Benjamin T. Marshall

Several studies have presented methods for estimating daytime or nighttime atomic oxygen (O) from measurements made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics satellite. In the present study, we describe algebraic formulas adapted from the standard SABER Version 2 method for estimating daytime and nighttime O based on the assumption that ozone in the upper mesosphere is in equilibrium. We highlight uncertainties in the calculations that lead to global mean differences ranging up to a factor of two or more in the nighttime O concentration. Important considerations are the choice of which reactions are included in the ozone budget and the values of uncertain parameters used in the model of emissions from vibrationally excited hydroxyl. SABER observations cover almost all local times. Since O is long‐lived in the upper mesosphere, the dominant source of diurnal variation is transport by tidal winds. Even when accounting for this transport, there are appreciable differences between daytime and nighttime O. Daytime O is higher than is consistent with the nighttime O that is estimated from several methods. The estimated daytime O has a strong and nearly linear dependence on ozone while the nighttime O is sensitive to multiple parameters in the model of OH airglow emissions. The day/night discrepancy supports other evidence that the SABER daytime mesospheric ozone has large uncertainties and needs to be updated.

Time series of infrared radiated power by thermospheric nitric oxide (NO) and carbon dioxide (CO₂), and their total power (NO + CO₂) (measured by the SABER instrument on the NASA TIMED satellite from 2002 through 2023) have been analyzed for long‐term trends. Solar and geomagnetic indices (F_10.7, Ap, Dst) are used with multiple linear regression to provide trend approximations for the radiated infrared power. There are no statistically significant trends observed for NO and total radiated power, and the trend in CO₂ radiated power is not statistically significant at 2‐sigma (95%) confidence level. The thermosphere continues to radiate a constant amount of infrared energy over time after accounting for natural variability, despite more than two decades of cooling due to increasing CO₂. These results demonstrate energy conservation on decadal timescales and validate the mechanism of thermospheric greenhouse cooling. The long‐term radiometric stability of the SABER instrument enables these results.

Earth experienced the strongest geomagnetic storm in 20 years over 10–13 May 2024. The Ap and Dst geomagnetic indices were 273 and −291.94 nT on 11 May. The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics satellite observed significant enhancement in thermospheric infrared emission at 15, 5.3, 4.3, and 1.27 μm. On 11 May the daily global power radiated by nitric oxide (NO) at 5.3 μm was 1.41 TW and by carbon dioxide (CO ₂ ) at 15 μm was 1.35 TW. These are the largest single day power values observed by SABER in 22 years and the first time the daily power radiated by NO exceeded that of CO ₂ . The total infrared power (above background) radiated during the storm was 2.64 TW (2.28 × 10 ¹⁷ J). Significant enhancement in limb radiance observed at 4.3 μm (to 250 km tangent height) is likely indicative of NO + formation during the storm.

Time series of radiative cooling of the upper mesosphere and lower thermosphere (UMLT) by carbon dioxide (CO ₂ ) are examined for evidence of trends over 20 years. Radiative cooling rates in K day ⁻¹ provided by the SABER instrument are converted to time series of infrared power radiated from three distinct layers between 0.1 hPa and 0.0001 hPa (65–105 km). Linear regression against time and a predictor for solar variability provides estimates of the trend in exiting longwave radiation (ELR) from these layers. Trends in ELR are not significantly different from zero at 95% or 99% confidence in each layer. These results demonstrate energy conservation in the UMLT on decadal time scales and show that the UMLT continues to radiate the same amount of energy it receives despite cooling and contracting over two decades. These results are enabled by the long‐term stability of the SABER instrument calibration.

Twenty‐two years (2002–2023) of infrared radiative cooling rate data derived from the SABER instrument on the NASA TIMED satellite are presented. Global daily and global annual infrared power (Watts, W) emitted by nitric oxide (NO) and carbon dioxide (CO ₂ ) illustrate the variability of the geospace environment on timescales from days to decades. The 11‐year solar cycle (SC) is evident in the global power data and in vertical profiles of infrared cooling rates (nW/m ³ ). The global annual power radiated by NO and CO ₂ are larger in 2023 than at any time since 2003 and 2002, respectively. The to‐date peak in NO infrared power in SC 25 is larger than in SC 24, is comparable to SC 20, but is less than in SCs 18–19 and 21–23. Two geomagnetic storms in 2023 radiated more than 1 TW and are in the top 10 strongest storms observed by SABER.

The Solar Occultation for Ice Experiment (SOFIE) has operated aboard the Aeronomy of Ice in the Mesosphere (AIM) satellite since 2007. SOFIE uses solar occultation to retrieve ozone (O ₃ ) profiles from ∼20 to 100 km altitude, typically at polar latitudes. This study validates SOFIE O ₃ profiles, including error analysis and comparisons with independent observations. Comparisons are made to the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE‐FTS) and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) satellite instruments. SOFIE shows qualitative and quantitative agreement with both data sets between 30 and 70 km and better overall agreement in the northern hemisphere. SOFIE and ACE mean differences are typically within 20% in the 30–70 km altitude range. SOFIE and MIPAS exhibit mean difference values within 30% in the winter and 20% for all other seasons averaged, between ∼30 and 60 km. Seasonal comparisons indicate similar variations in both hemispheres and through all seasons. The comparisons indicate that SOFIE is biased 5%–10% low at 30–70 km altitudes, with greater differences at higher and lower altitudes. The comparisons are challenging due to the low O ₃ concentrations at high altitudes, the limited number of coincidences, and the large diurnal variation in mesospheric O ₃ during twilight hours.

SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) is a 10-channel infrared radiometer that is one of four instruments on the NASA TIMED (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics) satellite mission to study the structure, energetics, chemistry, and dynamics of the Earth’s mesosphere and lower thermosphere. The TIMED spacecraft was launched into a 625 km circular polar orbit (74.1º inclination) via a Boeing Delta II rocket from Vandenberg Air Force Base on 7 December 2001. SABER continues to operate nominally and collect data routinely as it has for over 21 years. Over 2,200 peer-reviewed journal articles have been published worldwide using SABER data. A list of these articles is included in the Supporting Information accompanying this paper. This paper presents a detailed technical description of the SABER instrument including major subsystems of the instrument and technical performance parameters. This paper comprehensively describes the instrument and its components and provides final instrument design and performance parameters. The motivation for this paper is to document this information permanently for future reference. The Space Dynamics Laboratory (SDL) of Utah State University designed, fabricated, and calibrated the SABER instrument in close collaboration with NASA Langley Research Center, Hampton University, and Global Atmospheric Technologies and Science (GATS).

SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) is a 10-channel infrared radiometer that is one of four instruments on the NASA TIMED (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics) satellite mission to study the structure, energetics, chemistry, and dynamics of the Earth’s mesosphere and lower thermosphere. The TIMED spacecraft was launched into a 625 km circular polar orbit (74.1º inclination) via a Boeing Delta II rocket from Vandenberg Air Force Base on 7 December 2001. SABER continues to operate nominally and collect data routinely as it has for over 21 years. Over 2,200 peer-reviewed journal articles have been published worldwide using SABER data. A list of these articles is included in the Supporting Information accompanying this paper. The Space Dynamics Laboratory (SDL) of Utah State University designed, fabricated, and calibrated the SABER instrument in close collaboration with NASA Langley Research Center, Hampton University, and Global Atmospheric Technologies and Science (GATS). This paper provides a detailed technical description of the SABER instrument, including performance specifications and observed instrument performance.

The ability of satellite instruments to accurately observe long‐term changes in atmospheric temperature depends on many factors including the absolute accuracy of the measurement, the stability of the calibration of the instrument, the stability of the satellite orbit, and the stability of the numerical algorithm that produces the temperature data. We present an example of algorithm instability recently discovered in the temperature data set from the SABER instrument on the NASA TIMED satellite. The instability resulted in derived temperatures that were substantially colder than anticipated from mid‐December 2019 to mid‐2022. This algorithm‐induced change in temperature over 1 to 2 years corresponded to the expected temperature change over several decades from increasing anthropogenic CO ₂ . This paper highlights the importance of algorithm stability in developing Geospace Data Records (GDRs) for Earth’s mesosphere and lower thermosphere. A corrected version (Version 2.08) of the temperatures from SABER is described.

The ability of satellite instruments to accurately observe long-term changes in atmospheric temperature depends on many factors including the absolute accuracy of the measurement, the stability of the calibration of the instrument, the stability of the satellite orbit, and the stability of the numerical algorithm that produces the temperature data. We present an example of algorithm instability recently discovered in the temperature dataset from the SABER instrument on the NASA TIMED satellite. The instability resulted in derived temperatures that were substantially colder than anticipated from mid-December 2019 to mid-2022. This algorithm-induced change in temperature over one to two years corresponded to the expected change over several decades from increasing anthropogenic CO2. This paper highlights the importance of algorithm stability in developing Geospace Data Records (GDRs) for Earth’s mesosphere and lower thermosphere. A corrected version (Version 2.08) of the temperatures from SABER is described.