Wave‐like structures in the upper atmospheric nightglow brightness were observed on the night of 22 August 2017, approximately 8 hr following a total solar eclipse. These wave‐like perturbations are signatures of atmospheric gravity waves and associated traveling ionospheric disturbances (TIDs). Observations were made in the red line (OI 630.0 nm) and the green line (OI 557.7 nm) from Carbondale, IL, at 2–10 UTC on 22 August 2017. Based on wavelet analyses, the dominant time period in both the red and green lines was around 1.5 hr. Differential total electron content data obtained from Global Positioning System total electron content measurements at Carbondale, IL, and ionospheric parameters from digisonde measurements at Idaho National Laboratory and Millstone Hill showed a similar dominant time period. Based on these observations and their correlation with geomagnetic indices, the TIDs appear to be associated with geomagnetic disturbances. In addition, by modeling the ionosphere‐thermosphere system's response to the eclipse, it was seen that while the eclipse enhanced the O/N2 ratio and electron density (Ne) at 250 km during our observation period, it did not affect the TIDs. Vertical (7 m/s) and meridional (616 m/s) phase velocities of the TIDs were estimated using cross‐correlation analysis between red and green line brightness profiles and spectral analysis of the differential total electron content keogram, respectively. This provides a method to characterize the three‐dimensional wave properties of TIDs.
We present the first global images of the daytime ionosphere equatorial arcs as manifested in the 83.4‐nm airglow. These images were collected by the Limb‐Imaging Ionospheric and Thermospheric Extreme‐Ultraviolet Spectrograph that commenced operations on the International Space Station in early 2017. We compare these to simultaneous images of the ionospheric radiative recombination airglow at 135.6 nm measured between 250‐ and 350‐km tangent altitudes, where the emission is generated primarily by radiative recombination of ionospheric plasma. We find that these signatures of the dense crests of the Equatorial Ionization Anomaly, their symmetry, and daily variability at 1300–1600 LT over 1–6 April 2017 do not show any strong periodicity during this time. These results are also important to the joint interpretation of these two correlated extreme and far ultraviolet emission features measured under solar minimum conditions and the evaluation of absorption and radiative transfer effects that affect these emissions differently.
Energies and fluxes of precipitating electrons in an aurora over Lowell, MA on 22-23 June 2015 were derived based on simultaneous, high-resolution (≈ 0.02 nm) brightness measurements of N + 2 (427.8 nm, blue line), OI (557.7 nm, green line), and OI (630.0 nm, red line) emissions. The electron energies and energy fluxes as a function of time and look direction were derived by nonlinear minimization of model predictions with respect to the measurements. Three different methods were compared; in the first two methods, we constrained the modeled brightnesses and brightness ratios, respectively, with measurements to simultaneously derive energies and fluxes. Then we used a hybrid method where we constrained the individual modeled brightness ratios with measurements to derive energies and then constrained modeled brightnesses with measurements to derive fluxes. Derived energy, assuming Maxwellian distribution, during this storm ranged from 109 to 262 eV and the total energy flux ranged from 0.8 to 2.2 ergs⋅cm −2 ⋅s −1 . This approach provides a way to estimate energies and energy fluxes of the precipitating electrons using simultaneous multispectral measurements.
Emission profiles of the resonantly scattered OII 83.4 nm triplet can in principle be used to estimate O+ density profiles in the F2 region of the ionosphere. Given the emission source profile, solution of this inverse problem is possible but requires significant computation. The traditional Feautrier solution to the radiative transfer problem requires many iterations to converge, making it time consuming to compute. A Markov chain approach to the problem produces similar results by directly constructing a matrix that maps the source emission rate to an effective emission rate which includes scattering to all orders. The Markov chain approach presented here yields faster results and therefore can be used to perform the O+ density retrieval with higher resolution than would otherwise be possible.
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