Orals: Thu, 7 May, 08:30–12:30 | Room 0.94/95
The mesosphere – lower thermosphere (MLT) contains dust particles made of both ice and refractory materials. Since the MLT overlaps with the heights of meteor ablation, it contains small nanometric particles made of cosmic dust material known as meteor smoke. The smoke particles influence the charge balance and ion chemistry and may serve as condensation nuclei for the formation of the ice particles. The ice particles are observed in summer at mid and high latitudes near the mesopause as noctilucent clouds (NLC) or polar mesospheric clouds (PMC). The presence of ice particles in combination with charge interactions, neutral air turbulence and dynamics also leads to specific radar echoes, known as polar mesospheric summer echoes (PMSE). Radar observations of PMSE and PMC/NLC measurements with cameras or lidar are among the few long-term observations around the summer mesopause. PMC/NLC measurements with satellites, cameras or lidar and PMSE measurements with radar indicate there are changes over the last decades. Aside from the ice and the meteoric smoke, space debris is possibly a third source of dust in the MLT that increases over time.
The Maxidusty-2 (MXD2) allowed to measure dust, ions and neutrals from a rocket launched from Andoya, Norway (69.1° N, 16° E) on 5 July 2025 around 8:01 am local time. The MXD2 science payload included four dust in-situ detectors, a neutral gas instrument as well as a Faraday rotation experiment and Langmuir probes to measure electron density. Two independent and different instruments collected dust particles. NLC were observed at that time with the Alomar RMR lidar close by. PMSE were observed at the same time with the MAARSY radar close to the launch site and with the EISCAT radar in Ramfjord (69.6° N, 19.2° E) near Tromsoe at about 130 km distance. All in situ instruments recorded science data. The recovery was successful, and analysis of the collected refractory dust samples is ongoing. An overview of the campaign measurements is given. The initial analysis notably shows that the dust instruments measured a signal at the altitude of the NLC but only small signals at the altitude of higher PMSE layer. We discuss the results in terms of dust charging and the link between dust and the other parameters measured.
How to cite: Mann, I., Olsen, S. V., Eilertsen, Y., Yokoyama, Y., Tinguely, J.-C., Spicher, A., Hedin, J., Gumbel, J., Strelnikov, B., Schueler, K., Baumgarten, G., Latteck, R., Huyghebaert, D., Renkwitz, T., Trondsen, E., Clausen, L., Stamm, J., and Varberg, E.: Dust and ionospheric constituents measured in the MLT during noctilucent cloud conditions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2889, https://doi.org/10.5194/egusphere-egu26-2889, 2026.
During the summer of 2025, the Middle Atmosphere Alomar Radar System (MAARSY) was operated to observe polar mesospheric summer echoes (PMSE) in a 5-beam multistatic configuration. The experiment combined 5 beam directions at the MAARSY transmitter with a newly established receiver array near Stø, located approximately 48 km southwest of MAARSY. Multi-beam coherent radar imaging (CRI) was applied for both the bistatic (MAARSY– Stø) link, and the monostatic (MAARSY–MAARSY) link, enabling for the first time, imaging of the same PMSE volume from different viewing geometries. Using CRI with high angular and temporal resolution, four-dimensional (space–time) observations of sub-minute, kilometer-scale dynamics in the mesosphere–lower thermosphere (MLT) region are achieved. The measurements resolve small-scale dynamical processes associated with turbulence, and gravity waves. The occurrence, evolution, and motion of PMSE structures, including layering, and sub-layers are investigated using radar signal strength, line of sight Doppler shift velocities, and spectral widths. In addition, the SIMONe meteor radar network around Andøya is used for providing continuous horizontally resolved background wind fields at PMSE altitudes. The presented case studies provide high resolution temporal and spatial information on kilometer-scale PMSE dynamics and demonstrate the advantage of multi-static imaging for advancing the understanding of MLT instabilities and turbulence.
How to cite: Vazifehkhah Hafteh, M., Huyghebaert, D., Renkwitz, T., Latteck, R., and L. Chau, J.: Imaging Sub-minute Kilometer-Scale PMSE Dynamics and Layering Using a 5-Beam Multistatic Mode with the MAARSY Radar , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6747, https://doi.org/10.5194/egusphere-egu26-6747, 2026.
Vertical winds induced by the residual circulation are extremely challenging to retrieve from measurements. Multistatic meteor radar networks facilitate implementing more sophisticated tomographic wind retrievals, either based on Bayesian inversions such as the 3DVAR+DIV algorithm or the spherical volume velocity processing (SVVP). A vertical wind climatology obtained from the Nordic Meteor Radar Cluster (NORDIC) showed summer upwelling with vertical winds between 8-12 cm/s corresponding to a cooling rate of 80 K/d. During the winter season, the downwelling indicated values of -2 to -4 cm/s, resulting in a warming of 15-25 K/d. An analysis of the time series from 2022 to 2025 revealed a correlation between the vertical wind magnitude and the strength of the meridional wind during the summer months, as expected from the residual circulation. Furthermore, we compared winds observed with NORDIC to the meteorological reanalysis JAWARA.
How to cite: Stober, G., Liu, A., Kozlovsky, A., Kero, J., Pearl Poku, L., Krochin, W., Janches, D., Tsutsumi, M., Nozawa, S., Lester, M., and Mitchell, N.: Inferring the variability and magnitude of the vertical winds and associated heating/cooling rates from multistatic meteor radar measurements and meteorological reanalysis induced by the residual circulation , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4892, https://doi.org/10.5194/egusphere-egu26-4892, 2026.
The multilayered structure of sporadic E(Es) is a well-known observable phenomenon in equatorial and mid-latitudes. This phenomenon can be caused by the presence of additional altitude regions, caused by electric field, with nodes of the vertical ion drift velocity, where near these nodes the maximum rate of their vertical convergence is achieved, which leads to the formation of Es layers. In this case, regions with maximum ion convergence rate in the lower thermosphere (at an altitude of about 90-150 km) can be caused by an electric field, in addition with the propagation of atmospheric gravity waves and tidal wind.
In this case, the combined effect of electric field, zonal wind velocity and wind shear can lead to the formation of additional Es layers, in contrast to the case where only zonal wind or/and its vertical shear factor dominates in the vertical convergence of ions.
In the case of a combined effect of these factors, the disappearance of Es layers formed in the presence of only zonal wind velocity, its vertical shear or electric field is also possible.
In the equatorial region the factor of electric field in formation and dynamics of Es layers is significant.
These processes of formation of multilayer sporadic E and/or its disappearance, using the horizontal wind model (HWM14) data and electric field (with constant vertical and zonal components in the cases of various polarizations), are considered numerically in equatorial regions.
Evolution of sporadic E with Es-type two sub-layers sometimes could lead to the formation of the high density single Es layers.
In the equatorial regions, electric field influences the ion drift velocity and therefore also can cause the displacement of layers. Here we will show the predominance of the downward motion of the Es sublayers, under influence of the electric field and the possibility of their merging into one high-density Es layer localizing in their most observable regions (about 95-105 km) of the lower thermosphere.
Acknowledgements. This study is supported by the Shota Rustaveli National Science Foundation of Georgia Grant no. FR-21-22825.
How to cite: Dalakishvili, G., Didebulidze, G. G., and Todua, M.: The role of the electric field in formation of multilayered sporadic E(Es) in equatorial regions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10262, https://doi.org/10.5194/egusphere-egu26-10262, 2026.
Sudden Stratospheric Warmings (SSWs) provide a direct route for dynamical and chemical coupling between the troposphere, stratosphere, mesosphere and lower thermosphere (MLT), but the vertical structure and event-to-event diversity of the associated ozone response are still not well quantified. We examine five Northern Hemisphere warmings (2009, 2011, 2013, 2019, and 2025) using Aura/MLS and TIMED/SABER temperature and ozone observations together with ERA5 reanalysis. Polar-cap (≥70°N) time–height temperature and ozone diagnostics are used to track anomalies from the lower stratosphere to the upper mesosphere (down to 0.001 hPa).
Major midwinter SSWs followed by elevated stratopause (ES) formation (2009, 2013, 2019) exhibit the strongest vertically coherent response: pronounced mesospheric cooling and a strong enhancement of the secondary ozone maximum near 0.01–0.003 hPa (≈80–90 km), with ozone nearly doubling shortly after onset. In contrast, the April 2011 final warming and the March 2025 major–final event show only weak mesospheric anomalies. In the lower–middle stratosphere (100–10 hPa), ozone increases persist for weeks after onset, while ES-type events are followed later by marked upper-stratospheric ozone decreases (10–1 hPa), consistent with the descent of NOx-rich MLT air during post-SSW recovery. Agreement across MLS, SABER, and ERA5 indicates that these coupled signals are robust and that SSW morphology controls the vertical reach of stratosphere–MLT coupling. We additionally present preliminary diagnostics of the 2026 SSW to place this event in the same framework.
How to cite: Shapiro, A. and Foelsche, U.: Vertical structure of upper-stratospheric and mesospheric ozone during polar stratospheric warmings, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6868, https://doi.org/10.5194/egusphere-egu26-6868, 2026.
Solar Cycle 25 has approached its maximum phase, bringing an elevated frequency of solar eruptive events and associated geomagnetic disturbances. During 2024 and 2025, several intense geomagnetic storms have provided rare opportunities to examine the short-term coupling between space‐weather forcing and the middle atmosphere. Previous studies have shown that energetic particle precipitation (EPP) during geomagnetic storms can substantially modify the chemical composition of the mesosphere and lower thermosphere (MLT), particularly through the production of odd nitrogen (NOx) and odd hydrogen (HOx), which catalytically destroy ozone. In this presentation, we investigate the MLT ozone responses to several large geomagnetic storms occurring in 2024–2025 using MLS satellite observation. We will also estimate the particle forcing associated with these events using the observed ozone chemical responses. This analysis provides a testbed for climate model inputs.
How to cite: Jia, J., Orsolini, Y., Kero, A., Zhang, J., Thomas, N., Grandin, M., Van de Kamp, M., and Espy, P. J.: Ozone responses to the geomagnetic storms in 2024 and 2025, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17606, https://doi.org/10.5194/egusphere-egu26-17606, 2026.
During three ionospheric heating campaigns in 2025, including the 2025 Polar Aeronomy and Radio Science (PARS) summer school held by the University of Alaska Fairbanks, the University of Florida’s Ionospheric Radio Lab (IRL) performed a variety of active ionospheric heating experiments using the High-frequency Active Auroral Research Program’s (HAARP) Ionospheric Research Instrument (IRI). High frequency (HF) partial reflection and HF cross-modulation experiments were used to investigate the dynamic response of the mesosphere to short time-scale heating. ELF/VLF wave generation experiments were designed to identify the location of the ELF/VLF source region and to quantify the spatial distribution of the auroral electrojet currents. Additionally, VLF scattering experiments were designed to characterize mesospheric HF heating by moving the HAARP-generated scattering body in a proscribed manner.
UF made a concerted effort to detect the effects described above at seven widely spaced radio receiver locations, each of which was selected to be extremely radio quiet. Noise at each site was mitigated at the receiver by operating using a sinusoidal power generator. The logistical effort required all UF graduate students’ effort, and we are especially grateful for the efforts of our colleagues at Auburn University and at the University of Alaska Fairbanks for their help operating these remote sites.
In this paper, we present observations and analysis for the experimental efforts studying HF propagation, ELF/VLF wave generation, and VLF scattering with a particular emphasis on insights provided into mesospheric dynamics. We comment on the possible future impact of the (now-operational) HAARP Lidar on these analyses: a potentially important diagnostic for the mesospheric electron density and electron temperature, as well for as the spatial distribution of electrojet currents above HAARP.
How to cite: Moore, R. C., Burch, H., Camp, J., McCoy, R. W., and Santos, J.: Insights into Mesospheric Chemistry by Ionospheric Heating at HAARP , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20233, https://doi.org/10.5194/egusphere-egu26-20233, 2026.
The polar vortex is a system of strong westerly winds surrounding the cold polar region which forms in the middle atmosphere every winter. In the southern hemisphere the polar vortex is stronger and lasts longer than its northern counterpart. Consequently, the southern polar vortex provides sufficiently cold circumstances where massive ozone depletion by reactive chlorine oxides (ClOx) forms a large ozone hole after the polar night. Energetic electron precipitation (EEP) is an external driver which modifies ozone chemistry and, thereby, the thermal and dynamical balance in the wintertime middle atmosphere. Precipitating electrons originate from the near-Earth space and produce nitrogen (NOx) and hydrogen oxides (HOx) which catalytically destroy ozone. Earlier studies have shown that EEP-NOx both decreases ozone and deactivates chlorine oxides in the stratosphere in the southern hemisphere. Moreover, EEP is found to affect the strength of the polar vortex and even surface climate modes like the NAO (North Atlantic Oscillation) and the SAM (Southern Annular Mode), but the mechanisms causing these effects are still unclear. We study here the chemical and dynamical variability related to EEP and its seasonal evolution in the southern mesosphere and stratosphere using the POES and Aura satellite measurements and the ERA5 reanalysis data. We show that EEP increases NOx and decreases both ozone and ClO in the upper stratosphere in early winter. However, when EEP-NOx reaches the middle stratosphere during the spring, ClO is still decreased but ozone and temperature are increased, and the polar vortex becomes weaker. Moreover, we found that the correlation between EEP and the southern polar vortex has significantly changed during the last 80 years and is tightly related to the amount of chlorine in the stratosphere. These findings show that EEP weakens the southern springtime vortex and drives negative SAM at least partly via chlorine deactivation.
How to cite: Salminen, A., Asikainen, T., and Mursula, K.: Effect of energetic electron precipitation on ozone and the southern polar vortex: The role of chlorine deactivation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18818, https://doi.org/10.5194/egusphere-egu26-18818, 2026.
The longitudinal structures of EIA have been extensively studied by using satellite data. However, there are few observations and studies, due to the weak ionosphere near midnight. In this paper, we studied the longitudinal structures of EIA at 02:00 local time during geomagnetically quiet period, benefitted from the satellite orbits and high sensitivity of FY‐3D IPM. We found that the wavenumber 4 longitudinal structures of EIA still exist at 02:00 local time and are obvious at equinoxes. Compared with SSUSI F18 data, FY‐3D IPM data showed different characteristics of wavenumber 4 component of EIA longitudinal structures. Because of the different local time of data between SSUSI F18 and FY‐3D IPM, we consider that the longitudinal wavenumber 4 structures of EIA after midnight originated from the cross‐equatorial neutral wind rather than the electric field modulated by zonal neutral wind in daytime.
How to cite: Zhang, B., Fu, L., Mao, T., Jiang, F., and Wang, J.: Wavenumber 4 Longitudinal Structure of the Ionosphere after Midnight Based on the OI135.6 nm Night Airglow Using FY‐3D Ionospheric Photometer, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21711, https://doi.org/10.5194/egusphere-egu26-21711, 2026.
The Mesosphere and Lower Thermosphere (MLT, ~70–120 km) is a key transition region governing the coupling between the lower atmosphere and near-Earth space. Despite its central role in atmospheric chemistry and dynamics, the MLT remains one of the least observed domains, leading to large uncertainties in composition, temperature, density, and winds, particularly near the mesopause and below the turbopause. A long-standing “holy grail” of MLT research is the direct, global, and time-resolved measurement of atomic oxygen, the dominant energy carrier controlling the chemistry and thermal balance of the region, which has remained inaccessible until recent advances in terahertz (THz) receiver technology.
Keystone is one of the four ESA Earth Explorer 12 candidate missions and is currently undergoing Phase-0 science and system studies. Its primary scientific objective is to provide comprehensive, global, and time-resolved measurements of MLT chemistry, temperature, and dynamics, enabling improved understanding of vertical coupling and wave–mean flow interactions involving gravity waves, tides, and planetary waves from diurnal to seasonal timescales. The mission’s core payload is a high-spectral-resolution supra-THz (1–5 THz) radiometer, complemented by infrared and UV–visible limb instruments. Keystone will retrieve vertical profiles of key neutral species, including direct global measurements of atomic oxygen, together with temperature profiles and mesospheric winds derived from Doppler-shift spectroscopy. These simultaneous observations of neutral dynamics and composition also support improved understanding of the drivers of ionospheric variability, including the neutral wind dynamo governing electrodynamics in the E-region.
Beyond its fundamental science goals, Keystone addresses an important societal challenge. Improved constraints on MLT density and temperature provide physically consistent lower-boundary conditions for thermospheric density models used in satellite drag prediction. By reducing uncertainties propagated upward into the thermosphere, such constraints are expected to yield order-tens-of-percent improvements in residual drag and orbit propagation accuracy, supporting safer and more sustainable operation of the increasingly congested low and very-low-Earth-orbit environment.
How to cite: Gerber, D., Huebers, H.-W., Plane, J., Marsh, D., Savigny, C. V., Comas, M. G., Espy, P., Stephan, C., Wright, C., Gumbel, J., Spogli, L., Ward, W. E., Iorfida, E., and Veihelmann, B.: Keystone: a novel terahertz limb-sounding mission advancing chemistry, dynamics, and vertical coupling in the MLT, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22391, https://doi.org/10.5194/egusphere-egu26-22391, 2026.
A new sodium chemistry model, NaChem, has been developed to study the sodium layer in the mesosphere and lower thermosphere. The NaChem model solves the continuity equation of all species with no steady-state assumption. This work examines the Meteoric Input Function (MIF) using model data assimilation constrained by lidar observations, as well as the meteor measurements from the Arecibo Observatory (AO). Sodium number density from the Colorado State University (CSU) Lidar and the Andes Lidar Observatory (ALO) are used as reference profiles in NaChem to infer the MIF, while the AO MIF is derived from micro-meteor radiant distributions. Our results show that the CSU MIF agrees well with the AO MIF, but the ALO MIF exhibits significant differences. The inferred meteoroid material input rates are 53+/-23 t/d from CSU and 83+/-28 t/d from ALO. Our study also indicates that the sodium sink is mainly controlled by smoke uptake which is approximately three times more effective than the NaHCO3 dimerization process to remove sodium. Lastly, our sensitivity study reveals that more NO+ will directly lead to fewer observable Na atoms in the atmosphere.
How to cite: Huang, T.-Y., Li, Y., Urbina, J., Vargas, F., and Feng, W.: Comparisons of the meteoric input function derived from model-lidar data assimilation and Arecibo Observatory meteor measurements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11654, https://doi.org/10.5194/egusphere-egu26-11654, 2026.
The drivers of the southern summer mesopause are investigated through a series of simulations using the Kühlungsborn Mechanistic General Circulation Model (KMCM) compared to lidar and radar observations from 2010 to 2013, which were presented in Lübken et al., JGR (2015). In general, the simulations before and during the breakdown of the polar jet agree quite well with the observations in terms of mesospheric winds and mesopause jumps, i.e., cooling and altitude changes. After the breakdown, the agreement is less good, as the mesopause response is more pronounced in the simulations than in the observations.
In my presentation, I will discuss the reason for the qualitative differences during the summer, namely the interaction between gravity wave activity and the two different mechanisms responsible for the jumps. These are 1) the breakdown of the jet stream in November or December (allowing gravity waves from the lower atmosphere to propagate into the mesopause) and 2), the manifestation of interhemispheric coupling triggered by the warming of the northern winter stratosphere (which modifies the temperature gradient between the equatorial and polar regions). I will finish with an explanation for the differences between observations and simulations in the latter case due to a shift in the most cooled region relative to the mesopause.
How to cite: Schaefer-Rolffs, U. and Zülicke, C.: Local and Global Drivers of the Mesopause, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5417, https://doi.org/10.5194/egusphere-egu26-5417, 2026.
Our knowledge of the dynamics and chemistry of the mesosphere and lower thermosphere (MLT) has increased greatly over the last several decades, aided by extensive satellite and ground-based observations and advances in numerical models. Together they provide estimates of the climatology of the MLT and how it varies with season and over decadal timescales. However, we have limited capability in predicting MLT day-to-day variations, i.e., its weather. Empirical models that take as input the day of year and solar flux / geomagnetic activity indices remain the standard tool for predicting such things as the drag on space debris in low earth orbit. Such models can disagree on the state of the atmosphere by a factor of two. Using the specified dynamics version of the Whole Atmosphere Community Climate Model (SD-WACCM) we explore MLT weather variations in a simulation that covers the period 2005 to 2015. Here we focus on variations near the mesopause at representative equatorial and high-latitude sites. After removing seasonal variations, we find that the majority of day-to-day weather arises from changes in the amplitude and phase of atmospheric tides. Moreover, it is typical that at most 5 tidal modes are sufficient to capture most of the short-term variability. Using wavelet analysis, we show that tidal variations can be linked to both external forcing (e.g., solar flux) and variability that propagates from below. We confirm prior studies that have shown a link to sudden stratospheric warmings but also see variations correlated to the North Atlantic Oscillation, the El Niño-Southern Oscillation, and the Quasi-Biennial Oscillation. Additionally, we explore if persistence of tidal variability can be used to improve prediction of near term MLT dynamics and demonstrate improvements over climatological approaches. Taken together these finding provide a gateway to improved MLT weather prediction, with the potential to reduce uncertainty in targeted re-entry, collision avoidance and disruptions to radio communications and global positioning systems.
How to cite: Marsh, D., Sainsbury-Martinez, F., and Moffat-Griffin, T.: Towards predicting the weather of the mesosphere and lower thermosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13898, https://doi.org/10.5194/egusphere-egu26-13898, 2026.
Thermospheric mass density is a major source of uncertainty in spacecraft orbit prediction, particularly in low earth orbit. Since 2023, the Tianmu-1 constellation has deployed 12 satellites in sun-synchronous orbits at ~500 km altitude, each equipped with the Orbital Neutral Atmospheric Detectors (OADs) to provide in-situ measurements of thermospheric mass density and composition. In this study, density data from five Tianmu-1 satellites (TM02, TM03, TM07, TM11, and TM15) are used to construct a preliminary empirical thermospheric mass density model. The OAD measurements are firstly compared against the independent GRACE-FO accelerometer-derived density data. The results show that the calibrated Tianmu-1 densities agree well with GRACE-FO observations, with correlation coefficients exceeding XX and mean biases below XX%. The calibrated densities are then analyzed to quantify their responses to solar EUV flux and geomagnetic activity. Finally, an empirical density model is developed using the Empirical Orthogonal Function (EOF) decomposition. The EOF-based model reproduces the major spatial-temporal variability of the thermosphere and achieves a modeling accuracy of XX%, demonstrating the potential of the Tianmu-1 constellation for operational thermospheric mass density specification.
How to cite: Jin, Y., He, M., Zhang, X., Li, Y., and Ai, J.: Thermospheric Mass Density Observations and Empirical Modeling Using the Tianmu-1 Constellation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19094, https://doi.org/10.5194/egusphere-egu26-19094, 2026.
Understanding tidal variability in the lower thermosphere is essential for accurate prediction of ionospheric weather. In this study, we investigate lower-thermospheric tidal variability by applying rotated empirical orthogonal function (EOF) analysis to tides in temperature and wind fields at 80-110 km obtained from the JAWARA reanalysis over the past two decades. The rotated EOF analysis identifies the dominant modes of tidal variability as functions of latitude and altitude. The leading EOF modes exhibit latitudinal structures similar to the Hough modes predicted by classical tidal theory. Their principal component time series are compared with various meteorological indices (such as ENSO and QBO indices), allowing us to assess the relative importance of different meteorological processes for different tidal components (such as DE3 and SW2).
How to cite: Yamazaki, Y., Liu, H., Sato, K., Koshin, D., and Stolle, C.: Lower-thermospheric tidal variability as diagnosed by rotated empirical orthogonal function analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21665, https://doi.org/10.5194/egusphere-egu26-21665, 2026.
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. These constraints have been used to formulate a chemical upper boundary condition (UBC) for climate models in the context of solar forcing recommendations. We have updated the UBC with the recently released, reprocessed MIPAS version~8 data. We compare this updated NOy UBC model to data from the ACE-FTS solar occultation instrument which has been providing measurements since 2004 and is still actively providing data today. This 20+-year, long-term dataset will enable us to assess the validity of the assumptions underlying the UBC model, such as its climatological approach, outside of the time period of the data it was derived from. Any deviation will enable us to assess the projected, climate-change induced changes in middle atmospheric chemistry and transport, e.g. via changes in the Brewer-Dobson circulation.
How to cite: Bender, S., Funke, B., Lopez Puertas, M., Stiller, G., Bernath, P., and Boone, C.: EPP-NOy Upper-Boundary Condition, validation and long-term trends, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11983, https://doi.org/10.5194/egusphere-egu26-11983, 2026.
The Electrojet Zeeman Imaging Explorer (EZIE) mission employs measurements of the Zeeman-split O2 118.75 GHz polarized microwave emission to remotely sense magnetic fields associated with ionospheric electrojet currents. In addition to its primary science objectives, EZIE measurements are also sensitive to the mesospheric temperature altitude structure and line-of-sight Doppler shifts, enabling new measurements of the mesosphere and lower thermosphere (MLT).
We describe the technique used to retrieve mesospheric temperature profiles from EZIE brightness temperature spectra. The retrieval exploits the dependence of the O2 118.75 GHz spectral line shape on atmospheric temperature and pressure, as well as its polarization properties, using an iterative inversion framework applied to multi-polarization radiance measurements. Temperature information is encoded in the spectral width and shape of the emission, with the highest sensitivity in upper stratosphere and mesosphere.
We present initial EZIE temperature retrievals that reveal coherent mesospheric temperature structures consistent with wave-like variability in the MLT region. We also briefly discuss the sensitivity of the measurements to line-of-sight Doppler shifts associated with neutral winds, noting that vertical wind shear and broad contribution functions complicate direct wind interpretation. These results demonstrate the high potential of EZIE measurements to provide new constraints on mesospheric thermal structure and dynamics, complementing existing observational techniques and contributing to studies of MLT coupling processes.
How to cite: Araujo de Mesquita, R. L., Yee, J.-H., Swartz, W., Merkin, V., Starr, G., Garretson, J., Misra, S., Werner, F., and Schwartz, M.: A Novel Technique for Remote Sensing of Mesospheric Temperatures with the NASA EZIE Mission, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14879, https://doi.org/10.5194/egusphere-egu26-14879, 2026.
For many decades, hydroxyl (OH) airglow has been used to study atmospheric dynamics on different scales from infrasound and gravity waves to tides and planetary waves. These measurements refer to the upper mesosphere/lower thermosphere; they are mostly ground-based and only performed at night. In recent years, equivalent space-based measurements, i.e. nadir and off-nadir measurements, have also been carried out by instruments such as Suomi/VIIRS (Visible Infrared Imaging Radiometer Suite) and AWE (Atmospheric Wave Experiment).
Unlike ground-based measurements, satellite-based instruments can provide global or nearly global information depending on the orbit. However, nadir and off-nadir space-based measurements are subject to additional unwanted background signals. The main sources of this background radiation are moonlight reflected by clouds and the Earth's surface, as well as emissions from artificial lights on the ground. Whether the background radiation omits the analysis of space-based OH-airglow data with respect to atmospheric waves depends on the strength of the background signal and of its spatial and temporal variations compared to the dynamically-induced variations of the OH airglow.
Suomi/VIIRS operates in a spectral range that is not ideal for OH-airglow observations and does not utilise a dedicated background channel; OH-airglow measurements are only possible on moonless nights against a dark background. This limitation could be reduced by measuring the strongest OH-airglow emissions in the infrared, and by using a background channel. SOVA-S is one such concept. It was selected as one of four projects for the consolidation phase in the second ESA SCOUT cycle in 2025, focusing on OH(3-1) Q-branch measurements.
The measurement concept of SOVA-S is briefly introduced, along with the differences to AWE — an OH airglow mission in the infrared with an onboard background channel on the ISS. The conditions, under which atmospheric wave analyses should be possible with SOVA-S with regard to cloud cover, moon phase and surface albedo, are outlined; the underlying analyses were performed using the radiative transfer model SCIATRAN. Potential applications of these data in the context of applied research (e.g. the influence of middle atmospheric dynamics on the GNSS signal integrity) are presented.
How to cite: Wüst, S., Schall, A., Stöffelmair, U., and Bittner, M.: Measurements of Atmospheric Dynamics from Space: SOVA-S, an ESA SCOUT mission candidate , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10529, https://doi.org/10.5194/egusphere-egu26-10529, 2026.
Solar driven energetic particle precipitation (EPP) is an important factor in polar atmospheric ozone balance throughout mesosphere and stratosphere. EPP has previously been linked to ground-level regional climate variability, but the linking mechanism has remained ambiguous. Reported observed and simulated ground-level changes start well before the processes from the main candidate, the so-called EPP-indirect effect, would start. Here, we show that initial reduction of polar mesospheric ozone and the resulting change in atmospheric heating rapidly couples to dynamics, transferring the signal downwards through the mesosphere and stratosphere, resulting in shifting the tropospheric jet polewards. This pathway is not constrained to the polar vortex, rather, a subtropical route plays a key role. Our results show that the signal propagates downwards in timescales consistent with observed tropospheric level climatic changes linked to EPP. This pathway, from mesospheric ozone to regional climate, is independent of the EPP-indirect effect, and solves the long-standing mechanism problem for EPP effects on climate.
How to cite: Seppälä, A., Kalakoski, N., Verronen, P., Marsh, D., Karpechko, A., and Szelag, M.: From mesosphere to regional climate variability: Mechanism for downward coupling of polar mesospheric ozone loss, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14768, https://doi.org/10.5194/egusphere-egu26-14768, 2026.
Gravity waves are a fundamental component of middle-atmosphere dynamics, playing a key role in the redistribution of momentum and energy and thereby shaping the thermal structure and large-scale circulation of the stratosphere and mesosphere. Through their interaction with the mean flow, gravity waves contribute to processes such as the driving of the residual circulation, seasonal variability, and coupling between atmospheric layers. Despite their recognised importance, gravity wave activity remains highly variable in space and time and is still poorly represented in global circulation and climate models, highlighting the need for long-term observational constraints. This work aims to quantify gravity wave contributions in the stratosphere and lower mesosphere using temperature perturbations derived from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument over the period 2002–2025. Gravity wave potential energy, momentum fluxes, and wave amplitudes are used to construct climatologies describing the spatial structure and temporal variability of gravity wave activity. The analysis focuses on the Northern Hemisphere winter, when enhanced gravity wave potential energy is observed in the SABER seasonal climatology. Beyond seasonal variability, the ongoing analysis investigates interannual and long-term variations in gravity wave activity, with the aim of exploring potential links to changes in large-scale circulation and background conditions. To complement the satellite-based observations, wind perturbation variances derived from the Esrange meteor radar (68°N, 21°E) are used to characterise gravity wave signatures at high northern latitudes over the period 1999–2024. By combining long-term satellite and ground-based observations, this work seeks to improve the observational characterisation of gravity wave variability in the middle atmosphere.
How to cite: Jaen, J., Wright, C., and Hindley, N.: Long-term Observations of Gravity Wave Energy and Momentum Fluxes in the Middle Atmosphere from SABER/TIMED satellite, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19824, https://doi.org/10.5194/egusphere-egu26-19824, 2026.
Atmospheric tides propagating upward from the lower atmosphere undergo nonlinear interactions and modulate ionospheric plasma redistribution, leading to pronounced day-to-day variability in ionospheric parameters. This variability reflects the superposition of multiple tidal components with different periods, zonal wavenumbers, and mode structures, yet the dominant modes remain unclear. A hybrid method that combines space-based observations (ICON/MIGHTI), ground-based measurements (Chinese meteor radar chain), and empirical tidal modes (ETMs) is applied to extract the short-term tidal variability. The method is validated during the 2021 sudden stratospheric warming event, capturing the enhancement of the SW2 tidal amplitude, a strengthened first antisymmetric mode, and the phase advance in E-region neutral winds. Future work will extend this approach to assess the modal contributions of tides to the variability of ionospheric plasma drift.
How to cite: Ma, H., He, M., Zhou, X., and Liu, L.: Short-Term Tidal Modal Variability in the MLT Revealed by Combined ICON/MIGHTI and Meteor Radar Chain Observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16559, https://doi.org/10.5194/egusphere-egu26-16559, 2026.
In this report, we utilize data from the multi-ground-based instruments of the Chinese Meridian Project (CMP) and public national websites, including red-line all-sky airglow imagers, digisondes, GNSS-TEC receivers, and so on, to conduct an in-depth investigation into the formation and evolution processes as well as the accompanying physical mechanisms of two nighttime MSTID events occurring over the mid- and low-latitude regions of China. Specifically, we focus on the impacts of the hourly tidal-induced atmospheric dynamo process and its modulation effect on ionospheric electron density (airglow), which in turn affect the formation and evolution of these nighttime MSTIDs. The specific physical processes associated with the nighttime MSTIDs are discussed.
How to cite: Sun, L., Xu, J., Yuan, W., and Zhu, Y.: Formation and evolution of nighttime MSTID modulated by the atmospheric tides, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15839, https://doi.org/10.5194/egusphere-egu26-15839, 2026.
High-precision prediction of atmospheric environmental parameters is vital for high-altitude balloon experiments, aerospace missions, and climate simulation research. While traditional numerical weather prediction (NWP) models solve atmospheric partial differential equations (PDEs), their high computational cost limits short-term forecast timeliness. Pure data-driven deep learning models improve efficiency but often violate physical laws, leading to overfitting and poor generalization.
To address these issues, Physics-Informed Neural Networks (PINNs) integrate data-driven learning with physical equations by incorporating PDEs as soft constraints in the loss function. However, standard PINNs struggle with high-dimensional spatiotemporal prediction due to training instability and convergence difficulties, especially in multi-scale, nonlinear atmospheric systems.
In response to the above issues, this study proposes a new PINN framework that combines hard constraints and soft constraints for high-resolution short-term and near-term prediction of wind, temperature, density and air pressure within an altitude range of 10 to 70 km. The core innovation lies in a novel network design that enforces symbolic constraints and the equation of state via hard constraints, while incorporating atmospheric dynamics equations through soft constraints, thereby creating a complementary optimization mechanism. Specifically, hard constraints strictly ensure the positivity of key variables (such as air pressure and temperature) by modifying the output structure of the network. Soft constraints are based on the Navier-Stokes equation in spherical coordinate form, introducing the residual terms of momentum conservation and mass conservation into the loss function as physical regularization terms. In addition, this study is the first to verify the model using actual stratospheric balloon flight test data. By comparing the observation results of the SENSORs project in the Qinghai region of China in 2019, the prediction accuracy and stability of the model in real scenarios are evaluated.
The experimental results show that the hybrid constrained PINN framework proposed in this study has achieved remarkable effects in the case of Qinghai region (90°-100°E, 30°-40°N). This method effectively suppresses non-physical oscillations while maintaining the physical consistency of the prediction results, reducing the root mean square error of short-term and near-term forecasts by approximately 28% compared to pure data-driven models. This method demonstrates superior generalization performance and stability in tasks ranging from sparse training data (0.5°×0.5°×2 km) to high-resolution predictions (0.25°×0.25°×1 km). Meanwhile, the collaborative mechanism of hard constraints and soft constraints significantly enhances the physical interpretability of the model, providing a new reliable approach for high-precision and high-efficiency numerical prediction in complex atmospheric environments.
How to cite: Liu, Z. and Yang, J.: A New Hybrid PINN for High-Resolution Spatiotemporal Nowcasting of Stratospheric and Mesospheric States, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17676, https://doi.org/10.5194/egusphere-egu26-17676, 2026.
This study investigates the modulation of the Quasi-Two-Day Wave (Q2DW) by the Quasi-Biennial Oscillation (QBO) in the mesosphere and lower thermosphere during 2012–2019, building on the framework of He and Forbes et al. (2021, Geophysical Research Letters). Meteor radar observations are used to characterize Q2DW variability, and a multivariate phase-based representation of the QBO and seasonal cycle is employed to quantify their joint influence. A statistical coupling analysis is applied to identify dominant modes linking QBO variability to Q2DW activity and to reconstruct the Q2DW field from the derived drivers. The results show that inclusion of the QBO significantly improves the representation of Q2DW variability, demonstrating a clear QBO modulation.
How to cite: He, M.: Seasonal and Quasi-Biennial Oscillation Control of Quasi-Two-Day Wave Variability, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15919, https://doi.org/10.5194/egusphere-egu26-15919, 2026.
This contribution presents a climatology of the atmospheric conditions that was created to support feasibility studies for the Changing Atmosphere Infra-Red Tomography explorer (CAIRT) candidate mission to ESA Earth Explorer 11. This climatology provides the mean and standard deviation of 35 atmospheric parameters (BrONO2, C2H2, C2H6, CCl4, CF4, CFC11, CFC12, CH4, ClO, ClONO2, CO, CO2, H2O, H2SO4, HCFC22, HCN, HDO, HNO3, HO2NO2, N2O, N2O5, NH3, NO, NO2, O, O1D, O2, O3, OCS, PAN, SF6, SO2, temperature, pressure and surface pressure) on a vertical grid between 0 and 200 km with 1 km spacing, five latitude bands (90°S–70°S, 55°S–35°S, 20°S–20°N, 35°N–55°N and 70°N–90°N), four months corresponding to different seasons (January, April, July, and October) and two overpass local times (09:30 and 21:30).
Since no single atmospheric model or dataset provides all relevant trace gases across the required vertical domain, this climatology was created by blending outputs from multiple simulations of different models : WACCM-ACOM, WACCM-AMIP, WACCM-X and BASCOE. For two species (CF4 and HDO), no model simulation has been found and their climatology is based on ACE-FTS observations. This contribution will describe the input models and observations and how they have been merged vertically when necessary. This climatology, named CAIRT ERS (Extended Reference Scenario) can be downloaded here: https://doi.org/10.5281/zenodo.10022129.
How to cite: Errera, Q., Flunger, J., Funke, B., Hoffmann, A., Höpfner, M., Raspollini, P., Ungermann, J., and Sinnhuber, B.-M.: Climatology of middle atmospheric conditions to support studies of future satellite middle atmospheric missions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19902, https://doi.org/10.5194/egusphere-egu26-19902, 2026.
During times of high solar activity an increased amount of solar coronal mass ejections (CME) are observed and initiate geomagnetic storms. These solar wind particles are guided and accelerated by Earth's magnetic field and get redirected towards the polar region, where they precipitate into the atmosphere of Earth. In conjungtion with varying solar activity these SPEs and geomagnetic storms lead to increased ionization and dissociation of gases in the mesosphere and lower thermosphere of Earth. This leads to the photochemical creation of NOx and HOx species which influence the ozone chemistry of Earth's polar regions a short time after the CMEs.
To be able to study these events we use the ICOsahedral Non-hydrostatic model (ICON), a numerical weather and climate model developed by the German Weather Service (DWD), the Max-Planck Institute of Meteorology (MPI-M) and various codevelopers. Specifically we use the upper atmosphere extension (UA-ICON) and an external interactive chemistry model to study specific periods of high solar activity. This is a summary showcasing the different additions that have been made to the model to aid our studies, including an updated photolysis mechanism, fitting of geomagnetic data on the model grid, updated Lyman-α process and photoionization in the extreme UV and Schumann-Runge Continuum.
How to cite: Siebelts, A., Sinnhuber, M., and Kunze, M.: Influence of solar activity on the chemistry of the MLT-region modelled with ICON-ART, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6500, https://doi.org/10.5194/egusphere-egu26-6500, 2026.
The stratospheric polar vortex (SPV) profoundly affects northern hemisphere weather and climate, with its dynamics influenced by terrestrial and solar factors. Despite established terrestrial influences, the quantitative effects of solar energetic particles have not yet been fully understood. This study presents a quantitative analysis of 27 intense solar proton events (SPEs) from 1986 to 2020, revealing a significant correlation between the integrated flux of SPEs and enhanced SPV wind speeds across altitudes. Notably, the wind speed enhancements, ranging from 1.8 m/s (15.1%) at 100 hPa to 3.0 m/s (7.3%) at 1 hPa, demonstrate an altitude‐dependent pattern, with the greatest impacts of 5.8 m/s (19.1%) at 5 hPa. A partial correlation analysis identifies SPEs as the dominant driver of SPV enhancement in the middle and lower stratosphere, while ultraviolet radiation dominates at the stratopause. We propose a mechanism involving the amplification of the meridional temperature gradient due to differential ozone responses, thereby linking solar activity to the modulation of the SPV. These findings enhance our understanding of solar‐terrestrial interactions and their implications for climate modeling.
How to cite: Li, Y., Li, H., Wang, Y., Sun, J., and Wang, C.: Impact of Solar Proton Events on the Stratospheric Polar Vortex in the Northern Hemisphere: A Quantitative Analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5016, https://doi.org/10.5194/egusphere-egu26-5016, 2026.
This study presents an integrated investigation of Gigantic Jets (GJs), encompassing an analysis of parent thunderstorm conditions and a quantitative assessment of their chemical impact on the middle atmosphere via a novel modelling approach. We focus on a remarkable sequence of five GJs observed within 7 minutes from an isolated thunderstorm over South China on 18 August 2022. Analysis reveals the event was associated with a high-altitude -10 ℃ isotherm, substantial convective available potential energy (~2158 J/kg), pronounced upper-level wind shear (~14.5 m/s), and dominant intracloud lightning activity preceded by narrow bipolar events.
To quantify the chemical perturbations, we developed the first one-dimensional plasma-chemical model that couples time-dependent electron kinetics with a comprehensive atmospheric reaction scheme. Simulations indicate that GJ discharges induce transient yet significant perturbations, most notably ozone depletion and nitrogen oxide (NOx) enhancement within the 40–50 km altitude range, driven by electron-impact ionization and subsequent ion-molecule chemistry. The model also captures the characteristic blue-to-red spectral transition in optical emissions, linking it to the excitation dynamics of N2 states.
Addressing computational efficiency and parametric uncertainty in traditional models, this research innovatively integrates a Physics-Informed Neural Network (PINN) into the framework. The PINN, constrained by the underlying physicochemical equations, learns the mapping from background atmospheric parameters and electric fields to species concentrations. This hybrid approach enables rapid, physically consistent predictions of chemical perturbations and provides a robust tool for sensitivity analysis, highlighting the altitude-dependent sensitivity of key reaction pathways.
By synthesizing multi-platform observations, detailed plasma-chemical modelling, and advanced machine learning techniques, this work provides a comprehensive understanding of GJs, establishing a powerful and scalable framework for assessing the role of transient luminous events in middle atmospheric chemistry.
How to cite: Zhao, Y., Lu, G., Huang, H., Huang, X., Meng, Z., and Guo, M.: Bridging Observations, Chemistry, and AI: A Comprehensive Study of Gigantic Jets from Parent Thunderstorms to Mesospheric Chemical Impact, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4904, https://doi.org/10.5194/egusphere-egu26-4904, 2026.
Following the increase of greenhouse gas emissions, atmospheric models predict a strengthening of the middle atmospheric Brewer-Dobson circulation (BDC). Changes in the BDC, inferred from age of air (AoA) trends, can influence UTLS exchange processes, including stratosphere–troposphere transport of ozone. While models predict an acceleration of the BDC (i.e. a decrease of AoA), in-situ balloon observations suggest the opposite, although not significantly, given the limited number of observations and the substantial uncertainties (Garny et al., 2024a). Additionally, meteorological reanalyses disagree on the sign and magnitude of AoA trends, despite providing an optimized estimate of atmospheric circulation constrained by observations.
The Changing Atmosphere Infrared Tomography explorer (CAIRT) was proposed for ESA’s Earth Explorer 11 to address these inconsistencies. CAIRT was foreseen to achieve a precision of 0.5 years on the age of air, a requirement to assess long-term trends.
This contribution aims to evaluate the capability of CAIRT to achieve this precision. Synthetic CAIRT profiles of six long-lived species (SF6, CH4, N2O, CFC11, CFC12 and HCFC22) are simulated by the Belgian Assimilation System for Chemical ObsErvations (BASCOE) chemistry transport model, considering CAIRT’s expected measurement errors and spatial resolution. CAIRT AoA observations, derived from the six long-lived species using the method of Voet et al. (2025), are compared to clock tracer AoA, simulated by the BASCOE model, to evaluate the agreement. The analysis is repeated three times by driving the model with the meteorological reanalyses MERRA2, ERA5, and JRA-3Q, respectively, to check if CAIRT precision would be sufficient to evaluate meteorological reanalyses.
How to cite: Vervalcke, S., Errera, Q., Voet, F., Höpfner, M., Funke, B., Sinnhuber, B.-M., Hoffmann, A., Preusse, P., Bender, S., and Ungermann, J.: Evaluating the precision of age of air derived from trace gas satellite observations , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16872, https://doi.org/10.5194/egusphere-egu26-16872, 2026.
The important role of the magnitude, direction, and shear of the neutral wind in the formation and localization of sporadic ionospheric E(Es) layers, recently noted by the authors (Dalakishvili et al., JASTP, 2020; Didebulidze et al., Atmosphere, 2020; 2023; 2025; JASTP, 2025), allowed us to better understand the observed relationship between this phenomenon and the nightglow intensity of the oxygen green 557.7 nm line.
The predominantly descending tendency of the Es layers at mid-latitudes and their localization at it more observable height region (around 95-105km) of the lower thermosphere are close to the peak height (around 95km) of the volume emission rate (VER) of the 557.7nm line.
In these cases, the Es layers can be formed by neutral wind velocity with a northerly, westerly, or descending component. Such a neutral wind, can be tidal in origin or/and originate from atmospheric gravity waves (AGWs), which can also cause an increase in the green line intensity, due to increased oxygen reach downstream flux to the height of the green line luminous layer.
Using the Barth two-step mechanism of O(1S) excitation and estimating corresponding VER of the 557.7nm line and its integral intensity, the downward flux of neutrals caused by the tidal wind, and the approximate speed of neutral wind, the possibility of formation of Es layers and their localization at an altitude close to the luminous layer is shown.
The emphasizes will be on the formation of Es layers during tectonic events by the influence of AGWs, which sometimes are characterized by an increase in the 557.7nm line intensity. In this case, AGWs can form Es layers and also influence the downward flux of neutral particles as they dissipate above the green line emission layer.
Acknowledgements. This study is supported by the Shota Rustaveli National Science Foundation of Georgia Grant no. FR-21-22825.
How to cite: Didebulidze, G. G., Dalakishvili, G., and Todua, M.: Relationship between formation and localization of the ionospheric sporadic E(Es) layers and the oxygen green 557.7nm line nightglow intensity , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17219, https://doi.org/10.5194/egusphere-egu26-17219, 2026.
The ICON and GOLD missions provide a unique opportunity to investigate equatorial ionospheric dynamics and their role in the formation and evolution of equatorial plasma bubbles (EPBs). In this study, we examine the seasonal and solar cycle dependences of different EPB types, focusing on their spatial distributions and the underlying mechanisms responsible for their variations. We aim to address two key science questions: (1) What are the statistical characteristics of different EPB types across seasons and solar activity levels, and what are the corresponding background equatorial ionospheric conditions?(2) What primary factors drive the observed seasonal and solar cycle dependencies of these EPB types? EPB types are classified based on the spatial structures observed by GOLD, while the associated background ionosphere–thermosphere state is primarily inferred from ICON measurements, supplemented by ground-based observations where available. This study aims to provide critical insights that will help identify the root causes of EPB formation and contribute to the development of predictive strategies based on specific spatial characteristics.
How to cite: Zhan, W., Chen, Y., and He, M.: Investigation of spatial distribution of equatorial plasma bubbles and the potential causing factors, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15777, https://doi.org/10.5194/egusphere-egu26-15777, 2026.
Atomic oxygen is a critical species in the mesosphere and lower thermosphere, governing the chemistry, airglow, and energy budget (taking part in exothermic chemical processes and microwave cooling processes). It participates in chemical reactions in that region. Hence, it is involved in the coupling between dynamics, chemistry and energetics. However, to date no satellite mission has measured atomic oxygen directly. It and related photochemically active species (atomic hydrogen, hydroxyl and hydroperoxyl) are deduced through indirect methods from airglow observations. Such techniques are based on the assumption of ozone photochemical equilibrium. In time of Sudden Stratospheric Warmings (SSWs) strong dynamical perturbations of the mesopause chemical system occur. With 3D modelling we find that ozone strongly deviates from photochemical equilibrium in the mesopause region during SSW events and nighttime conditions. The lower boundary of ozone equilibrium jumps up to a height of 90 km, implying that traditional techniques for retrieving atomic oxygen, atomic hydrogen, and chemical heat from airglow observations cannot be applied at times of SSWs below 90 km under nighttime conditions. We discuss and explain our results in terms of characteristic times. Additionally, to better understand the behavior of exothermic chemical heat, we calculate odd-hydrogens photochemical equilibria and characteristic times, which are involved into exothermic chemical reactions.
How to cite: Naranjo Villalón, K., Stephan, C., Ward, W., and Grygalashvyly, M.: Chemical equilibria and characteristic times in the mesopause region during SSW events., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-227, https://doi.org/10.5194/egusphere-egu26-227, 2026.
The hydroxyl radical is a key player in the chemistry and energy balance of the middle terrestrial atmosphere and numerous studies have investigated the relevant photochemical processes. Nevertheless, several gaps exist in the understanding of its photochemistry, including the details of its production by the H + O3 reaction. A detailed understanding of the sources for mesospheric OH is necessary for the interpretation of the prominent OH Meinel band emissions. This knowledge is also a prerequisite for estimates of the heating efficiency of the highly exothermic H + O3 reaction, a key factor included in photochemical models of the upper atmosphere.
We will report on our laboratory measurements to investigate the production pathways and yields of highly vibrationally excited hydroxyl radical, OH(v), produced from H + O3. This knowledge is critical for a reliable analysis and interpretation of data from ground- and space-based observations of the nightglow OH Meinel band emission.
Research supported by NASA Heliophysics (LNAPP) under Grant 80NSSC23K0694.
How to cite: Kalogerakis, K. S. and Robertson, R. M.: Laboratory Studies of OH(v) Production from the H + O3 Reaction, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15357, https://doi.org/10.5194/egusphere-egu26-15357, 2026.
The sodium (Na) layer is a valuable tracer for mesosphere and lower thermosphere (MLT) dynamics. Integrating the observations from the instrument Optical Spectrograph and InfraRed Imaging System (OSIRIS) on the Odin satellite with simulation from the Specified Dynamics Whole Atmosphere Community Climate Model (SD-WACCM), we quantify high-latitude Na transport within a transformed Eulerian-mean framework. The mean residual circulation drives a seasonally reversing transport poleward of 60°: winter downdrafts deplete Na, while summer upwelling enhances it. This transport is modulated by gravity wave–driven mixing and molecular diffusion, with rapid chemistry limiting Na residence time. These coupled processes collectively regulate the Na layer's column abundance, peak density, and vertical extent, explaining observed hemispheric asymmetries and establishing Na as a sensitive diagnostic for MLT circulation-chemistry coupling.
How to cite: Wu, J.: Transport of the High-Latitude Sodium Layer in the Mesosphere and Lower Thermosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8673, https://doi.org/10.5194/egusphere-egu26-8673, 2026.
This study investigates the response of the mesospheric and lower thermospheric (MLT) sodium (Na) layer to the 2002 Southern Hemisphere sudden stratospheric warming (SSW) event using model simulations. Simulations from the Whole Atmosphere Community Climate Model (WACCM) metal layer dataset reveal a marked decrease in sodium number density occurring during the SSW. The latitudinal evolution of sodium number density displays a distinct northward propagation toward near-equatorial regions. Furthermore, ground-based sodium lidar observations at 23°S in Brazil record a significant reduction in sodium number density approximately 10 days following the SSW onset. Planetary wave components derived from WACCM simulations of Na density and temperature are closely associated with the observed modulation in the Na layer. These findings indicate that SSWs can induce cross-hemispheric responses in the sodium layer, likely mediated by enhanced planetary wave activity.
How to cite: Li, S., Ye, H., Wu, J., and Xue, X.: Sodium Layer Responses to the Sudden Stratospheric Warming, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17434, https://doi.org/10.5194/egusphere-egu26-17434, 2026.
Kelvin-Helmholtz (KH) instability driven by neutral wind shear is an important mechanism for the generation of sporadic-E (Es) layer irregularities. However, direct observational evidence describing the morphological evolution of these instabilities across different height regimes in the mesosphere and lower thermosphere (MLT) region, from collision-dominated to magnetized, remains rare. Here we present high-resolution lidar observations of the Ca⁺ layer at Beijing (40.5°N, 116.0°E), revealing structural morphology at different heights. In the lower E region (~110 km), we identify a cat's eye characteristic of KH turbulence, indicating that ions are effectively dragged by neutral motion due to high ion-neutral collision frequency. In addition to the cat's-eye features, the Ca⁺ ion layer also exhibits quasi-sinusoidal structures and streak-like features, demonstrating a pronounced periodicity. In contrast, at higher altitudes (>120 km) extending to 180 km, these layers evolve into isolated patches and streaks. Using numerical simulations with a coupled neutral ion fluid model, we successfully reproduce these height-dependent features. The model shows that although neutral wind waves at ~110 km altitude induce quasi sinusoidal modulation, the dominant role of the Lorentz force at high altitudes (~180 km) constrains ion motion along magnetic field lines, causing plasma to aggregate into dense clumps rather than overturning waves. These results provide observational verification of neutral turbulence modulating ionospheric plasma.
How to cite: Guo, J., Yu, T., Du, L., Hao, W., Wang, J., Yan, X., Yu, Y., Qi, Y., Zheng, H., and Yang, G.: Evolutionary Structures of Kelvin–Helmholtz Instability in the Ionosphere Ca⁺ Layer Observed by Lidar, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6323, https://doi.org/10.5194/egusphere-egu26-6323, 2026.
Posters virtual: Mon, 4 May, 14:00–18:00 | vPoster spot 4
EGU26-2435 | ECS | Posters virtual | VPS27
Influence of diurnal tide on the low-latitude UMLT mean zonal wind: Evidence from momentum flux estimation using ICON-MIGHTI windsMon, 04 May, 14:45–14:48 (CEST) vPoster spot 4
The influence of dissipating solar diurnal tides in driving the mean zonal wind in the upper mesosphere and lower thermosphere (UMLT) is investigated using the zonal and meridional winds observed by the Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI) instrument onboard the Ionospheric Connection Explorer (ICON) satellite over the region of interest having a latitudinal and longitudinal extent of 5° N - 15°N and 67.5°E - 90°E, respectively, for the years 2020, 2021 and 2022. The mean zonal wind exhibits consistent seasonal variation with large westward winds at 91-103 km during January-March and September-December, however with varying intensity (20-40 m/s) in all the three years. The diurnal tidal amplitude in meridional wind (DTV) also displays similar seasonal variation with maximum amplitudes reaching ~80–100 m/s. The seasonal variation of westward acceleration due to diurnal tide momentum deposition is found to be maximum during January-March (18-43 m/s/day) and September-December (40-55 m/s/day) and reveals similar seasonal variation and intensity of the mean westward winds. This clearly indicates that the potential role of diurnal tide in driving the mean zonal flow. The westward acceleration induced by the vertical gradient of meridional flux of zonal momentum (Fmeridional) due to diurnal tide exceeds the convergence of vertical flux of zonal momentum (Fzonal) due to diurnal tide during January-March, while the westward acceleration induced by both Fzonal and Fmeridional are larger and comparable during September-December.
How to cite: Basu, S. and Sundararajan, Dr. S.: Influence of diurnal tide on the low-latitude UMLT mean zonal wind: Evidence from momentum flux estimation using ICON-MIGHTI winds, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2435, https://doi.org/10.5194/egusphere-egu26-2435, 2026.
EGU26-2620 | Posters virtual | VPS27
Tracing low-latitude thermospheric gravity waves in a whole-atmosphere simulation to their sourcesMon, 04 May, 14:48–14:51 (CEST) vPoster spot 4
We performed a one-year long simulation using the upper-atmosphere configuration of the Icosahedral Nonhydrostatic model (UA-ICON). The simulation has a horizontal resolution of 20 km and 180 vertical levels between the ground and 150 km. At 110 km height and every hour we extracted the gravity wave vectors and amplitudes with the small-volume few-wave decomposition method S3D, which is part of the software package JUWAVE. We focus on low-latitudes, i.e. +/- 40 degrees. The model simulates clear signatures of gravity wave activity above convective hotspots over summer continents. Ray tracing shows that the largest perturbations in the thermosphere are likely primary waves from developing convection. These signatures are most prominent in waves with short horizontal scales and long vertical wavelengths. In turn, horizontally short waves with smaller vertical wavelengths cannot be traced down to the lower stratosphere. For horizontally long waves, we find a clear diurnal/longitudinal pattern in the gravity wave activity, which results from interactions with tides. The study has broad implications of how whole-atmosphere high-resolution models may help forecast thermospheric density and ionospheric perturbations, both from the numerical weather prediction perspective, as well as empirically based on known patterns of lower-atmospheric variability.
How to cite: Stephan, C.: Tracing low-latitude thermospheric gravity waves in a whole-atmosphere simulation to their sources, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2620, https://doi.org/10.5194/egusphere-egu26-2620, 2026.
