| 1. |
- Alaniz, Monica, et al.
(författare)
-
The SQUID sounding rocket experiment
- 2011
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Ingår i: Proceedings of the 20th ESA Symposium on European Rocket and Balloon Programmes and Related Research. - : European Space Agency. - 9789290922643 ; , s. 159-166
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Konferensbidrag (refereegranskat)abstract
- The objective of the SQUID project is to develop and in flight verify a miniature version of a wire boom deployment mechanism to be used for electric field measurements in the ionosphere. In February 2011 a small ejectable payload, built by a team of students from The Royal Institute of Technology (KTH), was launched from Esrange on-board the REXUS-10 sounding rocket. The payload separated from the rocket, deployed and retracted the wire booms, landed with a parachute and was subsequently recovered. Here the design of the experiment and post fight analysis are presented.
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| 2. |
- Alday, Juan, et al.
(författare)
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New constraints on Ganymede's hydrogen corona : Analysis of Lyman-alpha emissions observed by HST/STIS between 1998 and 2014
- 2017
-
Ingår i: Planetary and Space Science. - : Elsevier. - 0032-0633 .- 1873-5088. ; 148, s. 35-44
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Tidskriftsartikel (refereegranskat)abstract
- Far-ultraviolet observations of Ganymede's atmospheric emissions were obtained with the Space Telescope Imaging Spectrograph (STIS) onboard of the Hubble Space Telescope (HST) on several occasions between 1998 and 2014. We analyze the Lyman-alpha emission from four HST campaigns in order to constrain the abundance and variation of atomic hydrogen in Ganymede's atmosphere. We apply a forward model that estimates surface reflection and resonant scattering in an escaping corona of the solar Lyman-alpha flux, taking into account the effects of the hydrogen in the interplanetary medium. The atmospheric emissions around Ganymede's disk derived for the observations taken between 1998 and 2011 are consistent with a hydrogen corona in the density range of (5-8) x 10(3) cm(-3) at the surface. The hydrogen density appears to be generally stable in that period. In 2014, Ganymede's corona brightness is approximately 3 times lower during two observations of Ganymede's trailing hemisphere and hardly detectable at all during two observations of the leading hemisphere. We also investigate extinction of Ganymede's coronal emissions in the Earth's upper atmosphere or geocorona. For small Doppler shifts, resonant scattering in the geocorona of the moon corona emissions can effectively reduce the brightness observed by HST. In the case of the 2014 leading hemisphere observations, an estimated extinction of 80% might explain the non-detection of Ganymede's hydrogen corona. Geocoronal extinction might also explain a previously detected hemispheric difference from Callisto's hydrogen corona.
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| 3. |
- Andersson, L, et al.
(författare)
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Electron signatures and Alfven waves
- 2002
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 107:A9
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Tidskriftsartikel (refereegranskat)abstract
- [1] We identify two distinct electron populations associated with Alfven waves in the Freja data set using the high time resolution state of the art electron detector. One of the populations, detected together with an Alfven wave, is field-aligned and can be seen as trapped within the wave. The other electron population is detected before the wave and consists of electrons which have left the wave at a point with a velocity higher than the local Alfven speed. In the paper, the electrons leaving wave are modeled for different density profiles and are compared with the observed data. Depending on the density profile, the model can produce the same energy-time and pitch angle-time dispersion that is observed in the Freja data. The conclusion of the paper is that the Alfven wave can explain the observed particle signatures. It is shown that the Alfven wave acceleration can create electron signatures similar to inverted-V structures. The density distribution along a flux tube has an important role in the type of particle signatures that can be detected at low altitudes.
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| 4. |
- Archer, Jenny, et al.
(författare)
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Dynamics and characteristics of black aurora as observed by high resolution ground-based imagers and radar
- 2011
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 32:11, s. 2973-2985
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution, multi-spectral data from the ground-based low-light auroral imager ASK (Auroral Structure and Kinetics) are used to characterize the fine structure of black aurora. Sixteen events comprising sheared and unsheared black arcs, as well as black patches and rings, constitute the analysed dataset. Simultaneous measurements of emissions caused by high- and low-energy precipitation make it possible to relate the characteristics of different black structures to the energy of the precipitating electrons. The reductions of high-energy particles versus low-energy particles in the black regions compared to the diffuse background are investigated for the different forms of black aurora. Two separate mechanisms have been suggested to cause black aurora. The larger reduction of high-energy precipitation within the fine-scale black structures discussed here favours a magnetospheric mechanism that blocks high-energy electrons from being scattered into the loss cone. European Incoherent SCATter radar (EISCAT) electron density profiles are available for one of the nights, and are compared to the optical measurements.
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| 5. |
- Arriaga, I., et al.
(författare)
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SMILE - A miniaturized fluxgate magnetometer
- 2007
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Ingår i: 18TH ESA SYMPOSIUM ON EUROPEAN ROCKET AND BALLOON PROGRAMMES AND RELATED RESEARCH. ; , s. 569-572
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Konferensbidrag (refereegranskat)abstract
- The SMILE (Small Magnetometer in Low-mass Experiment) instrument is a miniaturized digital fluxgate magnetometer that combines a miniature triaxial sensor with volume compensation with digital data processing implemented in a single FPGA. This report presents first results of numerical simulations of the sensor. We also discuss the digital solutions used in SMILE.
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| 6. |
- Ashrafi, M., et al.
(författare)
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Modelling of N(2)1P emission rates in aurora using various cross sections for excitation
- 2009
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 27:6, s. 2545-2553
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of N(2)1P auroral emissions from the (4,1) and (5,2) bands have been made at high temporal and spatial resolution in the region of the magnetic zenith. The instrument used was the auroral imager ASK, situated at Ramfjordmoen, Norway (69.6 N, 19.2 E) on 22 October 2006. Measurements from the European Incoherent Scatter Radar (EISCAT) have been combined with the optical measurements, and incorporated into an ionospheric model to obtain height profiles of electron density and emission rates of the N(2)1P bands. The radar data provide essential verification that the energy flux used in the model is correct. One of the most important inputs to the model is the cross section for excitation to the B-3 Pi(g) electronic state, as well as the cross sections to higher states from which cascading into the B state occurs. The balance equations for production and loss of the populations of all levels in each state are solved in order to find the cascade contributions. Several sets of cross sections have been considered, and selected cross sections have been used to construct "emission" cross sections for the observed bands. The resulting brightnesses are compared with those measured by ASK. The importance of specific contributions from cascading is found, with more than 50% of the total brightness resulting from cascading. The cross sections used are found to produce a range of brightnesses well within the uncertainty of both the modelled and measured values.
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| 7. |
- Balmer, G., et al.
(författare)
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ISAAC : A REXUS STUDENT EXPERIMENT TO DEMONSTRATE AN EJECTION SYSTEM WITH PREDEFINED DIRECTION
- 2015
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Ingår i: EUROPEAN ROCKET AND BALLOON. - 9789292212940 ; , s. 235-242
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Konferensbidrag (refereegranskat)abstract
- ISAAC - Infrared Spectroscopy to Analyse the middle Atmosphere Composition was a student experiment launched from SSC's Esrange Space Centre, Sweden, on 29th May 2014, on board the sounding rocket REXUS 15 in the frame of the REXUS/BEXUS programme. The main focus of the experiment was to implement an ejection system for two large Free Falling Units (FFUs) (240 mm x 80 mm) to be ejected from a spinning rocket into a predefined direction. The system design relied on a spring-based ejection system. Sun and angular rate sensors were used to control and time the ejection. The flight data includes telemetry from the Rocket Mounted Unit (RMU), received and saved during flight, as well as video footage from the GoPro camera mounted inside the RMU and recovered after the flight. The FFUs' direction, speed and spin frequency as well as the rocket spin frequency were determined by analyzing the video footage. The FFU-Rocket-Sun angles were 64.3 degrees and 104.3 degrees, within the required margins of 90 degrees +/- 45 degrees. The FFU speeds were 3.98 m/s and 3.74 m/s, lower than the expected 5 +/- 1 m/s. The FFUs' spin frequencies were 1.38 Hz and 1.60 Hz, approximately half the rocket's spin frequency. The rocket spin rate slightly changed from 3.163 Hz before the ejection to 3.117 Hz after the ejection of the two FFUs. The angular rate, sun sensor data and temperature on the inside of the rocket module skin were also recorded. The experiment design and results of the data analysis are presented in this paper.
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| 8. |
- Belyayev, Serhiy, et al.
(författare)
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Digital fluxgate magnetometer : design notes
- 2015
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Ingår i: Measurement science and technology. - : Institute of Physics Publishing (IOPP). - 0957-0233 .- 1361-6501. ; 26:12
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Tidskriftsartikel (refereegranskat)abstract
- We presented an approach to understanding the performance of a fully digital fluxgate magnetometer. All elements of the design are important for the performance of the instrument, and the presence of the digital feed-back loop introduces certain peculiarities affecting the noise and dynamic performance of the instrument. Ultimately, the quantisation noise of the digital to analogue converter is found to dominate the noise of the current design, although noise shaping alleviates its effect to some extent. An example of magnetometer measurements on board a sounding rocket is presented, and ways to further improve the performance of the instrument are discussed.
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| 9. |
- Belyayev, Serhiy, et al.
(författare)
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Effect of second harmonic in pulse-width-modulation-based DAC for feedback of digital fluxgate magnetometer
- 2018
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Ingår i: Measurement science and technology. - : Institute of Physics Publishing. - 0957-0233 .- 1361-6501. ; 29:4
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Tidskriftsartikel (refereegranskat)abstract
- Digital fluxgate magnetometers employ processing of the measured pickup signal to produce the value of the compensation current. Using pulse-width modulation with filtering for digital to analog conversion is a convenient approach, but it can introduce an intrinsic source of nonlinearity, which we discuss in this design note. A code shift of one least significant bit changes the second harmonic content of the pulse train, which feeds into the pick-up signal chain despite the heavy filtering. This effect produces a code-dependent nonlinearity. This nonlinearity can be overcome by the specific design of the timing of the pulse train signal. The second harmonic is suppressed if the first and third quarters of the excitation period pulse train are repeated in the second and fourth quarters. We demonstrate this principle on a digital magnetometer, achieving a magnetometer noise level corresponding to that of the sensor itself.
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| 10. |
- Bergström, Rasmus, et al.
(författare)
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SCATTERING OF RADAR WAVES ON AEROSOLS IN PLASMAS
- 2015
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Ingår i: EUROPEAN ROCKET AND BALLOON. - 9789292212940 ; , s. 87-94
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Konferensbidrag (refereegranskat)abstract
- To study the physical mechanisms of phenomena such as polar mesospheric summer echoes, the SCRAP (Scattering of Radar waves on Aerosols in Plasmas) experiment aimed to validate theories on density fluctuations in dusty plasmas. The SCRAP team developed two identical free falling units (FFUs) designed to create a cloud of copper particles once they eject from the REXUS17 sounding rocket 124 seconds after launch. By using the EISCAT incoherent scatter radar system to observe the cloud, the SCRAP experiment proposed to relate theoretical predictions to a controlled object. The SCRAP experiment was launched from ESRANGE on March the 17th 2015. The FFUs GPS signal was lost during launch and the units were therefore not found. Moreover, no backscattering from the copper cloud was observed by the radar.
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| 11. |
- Blixt, E. M., et al.
(författare)
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Dynamic rayed aurora and enhanced ion-acoustic radar echoes
- 2005
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 23:1, s. 3-11
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Tidskriftsartikel (refereegranskat)abstract
- The generation mechanism for naturally enhanced ion-acoustic echoes is still debated. One important issue is how these enhancements are related to auroral activity. All events of enhanced ion-acoustic echoes observed simultaneously with the EISCAT Svalbard Radar (ESR) and with high-resolution narrow field-of-view auroral imagers have been collected and studied. Characteristic of all the events is the appearance of very dynamic rayed aurora, and some of the intrinsic features of these auroral displays are identified. Several of these identified features are directly related to the presence of low energy (10-100 eV) precipitating electrons in addition to the higher energy population producing most of the associated light. The low energy contribution is vital for the formation of the enhanced ion-acoustic echoes. We argue that this type of aurora is sufficient for the generation of naturally enhanced ion-acoustic echoes. In one event two imagers were used to observe the auroral rays simultaneously, one from the radar site and one 7 kin away. The data from these imagers shows that the auroral rays and the strong backscattering filaments (where the enhanced echoes are produced) are located on the same field line, which is in contrast to earlier statements in the litterature that they should be separated.
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| 12. |
- Blixt, E. M., et al.
(författare)
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Optical flow analysis of the aurora borealis
- 2006
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Ingår i: IEEE Geoscience and Remote Sensing Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1545-598X .- 1558-0571. ; 3:1, s. 159-163
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Tidskriftsartikel (refereegranskat)abstract
- Optical observations of the aurora have traditionally focused on the structure, intensity, and wavelength of the emissions. But the apparent motion of auroral forms offers another important diagnostic tool for investigating this poorly understood phenomenon. Prior analyses of auroral motion have focused on tracing individual features. In this letter, we investigate the feasibility of deriving the entire two-dimensional velocity field automatically using robust optical flow estimation. The analysis is applied to two narrow-field video sequences. Both examples are rich in small-scale structure and motion, but appear very different to the eye. The robust optical flow estimator performed well for regions of dense turbulent motion, while sheared flow and flow which is perpendicular to image intensity gradients, was poorly resolved. The relative magnitude of the outliers provides a quantitative measure of the validity of the underlying flow model and, hence, a means of automatically differentiating among auroral forms with differing physical origins. The technique can be used to deduce ionospheric electric fields and neutral winds, and the flow fields yield important physical information about the generation mechanism.
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| 13. |
- Blomberg, Lars G., et al.
(författare)
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EMMA - the electric and magnetic monitor of the aurora on Astrid-2
- 2004
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 22:1, s. 115-123
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Tidskriftsartikel (refereegranskat)abstract
- The Astrid-2 mission has dual primary objectives. First, it is an orbiting instrument platform for studying auroral electrodynamics. Second, it is a technology demonstration of the feasibility of using micro-satellites for innovative space plasma physics research. The EMMA instrument, which we discuss in the present paper, is designed to provide simultaneous sampling of two electric and three magnetic field components up to about 1 kHz. The spin plane components of the electric field are measured by two pairs of opposing probes extended by wire booms with a separation distance of 6.7 m. The probes have titanium nitride (TiN) surfaces. which has proved to be a material with excellent properties for providing good electrical contact between probe and plasma. The wire booms are of a new design in which the booms in the stowed position are wound around the exterior of the spacecraft body. The boom system was flown for the first time on this mission and worked flawlessly. The magnetic field is measured by a tri-axial fluxgate sensor located at the tip of a rigid. hinged boom extended along the spacecraft spin axis and facing away from the Sun. The new advanced-design fluxgate magnetometer uses digital signal processors for detection and feedback, thereby reducing the analogue circuitry to a minimum. The instrument characteristics as well as a brief review of the science accomplished and planned are presented.
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| 14. |
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| 15. |
- Blöcker, Aljona, et al.
(författare)
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Variability of Io's poynting flux : A parameter study using MHD simulations
- 2020
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Ingår i: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 192
-
Tidskriftsartikel (refereegranskat)abstract
- Io's plasma interaction creates an electromagnetic coupling between Io and Jupiter through Alfvén waves triggering the generation of auroral footprints in Jupiter's southern and northern hemispheres. The brightness of Io's footprints undergoes periodic variations that are primarily modulated by Io's local plasma interaction through the Poynting flux radiated away from the moon. The periodic pattern with two maxima near 110∘ and 290∘ Jovian longitude where Io crosses the dense plasma sheet is generally understood. However, some characteristics, like the 2-4 times stronger brightening of the southern footprint near Jovian longitude 110∘ or the lack of response to Io's eclipse passage, are not fully understood. We systematically study variations in Io's plasma interaction and the Poynting flux using a 3D magnetohydrodynamic model, performing a series of simulations with different upstream plasma conditions and models of Io's atmosphere. Our results indicate that the strong Jovian magnetic field near 110∘ plays a more important role than previously estimated for the strong brightening there. We find that the Poynting flux is not fully saturated for a wide range of possible atmospheric densities (6 ×1018 - 6 ×1021 m-2) and that density changes in the atmosphere by a factor of > 3, as possibly happening during Io's eclipse passage, lead to a change of the Poynting flux by > 20%. Assuming that these expected changes in Poynting flux also apply to the footprints, the non-detection of a dimming in the footprint during the eclipse by Juno-UVS suggests that Io's global atmospheric density decreases by a factor of < 2.5. We show that for smaller atmospheric scale heights (i.e. a more confined atmosphere), changes in the atmospheric density have less effect on the Poynting flux. The missing response of the footprint to the eclipse hence might also be consistent with a density decrease by a factor of > 3, if the effective atmospheric scale height is small (< 120 km). Finally, we provide new analytical approximations that can be used for analyzing the effect of the local interaction responsible for the footprint variability in future studies.
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| 16. |
- Bordogna, Marco Tito, et al.
(författare)
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MUSCAT experiment : active free falling units for in situ measurements of temperature and density in the middle atmosphere
- 2013
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Ingår i: European Space Agency. - ESTEC, Noordwijk, The Netherlands : ESA Communications. - 9789290922858 ; , s. 575-582
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The main scientific objective of the MUSCAT Experimentis to develop a technique to reconstruct temperatures and density profiles in the middle atmosphere using active spherical probes. The MUSCAT experiment was launched on May 9, 2013 on the REXUS-13 sounding rocket from Esrange, in northern Sweden. The experiment ejected four probes that collected raw GPS signal. The experiment design and preliminary results are presented here.
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| 17. |
- Cai, L., et al.
(författare)
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Effect of Polar Cap Patches on the High-Latitude Upper Thermospheric Winds
- 2024
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 129:8
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on the poorly known effect of polar cap patches (PCPs) on the ion-neutral coupling in the F-region. The PCPs were identified by total electron content measurements from the Global Navigation Satellite System (GNSS) and the ionospheric parameters from the Defense Meteorological Satellite Program spacecraft. The EISCAT incoherent scatter radars on Svalbard and at Tromsø, Norway observed that PCPs entered the nightside auroral oval from the polar cap and became plasma blobs. The ionospheric convection further transported the plasma blobs to the duskside. Simultaneously, long-lasting strong upper thermospheric winds were detected in the duskside auroral oval by a Fabry-Perot Interferometer (FPI) at Tromsø and in the polar cap by the Gravity Recovery and Climate Experiment satellite. Using EISCAT ion velocities and plasma parameters as well as FPI winds, the ion drag acting on neutrals and the time constant for the ion drag could be estimated. Due to the arrival of PCPs/blobs and the accompanied increase in the F-region electron densities, the ion drag is enhanced between about 220 and 500 km altitudes. At the F peak altitudes near 300 km, the median ion drag acceleration affecting neutrals more than doubled and the associated median e-folding time decreased from 4.4 to 2 hr. The strong neutral wind was found to be driven primarily by the ion drag force due to large-scale ionospheric convection. Our results provide a new insight into ionosphere-thermosphere coupling in the presence of PCPs/blobs.
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| 18. |
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| 19. |
- Dahlgren, Hanna, et al.
(författare)
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Coexisting structures fromhigh- and low-energy precipitation in fine-scale aurora
- 2015
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 42:5, s. 1290-1296
-
Tidskriftsartikel (refereegranskat)abstract
- High-resolution multimonochromatic measurements of auroral emissions have revealed the first optical evidence of coexisting small-scale auroral features resulting from separate high- and low-energy populations of precipitating electrons on the same field line. The features exhibit completely separate motion and morphology. From emission ratios and ion chemistry modeling, the average energy and energy flux of the precipitation is estimated. The high-energy precipitation is found to form large pulsating patches of 0.1Hz with a 3Hz modulation, and nonpulsating coexisting discrete auroral filaments. The low-energy precipitation is observed simultaneously on the same field line as discrete filaments with no pulsation. The simultaneous structures do not interact, and they drift with different speeds in different directions. We suggest that the high- and low-energy electron populations are accelerated by separate mechanisms, at different distances from Earth. The small-scale structures could be caused by local instabilities above the ionosphere.
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| 20. |
- Dahlgren, Hanna, et al.
(författare)
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Electrodynamics and energy characteristics of aurora at high resolution by optical methods
- 2016
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 121:6, s. 5966-5974
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Tidskriftsartikel (refereegranskat)abstract
- Technological 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 Auroral Structure and Kinetics (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 electron multiplying CCDs in parallel for three different narrow spectral regions. ASK is specifically designed to utilize a new optical technique 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 aurora.
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| 21. |
- Dahlgren, Hanna, et al.
(författare)
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Energy and flux variations across thin auroral arcs
- 2011
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 29:10, s. 1699-1712
-
Tidskriftsartikel (refereegranskat)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 and the EISCAT radar. The energy and flux of the precipitating electrons, volume emission rates and local electric fields in the ionosphere have been determined at high temporal (up to 30 Hz) and spatial (down to tens of metres) resolution. A new time-dependent inversion model is used to derive energy spectra from EISCAT electron density profiles. The energy and flux are also derived independently from optical emissions combined with ion-chemistry modelling, and a good agreement is found. A robust method to obtain detailed 2-D maps of the average energy and number flux of small scale aurora is presented. The arcs are stretched in the north-south direction, and the lowest energies are found on the western, leading edges of the arcs. The large ionospheric electric fields (250 mV m(-1)) found from tristatic radar measurements are evidence of strong currents associated with the region close to the optical arcs. The different data sets indicate that the arcs appear on the boundaries between regions with different average energy of diffuse precipitation, caused by pitch-angle scattering. The two thin arcs on these boundaries are found to be related to an increase in number flux (and thus increased energy flux) without an increase in energy.
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| 22. |
- Dahlgren, Hanna, 1980-
(författare)
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Fine-scale morphology and spectral characteristics of active aurora
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ground-based and in-situ observations of the aurora demonstrate an extreme richness in fine structure, with spatial scales down to tens of metres and time variations occurring on a fraction of a second. To further our understanding of the aurora, it is esssential to understand the mechanisms responsible for the small-scale structuring, since this is an intrinsic property of the auroral plasma. Still many questions about dynamics and structuring of aurora on small scales remain unanswered. In this thesis the low-light optical instrument ASK (Auroral Structure and Kinetics) is used to image small-scale structures in the aurora at very high spatial and temporal resolution. ASK is a multi-spectral instrument, imaging the aurora in three selected emission lines simultaneously. This provides information on the energy of the precipitating electrons. The SIF (Spectrographic Imaging Facility) instrument has been used in conjunction with ASK, to give a more complete picture of the spectral characteristics of the aurora, and to determine the contamination of the emission lines by other emissions. Data from ASK and SIF is used to study the relation between the morphology and dynamics of small-scale structures in the aurora and the energy of the precipitating electrons. By comparing electron density profiles provided by EISCAT (European Incoherent SCATter) measurements with modeling results, information on characteristic energy and energy flux of the precipitating electrons can be obtained. One of the ASK channels is imaging a metastable O+ emission, which has a lifetime of 5 s. By tracing the afterglow in this channel optically a direct measure of the E × B drift and thus of the local ionospheric electric fields is provided.
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| 23. |
- Dahlgren, Hanna, et al.
(författare)
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First direct optical observations of plasma flows using afterglow of O+ in discrete aurora
- 2009
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Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 71:2, s. 228-238
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Tidskriftsartikel (refereegranskat)abstract
- Imaging of active structured aurora in the forbidden O+ ion line at 732.0 nm provides a possibility of direct observation of plasma drifts in the topside ionosphere. The metastable O+ P-2 state has a radiative lifetime of 5 s, so the oxygen ions can be detected after the precipitation creating them has ceased. The decay time of the O+ emission is studied and modelled with a time-dependent electron transport and ion chemistry model. Four examples are given of O+ afterglow observed with the multi-spectral imager, auroral structure and kinetics (ASK), which was located near Tromso, Norway, in 2006. Estimates are given of drift velocities resulting from the analysis of the afterglow motions. Bulk plasma velocities of 340 and 720 m/s directed eastwards were found for two afterglowing arc filaments, corresponding to southward electric fields of 18 and 40 mV/m, respectively.
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| 24. |
- Dahlgren, H., et al.
(författare)
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Monoenergetic high-energy electron precipitation in thin auroral filaments
- 2012
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 39:20, s. L20101-
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Tidskriftsartikel (refereegranskat)abstract
- The energy distribution of the electron precipitation responsible for extremely narrow (70 m) and dynamic auroral filaments is found to be sharply peaked at around 8 keV. The events were captured with high resolution low-light optical imagers located near Tromso, Norway. The method uses imaging in two emissions which have different energy dependent responses to auroral electron precipitation. The key feature of the events was that no difference in the altitude of the two emissions was detected, nor any time-of-flight dispersion, thus leading to the conclusion that the filaments were caused by monoenergetic precipitation. Comparisons with an electron transport and ion chemistry model show that the high energy filaments were embedded in a region of lower energy precipitation of about 4 keV. There is currently no consistent theory to explain the characteristics of the observed auroral structures.
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| 25. |
- Dahlgren, Hanna, 1980-, et al.
(författare)
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Morphology and dynamics of aurora at fine scale : first results for the ASK instrument
- 2008
-
Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 26:5, s. 1041-1048
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Tidskriftsartikel (refereegranskat)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. The three emission species studied are O-2(+) (5620 angstrom), O+ (7319 angstrom) and O (7774 angstrom). ASK was installed and operated for the first time in an observational campaign on Svalbard, from December 2005 to March 2006. The measurements were supported by data from the Spectrographic Imaging Facility (SIF). The relation between the morphology and dynamics of the visible aurora and its spectral characteristics is studied for selected events from this period. In these events it is found that dynamic aurora is coupled to high energy electron precipitation. By studying the O-2(+)/O intensity ratio we find that some auroral filaments are caused by higher energy precipitation within regions of lower energy precipitation, whereas other filaments are the result of a higher particle flux compared to the surroundings.
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