| 1. |
- Mella, M. R., et al.
(author)
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Sounding rocket study of two sequential auroral poleward boundary intensifications
- 2011
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In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116, s. A00K18-
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Journal article (peer-reviewed)abstract
- The Cascades-2 sounding rocket was launched on 20 March 2009 at 11: 04: 00 UT from the Poker Flat Research Range in Alaska, and flew across a series of poleward boundary intensifications (PBIs). The rocket initially crosses a diffuse arc, then crosses the equatorward extent of one PBI (a streamer), and finally crosses the initiation of a separate PBI before entering the polar cap. Each of the crossings have fundamentally different in situ electron energy and pitch angle structure, and different ground optics images of visible aurora. It is found that the diffuse arc has a quasi-static acceleration mechanism, and the intensification at the poleward boundary has an Alfvenic acceleration mechanism. The streamer shows characteristics of both types of acceleration. PFISR data provide ionospheric context for the rocket observations. Three THEMIS satellites in close conjunction with the rocket foot point show earthward flows and slight dipolarizations in the magnetotail associated with the in situ observations of PBI activity. An important goal of the Cascades-2 study is to bring together the different observational communities (rocket, ground cameras, ground radar, satellite) with the same case study. The Cascades-2 experiment is the first sounding rocket observation of a PBI sequence, enabling a detailed investigation of the electron signatures and optical aurora associated with various stages of a PBI sequence as it evolves from an Alfvenic to a more quasi-static structure.
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| 2. |
- Ashrafi, M., et al.
(author)
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Modelling of N(2)1P emission rates in aurora using various cross sections for excitation
- 2009
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In: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 27:6, s. 2545-2553
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Journal article (peer-reviewed)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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| 3. |
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| 4. |
- Germany, G A, et al.
(author)
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Remote determination of auroral energy characteristics during substorm activity
- 1997
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 24, s. 995-998
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Journal article (peer-reviewed)abstract
- Ultraviolet auroral images from the Ultraviolet Imager (UVI) onboard the POLAR satellite can be used as quantitative remote diagnostics of the auroral regions, yielding estimates of incident energy characteristics, compositional changes, and other higher order data products. Here incident energy estimates derived from UVI are compared with in situ measurements of the same parameters from an overflight by the DMSP F12 satellite coincident with the UVI image times during substorm activity occurring on May 19, 1996. This event was simultaneously observed by WIND, GEOTAIL, INTERBALL, DMSP and NOAA spacecraft as well as by POLAR.
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| 5. |
- Ivchenko, Nickolay V., et al.
(author)
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Observation of O+4P-D-4(0) lines in proton aurora over Svalbard
- 2004
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 31:10
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Journal article (peer-reviewed)abstract
- Spectra of a proton aurora event show lines of O+ P-4-D-4(0) multiplet (4639-4696 Angstrom) enhanced relative to the N(2)(+)1N(0,2) compared to normal electron aurora. Conjugate satellite particle measurements are used as input to electron and proton transport models, to show that p/H precipitation is the dominant source of both the O+ and N(2)(+)1N emissions. The emission cross-section of the multiplet in p collisions with O and O-2 estimated from published work does not explain the observed O+ brightness, suggesting a higher emission cross-section for low energy p impact on O.
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| 6. |
- Ivchenko, Nickolay V., et al.
(author)
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Observation of O+ (P-4-D-4(0)) lines in electron aurora over Svalbard
- 2004
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In: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 22:8, s. 2805-2817
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Journal article (peer-reviewed)abstract
- This work reports on observations of O+ lines in aurora over Svalbard, Norway. The Spectrographic Imaging Facility measures auroral spectra in three wavelength intervals(H-beta, N-2(+) 1N(0,2) and N-2(+) 1N(1,3)). The oxygen ion P-4-D-4(0) multiplet (4639-4696 Angstrom) is blended with the N-2(+) 1N(1,3) band. It is found that in electron aurora, the brightness of this multiplet, is on average, about 0.1 of the N-2(+) 1N(0,2) total brightness. A joint optical and incoherent scatter radar study of an electron aurora event shows that the ratio is enhanced when the ionisation in the upper E-layer (140-190 km) is significant with respect to the E-layer peak below 130 km. Rayed arcs were observed on one such occasion, whereas on other occasions the auroral intensity was below the threshold of the imager. A one-dimensional electron transport model is used to estimate the cross section for production of the multiplet in electron collisions, yielding 0.18 x 10(-18) cm(2).
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| 7. |
- Jokiaho, O., et al.
(author)
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Rotational temperature of N-2(+) (0,2) ions from spectrographic measurements used to infer the energy of precipitation in different auroral forms and compared with radar measurements
- 2008
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In: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 26:4, s. 853-866
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Journal article (peer-reviewed)abstract
- High resolution spectral data are used to estimate neutral temperatures at auroral heights. The data are from the High Throughput Imaging Echelle Spectrograph (HiTIES) which forms part of the Spectrographic Imaging Facility (SIF), located at Longyearbyen, Svalbard in Norway. The platform also contains photometers and a narrow angle auroral imager. Quantum molecular spectroscopy is used for modelling N-2(+) 1NG (0,2), which serves as a diagnostic tool for neutral temperature and emission height variations. The theoretical spectra are convolved with the instrument function and fitted to measured rotational transition lines as a function of temperature. Measurements were made in the magnetic zenith, and along a meridian slit centred on the magnetic zenith. In the results described, the high spectral resolution of the data (0.08 nm) allows an error analysis to be performed more thoroughly than previous findings, with particular attention paid to the correct subtraction of background, and to precise wavelength calibration. Supporting measurements were made with the Svalbard Eiscat Radar (ESR). Estimates were made from both optical and radar observations of the average energy of precipitating electrons in different types of aurora. These provide confirmation that the spectral results are in agreement with the variations observed in radar profiles. In rayed aurora the neutral temperature was highest (800 K) and the energy lowest (1 keV). In a bright curling arc, the temperature at the lower border was about 550 K, corresponding to energies of 2 keV. The radar and modelling results confirm that these average values are a lower limit for an estimation of the characteristic energy. In each event the energy distribution is clearly made up of more than one spectral shape. This work emphasises the need for high time resolution as well as high spectral resolution. The present work is the first to provide rotational temperatures using a method which pays particular attention to errors in measurement and fitting, and background subtraction.
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