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The Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) was launched aboard NASA's Ionospheric Connection (ICON) Explorer satellite in October 2019 to measure winds and temperatures on the limb in the upper mesosphere and lower thermosphere (MLT). Temperatures are observed using the molecular oxygen atmospheric band near 763 nm from 90–127 km altitude in the daytime and 90–108 km in the nighttime. Here we describe the measurement approach and methodology of the temperature retrieval, including unique on-orbit operations that allow for a better understanding of the instrument response. The MIGHTI measurement approach for temperatures is distinguished by concurrent observations from two different sensors, allowing for two self-consistent temperature products. We compare the MIGHTI temperatures against existing MLT space-borne and ground-based observations. The MIGHTI temperatures are within 7 K of these observations on average from 90–95 km throughout the day and night. In the daytime on average from 99–105 km, MIGHTI temperatures are higher than coincident observations by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on NASA's TIMED satellite by 18 K. Because the difference between the MIGHTI and SABER observations is predominantly a constant bias at a given altitude, conclusions of scientific analyses that are based on temperature variations are largely unaffected. [ABSTRACT FROM AUTHOR]

We present a method for estimating incident photoelectrons' energy spectra as a function of altitude by combining global scale far‐ultraviolet (FUV) and radio‐occultation (RO) measurements. This characterization provides timely insights important for accurate interpretation of ionospheric parameters inferred from the recently launched Ionospheric Connection Explorer (ICON) observations. Quantification of photoelectron impact is enabled by the fact that conjugate photoelectrons (CPEs) directly affect FUV airglow emissions but not RO measurements. We demonstrate a technique for estimation of photoelectron fluxes and their spectra by combining coincident ICON and COSMIC2 measurements and show that a significant fraction of ICON‐FUV measurements is affected by CPEs during the winter solstice. A comparison of estimated photoelectron fluxes with measured photoelectron spectra is used to gain further insights into the estimation method and reveals consistent values within 10–60 eV. Plain Language Summary: The impact of solar radiation on the atmosphere produces highly energetic electrons, which travel freely along the magnetic Earth's field lines from one hemisphere to the other. When these electrons flow from the sunlit side into the nightside hemisphere, they interact with the neutral species and produce noticeable effects in the ionosphere such as an increase in electron temperature and enhancement of airglow emissions. This study presents a method to quantify the amount of precipitating electrons and their energy on a global scale using two recent satellite missions, ICON and COSMIC2. Our results demonstrate that coincident far‐ultraviolet (ICON) and radio‐occultation (COSMIC2) measurements from space are valuable resources to study precipitating electrons in the ionosphere and their impact on inferring ionospheric plasma parameters. Key Points: Nightglow emissions excited by photoelectrons originating in the magnetically conjugate hemisphere are observed by the ICON missionConjugate photoelectron energy spectra are derived for the first time using global scale far‐ultraviolet and radio‐occultation observationsComparison of estimated photoelectron fluxes with measurements on a rocket flight shows consistent characteristics at all altitudes [ABSTRACT FROM AUTHOR]

The Far Ultra Violet (FUV) ultraviolet imager onboard the NASA‐ICON mission is dedicated to the observation and study of the ionosphere dynamics at mid and low latitudes. We compare O+ density profiles provided by the ICON FUV instrument during nighttime with electron density profiles measured by the COSMIC‐2 constellation (C2) and ground‐based ionosondes. Co‐located simultaneous observations are compared, covering the period from November 2019 to July 2020, which produces several thousands of coincidences. Manual scaling of ionogram sequences ensures the reliability of the ionosonde profiles, while C2 data are carefully selected using an automatic quality control algorithm. Photoelectron contribution coming from the magnetically conjugated hemisphere is clearly visible in FUV data around solstices and has been filtered out from our analysis. We find that the FUV observations are consistent with the C2 and ionosonde measurements, with an average positive bias lower than 1 × 1011e/m3. When restricting the analysis to cases having an NmF2 value larger than 5 × 1011e/m3, FUV provides the peak electron density with a mean difference with C2 of 10%. The peak altitude, also determined from FUV observations, is found to be 15 km above that obtained from C2, and 38 km above the ionosonde value on average. Key Points: We compare ICON‐FUV NmF2 and hmF2 observations with those provided by COSMIC‐2 and ionosondesFar Ultra Violet Imaging Spectrograph (FUV) observations are affected by conjugate photoelectrons mainly around solsticesThe FUV performance during nighttime allows for reliable electron density measurement [ABSTRACT FROM AUTHOR]