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Publications (10 of 28) Show all publications
Dahlgren, H., Schlatter, N. M., Ivchenko, N., Roth, L. & Karlsson, A. (2017). Relation of anomalous F region radar echoes in the high-latitude ionosphere to auroral precipitation. Annales Geophysicae, 35(3), 475-479
Open this publication in new window or tab >>Relation of anomalous F region radar echoes in the high-latitude ionosphere to auroral precipitation
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2017 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 35, no 3, p. 475-479Article in journal (Refereed) Published
Abstract [en]

Non-thermal echoes in incoherent scatter radar observations are occasionally seen in the high-latitude ionosphere. Such anomalous echoes are a manifestation of plasma instabilities on spatial scales matching the radar wavelength. Here we investigate the occurrence of a class of spatially localized anomalous echoes with an enhanced zero Doppler frequency feature and their relation to auroral particle precipitation. The ionization profile of the E region is used to parametrize the precipitation, with nmE and hmE being the E region peak electron density and the altitude of the peak, respectively. We find the occurrence rate of the echoes to generally increase with nmE and decrease with hmE, thereby indicating a correlation between the echoes and high-energy flux precipitation of particles with a high characteristic energy. The highest occurrence rate of > 20% is found for hmE = 109 km and nmE D 10(11.9) m(-3), averaged over the radar observation volume.

Place, publisher, year, edition, pages
Copernicus Gesellschaft, 2017
Keywords
Ionosphere (auroral ionosphere particle precipitation, plasma waves and instabilities)
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-205454 (URN)10.5194/angeo-35-475-2017 (DOI)000398189600002 ()
Funder
Swedish Research Council, 350-2012-6591VINNOVA, 2014-01459
Note

QC 20170524

Available from: 2017-05-24 Created: 2017-05-24 Last updated: 2018-02-28Bibliographically approved
Dahlgren, H., Lanchester, B. S., Ivchenko, N. & Whiter, D. K. (2017). Variations in energy, flux, and brightness of pulsating aurora measured at high time resolution. Annales Geophysicae, 35(3), 493-503
Open this publication in new window or tab >>Variations in energy, flux, and brightness of pulsating aurora measured at high time resolution
2017 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 35, no 3, p. 493-503Article in journal (Refereed) Published
Abstract [en]

High-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.

Place, publisher, year, edition, pages
COPERNICUS GESELLSCHAFT MBH, 2017
Keywords
Ionosphere (auroral ionosphere, particle precipitation), magnetospheric physics (magnetosphere-ionosphere-interactions)
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-205451 (URN)10.5194/angeo-35-493-2017 (DOI)000398189900001 ()2-s2.0-85016499071 (Scopus ID)
Note

QC 20170524

Available from: 2017-05-24 Created: 2017-05-24 Last updated: 2017-11-13Bibliographically approved
Kataoka, R., Fukuda, Y., Uchida, H. A., Yamada, H., Miyoshi, Y., Ebihara, Y., . . . Hampton, D. (2016). High-speed stereoscopy of aurora. Annales Geophysicae, 34(1), 41-44
Open this publication in new window or tab >>High-speed stereoscopy of aurora
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2016 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 34, no 1, p. 41-44Article in journal (Refereed) Published
Abstract [en]

We performed 100aEuro-fps stereoscopic imaging of aurora for the first time. Two identical sCMOS cameras equipped with narrow field-of-view lenses (15A degrees by 15A degrees) were directed at magnetic zenith with the north-south base distance of 8.1aEuro-km. Here we show the best example that a rapidly pulsating diffuse patch and a streaming discrete arc were observed at the same time with different parallaxes, and the emission altitudes were estimated as 85-95aEuro-km and > aEuro-100aEuro-km, respectively. The estimated emission altitudes are consistent with those estimated in previous studies, and it is suggested that high-speed stereoscopy is useful to directly measure the emission altitudes of various types of rapidly varying aurora. It is also found that variation of emission altitude is gradual (e.g., 10aEuro-km increase over 5aEuro-s) for pulsating patches and is fast (e.g., 10aEuro-km increase within 0.5aEuro-s) for streaming arcs.

Place, publisher, year, edition, pages
Copernicus GmbH, 2016
Keywords
Ionosphere, auroral ionosphere
National Category
Geophysics Physical Sciences
Identifiers
urn:nbn:se:kth:diva-186019 (URN)10.5194/angeo-34-41-2016 (DOI)000373596900004 ()2-s2.0-84957309502 (Scopus ID)
Note

QC 20160509

Available from: 2016-05-09 Created: 2016-04-29 Last updated: 2017-11-30Bibliographically approved
Goenka, C., Semeter, J., Noto, J., Baumgardner, J., Riccobono, J., Migliozzi, M., . . . Akbari, H. (2016). Multichannel tunable imager architecture for hyperspectral imaging in relevant spectral domains. Applied Optics, 55(12), 3149-3157
Open this publication in new window or tab >>Multichannel tunable imager architecture for hyperspectral imaging in relevant spectral domains
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2016 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 55, no 12, p. 3149-3157Article in journal (Refereed) Published
Abstract [en]

In this paper, we present a technique for dimensionality reduction in hyperspectral imaging during the data collection process. A four-channel hyperspectral imager using liquid crystal Fabry-Perot etalons has been built and used to verify this method for four applications: auroral imaging, plant study, landscape classification, and anomaly detection. This imager is capable of making measurements simultaneously in four wavelength ranges while being tunable within those ranges, and thus can be used to measure narrow contiguous bands in four spectral domains. In this paper, we describe the design, concept of operation, and deployment of this instrument. The results from preliminary testing of this instrument are discussed and are promising and demonstrate this instrument as a good candidate for hyperspectral imaging.

Place, publisher, year, edition, pages
Optical Society of America, 2016
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-187821 (URN)10.1364/AO.55.003149 (DOI)000374388600037 ()2-s2.0-84971601520 (Scopus ID)
Note

QC 20160531

Available from: 2016-05-31 Created: 2016-05-30 Last updated: 2017-11-30Bibliographically approved
Hirsch, M., Semeter, J., Zettergren, M., Dahlgren, H., Goenka, C. & Akbari, H. (2016). Reconstruction of Fine-Scale Auroral Dynamics. IEEE Transactions on Geoscience and Remote Sensing, 54(5), 2780-2791
Open this publication in new window or tab >>Reconstruction of Fine-Scale Auroral Dynamics
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2016 (English)In: IEEE Transactions on Geoscience and Remote Sensing, ISSN 0196-2892, E-ISSN 1558-0644, Vol. 54, no 5, p. 2780-2791Article in journal (Refereed) Published
Abstract [en]

We present a feasibility study for a high-frame-rate Short-baseline auroral tomographic imaging system useful for estimating parametric variations in the precipitating electron number flux spectrum of dynamic auroral events. Of particular interest are auroral substorms, which are characterized by spatial variations of order 100 m and temporal variations of order 10 ms. These scales are thought to be produced by dispersive Alfven waves in the near-Earth magnetosphere. The auroral tomography system characterized in this paper reconstructs the auroral volume emission rate, to estimate the characteristic energy and location in the direction perpendicular to the geomagnetic field of peak electron precipitation flux, using a distributed network of precisely synchronized ground-based cameras. As the observing baseline decreases, the tomographic inverse problem becomes highly ill-conditioned; as the sampling rate increases, the signal-to-noise ratio degrades and synchronization requirements become increasingly critical. Our approach to these challenges uses a physics-based auroral model to regularize the poorly observed vertical dimension. Specifically, the vertical dimension is expanded in a low-dimensional basis, consisting of eigenprofiles computed over the range of expected energies in the precipitating electron flux, while the horizontal dimension retains a standard orthogonal pixel basis. Simulation results show typical characteristic energy estimation error less than 30% for a 3-km baseline achievable within the confines of the Poker Flat Research Range, using GPS-synchronized electron-multiplying charge-coupled device cameras with broadband BG3 optical filters that pass prompt auroral emissions.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2016
Keywords
Aurora, ionosphere, optical tomography, remote sensing
National Category
Geochemistry Geophysics
Identifiers
urn:nbn:se:kth:diva-187792 (URN)10.1109/TGRS.2015.2505686 (DOI)000374968500023 ()2-s2.0-84953246205 (Scopus ID)
Note

QC 20160530

Available from: 2016-05-30 Created: 2016-05-30 Last updated: 2017-11-30Bibliographically approved
Schlatter, N. M., Belyey, V., Gustavsson, B., Ivchenko, N., Whiter, D., Dahlgren, H., . . . Grydeland, T. (2015). Auroral ion acoustic wave enhancement observed with a radar interferometer system. Annales Geophysicae, 33(7), 837-844
Open this publication in new window or tab >>Auroral ion acoustic wave enhancement observed with a radar interferometer system
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2015 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 33, no 7, p. 837-844Article in journal (Refereed) Published
Abstract [en]

Measurements of naturally enhanced ion acoustic line (NEIAL) echoes obtained with a five-antenna interferometric imaging radar system are presented. The observations were conducted with the European Incoherent SCATter (EIS-CAT) radar on Svalbard and the EISCAT Aperture Synthesis Imaging receivers (EASI) installed at the radar site. Four baselines of the interferometer are used in the analysis. Based on the coherence estimates derived from the measurements, we show that the enhanced backscattering region is of limited extent in the plane perpendicular to the geomagnetic field. Previously it has been argued that the enhanced backscatter region is limited in size; however, here the first unambiguous observations are presented. The size of the enhanced backscatter region is determined to be less than 900 x 500 m, and at times less than 160m in the direction of the longest antenna separation, assuming the scattering region to have a Gaussian scattering cross section in the plane perpendicular to the geomagnetic field. Using aperture synthesis imaging methods volumetric images of the NEIAL echo are obtained showing the enhanced backscattering region to be aligned with the geomagnetic field. Although optical auroral emissions are observed outside the radar look direction, our observations are consistent with the NEIAL echo occurring on field lines with particle precipitation.

Keywords
Ionosphere, Auroral ionosphere
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-173181 (URN)10.5194/angeo-33-837-2015 (DOI)000358800400004 ()2-s2.0-84937413733 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20150914

Available from: 2015-09-14 Created: 2015-09-07 Last updated: 2017-12-04Bibliographically approved
Dahlgren, H., Lanchester, B. S. & Ivchenko, N. (2015). Coexisting structures fromhigh- and low-energy precipitation in fine-scale aurora. Geophysical Research Letters, 42(5), 1290-1296
Open this publication in new window or tab >>Coexisting structures fromhigh- and low-energy precipitation in fine-scale aurora
2015 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 5, p. 1290-1296Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
aurora, fine-scale structure, multispectral observations, high-energy precipitation, low-energy precipitation, pulsations
National Category
Geosciences, Multidisciplinary
Identifiers
urn:nbn:se:kth:diva-165220 (URN)10.1002/2015GL063173 (DOI)000351847600002 ()2-s2.0-84925872747 (Scopus ID)
Note

QC 20150506

Available from: 2015-05-06 Created: 2015-04-24 Last updated: 2017-12-04Bibliographically approved
Kataoka, R., Fukuda, Y., Miyoshi, Y., Miyahara, H., Itoya, S., Ebihara, Y., . . . Ivchenko, N. (2015). Compound auroral micromorphology: ground-based high-speed imaging. EARTH PLANETS AND SPACE, 67, Article ID 23.
Open this publication in new window or tab >>Compound auroral micromorphology: ground-based high-speed imaging
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2015 (English)In: EARTH PLANETS AND SPACE, ISSN 1880-5981, Vol. 67, article id 23Article in journal (Refereed) Published
Abstract [en]

Auroral 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 sector.

Keywords
Aurora, Magnetosphere-ionosphere coupling, Wave-particle interaction
National Category
Geology
Identifiers
urn:nbn:se:kth:diva-162955 (URN)10.1186/s40623-015-0190-6 (DOI)000350331100001 ()2-s2.0-84923358601 (Scopus ID)
Note

QC 20150401

Available from: 2015-04-01 Created: 2015-03-26 Last updated: 2015-04-01Bibliographically approved
Zettergren, M. D., Semeter, J. L. & Dahlgren, H. (2015). Dynamics of density cavities generated by frictional heating: Formation, distortion, and instability. Geophysical Research Letters, 42(23), 10120-10125
Open this publication in new window or tab >>Dynamics of density cavities generated by frictional heating: Formation, distortion, and instability
2015 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 23, p. 10120-10125Article in journal (Refereed) Published
Abstract [en]

A simulation study of the generation and evolution of mesoscale density cavities in the polar ionosphere is conducted using a time-dependent, nonlinear, quasi-electrostatic model. The model demonstrates that density cavities, generated by frictional heating, can form in as little as 90 s due to strong electric fields of ∼120 mV/m, which are sometimes observed near auroral zone and polar cap arcs. Asymmetric density cavity features and strong plasma density gradients perpendicular to the geomagnetic field are naturally generated as a consequence of the strong convection and finite extent of the auroral feature. The walls of the auroral density cavities are shown to be susceptible to large-scale distortion and gradient-drift instability, hence indicating that arc-related regions of frictional heating may be a source of polar ionospheric density irregularities.

Place, publisher, year, edition, pages
Blackwell Publishing, 2015
Keywords
density cavities, high latitude, instabilities, ionosphere
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-181820 (URN)10.1002/2015GL066806 (DOI)000368343900004 ()2-s2.0-84953635236 (Scopus ID)
Note

QC 20160210. QC 20160216

Available from: 2016-02-10 Created: 2016-02-05 Last updated: 2017-11-30Bibliographically approved
Goenka, C., Semeter, J., Noto, J., Baumgardner, J., Riccobono, J., Migliozzi, M., . . . Akbari, H. (2015). LiCHI - Liquid Crystal Hyperspectral Imager for simultaneous multispectral imaging in aeronomy. Optics Express, 23(14), 17772-17782
Open this publication in new window or tab >>LiCHI - Liquid Crystal Hyperspectral Imager for simultaneous multispectral imaging in aeronomy
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2015 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 14, p. 17772-17782Article in journal (Refereed) Published
Abstract [en]

A four channel hyperspectral imager using Liquid Crystal Fabry-Perot (LCFP) etalons has been built and tested. This imager is capable of making measurements simultaneously in four wavelength ranges in the visible spectrum. The instrument was designed to make measurements of natural airglow and auroral emissions in the upper atmosphere of the Earth and was installed and tested at the Poker Flat Research Range in Fairbanks, Alaska from February to April 2014. The results demonstrate the capabilities and challenges this instrument presents as a sensor for aeronomical studies. (C) 2015 Optical Society of America

Place, publisher, year, edition, pages
Optical Society of America, 2015
Keywords
Aeronomy, Fabry-Perot, Liquid crystal, Multispectral, Rotational temperature, Tunable filter
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-174943 (URN)10.1364/OE.23.017772 (DOI)000361033900013 ()26191839 (PubMedID)2-s2.0-84957582496 (Scopus ID)
Note

QC20151019

Available from: 2015-10-19 Created: 2015-10-09 Last updated: 2017-12-01Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-5596-346X

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