11:15 AM - 11:30 AM
[PEM10-08] Optimization of Fabry-Perot interferometer for auroral 427.8-nm emission: Observation in 2023-2024 at Skibotn, Norway
Keywords:sunlit aurora, ion upflow, nitrogen molecular ion, 427.8 nm, Fabry Perot interferometer
Several artificial satellite missions since the 1960s have reported the existence of ions in the magnetosphere that originated from the Earth’s ionosphere. AKEBONO observed that heavy molecular ions such as N2+ are also transported to high altitudes in addition to electrons and O+ (Yau et al., 1993). However, the heating mechanisms responsible for the vertical transport of N2+ into the magnetosphere are not fully understood.
Blue 427.8-nm aurora has been often observed before dawn because of resonant scattering of sunlight by N2+. This blue aurora has been considered as a consequence of the N2+ upflow (e.g., IAGA, 1963, Shiokawa et al., 2019). By measuring the Doppler shift of this blue aurora using a ground Fabry-Perot interferometer (FPI), it may be possible to estimate the N2+ upflowing velocity. We observed the auroral 427.8 nm emission by an FPI at the EISCAT Tromsø site in Norway, in the winter of 2022-2023. However, only a few interference fringes were obtained, and the measurement error was very large. Based on a model calculation of the FPI measurement, we found that the measurement uncertainty in the derived Doppler shift can be moderately large due to the small counts of the interference fringe image, resulting in statistically significant errors. One of the reasons for this small count is probably due to de-focused fringe images at a wavelength of 427.8 nm in the measurement of multi-channel FPI.
We conducted a campaign observation to obtain fringe images from the 427.8 nm emission at Skibotn, Norway, in October 2023. The nitrogen molecular ions aurora due to particle precipitation was observed with fixed directional observations (north and 45° zenith angle). The fringe image has demonstrated a substantial increase in the number of fringes, rising from three to fifteen. This development allows for more precise calculations of the Doppler shift. Because of the fixed directional observation, only speed fluctuations of N2+ could be estimated. But it shows a much better time resolution of 9 minutes and less standard deviation of 69 m/s compared to a standard deviation of 52 m/s for a nightly-averaged fringe before the camera adjustments. In this presentation, we will report the results of these analyses. In addition, we will report results from another campaign observation in March 2024.
Blue 427.8-nm aurora has been often observed before dawn because of resonant scattering of sunlight by N2+. This blue aurora has been considered as a consequence of the N2+ upflow (e.g., IAGA, 1963, Shiokawa et al., 2019). By measuring the Doppler shift of this blue aurora using a ground Fabry-Perot interferometer (FPI), it may be possible to estimate the N2+ upflowing velocity. We observed the auroral 427.8 nm emission by an FPI at the EISCAT Tromsø site in Norway, in the winter of 2022-2023. However, only a few interference fringes were obtained, and the measurement error was very large. Based on a model calculation of the FPI measurement, we found that the measurement uncertainty in the derived Doppler shift can be moderately large due to the small counts of the interference fringe image, resulting in statistically significant errors. One of the reasons for this small count is probably due to de-focused fringe images at a wavelength of 427.8 nm in the measurement of multi-channel FPI.
We conducted a campaign observation to obtain fringe images from the 427.8 nm emission at Skibotn, Norway, in October 2023. The nitrogen molecular ions aurora due to particle precipitation was observed with fixed directional observations (north and 45° zenith angle). The fringe image has demonstrated a substantial increase in the number of fringes, rising from three to fifteen. This development allows for more precise calculations of the Doppler shift. Because of the fixed directional observation, only speed fluctuations of N2+ could be estimated. But it shows a much better time resolution of 9 minutes and less standard deviation of 69 m/s compared to a standard deviation of 52 m/s for a nightly-averaged fringe before the camera adjustments. In this presentation, we will report the results of these analyses. In addition, we will report results from another campaign observation in March 2024.