Nightglow emission signatures observed from space- and ground-based instruments are commonly used as proxies for atmospheric composition, especially for the altitude region around 100 km that cannot be easily studied in situ. Monitoring the intensity and temporal evolution of such proxies by remote sensing is often the method of choice to study a plethora of phenomena in this region of the atmosphere. Thus, the quantitative details relevant to the production and deactivation of excited atomic and molecular precursors responsible for prominent nightglow emissions are required to study atmospheric composition, radiative and energy balance, wave propagation and dissipation, as well as transport dynamics. Significant gaps and uncertainties exist in the understanding of the above processes and, as our recent studies on nightglow emissions revealed, substantial revisions of the relevant atmospheric models are warranted.

We will present a progress report on our efforts to advance the understanding of key mesospheric nightglow emissions by investigating the recently established coupling between the OH Meinel and the O₂ Atmospheric band emissions, mediated by collisions of O atoms with vibrationally excited OH.

This work is supported by the U.S. National Science Foundation (NSF) under Grants AGS-2009960 and AGS-2113888.

How to cite: Kalogerakis, K. S.: Understanding the Coupled OH Meinel and O2 Atmospheric Band Nightglow Emissions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4518, https://doi.org/10.5194/egusphere-egu23-4518, 2023.

The variability of the upper atmosphere is largely influenced by dynamical forcing from the lower and middle atmosphere. The Mesosphere and Lower Thermosphere (MLT) is the transition region between the middle atmosphere and the upper atmosphere, and it determines dynamical forcing to the upper atmosphere from below. It is thus of high importance to know, describe, and understand the dynamical processes within the MLT to quantify dynamics. Therein, General Circulation Models (GCMs) have been a significant tool to explain MLT processes.

However, developing the right parameterizations that allow to accurately model near-to-realistic states of the MLT by GCMs is challenging, which is reflected in a large diversity of results from different models in comparison to observations, e.g., of winds and temperatures at the MLT.

In recent years, the community model ICON (Icosahedral Nonhydrostatic Weather and Climate Model) has been expanded into altitudes up to 150 km, named the UA (Upper Atmosphere) branch. UA-ICON is increasingly being applied to model and to understand MLT processes and how they are controlled by the lower and middle atmosphere.

We present newly developed capabilities of UA-ICON. Examples are mesospheric cooling during stratospheric warming events, low summer mesopause temperatures through appropriate specification of gravity wave parameterizations and runs of high spatial resolution. Results are discussed in comparison with observations and with predictions by other GCMs.

How to cite: Stolle, C., Kunze, M., Siddiqui, T., Zülicke, C., Amiramjadi, M., Yamazaki, Y., Baumgarten, G., Borchert, S., and Schmidt, H.: Dynamics and variability of the MLT represented by UA-ICON, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14102, https://doi.org/10.5194/egusphere-egu23-14102, 2023.

Based on the hourly output from the 2000–2014 simulations of the National Center for Atmospheric Research’s vertically extended version of the Whole Atmosphere Community Climate Model in specified dynamics configuration, we examine the roles of planetary waves, gravity waves and atmospheric tides in driving the mean meridional circulation in the lower thermosphere and its response to the sudden stratospheric warming phenomenon with an elevated stratopause in the northern hemisphere. Sandwiched between the two summer-to-winter overturning circulations in the mesosphere and the upper thermosphere, the climatological lower thermosphere mean meridional circulation is a narrow gyre that is characterized by upwelling in the middle winter latitudes, equatorward flow near 120 km, and downwelling in the middle and high summer latitudes. Following the onset of the sudden stratospheric warmings, this gyre reverses its climatological direction, resulting in a “chimney-like” feature of un-interrupted polar descent from the altitude of 150 km down to the upper mesosphere. This reversal is driven by the westward-propagating planetary waves, which exert a brief but significant westward forcing between 70 and 125 km, exceeding gravity wave and tidal forcings in that altitude range. The attendant polar descent potentially leads to a short-lived enhanced transport of nitric oxide into the mesosphere (with excess in the order of 1. parts per million), while carbon dioxide is decreased.

How to cite: Orsolini, Y., Zhang, J., and Limpasuvan, V.: Abrupt Change in the Lower Thermospheric Mean Meridional Circulation during Sudden Stratospheric Warmings and its Impact on Trace Species, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14077, https://doi.org/10.5194/egusphere-egu23-14077, 2023.

The German Federal Ministry of Education and Research (Bundesministerium für Bildung und Forschung, BMBF) has launched a research initiative in 2013/2014 called ROMIC (Role of the Middle Atmosphere in Climate). The second phase of this project extends until 2024. The aim of ROMIC is to improve our understanding of long term variations in the stratosphere, mesosphere, and lower thermosphere and to investigate their potential role for
climate changes in the troposphere. This includes to study coupling mechanisms between various layers and the relative importance of anthropogenic and natural forcing, e.\ g., by the Sun. Scientists at a total of 13 research institutes in Germany are involved and cover a large range of experimental and theoretical topics relevant for ROMIC. Most projects are linked to international activities and cooperations. Some scientific highlightsfrom the research projects within ROMIC will be presented.

How to cite: Lübken, F.-J.: Scientific Highlights from ROMIC, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5246, https://doi.org/10.5194/egusphere-egu23-5246, 2023.

The polar mesospheric clouds (PMCs) obtained from Aeronomy of Ice in the Mesosphere (AIM)/Cloud Imaging and Particle Size (CIPS) and Himawari-8/Advanced Himawari Imager (AHI) observations are analyzed for the multi-year climatology and interannual variations. The PMCs dependence on mesospheric temperature and water vapor (H2O) are further investigated with data from Microwave Limb Sounder (MLS). Our analysis shows that PMCs onset date and occurrence rate are strongly dependent on the atmospheric environment, i.e. underlying seasonal behavior of temperature and water vapor. Upper-mesospheric dehydration by PMCs is evident in MLS water vapor observations, The spatial patterns of the depleted water vapor resemble the PMCs distribution over the Arctic and Antarctic region during the days after summer solstice. Year-to-year variabilities of the PMCs occurrence rate and onset date are highly correlated with the mesospheric temperature and H2O variations, particularly in the southern hemisphere (SH). The global increase of mesospheric H2O during the last decade may explain the increased PMCs occurrence in the northern hemisphere (NH). Although mesospheric temperature and H2O exhibits a strong 11-year variation, little solar cycle signature is found in the PMCs occurrence during 2005-2021.

How to cite: Lee, J. and Wu, D.: The Sensitivity of Polar Mesospheric Clouds to Mesospheric Temperature and Water Vapor, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-907, https://doi.org/10.5194/egusphere-egu23-907, 2023.

Besides the well-known 11 year solar cycle, the Sun occasionally produces strong eruptions on the Sun‘s surface and in the corona. They can first be seen as flare events in electromagnetic spectrum down to X ray wavelengths. Within these strong eruptions, particles in the solar plasma, mainly protons, are accelerated to high energies that hit the Earth within hours after the event. In addition, plasma clouds can be accelerated and ejected into the interplanetary space and, provided they are directed to the Earth, can cause severe geomagnetic disturbances. This results in a further energetic particle precipitation event a few days after the primary solar eruption. The strength of these events spans orders of magnitude, with the strongest having dramatic impact on the ionosphere and the middle atmosphere affecting even human activities. Here we study the chemical impact and dynamical of solar events on the middle atmosphere which are on the very extreme side but still within the range of a one per millennia event.

We first derive a reference example of an extreme solar event from historical records of solar proton events and from analyzed distributions of energy spectra for geomagnetic storms. We then take ionization rates calculated from strong observed events and scale them to represent the extreme events. Finally, we combine the solar proton event with the geomagnetic storm as both events typically impact different parts of the atmosphere. The ionization rates for the extreme event are then used in simulations in the KASIMA and EMAC model which both include energetic particle induced chemistry.In order to represent different dynamical situations in the middle atmosphere which are important for the vertical coupling between the mesosphere-lower thermosphere (MLT) region and the stratosphere we select specific periods of the ERA-Interim dataset with a special focus on sudden stratospheric warmings (SSW) and apply the event for those situations. The simplified production efficiency of NOx and HOx in the models is further compared to an ion chemistry model where the extreme ionization rates are applied. The case of a SSW which shows an elevated stratosphere synchronized with the extreme event is studied in detail as a kind of worst case scenario.

How to cite: Reddmann, T., Borthakur, M., Sinnhuber, M., Usoskin, I., Wissing, J. M., and Wissing, J. M.: The impact of extreme solar events on the atmosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13994, https://doi.org/10.5194/egusphere-egu23-13994, 2023.

Atmospheric gravity waves transport energy and momentum through the atmosphere and can travel large horizontal and vertical distances from the troposphere to the mesosphere and higher. They contribute to atmospheric dynamics and among others drive the meridional pole-to-pole circulation in the mesosphere. Thus, knowing about gravity waves, their spatio-temporal characteristics, their interaction with other waves and the atmospheric background is attracting more and more attention in order to further improve climate and even meteorological models.

In the upper mesosphere / lower thermosphere (UMLT) region around an altitude of 80km to 100km, OH airglow can be utilized for passive remote sensing and continuous nightly observations of atmospheric dynamics, especially of gravity waves. The OH airglow layer is a chemiluminescent layer with a strong emission in the short wave infrared spectral range (at about 1500nm) and is located at an altitude of about 86-87km with a layer halfwidth of about 4km. The OH airglow intensity is modulated by traversing atmospheric gravity waves which lead amongst others to a vertical transport of atomic oxygen. Observing the OH airglow with short-wave infrared imagers allows characterizing gravity waves. From these observations the horizontal wave parameters (horizontal wavelength, horizontal direction of propagation, etc.) can be derived.

In this study we present measurements of two ground-based FAIM (Fast Airglow IMager) systems, which are cameras sensitive in the short-wave infrared region observing the OH airglow layer with a high temporal resolution. The cameras are located at Oberpfaffenhofen, Germany and Otlica, Slovenia, about 300km apart from each other and are pointing to the same volume at about 87km located in the Alpine Region above Northern Italy. We developed a novel tomographic algorithm to allow for a three-dimensional reconstruction of the airglow layer by combining images from the two viewing angles. In order to solve the highly underdetermined equation system, prior knowledge of the OH airglow layer vertical profile is needed e.g. from multi-year observations of SABER on the TIMED satellite on a statistical basis, or Gaussian and Chapman basis functions. This allows us, among others, to derive the vertical wavelength of the waves, their three-dimensional propagation direction, and their three-dimensional structure. From that knowledge, further wave parameters but also the horizontal wind along the wave propagation can be estimated via the wave’s dispersion relation.

We will explain the tomographic reconstruction method, its capabilities and limits and will present a detailed case study showing a 3D-reconstructed gravity wave and the derivation of its parameters.

This work received funding from the Bavarian State Ministry of the Environment and Consumer Protection.

How to cite: Hannawald, P., Noll, S., Wüst, S., and Bittner, M.: 3D reconstruction of atmospheric gravity waves and derivation of vertical wave parameters with tomography applied to data from two ground-based cameras observing OH airglow, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7554, https://doi.org/10.5194/egusphere-egu23-7554, 2023.

Tektites are a naturally occurring form of cosmic impact ejecta, produced in ~ 2 or 3% of impact events from melted and mixed silicate sediments that are launched into space where they devolatilize and quench to solid glass.  Australasian tektites (AAT) make up the largest and most recent of the known tektite strewnfields, covering ~1/4 of Earth’s surface with 30 to 60 billion tons of melt glass.  In southeast Asia, the Indochinite sub-family of these glassy objects appear mainly as fractured and sometimes contorted fragments of formerly hollow spheroid predecessors.  Surface textures, bulk and detailed morphometrics of Indochinite fragment-form tektites record a tortured history that is not consistent with mere hypersonic atmospheric reentry into a standard atmospheric column.  The tektites show rapid bulk reheating and surface effects consistent with high-voltage arcing disruption.  The overall region where these fragment-form tektites fell has a surface that was laterized within hours of their arrival, pulsed with heat and moisture to the point of degrading the rocks and soil the tektites lie within.  Clear ablation signatures on symmetric ablated spheroid AAT of Australia and the Central Indian Ocean basin indicate their source as the N. American Great Lakes region.  The Marine Isotope Stage MIS20 epoch (deep ice age) of the event and Michigan Basin geology suggest several thousand cubic km of disrupted Laurentide Ice Sheet may have been injected across the exosphere via oblique ricochet impact, lingering as degenerate byproducts for a day or more.  High-potential E-field and regional disruption of the atmospheric column from exosphere to surface over southeast Asia is indicated.

How to cite: Harris, T.: Impact ejecta glass records atmospheric columnar disruption and strong E-field, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4027, https://doi.org/10.5194/egusphere-egu23-4027, 2023.

A gigantic submarine volcano erupted near Tonga Island on 15 January 2022 generating a tsunami and related atmospheric and oceanic waves across the globe. This violent volcano triggered extreme disturbances just above the volcanic center that reached near Earth’s stratosphere. This geophysical event generated acoustic-gravity waves to propagate upward and induce significant global perturbations and holes in the mesosphere and lower thermosphere (MLT) regions. Here, we study the MLT region’s response to the Tonga-induced perturbations using ground-based Global Positioning System (GPS)-total electron content (TEC) data from GPS receivers spread in the South American continent. The possible propagation mechanism of the Tonga-related ionospheric holes and perturbations mediated by neutral wind-driven dynamo fields, vertical drifts, and the contribution of geomagnetic conditions will also be discussed. 

How to cite: Khadka, S., Valladares, C., and Gerrard, A.: Ionospheric Hole in the MLT Regions after Submarine Volcanic Eruptions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16759, https://doi.org/10.5194/egusphere-egu23-16759, 2023.