26 research outputs found
Observation of O+ 4P-4D0 lines in proton aurora over Svalbard
Spectra of a proton aurora event show lines of O+ 4P-4D0 multiplet (4639–4696 Å) enhanced relative to the N2 +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 N2 +1N emissions. The emission cross-section of the multiplet in p collisions with O and O2 estimated from published work does not explain the observed O+ brightness, suggesting a higher emission cross-section for low energy p impact on O
Some Unusual Reactions of Meldrum's Acid. Synthesis of Cinnamic Acids, Coumarins and 2-Benzyl-1-Indanone
Observation of O+ (4P-4D0) lines in electron aurora over Svalbard
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, N+2 1N(0,2) and N+2 1N(1,3)). The oxygen ion 4P-4D0 multiplet (4639–4696 A° ) 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 0.18×10-18 cm2
High resolution measurements and modeling of auroral hydrogen emission line profiles
Measurements in the visible wavelength range at
high spectral resolution (1.3 A° ) have been made at Longyearbyen,
Svalbard (15.8 E,78.2 N) during an interval of intense
proton precipitation. The shape and Doppler shift of hydrogen
Balmer beta line profiles have been compared with
model line profiles, using as input ion energy spectra from
almost coincident passes of the FAST and DMSP spacecraft.
The comparison shows that the simulation contains the important
physical processes that produce the profiles, and confirms
that measured changes in the shape and peak wavelength
of the hydrogen profiles are the result of changing
energy input. This combination of high resolution measurements
with modeling provides a method of estimating the
incoming energy and changes in flux of precipitating protons
over Svalbard, for given energy and pitch-angle distributions.
Whereas for electron precipitation, information on the incident
particles is derived from brightness and brightness ratios
which require at least two spectral windows, for proton precipitation
the Doppler profile of resulting hydrogen emission
is directly related to the energy and energy flux of the incident
energetic protons and can be used to gather information
about the source region. As well as the expected Doppler
shift to shorter wavelengths, the measured profiles have a significant
red-shifted component, the result of upward flowing
emitting hydrogen atoms