A comparison between auroral particle characteristics and atmospheric composition inferred from analyzing optical emission measurements alone and in combination with incoherent scatter radar measurements

Abstract

Abstract. On day 59 of 1987 a well calibrated set of photometric observations of auroral emissions (427.8, 630.0, 844.6, and 871.0 nm) was obtained at Sondre Stromfjord, Greenland coincident with incoherent scatter radar measurements of electron density. Ratios of these optical emissions were used to correct for atmospheric extinction and to infer the average energy of the precipitating electrons and the deviations in the atmospheric composition induced by auroral heating. Previously, the radar data taken alone had been used to infer the average energy of the auroral particles. For the first time a comparison is made of the results from this optical ratio technique with those obtained by combining the optical data with the radar data and with results obtained using the radar data alone. Specifically, we compare the average energy inferred by these techniques as well as the changes in the atomic oxygen to molecular nitrogen ratio in the lower thermosphere. This study shows the critical importance of characterizing the atmospheric scattering if reliable results are to be derived. In particular, it is shown that on occasion the optical technique may be even more reliable than using radar and optics together since, because of light scattering, the radar and the optics are sometimes observing different parts of the aurora. Magnetometer data are used to estimate local Joule heating. The combined data are also used to address the question of whether observed composition changes were produced locally.

Particle precipitations during NEIAL events: simultaneous ground based observations at Svalbard

“…To this end we have studied 3 slightly different approaches: Hecht et al (1999) and references therein, Vallance-Jones et al (1987) and Rees et al (1988) and references therein. The first model uses the ratios 844.6/427.8 and 630.0/427.8, and from this model it is also possible to deduce a scaling factor of oxygen (f O ), which represent changes in the O/N 2 ratio at altitudes between 110-140 km .…”

“…In the perspective above, the reason to include the 844.6/427.8 ratio in addition to the 630.0/427.8, is to correct for the variation in oxygen concentration (Hecht et al, 1999). Additionally, the 844.6/427.8 has the advantage of not being affected by temporal changes in the auroral emission, as well as being almost proportional to the N + 2 rotational temperature (Vallance- Jones et al, 1987).…”

“…The spectral energy distribution of primary electrons in the range of 100 eV to some tens of keV is often found to be almost Maxwellian (Rees and Luckey, 1974). However, satellite data collected over the years show that the spectra can often be more sharply peaked than a Maxwellian distribution, closer to a Gaussian energy distribution Hecht et al 1999). The Maxwellian form is mostly related to diffuse aurora, while the Gaussian form is associated with discrete aurora (Lyons, 1992).…”

Simultaneous observations of lower thermospheric composition change during moderate auroral activity from Kangerlussuaq and Narsarsuaq, Greenland

“…In this work, for convenience, the same model atmosphere (MSIS-83 atmosphere for day 59 of 1987) is used as was done by Hecht et al [1999], who also analyzed data from Greenland. Note …”

The variability of Joule heating, and its effects on the ionosphere and thermosphere

“…For example, Joule heating causes ion upwelling (Kivanc and Heelis, 1999), gravity waves (Williams et al, 1988;Buonsanto et al, 1999;Balthazor et al, 1997), winds, which in turn change the F-region electron concentrations (Emery et al, 1999) and thermospheric composition (Hecht et al, 1999;Mikhailov and Foster, 1997).…”