The ICOsahedral Non-hydrostatic model (ICON) framework is the open-source numerical weather prediction and climate model jointly developed by the German Weather Service (DWD), the Max-Planck Institute of Meteorology (MPI-M), Deutsches Klimarechenzentrum (DKRZ), the Karlsruhe Institute of Technology (KIT), and the Center for Climate Systems Modeling (C2SM). A consolidated climate setup with interactive ocean, land surface and atmosphere is being developed and tested. However, while ICON's basic setup includes monthly varying solar TSI and SSI forcing, the ability to prescribe higher-frequency UV irradiances and energetic particle precipitation (EPP) to change atmospheric composition has not been considered.

The upper atmosphere extension of ICON (UA-ICON) is currently a modelling framework allowing the analysis of dynamic phenomena from the ground to the lower thermosphere (150 km). Implementing varying solar forcing and interactive chemistry is expected to hugely influence the thermal structure and composition in the mesosphere/lower thermosphere (MLT).

Updated historical forcing datasets for the 7th phase of the Coupled Model Intercomparison Project (CMIP7) are now available for evaluation. These include daily varying spectral solar irradiance (SSI), total solar irradiance (TSI), and ion pair production rates for solar protons, cosmic rays, and medium-energy electrons to model EPP. Implementing these solar forcing data and the interactive chemistry is still ongoing work, and we present the first results of this effort, focusing on the MLT and UA-ICON.

How to cite: Kunze, M., Sinnhuber, M., Siebelts, A., Kerkweg, A., Hartung, K., Kern, B., and Jöckel, P.: CMIP7 solar forcing – evaluation of solar impacts with UA-ICON, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5564, https://doi.org/10.5194/egusphere-egu25-5564, 2025.

The coupling between the stratosphere and the mesosphere-lower thermosphere (MLT) has been known for several years. Its investigation was further pushed during the deep minimum of solar cycle 24 when the upper atmosphere was less affected by solar and geomagnetic forcing and by variability due to atmospheric forcing from below became more significant in observations. Another aspect supporting the understanding of the vertical atmosphere coupling has been the increased availability of globally distributed observations and of sophisticated general circulation models reaching up to the thermosphere.    

A negative correlation between the strength of the northern stratospheric polar winter vortex and solar-migrating semidiurnal tides (SW2) in winds at around 100 km altitude has been derived recently by Pedatella and Harvey (2022) based on 38 years of SD-WACCM-X model data. Observational evidence of this correlation was provided shortly afterwards by Kumar et al. (2023) using 26 years of geomagnetic observations of the equatorial electrojet, the latter being largely driven by thermospheric winds.

In this study, we have used a 60-year free-run simulation by the upper atmospheric extension of the ICOsahedral Non-hydrostatic (UA-ICON) general circulation model to explore the influence of northern hemisphere (NH) and southern hemisphere (SH) stratospheric polar vortex variability on the MLT. This study also elucidates the response of SW2 in MLT winds to variations in the strength of polar vortices. A weak NH polar vortex is associated with an increase in SW2, while a strong NH vortex results in a decrease in SW2. The response of SW2 to changes in the strengths of the SH polar vortex is similar, although considerably weaker. The NH polar vortex variability can explain around 40 − 50% of the variability in the SW2 during NH winter. The SH polar vortex, however, accounts for only a small fraction of the variability (up to ∼ 5%) in SW2, highlighting hemispheric differences in the response to stratospheric polar vortex variability.

References:

Kumar, S., Siddiqui, T. A., Stolle, C. and Pallamraju, D., Impact of strong and weak stratospheric polar vortices on geomagnetic semidiurnal solar and lunar tides. Earth Planets Space, 75, 52, https://doi.org/10.1186/s40623-023-01810-x, 2023.

Pedatella, N.M. and Harvey, V. L., Impact of strong and weak stratospheric polar vortices on the mesosphere and lower thermosphere. Geophys. Res. Lett. 49, e2022GL098877. https://doi.org/10.1029/2022GL098877, 2022.

How to cite: Stolle, C., Kumar, A., Yamazaki, Y., Pedatella, N. M., Kunze, M., Stephan, C. C., Siddiqui, T. A., and Krishna, M. V. S.: Impact of Weak and Strong Polar Vortices in the Northern and Southern Hemispheres on Solar-Migrating Semidiurnal Tides in the lower thermosphere using UA-ICON model simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3334, https://doi.org/10.5194/egusphere-egu25-3334, 2025.

We conducted high-resolution nested simulations over Andøya, Norway (ALOMAR) with UA-ICON to be co-analyzed with mesospheric measurements collected during the NASA Vorticity Experiment (VortEx) sounding rocket campaign in March 2023. The UA-ICON model was configured with 180 vertical levels, a model top at 150 km, and a global horizontal resolution of R2B7 (~20 km). One-way nesting was applied to achieve progressively finer resolutions of R2B8 (~10 km), R2B9 (~5 km), R2B10 (~2.5 km), and R2B11 (~1.25 km). For the global domain (~20 km horizontal resolution), the dynamic situation during the campaign is specified (specified dynamics, SD) by nudging to ECMWF operational analyses up to an altitude of 50 km. At resolutions finer than 5 km, UA-ICON resolves a significant portion of the gravity wave (GW) spectrum. Consequently, GW and convective parameterizations were disabled to isolate the effects of resolved GWs. Observational data from the campaign include wind measurements from the rocket flight, along with temperature and wind profiles up to ~80 km from the Rayleigh-Mie-Raman (RMR) lidar, and horizontal wind fields from the MF Saura and SIMONe Norway radar systems. We present and discuss initial results from comparisons between the simulations and the observations collected during the VortEx campaign. UA-ICON spectra exhibit the characteristic frequency spectrum of gravity waves, following the $\omega^{-2}$ relationship, validated by the observed Lidar spectrum. The simulations align well with observations, demonstrating UA-ICON's effectiveness in studying MLT dynamics.

How to cite: Morfa Avalos, Y. A., Kunze, M., Siddiqui, T. A., Zuelicke, C., Stephan, C. C., Stolle, C., Strelnikova, I., Baumgarten, G., Wing, R., Gerding, M., Renkwitz, T., Mossad, M., Lehmacher, G. A., Borchert, S., and Chau, J. L.: Resolved Gravity Waves in High-Resolution Nested UA-ICON Simulations Compared to Mesospheric Observations of the VortEx Campaign, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3199, https://doi.org/10.5194/egusphere-egu25-3199, 2025.

In this paper, we estimate the adiabatic cooling and warming in the MLT utilizing the SABER CO₂ VMR displacement from the global mean. This confirms that the summer mesopause temperature is largely controlled by adiabatic cooling instead of any absorptive heating or chemical heating. Because the adiabatic cooling is dynamically driven by waves from below, the summer polar mesopause is mostly sensitive to the changes in the stratosphere and mesosphere, for example, Sudden Stratospheric Warmings (SSWs) and polar vortex. And it well explains that the Aeronomy of Ice In the Mesosphere (AIM) satellite did not observe solar cycle responses in PMCs over the latest solar cycles. Unlike UV radiative heating in the upper atmosphere, dynamical cooling and mesosphere dynamics may have a complex relationship with the solar cycle. The paper also reveals a previously overlooked layer of adiabatic warming in summer and cooling in winter in the lower thermosphere due to downwelling and upwelling. Because this process is embedded in the thermosphere where mean temperature rises sharply driven by diffusive heating (or heat conduct from the upper thermosphere), it is not obvious without removing the global mean temperature. The mesosphere is the opposite, being lacking of strong heating sources. The heating layer (~100 K) in the summer lower thermosphere is substantial. Auroral heating also occurs in the magnetic polar lower thermosphere. How the adiabatic heating and cooling in the polar lower thermosphere interacts with auroral heating and the Joule heating driven adiabatic heating and cooling during geomagnetic active times warrants further investigations.   

How to cite: Yue, J. and Wang, N.: Estimation of Adiabatic Cooling and Warming in the Mesosphere and Lower Thermosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-185, https://doi.org/10.5194/egusphere-egu25-185, 2025.

In the mesosphere and lower thermosphere (MLT) region, residual circulations driven by gravity wave and tidal breaking/dissipation significantly impact constituent distribution and the height and temperature of the mesopause.  Distributions of CO2 can be used as a proxy for the residual circulations. NASA TIMED Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) CO2 volume mixing ratio (VMR) and temperature measurements from 2003 to 2020 are used to study the monthly climatology of MLT residual circulations and mesopause heights. Our analyses show that (a) mesopause height strongly correlates with the CO2 VMR vertical gradient during solstices; (b) mesopause height has a discontinuity at midlatitude in the summer hemisphere, with a lower mesopause height at mid-to-high latitudes as a result of adiabatic cooling driven by strong adiabatic upwelling; (c) residual circulations have strong seasonal variations at mid- to high latitudes, but they are more uniform at low latitudes; and (d) the interannual variability of the residual circulations and mesopause heights is larger in the Southern Hemisphere (SH; 4–5 km) than in the Northern Hemisphere (NH; 0.5–1 km).

How to cite: Qian, L., Wang, N., Yue, J., Wang, W., Mlynczak, M., and Russell III, J.: Climatology of Mesosphere and Lower Thermosphere Residual Circulations and Mesopause Height Derived From NASA TIMED/SABER Observations , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5252, https://doi.org/10.5194/egusphere-egu25-5252, 2025.

Long-term observations of mesospheric-lower thermospheric winds from six meteor radars located at middle and polar latitudes in both hemispheres, covering two recent solar cycles, are analysed to construct climatologies of atmospheric tides and gravity waves (GWs). The obtained climatologies of diurnal and semidiurnal tides and GWs are compared to numerical simulations using three general circulation models (GCMs), namely the Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA), the Whole Atmosphere Community Climate Model eXtension - Specified Dynamics (WACCM-X-SD), and the Upper Atmosphere ICOsahedral Non-hydrostatic (UA-ICON) model. Despite of generally good agreement with radar observations, there are substantial differences between the GCMs in reproducing key features of the MLT dynamics, e.g., the hemispheric zonal summer wind reversal. The differences are attributed in particular to sub-grid parameterisations of GWs in GCMs.

How to cite: Pokhotelov, D., Stober, G., Kuchar, A., Liu, H., Liu, H.-L., and Jacobi, C.: Climatologies of MLT winds and waves retrieved from long-term radar observations and GCMs, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7418, https://doi.org/10.5194/egusphere-egu25-7418, 2025.

Neutral metal layers such as Na, Mg, and Fe occur in the Earth's mesosphere and lower thermosphere (80-120 km) region due to the ablation of cosmic dust. These layers provide important tracers of chemical and dynamical processes within this region. Nonmigrating diurnal tides are persistent global oscillations in atmospheric fields (e.g., wind, temperature, and density) with a period of 24 hours and nonsynchronous propagation with the sun. A complex combination of tidal forcing, chemistry, and photochemistry drives the diurnal cycle of these meteoric atoms. However, the mechanism behind their diurnal variation is not yet fully understood.

The influence of nonmigrating diurnal tides on Na layer variability in the mesosphere and lower thermosphere regions is investigated for the first time using data from the Optical Spectrograph and InfraRed Imaging System (OSIRIS) on the Odin satellite and Specified Dynamics Whole Atmosphere Community Climate Model (SD-WACCM) with metal chemistry. The Na density from OSIRIS exhibits a clear longitudinal variation indicative of the presence of tidal components. Similar variability is seen in the SD-WACCM result. Analysis shows a significant relationship between the nonmigrating diurnal tides in Na density and the corresponding temperature tidal signal. Below 90 km, the three nonmigrating diurnal tidal components in Na density show a significant positive correlation with the temperature tides. Conversely, the phase mainly indicates a negative correlation above 95 km. Around the metal layer peak, the response of the Na density to a 1 K change in tidal temperature is estimated to be 120 cm⁻³.

How to cite: Wu, J., Feng, W., Xue, X., Marsh, D., and Plane, J.: Effects of nonmigrating diurnal tides on the Na layer in the mesosphere and lower thermosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7659, https://doi.org/10.5194/egusphere-egu25-7659, 2025.

Geomagnetic storms can lead to energetic particle precipitation (EPP), which increase ionization levels in the atmosphere, enhancing NOx/HOx concentrations, thus destroying ozone in the polar mesosphere and stratosphere. There has been many studies to study the impact of solar proton on ozone, but the contributions of solar proton and energetic electron precipitation under different space weather especially geomagnetic storms events to the changes in middle/upper atmospheric in different seasons are not well quantified. It is also important to study long term changes in ozone due to solar activities including geomagnetic storms to understand how they affect global climate and atmospheric chemical processes.

In this work, we have carried out long term simulations (1980-2019) using the Whole Atmosphere Community Climate Model (WACCM), with detailed D-region (60-90 km) chemistry. The model uses a specific-dynamic version with nudging of Modern-Era Retrospective analysis for Research and Applications (MERRA-2) reanalysis. First, we have made comprehensive model validations using various satellite measurements, which shows the model with detailed D region ion-nuetral chemistry has better performance in reproducing some key neutral chemical species (e.g., NOx, HOx, HNO₃ etc) affected by EPP. In order to highlight how different geomagnetic storms events (strong or quite conditions) affected stratospheric ozone in different seasons, we use a composite analysis method. Interestingly, The ozone loss is more noticeable in summer than in winter. Surprisingly, ozone changes usually become more noticeable after one month. To investigate the impact of medium energy electron (MEE, 30-1000 keV) precipitation on the middle and upper atmosphere, several model sensitivity experiments have been made. Results shows MEE has a significant impact in the mesosphere with small contribution to stratosphere ozone depletion (2-5% in the Antarctic winter).

How to cite: Chang, S., Chen, Z., M.C.Plane, J., P.Chipperfield, M., R.Marsh, D., Feng, W., and Zhang, Y.: The Impact of Geomagnetic Storms on Antarctic Stratospheric Ozone: Modelling Study Based on the WACCM-D , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11190, https://doi.org/10.5194/egusphere-egu25-11190, 2025.

We present analysis of the chemical and dynamical variability in the mesosphere and lower thermosphere (MLT) during the 2018-2019 sudden stratospheric warming (SSW) as simulated by the high resolution (~25 km horizontal and 0.1 scale height vertical resolution) version of the Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (WACCM-X). The WACCM-X simulations make use of new capabilities, including the spectral element dynamical core and the ability to constrain the lower atmosphere meteorology in WACCM-X at high-resolutions. Compared to standard resolution (~200 km horizontal and 0.25 scale height vertical resolution) WACCM-X simulations, the high-resolution simulations are in better agreement with Thermosphere Ionosphere Mesosphere Energetics Dynamics-Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED-SABER) and Atmosphere Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) observations. In particular, the high-resolution simulations better reproduce the Northern Hemisphere middle-high latitude winds in the MLT. The downward transport of nitric oxide (NO) following the SSW is also better reproduced in the high-resolution simulations. The results demonstrate the importance of capturing mesoscale processes for accurately simulating the chemistry and dynamics of the MLT.      

How to cite: Pedatella, N., Harvey, V. L., Liu, H., and Datta-Barua, S.: High resolution simulations of the chemistry and dynamics in the mesosphere and lower thermosphere during the 2018-2019 sudden stratosphere warming, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7273, https://doi.org/10.5194/egusphere-egu25-7273, 2025.

The Mesosphere and Lower Thermosphere (MLT) act as a critical region for the propagation and dissipation of atmospheric waves, such as gravity waves, tides, and planetary waves, playing a significant role in the global atmospheric circulation system. These waves, particularly gravity waves, dissipate and break in the MLT, converting their energy into turbulence and generating localized turbulent structures. The turbulence produced in turn can modulate wave propagation, with part of the dissipated energy potentially re-exciting new waves. Atmospheric turbulence in the MLT significantly influences the transport of energy, momentum, and matter, making it a key mechanism for understanding the coupling across the entire atmospheric system. The studies of MLT atmospheric turbulence can also promote the fine modeling of the middle and upper atmosphere.

By integrating ground-based MF radar observations over (39.4°N, 116.7° E) with TIMED/SABER satellite data, we investigated the variations of atmospheric turbulence energy dissipation rate (ε) and the turbopause, as well as their relationship with atmospheric wave dynamics in the MLT region. Results show that the atmospheric ε is modulated by different periods at different altitudes. The ε is subject to 12 h and 24 h periodic variations. The 12 h periodic variation is more obvious at higher altitudes than the 24 h periodic variation at lower altitudes with the dividing layer at about 90 km. Advanced analysis of turbopause are based on the total wave variations based on SABER/TIMED. We first propose a new method for identifying the wave-turbopause by employing the conservation of energy principle, and introducing an energy index to delineate the turbopause layer’s boundaries. This method defines a set of parameters including the lower boundary height, upper boundary height, turbopause height, and turbopause layer thickness. Applying this method to long-term SABER data over Beijing, we find that the turbopause layer exhibits distinct seasonal and interannual variations. The average heigh of lower boundary is 69 km, and the average heigh of upper boundary is 94 km. Global characteristics of the turbopause layer are provided, which are quite valuable to enhancing our further atmospheric modeling and empirical studies.

How to cite: Xiao, C.: The Activity of Atmospheric Turbulence in the MLT, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20108, https://doi.org/10.5194/egusphere-egu25-20108, 2025.

Polar winter descent of NOy produced by energetic particle precipitation (EPP) in the mesosphere and lower thermosphere affects polar stratospheric ozone by catalytic reactions. This, in turn, may affect regional climate via radiative and dynamical feedbacks. NOy observations by MIPAS/Envisat during 2002--2012 have provided observational constraints on the solar-activity modulated variability of stratospheric EPP-NOy.

ESA’s Earth Explorer 11 candidate Changing Atmosphere Infra-Red Tomography (CAIRT) will observe the atmosphere from about 5 to 115 km with an across-track resolution of 30 to 50 km within a 500 km wide field of view. CAIRT will provide NOy and tracer observations from the upper troposphere to the lower thermosphere with unprecedented spatial resolution. We present the science studies using WACCM-X high resolution model runs simulating modelling a Sudden Stratospheric Warming event to assess its potential to advance our understanding of the EPP-climate link and to improve upon the aforementioned constraints in the future.

How to cite: Bender, S., Funke, B., Lopez Puertas, M., Garcia-Comas, M., Stiller, G., von Clarmann, T., Höpfner, M., Sinnhuber, B.-M., Sinnhuber, M., Errera, Q., Poli, G., Ungermann, J., Preusse, P., Rhode, S., Liu, H., and Pedatella, N.: EPP-climate link by reactive nitrogen polar winter descent: Science studies for the EE11 candidate mission CAIRT, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11666, https://doi.org/10.5194/egusphere-egu25-11666, 2025.

NASA’s Atmospheric Waves Experiment (AWE) mission is a Heliophysics Small Explorers Mission of Opportunity designed to investigate how terrestrial weather affects space weather, via small-scale atmospheric gravity waves (AGWs) produced in Earth’s atmosphere. Following its launch to the International Space Station (ISS) in November 2023, AWE began a 2-year mission to explore the global distribution of AGWs, study the processes controlling their propagation throughout the upper atmosphere, and estimate their impacts on the ionosphere – thermosphere – mesosphere (ITM) system. The AWE science instrument consists of the Advanced Mesospheric Temperature Mapper (AMTM) — a wide field-of-view Shortwave Infrared (SWIR) imager that quantifies gravity wave-induced temperature disturbances in the hydroxyl (OH) airglow layer, which lies near the mesopause at ~87 km altitude. The AMTM’s four identical telescopes make continuous nighttime observations of the P₁(2) and P₁(4) emission lines of the OH (3,1) band and the Q₁(1) emission line in the OH (2,0) band, as well as the atmospheric background, from which the OH layer temperature is derived. AWE images are collected once per second, co-added, and processed into temperature swaths using correction algorithms derived from ground calibration test results. Global coverage of the OH layer is provided about every four days, which enables regional and seasonal studies, as well as characterization of AGW ‘hot spots.’ This paper will present an overview of the AWE mission and discuss initial science results.

How to cite: Scherliess, L., Taylor, M., Pautet, P.-D., Zhao, Y., Lamborn, B., Latvakoski, H., Cantwell, G., Sevilla, P., Syrstad, E., Forbes, J., Eckermann, S., Fritts, D., Janches, D., Liu, H., and Snively, J.: The Atmospheric Waves Experiment (AWE), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14797, https://doi.org/10.5194/egusphere-egu25-14797, 2025.

The Atmosphere Waves Experiment (AWE) is a NASA mission launched on November 9, 2023, and installed on the International Space Station (ISS). Its primary goal is to detect and characterize atmospheric gravity waves (AGWs) by measuring Earth’s mesospheric hydroxyl (OH) airglow with its key instrument, the Advanced Mesospheric Temperature Mapper (AMTM). Since its deployment, AWE has been quantifying the seasonal and regional variability of AGWs, investigating their occurrence and potential sources, and enabling the assessment of their broader impact on the atmosphere by comparing measurements at different altitudes by other instruments. AWE has collected extensive imagery and temperature data capturing distinct mesospheric phenomena, including mesospheric bores, signatures of a hurricane, and instability- and convection-driven disturbances. These observations are now publicly available for the first several months of the mission. In this work, we compare AWE’s dataset to total electron content (TEC) maps derived from GNSS data processed by the System for Rapid Analysis of Ionospheric Dynamics (S-RAID) (Inchin et al., 2023), which analyzes data from approximately 2,700 stations across the continental United States (CONUS). S-RAID applies common bandpass filters to isolate traveling ionospheric disturbances (TIDs) with periods shorter than two hours. By comparing AWE’s measurements at the approximate OH airglow height of 87 km with the GNSS data at an average ionospheric pierce point (IPP) of 300 km, we identify wave parameters and potentially determine which signatures correspond to upward-propagating gravity waves. These signals, in turn, can be traced back to various tropospheric sources, such as those mentioned above.

How to cite: Aguilar Guerrero, J., Bergsson, B., Mesfin, S., Inchin, P., Zettergren, M., Scherliess, L., Zhao, Y., and Pautet, D.: Observing Mesospheric Gravity Waves with NASA’s AWE Mission and Correlating to GNSS TEC Maps, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13773, https://doi.org/10.5194/egusphere-egu25-13773, 2025.

Several studies have shown the importance of solar tides for the dynamics in the MLT region. The solar tidal modes generated
in the troposphere and stratosphere increase in amplitude as they propagate vertically, transporting energy and momentum
to higher layers and enhancing layer mixing. The energy and momentum deposition by wave breaking alters the angular
momentum and kinetic energy budget and forces the global circulation in the MLT.

The majority of observations of solar tides have been derived from satellite data. Temperature and wind measurements from
satellites in geostationary orbits have been successfully used to derive tidal amplitudes around the equator. At higher latitudes,
however, the temporal resolution of the derived data product is limited by the orbital geometry of the satellites. With a revis-
iting time of several hours, the data set must be sampled over long periods to derive spectral components with periods of 8,
12, or 24 hours. In contrast, ground-based observations provide a comparably high time resolution of 0.5-1 hours, which is
suitable for investigating the short-time variability of solar tides. Observations of tidal amplitudes derived from ground-based
measurements using meteor radar systems, LIDARs, and microwave radiometers, are reported but are rare.

TEMPERA-C is a newly developed fully polarimetric ground-based microwave radiometer for temperature observations in the middle atmo-
sphere. It is designed to measure the four Stokes components of the Zeeman-split fine structure emission line of oxygen at 53
GHz. Compared to single polarized instruments, TEMPERA-C has an increased altitude coverage for temperature retrievals
with an upper limit of 60 km. By resolving the Zeeman-split emission line with a digital correlator with high frequency
resolution, retrievals of magnetic field features are possible. However, the calibration of a fully polarimetric instrument is more
complex than in the case of single polarization.

For a test campaign, TEMPERA-C measured continuously from March to November 2024 at the Jungfraujoch high-altitude
research station. In my presentation, I will focus on how thermal tides and other wave modes can be derived from this dataset.
I will also introduce the instrument, present a simplified calibration method, and discuss the influence of the Earth’s magnetic
field on the measured spectra.

How to cite: Krochin, W., Stober, G., and Murk, A.: Thermal tide observations from ground-based measurements of the Zeeman-split emission lines of oxygen at 53 GHz, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3786, https://doi.org/10.5194/egusphere-egu25-3786, 2025.

The mesosphere and lower thermosphere (MLT) region is a key transition zone between Earth’s lower and upper atmospheres, where energetic processes, wave dynamics, and chemical reactions converge. Understanding the temperature and chemical composition in this region is crucial for interpreting processes at higher altitudes. Despite the MLT’s importance in mediating couplings between the lower and upper atmosphere, direct in-situ measurements are inherently challenging due to the low-density, high-altitude, and high-speed environment. However, recent advances in compact, high-sensitivity mass spectrometers offer novel opportunities to investigate some of the most pressing open questions in MLT research. In this work, we highlight how state-of-the-art mass spectrometry can address uncertainties in key processes governing the composition and temperature of the MLT. We outline how measurements of species such as atomic and molecular oxygen, molecular nitrogen, trace metals from meteoric or anthropogenic sources, and reactive radicals can inform MLT models. Our goal is to provide data that will enable the integration of mass spectrometry findings into a range of models, including regional and global climate models, that incorporate long-term measurements, potentially revealing hidden trends in chemical composition and temperature. Such temperature drifts could be indicative of climate change affecting this region of the atmosphere as well.

How to cite: Fausch, R., Vorburger, A., and Wurz, P.: Analyzing the MLT region with mass spectrometers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16063, https://doi.org/10.5194/egusphere-egu25-16063, 2025.

The underlying physics of the Turbopause, from approximately 80-120 km, remains one of the most poorly understood topics in aeronomy today. However, the composition and dynamics of this region have a profound impact on the local and global climatological behavior of the thermosphere-ionosphere system. A detailed understanding of this region is critical to modern general circulation models and accurately predicting high-altitude weather systems within the mesosphere and lower thermosphere (MLT), which can have a detrimental effect on space and ground-based products. To improve our understanding of the Turbopause we propose the first modern measurements of O, O₂ , N₂, NO, CO₂, H₂O, O₃, and Ar spanning an altitude of 80 to 120 km. To achieve this, we present the Mass Spectrometry of the Turbopause Region (MSTR) program, a NASA HTIDES-funded technology development effort led by Orion Space Solutions (OSS) in partnership with the Southwest Research Institute (SwRI). MSTR is a novel, compact Cryogenically cooled Time-Of-Flight Mass Spectrometer (CTOF-MS) designed to integrate with a variety of aerospace platforms, including sounding rockets, small satellites, and advanced payloads. The flight prototype has a current SWAP of approximately 61 x 27 x 9 centimeters (volume: ~14800 cm3), 8 kg, and 20 to 25 W. MSTR is capable of sampling both ion and neutral elements and has demonstrated a resolving power at full width, half maximum of better than 3500 (predicted 5000), and a mass capability of 2u to 1500u. For integration with low-altitude sounding rockets, the instrument features an integrated 3D printed, liquid helium subcooled nosecone, to reduce and collapse the impinging bow shock experienced during supersonic flight. The MSTR CTOF-MS and cryogenic nosecone have undergone laboratory characterization and TRL advancement. The scientific objectives of the MSTR instrument are to provide simultaneous, in-situ, measurements of the chemistry and structure of the Turbopause as a function of altitude. The MSTR team plans to operate coincidentally with SABER overflights and ground-based LIDAR measurements to characterize the transport of NO across the Turbopause and compare measured CO₂ profiles to those retrieved by remote IR radiometry. Ultimately, the MSTR instrument hopes to improve our understanding of the complex temporal-spatial dynamics of the Turbopuase and MLT and provide valuable data to validate global circulation models.

How to cite: Anderson, L., Miller, G., Blase, R., and Fish, C.: In-Situ Sounding of the Chemistry and Dynamics of the Turbopause: The Development of a Novel Cryogenic Time-Of-Flight Mass Spectrometer, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13929, https://doi.org/10.5194/egusphere-egu25-13929, 2025.

Rayleigh lidars, in particular as part of the NDACC (Network for the Detection of Atmospheric Composition Change) network, have been observing the stratosphere and mesosphere (also known as the 'middle atmosphere' (MA)) with excellent vertical resolution for many years. Data from the lidars at the Observatoire de Haute-Provence (1978-2024), Table Mountain in California (1989-2024), Mauna Loa in Hawaii (2000-2024), Hohenpeissenberg (1987-2024) and Kühlungsborn (2012-2024) in Germany, Rio Grande in Argentina (2017-2024) and Réunion Island (1994-2024) have made it possible to obtain a unique dataset of temperature profiles between 30 and 80 km. This dataset makes it possible to establish a climatology of MA at several latitudes and over several decades.

Seasonal variations are represented by annual and semi-annual sinusoids. The behaviour of the amplitudes is similar at all sites: stable in the stratosphere, a decrease at the stratopause followed by a constant increase in the mesosphere; the opposite is true for the biannual amplitude, with a slight increase followed by stagnation in the mesosphere. The strength of the annual amplitudes measured at mid-latitudes is about 6 K in the stratosphere, with a decrease to 2 K in the stratopause, followed by an increase to 16 K in the mesosphere. These amplitudes are halved at tropical sites.

The temporal extent of the data series also allows us to analyse the response of the atmosphere to variations in solar activity, showing that these can cause variations of up to 3 K. The influence of the QBO (Quasi-Biennial Oscillation) produces variations that can exceed variations of about 1 K. There is also a general cooling of the atmosphere. We also observe a general cooling of the AM, which varies from site to site: for example, Reunion Island records a cooling of up to 3 K/decade in the mesosphere, while the Haute-Provence site measures a cooling of 1.5 K/decade.

These lidars have also been used to validate measurements made by limb observations from space. The main objective of this study is therefore to provide complete climatologies of the middle atmosphere from several points on the globe, in order to ensure continuity between several successive limb targeting missions. The production of temperature profiles from experiments such as GOMOS or OMPS shows that it is possible to obtain excellent precision in the measurement of temperature profiles. As the observations are made at different times of the day, atmospheric tides must also be taken into account.

How to cite: Da Costa, P., Keckhut, P., and Hauchecorne, A.: Re-evaluation of inter-annual variability using lidars Temperature extending over several decades of observation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20552, https://doi.org/10.5194/egusphere-egu25-20552, 2025.

Ozone (O₃) plays a critical role in the atmosphere by absorbing harmful ultraviolet solar radiation and also shaping the thermal structure and dynamics of the stratosphere. Variability in O₃ levels is driven by a complex interplay of factors, including long-term climate change, the abundance of ozone-depleting substances (ODSs), and non-linear interactions between transport and chemical processes. Changes in tropical stratospheric O₃ are particularly intricate due to a strong altitude dependence (WMO, 2022). In the tropical middle stratosphere, a region characterized by strong O₃ production and loss, during the early 2000s satellite measurements revealed an unexpected decline in O₃. Since then, O₃ levels in this region have increased again, but the underlying mechanisms driving such variability remain insufficiently understood, highlighting the need to investigate further the processes driving O₃ concentrations.

In this study, we show the pivotal role of causal inference in disentangling the complex chemical-dynamical influences on O₃ behavior in the narrower region of the tropical (10°S-10°N) middle (10 hPa) stratosphere. Causal inference can add significant value to traditional statistical methods by inferring causal relationships, distinguishing genuine causal links from spurious correlations, and quantifying their strength. The framework integrates qualitative physical knowledge through a causal graph applied to satellite observations and state-of-the-art 3-D chemical-transport model (CTM) TOMCAT simulations. By leveraging causal inference, we provide robust insights into the drivers of O₃ fluctuations and showcase the method’s potential for uncovering causal relationships in stratospheric chemistry-dynamics interactions. To validate this approach, we first construct a simplified toy model that reproduces major chemical-dynamical interactions in tropical middle stratospheric O₃ that are based on the NO_x (=NO + NO₂) catalytic ozone destruction cycle and stratospheric dynamics via stratospheric residual velocity w*. Using this toy model, we demonstrate that causal discovery reproduces the connections between w*, nitrous oxide (N₂O), nitrogen dioxide (NO₂), and O₃ in the tropical middle stratosphere. This successful application establishes a foundation for extending causal effect estimation to observed and modelled chemical processes, including their time lags. We split the periods 2004-2018 into two subperiods (i.e. 2004-2011 when O₃ concentrations declined, and 2012-2018 when O₃ concentrations increased in the tropical middle stratosphere) to demonstrate differences in the w*-N₂O connection that drives distinct O₃ behaviors. Additionally, a process-oriented analysis of different Quasibiennial oscillation (QBO) regimes, combined with bootstrap aggregation, reveals robust patterns in chemical-dynamical interactions. These results highlight the potential of causal inference as a transformative tool for advancing our understanding of stratospheric O₃ variability and its response to dynamic forcing.

World Meteorological Organization (WMO). Scientific Assessment of Ozone Depletion: 2022, GAW Report No. 278, 509 pp.; WMO: Geneva, 2022.

How to cite: Galytska, E., Hassler, B., Iglesias-Suarez, F., Chipperfield, M., Dhomse, S., Feng, W., Runge, J., and Eyring, V.: From data to discovery: understanding tropical middle stratospheric ozone variability through causal inference, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15306, https://doi.org/10.5194/egusphere-egu25-15306, 2025.

The October effect is long known as a sharp decrease in the amplitude of radio waves with Very Low Frequency (VLF) reflected in the D-region (60-90km). However, the mechanism of the October effect is unclear until today. Recent studies show that neutral atmosphere dynamics might cause the October effect. Simultaneously with the October effect in the ionized D-region, there is a warming in the lower mesosphere, which we call the neutral October effect and which cannot be observed in spring, resulting in a spring-fall asymmetry. This spring-fall asymmetry is reproduced by MERRA-2 in years after 2005 only when satellite observations are assimilated in the mesosphere. Other models like WACCM-X, ERA5 and GAIA also have difficulties reproducing this asymmetry. Only CMAM30 can reproduce the neutral October effect. A modelling study and various analysis techniques are used to investigate the mechanism of the neutral October effect in the neutral atmosphere. Based on our results we assume that the onset of the planetary wave activity and westward gravity wave drag after the quiet summer season induces a poleward and downward motion resulting in the observed warming in the lower mesosphere. 

How to cite: Wendt, V. and Schneider, H.: The neutral October effect in the lower mesosphere simulated by different models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4006, https://doi.org/10.5194/egusphere-egu25-4006, 2025.

The year 2025 marks the 55^th anniversary of Paul Crutzen’s brilliant hypothesis that collisions of the carbon dioxide molecules with oxygen atoms is the dominant process responsible for excitation of the bending vibrational mode of carbon dioxide and, thus, the resulting 15-µm infrared (IR) emission from vibrationally excited CO₂ provides a remote sensing window into the temperature profiles, energy budget, and thermal balance of the upper atmosphere. The O + CO₂ problem has remained open for the past five decades due to unacceptably large discrepancies between the laboratory measurements of the rate constant for this process, its values retrieved from space-based observations, and the rate constant values used in general circulation models (GCMs) for estimating CO₂ cooling of the mesosphere and lower thermosphere (MLT).

We have been actively engaged in research efforts to address this problem by revisiting its different aspects, including theoretical analysis, atmospheric modeling, and laboratory experiments investigating the processes leading to the generation of the 15-µm emission in the Earth’s MLT region. This report discusses our recent progress on this topic. We will present non-local thermodynamic equilibrium (non-LTE) modeling calculations on the MLT 15-µm cooling using our recently published, optimized version of the Accelerated Lambda Iteration for Atmospheric Radiation and Molecular Spectra (ALI-ARMS) research code [Kutepov and Feofilov, 2024]. Detailed comparisons of these results with the parameterizations of this cooling used in GCMs and remote sensing by space-based observations will be discussed.

This research is supported by grants from the US National Science Foundation (AGS-2312191/92, AGS-2125760) and NASA (80NSSC21K0664).

References

Kutepov, A. and Feofilov, A., 2024. New routine NLTE15µmCool-E v1. 0 for calculating the non-local thermodynamic equilibrium (non-LTE) CO₂ 15 µm cooling in general circulation models (GCMs) of Earth’s atmosphere. Geoscientific Model Development, 17(13), 5331-5347.

How to cite: Kutepov, A., Feofilov, A., Rezac, L., and Kalogerakis, K.: Studies to Resolve a Persistent Upper Atmospheric Mystery, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7102, https://doi.org/10.5194/egusphere-egu25-7102, 2025.