Abstract. In the recent decade it became evident that we need to revise our picture of how gravity waves (GWs) reach the mesosphere and lower thermosphere (MLT). This has consequences for our understanding not just of the properties of the GWs themselves, but in particular of the global circulation in the MLT. Information on spectral distribution, direction, and zonal mean GW momentum flux is required to test the theoretical and modeling findings. In this study, we propose a constellation of two CubeSats for observing mesoscale GWs in the MLT region by means of temperature limb sounding in order to derive such constraints. Each CubeSat deploys a highly miniaturized spatial heterodyne interferometer (SHI) for the measurement of global oxygen atmospheric band emissions. From these emissions, the 3-D temperature structure can be inferred. We propose obtaining four independent observation tracks by splitting the interferograms in the center and thus gaining two observation tracks for each satellite. We present a feasibility study of this concept based on self-consistent, high-resolution global model data. This yields a full chain of end-to-end (E2E) simulations incorporating (1) orbit simulation, (2) airglow forward modeling, (3) tomographic temperature retrieval, (4) 3-D wave analysis, and (5) GW momentum flux (GWMF) calculation. The simulation performance is evaluated by comparing the retrieved zonal mean GWMF with that computed directly from the model wind data. A major question to be considered in our assessment is the minimum number of tracks required for the derivation of 3-D GW parameters. The main result from our simulations is that the GW polarization relations are still valid in the MLT region and can thus be employed for inferring GWMF from the 3-D temperature distributions. Based on the E2E simulations for gaining zonal mean climatologies of GW momentum flux, we demonstrate that our approach is robust and stable, given a four-track observation geometry and the expected instrument noise under nominal operation conditions. Using phase speed and direction spectra we show also that the properties of individual wave events are recovered when employing four tracks. Finally, we discuss the potential of the proposed observations to address current topics in the GW research. We outline for which investigations ancillary data are required to answer science questions.

Abstract. This paper presents a new dataset of nighttime atomic oxygen density [O], derived from OH(8–4) ro-vibrational band emissions, using a non-local thermal equilibrium model, with the aim of offering new insight into the atomic oxygen abundances in the mesopause region. The dataset is derived from the level-1 atmospheric background measurements observed by the Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument aboard Envisat, with the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) measurements for the atmospheric background. Raw data are reprocessed into monthly zonal mean values in 10∘ latitude bins with a fixed altitude grid of 3 km. The dataset spans from 70∘ S to 70∘ N in latitude and from 80 to 100 km in altitude, covering a time period from May 2002 to December 2011 at local times from 22:00 to 00:00 LT. The atomic oxygen density peaks at about 95 km and the highest values are in the range of 3–8 × 1011 atoms cm−3, depending on latitude and season. There is a rapid decrease of [O] below the peak. The annual oscillation (AO), semiannual oscillation (SAO) and the solar cycle impact are distinguished from the [O] longtime series variations. This new GOMOS [O] dataset conforms to other published datasets and is consistent with the [O] datasets obtained from the Scanning Imaging Absorption Spectrometer for Atmospheric CHartographY (SCIAMACHY) OH airglow measurements within about ±20 %.

Abstract. Hydroxyl (OH) short-wave infrared emissions measured by the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) were used in this study to simulate OH 1.6 μm and 2.0 μm radiances as measured by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument. This paper presents a retrieval model to perform an inversion of OH(v) number densities in order to simulate OH ro-vibrational emission radiances using a non-linear regularized global fit technique. OH 1.6 μm and 2.0 μm radiances as measured by SABER were retrieved from OH limb measurements recorded by SCIAMACHY channel 6 for altitudes in the range of 80–96 km. The main source of uncertainty in the retrieval is related to the Einstein coefficients. Systematic deviations of up to 88 % were found between SABER OH 1.6 μm and 2.0 μm radiance measurements and the corresponding simulations obtained from SCIAMACHY OH data. The radiometric calibration of the instruments could potentially explain the differences between the two measurements.

Abstract. In the recent decade it became evident that we need to revise our picture of how gravity waves (GWs) reach the mesosphere and lower thermosphere (MLT). This has consequences for not just the properties of the GWs itself, but in particular for the global circulation in the MLT. Information on spectral distribution, direction and zonal mean GW momentum flux is required to test the theoretical and modeling findings. In this study, we propose a constellation of two CubeSats for observing mesoscale GWs in the MLT region by means of temperature limb sounding in order to derive such constraints. Each CubeSat deploys a highly miniaturized spatial heterodyne interferometer (SHI) for the measurement of global oxygen atmospheric band emissions. From these emissions, the 3-D temperature structure can be inferred. We propose to obtain four independent observation tracks by splitting the interferograms in the center and thus gaining 2 observation tracks for each satellite. We present a feasibility study of this concept based on self-consistent, high-resolution global model data. This yields a full chain of end-to-end (E2E) simulation incorporating 1) orbit simulation; 2) airglow forward modelling; 3) tomographic temperature retrieval; 4) 3-D wave analysis; and 5) GW momentum flux (GWMF) calculation. The simulation performance is evaluated by comparing the retrieved zonal-mean GWMF with that computed directly from the model wind data. A major question to be considered in our assessment is the minimum number of tracks required for the derivation of 3D GW parameters with sufficient accuracy. In particular, our simulations show that the GW polarization relations are still valid in the MLT region and can thus be employed for inferring GWMF from the 3--D temperature distributions. Based on the E2E simulations for gaining zonal-mean climatologies of GW momentum flux, we demonstrate that our approach is robust and stable, given a four-track observation geometry and the expected instrument noise under nominal operation conditions. Using phase-speed-direction spectra we show also that the properties of individual wave events are recovered when employing four tracks. Finally, we discuss the potential of the proposed observations to address current topics in the GW research. We outline for which investigations ancillary data are required to answer science questions.

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