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Abstract Patterns of ionospheric luminosity provide a unique window into our complex, coupled space environment. The aurora, for example, indicates plasma processes occurring thousands of km away, depositing immense amounts of energy into our polar ionospheres. Here we show observations of structured continuum emission associated with the dynamic aurora. The presence of weak ambient continuum emission has long been recognized. However, studies of its relationship to aurora are scarce and limited by observational constraints. We use spectrally resolved measurements to analyze these previously unexplained emissions, adding critical information about spatial structure, characteristic spectra, and location within auroral dynamics. Our findings demonstrate that the coupling among auroral processes, the plasma, and the neutral atmosphere can unfold at meso-scales and is more complex than previously reported. We suggest that the meso-scale auroral precipitation may, under certain circumstances, effectively couple to atmospheric chemistry and conditions to produce the continuum structure.

The joint European Space Agency and Chinese Academy of Sciences Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) mission will explore global dynamics of the magnetosphere under varying solar wind and interplanetary magnetic field conditions, and simultaneously monitor the auroral response of the Northern Hemisphere ionosphere. Combining these large-scale responses with medium and fine-scale measurements at a variety of cadences by additional ground-based and space-based instruments will enable a much greater scientific impact beyond the original goals of the SMILE mission. Here, we describe current community efforts to prepare for SMILE, and the benefits and context various experiments that have explicitly expressed support for SMILE can offer. A dedicated group of international scientists representing many different experiment types and geographical locations, the Ground-based and Additional Science Working Group, is facilitating these efforts. Preparations include constructing an online SMILE Data Fusion Facility, the discussion of particular or special modes for experiments such as coherent and incoherent scatter radar, and the consideration of particular observing strategies and spacecraft conjunctions. We anticipate growing interest and community engagement with the SMILE mission, and we welcome novel ideas and insights from the solar-terrestrial community.

The recently deployed Transition Region Explorer (TREx)-RGB (red-green-blue) all-sky imager (ASI) is designed to capture “true color” images of the aurora and airglow. Because the 557.7 nm green line is usually the brightest emission line in visible auroras, the green channel of a TREx-RGB camera is usually dominated by the 557.7 nm emission. Under this rationale, the TREx mission does not include a specific 557.7 nm imager and is designed to use the RGB green-channel data as a proxy for the 557.7 nm aurora. In this study, we present an initial effort to establish the conversion ratio or formula linking the RGB green-channel data to the absolute intensity of 557.7 nm auroras, which is crucial for quantitative uses of the RGB data. We illustrate two approaches: (1) through a comparison with the collocated measurement of green-line auroras from the TREx spectrograph, and (2) through a comparison with the modeled green-line intensity according to realistic electron precipitation flux measurements from low-Earth-orbit satellites, with the aid of an auroral transport model. We demonstrate the procedures and provide initial results for the TREx-RGB ASIs at the Rabbit Lake and Lucky Lake stations. The RGB response is found to be nonlinear. Empirical conversion ratios or formulas between RGB green-channel data and the green-line auroral intensity are given and can be applied immediately by TREx-RGB data users. The methodology established in this study will also be applicable to the upcoming SMILE ASI mission, which will adopt a similar RGB camera system in its deployment.

The existence of detached/isolated auroral structures in the subauroral ionosphere has been recognized and studied for decades. One major subset of such detached auroras is the so-called “isolated proton aurora” (IPA). IPA is characterized by substantial hydrogen emissions and thus inferred to be proton aurora, but is also accompanied by other emission lines. In particular, IPA is usually dominated by 557.7 nm green-line emissions in optical luminosity. To date, there is still a lack of dedicated spectrographic study and detailed comparison among structures in different emission lines of IPA. The intensity ratios between the 557.7 nm and hydrogen emissions in IPA have not been well established from concurrent observations or theoretical models. In this study, we report an IPA event during ∼0245–0345 UT on 12 October 2021, the Canada Thanksgiving storm night. Using multi-station, multi-wavelength optical instruments, including the Transition Region Explorer (TREx) spectrograph, we investigate the evolution and spectrographic properties of the IPA. In-situ and ground magnetometer data show evidence of electromagnetic ion cyclotron (EMIC) waves associated with the passage of IPA, supporting a causal link between the EMIC wave and the proton precipitation. The precipitating proton energies are estimated to range between a few keV and a few tens of keV according to the IPA emission heights inferred from triangulation analyses. Via careful examination of the spectral intensities and the elevation-angle profiles of the 557.7, 427.8, and 486.1 nm emissions based on the spectrograph data, we conclude that the 557.7 nm emissions contained in the IPA were unlikely to owe their source to energetic electron precipitation from the magnetosphere, but were the byproduct of the proton precipitation. The intensity ratio between the 557.7 nm (427.8 nm) and the 486.1 nm emissions of the IPA are confined within a relatively narrow range around ∼26 (∼4), which may serve as validation tests for existing and developing proton transport models.