Realistic modeling of the dynamics and variability in the mesosphere and lower thermosphere (MLT) is significant to understand the coupling of the whole atmosphere system. Here we present the simulations of the MLT temperatures at ~100 km altitude for one year during 2014 by Whole Atmosphere Community Climate Model with thermosphere-ionosphere extension (WACCM-X) constrained below ~90 km using meteorological analysis products of the high-altitude version of Navy Global Environmental Model (NAVGEM-HA). The model results are sampled at the same times and locations as the satellite observations from Thermosphere Ionosphere and Mesosphere Electric Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER). Comparisons of the daily mean temperatures show that the observed and modeled values are correlated (correlation coefficient equals to ~0.5-0.7) at latitudes away from the equator. Both the observations and simulations reveal an annual variation at mid-latitudes with the temperature maximum in summer and minimum in winter, and at lower latitudes the semiannual variation becomes stronger having the temperature maximums at equinoxes and minimums during solstices. However, the temperatures observed are on average ~5-10 K (3-5%) smaller than the model and the observations show a larger variability across all latitudes between 50^oS-50^oN. The WACCM-X simulations with constrains by NAVGEM-HA meteorological analyses are overall consistent with the SABER observations though some differences are noticed. Whole atmosphere models with high altitude observation constrains would be useful to improve the numerical simulations of the MLT variability and the atmosphere and ionosphere coupling.

How to cite: Liu, G., Klenzing, J., McDonald, S., Sassi, F., and Rowland, D.: WACCM-X simulations with NAVGEM-HA meteorological analyses and SABER observations of mesosphere and lower thermosphere temperature , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2912, https://doi.org/10.5194/egusphere-egu24-2912, 2024.

Future space missions dedicated to measuring CO₂ on a global scale can make advantageous use of the O₂ band at 1.27 µm to retrieve the air column. The 1.27 µm band is close to the CO₂ absorption bands at 1.6 and 2.0 µm, which allows a better transfer of the aerosol properties than with the usual O₂ band at 0.76 µm. However, the 1.27 µm band is polluted by the spontaneous dayglow of the excited state O₂(¹Δ), which must be removed from the observed signal.

We investigate here our quantitative understanding of the O₂(¹Δ) dayglow with a chemistry-transport model. We show that the previously reported -13% deficit in O₂(¹∆) dayglow calculated with the same model is essentially due a -20 to -30% ozone deficit between 45-60 km. We find that this ozone deficit is due to excessively high temperatures (+15 K) of the meteorological analyses used to drive the model in the mesosphere.

The use of lower analyzed temperatures (ERA5), in better agreement with the observations, slows down the hydrogen-catalyzed and Chapman ozone loss cycles. This effect leads to an almost total elimination of the ozone and O₂(¹Δ) deficits in the lower mesosphere. Once integrated vertically to simulate a nadir measurement, the deficit in modeled O₂(¹Δ) brightness is reduced to -4±3%. This illustrates the need for accurate mesospheric temperatures for a priori estimations of the O₂(¹Δ) brightness in algorithms using the 1.27 µm band.

How to cite: Diouf, M., Lefevre, F., Hauchecorne, A., and Bertaux, J.:  Three-dimensional modeling of the O2(1Δ) dayglow  and implications for ozone in the middle atmosphere., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1897, https://doi.org/10.5194/egusphere-egu24-1897, 2024.

Geomagnetic storms lead to significant depletion/enhancement in O/N2 column density and enhancement in nitric oxide (NO) in the thermosphere.  The O/N2 depletion is generally anti-correlated with NO enhancement on a global scale. However, the NO enhancement often extends beyond the equatorward edge of O/N2 depletion in latitude and/or the range of O/N2 depletion in longitude on a local scale. These behaviors are most likely driven by the storm-time equatorward wind that brings the O/N2 depleted and NO enhanced air from high to low latitudes, as well as zonal wind perturbations. On the other hand, the equatorward wind also depends on altitudes. Note that the peak NO density locates at an altitude around 110 km while the O/N2 column density is mostly contributed by local O andN2 density around 140 km and above. The different behaviors between NO and O/N2 are likely due to the altitude variations of the meridional winds during storms as revealed by TIEGCM simulations. The downward advection by vertical winds associated with storm-time meridional circulation perturbations may also contribute to the difference.

How to cite: Zhang, Y., Wang, W., and Paxton, L.: Drivers for different behaviors in storm-time thermospheric O/N2 ratio and nitric oxide density, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3615, https://doi.org/10.5194/egusphere-egu24-3615, 2024.

Throughout the winter, extreme circumpolar wind patterns are found in the altitude range of 30 to 70 km, reaching wind speeds up to 500 km/h. The circumpolar wind patterns form the Stratospheric Polar Vortex. In the Northern Hemisphere, weather extremes are known to be linked to distortions of the Polar Vortex. Recently, studies using observations and modelling have indicated that the extreme winds at the Polar Vortex Edge also play a crucial role in multistep upward coupling through gravity waves. Variations in the wind profiles affect gravity wave propagation and lead to wave generation and breakdown. Direct measurements of the mean winds and waves at the Polar Vortex Edge are rare and technically challenging. We use lidar and radar instruments to measure temperature, wind, and the occurrence of layered phenomena over northern Norway (ALOMAR, 69°N) and northern Germany (Kühlungsborn, 54°N). Using more than 10 years of measurements, we have collected a unique dataset, which contains measurements both inside and outside the Polar Vortex.

These observations are used to explore upward- and downward-propagating gravity waves in the complex dynamical setting near the Polar Vortex Edge. These unique wave-vortex interactions play a role in coupling layers above and below, and link large-scale flow to turbulence, frequently observed as layered phenomena, such as Polar Mesosphere Winter Echoes. The link between waves, turbulence, and the polar vortex will be discussed using observations and model data.

How to cite: Baumgarten, G., Franco-Diaz, E., Fiedler, J., Gerding, M., Latteck, R., Mossad, M., Renkwitz, T., Strelnikova, I., Strelnikov, B., and Wing, R.: Gravity Waves and Turbulence indicating multistep vertical coupling near the Polar Vortex Edge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16986, https://doi.org/10.5194/egusphere-egu24-16986, 2024.

State-of-the-art global chemistry-climate models such as WACCM cannot practically resolve the small-scale gravity waves (GWs) that are important in the mesosphere and lower thermosphere (MLT, ≈ 70-120km). A solution is the use of parametrizations that represent subgrid dissipating GWs (see e.g. Garcia et al., 2007). To reproduce key MLT features such as mesospheric jet reversals, pole-to-pole circulation and the summer mesopause, models rely on such schemes (McLandress, 1997; Holton & Alexander, 2000), though more development is needed. For example, WACCM tends to underestimate observed mesospheric densities of O, O₃ and NO, and overestimate observed densities of the Na and Fe layers produced from cosmic dust ablation. Increasing evidence suggests a reason for this is a missing vertical transport from subgrid propagating GWs, and a solution has recently been achieved when these effects were included in the WACCM GW scheme (Guarino et al., 2023). In the current work, we resolve subgrid waves natively using WACCM with Regional Refinement (WACCM-RR). WACCM-RR provides the unprecedented opportunity to model the global climate up to altitudes of 140 km, and resolve individual regions down to as far as 1/32° at a low computational cost compared to global high resolution models. Trends from a model using a 1/8° grid over the Continental US  (1° elsewhere), when compared to a global 1° model, are consistent with comparisons of standard WACCM models, to models using our updated GW scheme. For example, mesospheric densities of O, O₃ and CO₂ are increased, as predicted. A surprising contrast is a globally warmer atmosphere, likely due to sensitivity of the meridional circulation to GW activity in the refined region. The results point to the applicability of WACCM-RR for detailed investigations of wave-transport processes, and their impact on MLT dynamics and composition. We point out remaining questions and challenges.

How to cite: Kupilas, M., Gardner, C., Feng, W., Guarino, M. V., Marsh, D., and Plane, J.: Small-scale waves, big implications: a regionally refined perspective with the Whole Atmosphere Community Climate Model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9230, https://doi.org/10.5194/egusphere-egu24-9230, 2024.

Sudden stratospheric warmings (SSWs) are characterised by the rise of polar stratospheric temperatures by several tens of kelvins. Here, we investigate the SSW of 2009 using the ECHAM/MESSy (EMAC) chemistry climate model. We study in particular how the SSWs are affected by variable solar forcing: EUV photo-ionisation that dominates the changes during high solar activity and geomagnetic storms. The warmings are preceded by a slowing then reversal of the westerly winds in the stratospheric polar vortex which then becomes easterly and it is also closely associated to polar vortex breakdown. 20 ensemble members are considered and different onset dates of the free running ensembles for the SSW event in January are tested to see the development of the polar vortex and its breakdown in the different ensemble members. Ionisation rates from the AISSTORM model are used in this case. And the results are compared with a geomagnetic storm (consisting of mostly electrons that are in the range of a few kilo-electron volts (keVs) to about 1 MeV) included on the day of the SSW, i.e., 25^th of January. For the experiments considered here, the EUV photoionization was doubled and halved, and in both cases an increase in stratospheric temperature compared to the normal EUV was observed. Overall, effects of both EUV photoionization and particles on the temperature, wind fields, NOy and ozone in the middle atmosphere was observed. As ozone is one of the key species in radiative heating and cooling of the stratosphere, changes in its concentration can be linked to dynamical changes in the middle atmosphere.

How to cite: Borthakur, M. and Sinnhuber, M.: Quantifying the impact of variable solar forcing on Sudden Stratospheric Warmings (SSWs), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2910, https://doi.org/10.5194/egusphere-egu24-2910, 2024.

Satellite mega-constellations are one of the main reasons for the current exponential growth of space flight. The increasingly large number of objects in orbit has already raised much concern about space debris and requires mitigation strategies. The common strategy for low Earth orbit (LEO) objects is to ensure their re-entry into Earth’s atmosphere, where they ablate and burn up, injecting material into the mesosphere and lower thermosphere. We discuss the significance of this anthropogenic injection compared to the natural one originating from meteoric sources, which provide a constant flow of cosmic dust and larger meteoroids into Earth’s atmosphere. Our comparison indicates that already in 2019 the anthropogenic mass injection has been significant (2.8%) compared to the natural injection. This number will rise in the future due to the ongoing implementation of satellite mega-constellations. More than 5,000 constellation satellites are in orbit right now with more than 100,000 proposed. Considering a worst-case scenario, the injection of metals could increase up to 90% and the aerosol injection up to 94% compared to the natural injection. As the material is mainly injected into mesosphere heights, possible influences on mesospheric and even stratospheric chemistry, with effects on the ozone layer, cloud formation or the climate are thinkable. Recent, first observations already confirmed the existence of spacecraft ablation remnants in stratospheric aerosol particles. This  emphasizes our theoretically conjectured significance of anthropogenic dust injection . However, further studies, including observations and modeling, are urgently required to further elucidate any atmospheric effects. Precautions need to be discussed now in order to protect our atmosphere from yet another human-made influence, that is space waste.

How to cite: Glassmeier, K.-H. and Schulz, L.: Satellite mega-constellations and spacecraft re-entry: Are we harming Earth’s atmosphere?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3860, https://doi.org/10.5194/egusphere-egu24-3860, 2024.

How to cite: Hindley, N., Hoffmann, L., Moffat-Griffin, T., Noble, P., and Wright, C.: Long-term changes in gravity wave activity in the middle atmosphere from satellite and ground-based observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21520, https://doi.org/10.5194/egusphere-egu24-21520, 2024.

The chemical composition of Earth's lower thermosphere around an altitude of 180 km remains a largely uncharted territory. This altitude marks a critical transition region, where the atmosphere shifts from being dense and collision-dominated to a regime of free molecular flow. In this region, the altitude profiles of the present chemical species demonstrate their steepest gradients, a phenomenon crucial for understanding the dynamic interplay between the lower thermosphere and the mesosphere. Despite its importance, this region remains poorly explored due to limited in situ observations. Our focus is on the deployment of a highly miniaturized mass spectrometer, specifically designed for a CubeSat platform where it will be accommodated within 1U. This advanced instrumentation is designed to measure in situ all species present in this part of the atmosphere. Thanks to its novel ion source design, it is capable of measuring atoms, molecules, radicals, and isotopes, with exceptional sensitivity, dynamic range, mass range, and mass resolution even at the hyper-velocities of spacecraft during these measurements. The core of our discussion revolves around the expected data quality and performance capabilities of this mass spectrometer, particularly its operation at the perigee in the lower thermosphere. The data obtained from this innovative approach are expected to shed light on the complex dynamics at play in this scarcely studied region. We anticipate that these findings will significantly contribute to the scientific community’s understanding of the lower thermosphere, its coupling with the mesosphere, and the exosphere, filling a crucial gap in our current knowledge and potentially paving the way for future research in both atmospheric science and comparative planetology.

How to cite: Fausch, R. and Wurz, P.: Towards in situ measurements of the chemical composition of Earth’s lower thermosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8857, https://doi.org/10.5194/egusphere-egu24-8857, 2024.

The Changing-Atmosphere Infra-Red Tomography Explorer (CAIRT) is currently in Phase A as one of two final candidates for ESA’s Earth Explorer 11. As a Fourier transform infrared limb imager, CAIRT will observe simultaneously from the middle troposphere to the lower thermosphere at high spectral resolution and with unprecedented horizontal and vertical resolution. With this, CAIRT will provide critical information on (a) atmospheric gravity waves, circulation and mixing, (b) coupling with the upper atmosphere, solar variability and space weather and, (c) aerosols and pollutants in the upper troposphere and  lower stratosphere. In this presentation we will give an overview of CAIRT’s science goals and the expected mission performance, based on latest results from feasibility studies performed during Phase 0. 

How to cite: Funke, B., Chipperfield, M., Errera, Q., Friedl-Vallon, F., Godin-Beekmann, S., Hoepfner, M., Hoffmann, A., Malavart, A., Osprey, S., Polichtchouk, I., Preusse, P., Raspollini, P., Sinnhuber, B.-M., Verronen, P., and Walker, K.: The Changing-Atmosphere Infra-Red Tomography Explorer (CAIRT) Earth Explorer 11 candidate mission, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20214, https://doi.org/10.5194/egusphere-egu24-20214, 2024.

The dynamics in the atmosphere, especially the upper mesosphere and mesopause are significantly driven by atmospheric gravity waves. OH airglow offers an unique possibility to observe atmospheric dynamics in this altitude region with a high spatio-temporal resolution simultaneously using imager and spectrometer systems. Especially, characteristics of gravity waves as well as features like wave breaking and wave-wave interaction can be observed. Spectroscopic observations allow observing rotational temperature changes. Thus, both instrument types complement each other very well.

Since November 2022 two airglow imagers (FAIM) and one airglow spectrometer (GRIPS) with high temporal resolution (1 image every 2 seconds, 1 spectrum every 15 seconds) started routine observations during each night in cooperation with and at ESO’s Very Large Telescope (VLT) in the Atacama Desert at Cerro Paranal, Chile (24.6°S, 70.4°W).

During the night from 31^st July to 1^st August 2023 we observed an exceptional bright night that is much brighter than any other we observed so far: a single wave front propagates from West to East with an observed phase speed of about 60m/s. After the passing of the wave front the OH intensity decreases by around 50% within only one hour. Pronounced wave activity of small-scale waves is observed especially before the passing of the event. Similar events in literature are often stated as “wall events”, but seem to occur very rarely in the extent observed.

We present and interpret the wall event and discuss the observed phenomenon and its causes using data from multiple instruments and data sources.

How to cite: Hannawald, P., Schmidt, C., Wüst, S., Smette, A., and Bittner, M.: Exceptional bright OH airglow night at Cerro Paranal, Chile, with high wave activity and sudden brightness depletion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15169, https://doi.org/10.5194/egusphere-egu24-15169, 2024.

For more than 60 years, field strength measurements of the broadcasting station, Allouis (Central France), have been received at Kühlungsborn (54° N, 12° E), Mecklenburg, Northern Germany. Beginning with the year 1959 these so-called indirect phase-height measurements of low frequency radio waves (with a frequency of about 162 kHz) are used to examine trends and the long-term oscillations over Western Europe. The advantages of this method are the low costs and the simplicity of operation. Results of the updated fifth release (R5, 1959-2019) of standard-phase heights (SPH) are presented.

The statistical analysis of the SPH series shows a significant overall trend with a decrease of 116 m per decade indicating a subsidence of the long-radio wave reflection height of about 700 m during R5. As expected the daily time series of SPH shows in its spectrum dominant modes which are typical for the solar cycle, ENSO and for QBO bands, indicating solar and lower atmospheric influences. Solar cycle and ENSO (-QBO)-like band-pass show a growing increase of SPH up to 1987, followed by a decrease afterwards.

For summer months during solar minimum years, without solar influences and without stratopause altitude trend, a thickness temperature trend of the mesosphere is significant with a trend value of -0.47 ± 0.43 K/ decade. The overall cooling of the intrinsic mesospheric temperature during 60 years of observation is in the order of 3 K. 

How to cite: Peters, D. H. W. and Mani, S.: More than 60 years of measurements of Standard-Phase-Heights over Western Europe – Trends and long-term oscillations of the mesosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5620, https://doi.org/10.5194/egusphere-egu24-5620, 2024.

Atomic oxygen is one of the main species in the mesosphere and lower thermosphere (MLT) of the Earth’s atmosphere. Thus, atomic oxygen and the local temperature plays an important role for the energy balance in the MLT region. By remote sensing of the emission from the atomic oxygen fine-structure transitions at 2.06 THz and the 4.74 THz, atomic oxygen concentration profiles and neutral temperature profiles of the atmosphere can be derived.  By resolving the line profile, heterodyne spectroscopy enables access to layers of the atmosphere for which the oxygen line is saturated. The first spectrally resolved measurements of the 4.74-THz line of atomic oxygen in the atmosphere were performed with the heterodyne spectrometer GREAT on board of the airborne astronomic observatory SOFIA [1]. Based on the experiences from GREAT, the heterodyne spectrometer OSAS-B was developed as a balloon-borne instrument dedicated to the measurement of atomic oxygen in Earth’s atmosphere [2].

In this study, we investigate the feasibility of a satellite-borne heterodyne spectrometer for the retrieval of atomic oxygen concentration and temperature in the MLT. Compared to airborne observations, a satellite instrument has the advantage of a limb observation geometry which facilitates the retrieval. A satellite instrument also has the advantage of a fast and almost global coverage.

For investigating the feasibility of such an instrument, we use the vertical density and temperature profiles provided by the NRLMSIS 2.0 atmosphere model to simulate 2.06 THz and 4.74 THz emission spectra as measured by a satellite. We then apply retrieval algorithms for the atomic oxygen concentration and temperature and compare the retrieved profiles to the reference, i.e. the original NRLMSIS 2.0 profiles. We consider the scenario of a satellite in a circular orbit at an altitude of 500 km and an inclination of 8°. The emission spectra are simulated using radiative transfer under the assumption of local thermodynamic equilibrium.

By considering two separate heterodyne receivers with sensitivity of 11,000 K and 25,000 K noise temperature for the 2.06 THz and 4.74 THz lines, respectively, and data accumulated over 100 seconds of measurement time, corresponding to a ground track of 700 km, we can retrieve a vertical temperature profile from 100 km altitude to 300 km altitude with 5 % relative uncertainties and an atomic oxygen concentration profile from 120 km to 300 km with 5 % relative uncertainties. From 100 km to 120 km the uncertainty in the atomic oxygen concentration is higher and within 25 %.

[1] Richter, H. et al. Commun Earth Environ 2,19 (2021), doi: 10.1038/s43247-020-00084-5

[2] Wienold, M. et al. 48th IRMMW-THz, Montreal, Canada (2023), doi: 10.1109/IRMMW-THz57677.2023.10299165

How to cite: Hansen, P. B., Wienold, M., and Hübers, H.-W.: Feasibility study of a satellite-borne terahertz heterodyne spectrometer for the retrieval of atomic oxygen and temperature in the Earth's atmosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15735, https://doi.org/10.5194/egusphere-egu24-15735, 2024.

Polar winter descent of reactive nitrogen (NOy) produced by energetic particle precipitation (EPP) in the mesosphere and lower thermosphere affects polar stratospheric ozone by catalytic reactions. This, in turn, may have implications for regional climate via radiative and dynamical feedbacks. NOy observations taken by the MIPAS/Envisat instrument during 2002--2012 have provided observational constraints on the solar-activity modulated variability of stratospheric EPP-NOy amounts. These constraints have allowed to formulate a chemical upper boundary condition for climate models in the context of solar forcing recommendations for CMIP6. Recently, a reprocessed MIPAS version 8 dataset has been released. Compared to the previous version, we assess what impact the changes in this new data version have on the EPP-NOy quantification, and on the formulation of chemical upper boundary conditions for climate models.

The Earth Explorer 11 candidate “Changing Atmosphere Infra-Red Tomography” (CAIRT) will observe the altitude region from about 5 km to 115 km with an across-track resolution of 30 to 50 km within a 500 km wide field of view. This instrument will provide NOy and dynamical tracer observations from the upper troposphere to the lower thermosphere with unprecedented spatial resolution. Given that neither MIPAS nor any of the current instruments observes the lower thermosphere at this spatial resolution, we will assess the potential of this mission to advance our understanding of the EPP-climate link 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., and Ungermann, J.: EPP-climate link by reactive nitrogen polar winter descent revisited: MIPAS v8 reprocessing and future benefits by the EE11 candidate mission CAIRT, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10171, https://doi.org/10.5194/egusphere-egu24-10171, 2024.

This work analyzed the intraseasonal variability of non-migrating tides DE3 and gravity wave momentum fluxes (GWMF) in the mesosphere and lower thermosphere (MLT) region and discussed the possible connection with the tropospheric MJO. Based on the joint observations of the TIMED-TIDI satellite and the 120°E meridian meteor radar chain, we revealed a significant broad-band intra-seasonal signal in the DE3 amplitude around the equator with a clear seasonal dependence. The intraseasonal variability of DE3 in zonal winds (DE3-U) has a strong amplitude in boreal winter, up to 1-2 times the seasonal average, while the variability is usually within 20% during other seasons. The response of MLT DE3 tides to the MJO in different seasons was further discussed together with the MJO activity index. The results suggested that the DE3-U in boreal winter generally has a larger amplitude during MJO phases 4–6 (~10%–40%), while the amplitude is smaller for other MJO phases (~−10%–−40%). As for the GWMF estimation, the 12-year continuous observation of the Mohe meteor radar (53.5°N, 122.3°E) was analyzed. The results showed that intraseasonal GWMF variability is also prominent during boreal winter. Composite analysis for DJF season according to MJO phases revealed that the zonal GMWFs notably increased in MJO P4 by ~2–4 m²/s², and a Monte Carlo test was designed to examine the statistical significance. The response in zonal winds differs from the GMWF response by two MJO phases (i.e., 1/2π). Additionally, time-lagged composites revealed the strengthened westward GWMF occurred ~25–35 days after MJO P4, coincident with the MJO impact on the polar vortex as previous works revealed. Overall, this work emphasized that the tropical sources (MJO) impress the intraseasonal signal from the troposphere to the MLT region, either tropics or extratropics.

How to cite: Zhou, X., Yue, X., Liu, L., Chen, G., Lu, X., Yu, Y., and Hu, L.: Observed responses of tides and gravity waves in the MLT region to the Madden-Julian Oscillation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2764, https://doi.org/10.5194/egusphere-egu24-2764, 2024.

The vibrant green streaks of the 'picket fence' typically appear below a STEVE arc in the subauroral sky, at lower latitudes than the auroral oval. Recent studies suggest that, despite its aurora-like appearance, the picket fence may not be driven by magnetospheric particle precipitation but instead by local electric fields parallel to Earth's magnetic field. In this study, we investigate this hypothesis by quantitatively comparing observed picket fence optical spectra with emissions generated in a kinetic model driven by parallel electric fields in a realistic neutral atmosphere. We find that sufficiently large parallel electric fields can reproduce the observed ratio of N2 first positive to oxygen green line emissions, without producing N2+ first negative emissions. We find that, at a typical picket fence altitude of 110 km, parallel electric fields between 40 and 70 Td (~80 to 150 mV/m at 110 km) result in calculated spectral features consistent with observed ones, providing a benchmark for future observational and modeling studies. Additionally, we review studies which have identified similar features to the picket fence in the aurora, suggesting that a similar mechanism may be at work there. Since visible and ultraviolet auroral emissions are increasingly used to infer magnetospheric activity, it is important to better understand and quantify potential sources of emission beyond particle precipitation.

How to cite: Gasque, C., Janalizadeh, R., Harding, B., Gillies, M., and Yonker, J.: It's Not Easy Being Green: Quantitative Modeling of STEVE's Picket Fence Emissions Driven by Local Parallel Electric Fields, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12721, https://doi.org/10.5194/egusphere-egu24-12721, 2024.

Lightning-ionosphere interactions are well documented in the form of observations of fantastic optical emissions such as sprites and elves.  In order to better understand electromagnetic heating of the lower ionosphere (∼60-100 km altitude), a mesospheric photo-chemistry model is employed to interpret lightning-ionosphere interactions. The LIMA atmospheric chemistry model implements >150 chemical reactions, as do similar atmospheric chemistry models, such as WACCM, but the LIMA model has had success modeling so-called Long Recovery Events. Due to the large number of reactions and chemical species involved, however, it can be difficult to identify specific cause and effect mechanisms for the event of interest. This paper presents a simplified mesospheric chemistry model that accurately reproduces lightning-ionosphere interactions predicted by the full 167-reaction LIMA model (it maintains the accuracy of the full LIMA model for electron density, electron temperature, electrical conductivity, and electromagnetic field intensity as a function of time and space throughout the heating process).

How to cite: Moore, R. and Santos, J.: Lightning-Ionosphere Interactions: An Accurate, Simplified Nighttime Mesospheric Photochemistry Model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14619, https://doi.org/10.5194/egusphere-egu24-14619, 2024.