZIP file contains images in PNG format. The four sections of the images are:
Top-left: ASK1, N2 1P, 673.0 nm
Bottom-left: ASK2, O+ 2D-2P, 732.0 nm
Bottom-right: ASK3, OI, 777.4 nm
Top-right: The other 3 images reproduced in RGB format, with ASK1,2,3 in
the R,G,B channels respectively.
For more information see the readme.txt file.</span
Horizontal electric fields from flow of auroral O<sup>+</sup>(<sup>2</sup>P) ions at sub-second temporal resolution
Full text linkElectric fields are a ubiquitous feature of the ionosphere and are intimately linked with aurora through particle precipitation and field-aligned currents. They exhibit orderof- magnitude changes on temporal and spatial scales of seconds and kilometres respectively which are not easy to measure; knowing their true magnitude and temporal variability is important for a theoretical understanding of auroral processes. We present a unique method to estimate ionospheric electric fields in the region close to (kilometre scale) a dynamic auroral arc by solving the continuity equation for the metastable OC.2P/ ions, which emit as they move under the influence of electric fields during their 5 s lifetime. The main advantage of this optical method is the increase in temporal resolution over other methods such as ground-based radars. Simultaneous measurements of emission at 732.0 nm (from the OC.2P/ ions) and prompt emissions at 673.0 nm (N2) and 777.4 nm (O), all at high spatial (100 m) and temporal (0.05 s) resolution, are used in the solution of the continuity equation, which gives the dynamic changes of the OC ion population at all heights in a 3D volume close to the magnetic zenith. Perspective effects are taken into account by a new geometric method, which is based on an accurate estimate of the magnetic zenith position. The emissions resulting from the metastable ions are converted to brightness images by projecting them onto the plane of the ground, and the projected images are then compared with the measured images. The flow velocity of the ions is a free parameter in the solution of the continuity equation; the value that minimises the difference between the modelled and observed images is the extracted flow velocity at each time step.We demonstrate the method with an example event during the passage of a brightening arc feature, lasting about 10 s, in which the inferred electric fields vary between 20 and 120mVm1. These inferred electric fields are compared with SuperDARN measurements, which have an average value of 30mVm1. An excellent agreement is found in the magnitude and direction of the background electric field; an increase in magnitude during the brightening of the arc feature supports theories of small-scale auroral arc formation and electrodynamics.</p
Compound auroral micromorphology: ground-based high-speed imaging
Full text linkAuroral microphysics still remains partly unexplored. Cutting-edge ground-based optical observations using scientific complementary metal-oxide semiconductor (sCMOS) cameras recently enabled us to observe the fine-scale morphology of bright aurora at magnetic zenith for a variety of rapidly varying features for long uninterrupted periods. We report two interesting examples of combinations of fine-scale rapidly varying auroral features as observed by the sCMOS cameras installed at Poker Flat Research Range (PFRR), Alaska, in February 2014. The first example shows that flickering rays and pulsating modulation simultaneously appeared at the middle of a surge in the pre-midnight sector. The second example shows localized flickering aurora associated with growing eddies at the poleward edge of an arc in the midnight secto
Fine-scale dynamics of fragmented aurora-like emissions
No full textFragmented aurora-like emissions (FAEs) are small (few kilometres) optical structures which have been observed close to the poleward boundary of the aurora from the high-latitude location of Svalbard (magnetic latitude 75.3 N). The FAEs are only visible in certain emissions, and their shape has no magnetic-field-aligned component, suggesting that they are not caused by energetic particle precipitation and are, therefore, not aurora in the normal sense of the word. The FAEs sometimes form wave-like structures parallel to an auroral arc, with regular spacing between each FAE. They drift at a constant speed and exhibit internal dynamics moving at a faster speed than the envelope structure. The formation mechanism of FAEs is currently unknown. We present an analysis of high-resolution optical observations of FAEs made during two separate events. Based on their appearance and dynamics, we make the assumption that the FAEs are a signature of a dispersive wave in the lower E-region ionosphere, co-located with enhanced electron and ion temperatures detected by incoherent scatter radar. Their drift speed (group speed) is found to be 580-700 m s-1, and the speed of their internal dynamics (phase speed) is found to be 2200-2500 m s-1, both for an assumed altitude of 100 km. The speeds are similar for both events which are observed during different auroral conditions. We consider two possible waves which could produce the FAEs, i.e. electrostatic ion cyclotron waves (EIC) and Farley-Buneman waves, and find that the observations could be consistent with either wave under certain assumptions. In the case of EIC waves, the FAEs must be located at an altitude above about 140 km, and our measured speeds scaled accordingly. In the case of Farley-Buneman waves a very strong electric field of about 365 mV m-1 is required to produce the observed speeds of the FAEs; such a strong electric field may be a requirement for FAEs to occur.</p
Ionospheric Plasma Parameters Measured by SPIDER-2 Sounding Rocket During a Pulsating Aurora Event
No full textThe Small Payloads for Investigation of Disturbances in Electrojet by Rockets 2 (SPIDER-2) sounding rocket was launched from Esrange, Sweden, on the 19th of February 2020 at 23:14 UT. It traversed a pulsating aurora event, deploying eight free falling units which provided in situ multi-point measurements of the electric field, magnetic field and plasma parameters. In this article, the measured plasma parameters have been analyzed and compared with each other and with optical measurements obtained by ground based instrumentation. Peaks in electron density, thermal ion flux and optical emission have been found in the E region. Electron density profiles have been derived from the data collected by the Langmuir probes in two free falling units, the electron probes in the main rocket and the wave propagation experiment. A generally good agreement has been found among the different measurements in the up-leg of the trajectory, while the effect of the rocket wake was evident in the down-leg. The observed electron density profile has been found to agree with an incoming flux of high energetic electrons with energies around 20 keV. Auroral pulsations with a periodicity of 1-2 s have been recorded by an onboard photometer, a ground-based high speed camera, and the in situ thermal ion flux. The percentages of variation between the ON and OFF phases of the pulsations have been quantified for these quantities. The brightness measured by the photometer varies up to 68%, while the thermal ion flux measurements show only a 2.5% variation.</p
Alfven Waves and Spatio-Temporal Structuring in the Auroral Ionosphere [Elektronisk resurs]
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