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An example Hydrogen β profile. The shaded area indicates the chosen background region of the spectrum.
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Observations of hydrogen emissions along the magnetic zenith at Longyearbyen (78.2 N, 15.8 E geographic) are used to investigate the energy and source of protons precipitating into the high latitude region. During the hours around local solar noon (11:00 UT), measurements of the hydrogen Balmer ? line are severely affected by sunlight, such that mo...
Context in source publication
Context 1
... the integration period of this spectrum (08:45 UT to 10:01 UT on 30 November 2000). The twilight brightness, including the effect of atmospheric opacity, is now estimated by nor- malising the solar spectrum to the background emission level of the data spectrum. The wavelength range selected as the background area in the H β filter, , is shown in Fig. 3, which is a data sample taken when there was no daylight contami- nation. This shows that the background is well clear of the H β red wing. The normalising factor is therefore given ...
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Citations
... Svalbard is a unique location for such measurements, with particular challenges and opportunities for observations in the region of the magnetospheric cusp; although it is dark at noon in midwinter, measurements are affected by sunlight at heights above the shadow line (a fact that I used in my PhD research from Svalbard). The removal of this sunlit contribution from hydrogen profiles was achieved during an event with a bright and variable "cusp spot," seen in early data from the Imager for Magnetopause-to-Aurora Global Exploration mission (Robertson et al., 2006). Thus began a fascinating and productive time of combining ground-based spectrographic measurements with data from satellites, using particle spectra as input to modeling the hydrogen emission profiles, in collaboration with Marina Galand and our Boston colleagues, as well as Harald Frey (Lanchester et al., 2003). ...
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... The photolysis rate of NO 2 depends on solar zenith angle (Parrish et al., 1983), which in turn depends on day of year. Measurements were performed between days 81 and 134, and the noon solar zenith angle in Longyearbyen area varied from approximately 77 to 62 • (Robertson et al., 2006). Following Eq. (15) in Parrish et al. (1983), the minimum clear-sky photolysis rate for the start of the campaign was 0.0026 s −1 , and the maximum clear-sky photolysis rate for the end of the campaign was 0.0061 s −1 (black squares in Fig. A1a in Appendix A). ...
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Svalbard is a remote and scarcely populated Arctic archipelago and is considered to be mostly influenced by long-range-transported air pollution. However, there are also local emission sources such as coal and diesel power plants, snowmobiles and ships, but their influence on the background concentrations of trace gases has not been thoroughly assessed. This study is based on data of tropospheric ozone (O3) and nitrogen oxides (NOx) collected in three main Svalbard settlements in spring 2017. In addition to these ground-based observations and radiosonde and O3 sonde soundings, ERA5 reanalysis and BrO satellite data have been applied in order to distinguish the impact of local and synoptic-scale conditions on the NOx and O3 chemistry. The measurement campaign was divided into several sub-periods based on the prevailing large-scale weather regimes. The local wind direction at the stations depended on the large-scale conditions but was modified due to complex topography. The NOx concentration showed weak correlation for the different stations and depended strongly on the wind direction and atmospheric stability. Conversely, the O3 concentration was highly correlated among the different measurement sites and was controlled by the long-range atmospheric transport to Svalbard. Lagrangian backward trajectories have been used to examine the origin and path of the air masses during the campaign.
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... These stations are in darkness for 24 h a day between early November and late February, and are ideally located for monitoring optical radiation emitted from ionospheric projections of the dayside plasma sheet, cusp, low-latitude boundary, and mantle (Sandholt et al., 2002;Lorentzen and Moen, 2000;Newell and Meng, 1988). Robertson et al. (2006) devised a method to remove solar contamination and thereby extract H β contributions from spectroscopic measurements. Fortuitously, proton fluxes measured during DMSP-F12 overflights allowed confirmation of their extraction technique. ...
Auroral spectroscopy provided the first tool for remotely sensing the
compositions and dynamics of the high-latitude ionosphere. In 1885,
Balmer discovered that the visible hydrogen spectrum consists of a series
of discrete lines whose wavelengths follow a simple mathematical pattern, which
ranks among the first steps toward developing this tool. On 18 October 1939
Lars Vegard discovered the Hα (656.3 nm) and Hβ (486.1 nm) spectral lines of Balmer series emissions, emanating from a diffuse
structure, located equatorward of the auroral zone. Intense, first
positive bands of N2+ nearly covered the Hα emissions.
With more advanced instrumentation after World War II, auroral
spectroscopists Vegard, Gartlein and Meinel investigated other
characteristics of the auroral hydrogen emissions. The first three
lines of the Balmer series, including Hγ at 410 nm, were
identified in ground-based measurements prior to the space age. Based on
satellite observations, the Balmer lines Hδ and Hε at 410.13 and 396.97 nm, respectively, as well as extreme ultraviolet (EUV) Lyman
α (121.6 nm) hydrogen emissions, were also detected.
Doppler blue shifts in hydrogen emissions, established in the 1940s,
indicated that emitting particles had energies well into the kiloelectron volt range,
corresponding to velocities >1000 km s−1. Systematic spatial
separations between the locations of electron- and proton-generated aurorae
were also established. These observations in turn, suggested that protons,
ultimately of solar origin, precipitate into the topside ionosphere, where
they undergo charge-exchange events with atmospheric neutrals. Newly
generated hydrogen atoms were left in excited states and emitted the
observed Balmer radiation. Sounding rocket data showed that most of the
hydrogen radiation came from altitudes between 105 and 120 km.
Space-age data from satellite-borne sensors made two significant
contributions: (1) energetic particle detectors demonstrated the existence
of regions in the magnetosphere, conjugate to nightside proton aurora, where
conditions for breaking the first adiabatic invariants of kiloelectron volt protons
prevail, allowing them to precipitate through filled loss cones. (2) EUV
imagers showed that dayside hydrogen emissions appear in response to changes
in solar wind dynamic pressure or the polarity of the north–south component
of the interplanetary magnetic field.
... Ground based observation of Hβ hydrogen emis sion during proton penetration through the cusp was presented for the first time in (Robertson et al., 2006) based on the data of the scanning photometer at Long yearbyen observatory on Spitsbergen. The described case was characterized by Bz > 0 and a high solar wind pressure. ...
... Therefore, we can assume that Barentsburg observatory was below the cusp at that time. Robertson et al. (2006) showed that protons pene trated through the cusp according to the Hβ emission observations at Bz > 0 and a high solar wind pressure; sim ilar conditions also took place in our case: Bz = 25 nT, and pressure is 12 nPa. ...
The behavior of the Hα hydrogen emission at Barentsburg observatory during precipitation of high-energy solar protons and sudden impulse (SI) on January 22, 2012, was studied. The emission intensity was determined with a spectrometer, which gives the meridian arc spectrum image. It has been shown that the Hα emission luminosity onset coincides with SI and is caused by precipitation of solar wind protons through the cusp.
... Because of scattered sunlight approaching local noon, the H β profiles obtained were superimposed on a background containing significant Fraunhofer absorption near the H β rest wavelength. Although methods currently exist to account for this twilight component of the background (Robertson et al., 2006; Borovkov et al., 2005), the profiles were not chosen for analysis. ...
We present for the first time a numerical kinetic/fluid code for the ionosphere coupling proton and electron effects. It solves the fluid transport equations up to the eighth moment, and the kinetic equations for suprathermal particles. Its new feature is that for the latter, both electrons and protons are taken into account, while the preceding codes (TRANSCAR) only considered electrons. Thus it is now possible to compute in a single run the electron and ion densities due to proton precipitation. This code is successfully applied to a multi-instrumental data set recorded on 22 January 2004. We make use of measurements from the following set of instruments: the Defence Meteorological Satellite Program (DMSP) F-13 measures the precipitating particle fluxes, the EISCAT Svalbard Radar (ESR) measures the ionospheric parameters, the thermospheric oxygen lines are measured by an all-sky camera and the H<sub>a</sub> line is given by an Ebert-Fastie spectrometer located at Ny-Ålesund. We show that the code computes the H<sub>a</sub> spectral line profile with an excellent agreement with observations, providing some complementary information on the physical state of the atmosphere. We also show the relative effects of protons and electrons as to the electron densities. Computed electron densities are finally compared to the direct ESR measurements.
... Because of scattered sunlight approaching local noon, the H β profiles obtained were superimposed on a background containing significant Fraunhofer absorption near the H β rest wavelength. Although methods currently exist to account for this twilight component of the background (Robertson et al., 2006;Borovkov et al., 2005), the profiles were not chosen for analysis. ...
We present for the first time a numerical ki-netic/fluid code for the ionosphere coupling proton and electron effects. It solves the fluid transport equations up to the eighth moment, and the kinetic equations for suprathermal particles. Its new feature is that for the latter, both electrons and protons are taken into account, while the preceding codes (TRANSCAR) only considered electrons. Thus it is now possible to compute in a single run the electron and ion densities due to proton precipitation. This code is successfully applied to a multi-instrumental data set recorded on 22 January 2004. We make use of measurements from the following set of instruments: the Defence Meteorological Satellite Program (DMSP) F-13 measures the precipitating particle fluxes, the EISCAT Svalbard Radar (ESR) measures the ionospheric parameters, the thermospheric oxygen lines are measured by an all-sky camera and the H α line is given by an Ebert-Fastie spectrometer located at Ny-˚ Alesund. We show that the code computes the H α spectral line profile with an excellent agreement with observations, providing some complementary information on the physical state of the atmosphere. We also show the relative effects of protons and electrons as to the electron densities. Computed electron densities are finally compared to the direct ESR measurements.
We describe a high-throughput (5×10-4 cm2
sr) imaging spectrograph that uses an echelle grating operating at a
high dispersion order (24 to 43) to observe extended sources such as
atmospheric airglow and diffuse proton aurora at high spectral
resolution (approximately 0.02 nm). Instead of using a traditional
single slit, the implementation of the instrument described here uses
four (50 μm×25 mm) slits through which the radiation enters
the spectrograph. The field of view is selected using appropriate
foreoptics: the present implementation is a long, narrow configuration
of 0.1×50 deg. By placing interference filters in the beam path,
the instrument can simultaneously observe several spectral features
located anywhere in the visible band (approximately 300 to 1000 nm) at
high resolution. This design allows a single echelle grating and a
single detector (a CCD in the present implementation) to view the same
scene. The design is flexible; the number of slits and the slit
dimensions can be tailored to the trade-offs between resolution,
throughput, and number of spectral features depending upon the
measurement need. While the implementation described here covers only
the visible range, the use of different combinations of detector and
filter sets can extend its operation to other wavelength regions.
The H Balmer emissions were first identified in terrestrial aurora by Vegard (1939). The earliest photographic spectral observations are reviewed. In the subsequent decade, the intensity ratios for Halpha, Hbeta, and Hgamma were measured, and the well-known line broadening and blue shift were established. Recently, the Halpha, Hgamma, Hdelta, and H$\varepsilon$ features have been measured by OSIRIS on Odin. The Balmer components are resolved from other auroral features using sets of synthetic spectra. The measured intensity ratios are in good agreement with an extensive set of published model calculations. The presented observations are in the polar region averaged over limb tangent altitudes from 100 to 105 km, approximately perpendicular to the terrestrial magnetic field lines, for this geometry showing Doppler broadening without obvious Doppler shifts. The OSIRIS-measured full-width at half-height of the Halpha feature is 2.2 nm corresponding to an H atom velocity of 500 km s-1 and energy approximately 1.3 keV.
A case study with simultaneous European Incoherent Scatter and optical auroral observations was conducted in order to determine characteristics of the magnetosphere-ionosphere coupling from the viewpoint of the electrodynamics in the ionosphere. Particularly focused on were the relationships between ionospheric electron density depletion, perpendicular electric fields, and proton auroras. Intense electron density depletion was observed in the E and F regions poleward and in the vicinity of a thin equatorward moving arc. This depletion was associated with an intense, equatorward perpendicular electric field close to ˜80 mV/m and most likely with a downward field-aligned current (FAC), but it did not accompany detectable proton aurora. Hence the downward FA electric field in the lower magnetosphere associated with this depletion was weak or absent. The motion of the FAC system with the depletion and the arc presumably enabled the downward FAC to obtain enough current carriers as ionospheric electrons were lost by the evacuation process. The evacuation process associated with the downward FAC was, however, efficient enough to establish the depletion. On the other hand, a widely distributed proton aurora observed immediately after the depletion was associated with an intense, equatorward perpendicular electric field close to 90 mV/m, enhanced electron density, and most likely a downward FAC. No electron precipitation was associated with this proton aurora. Thus the electron density enhancement, providing the downward current carriers, had to be caused by the ionization of precipitating protons presumably accelerated by downward field-aligned electric fields in the lower magnetosphere.
