Abstract The 2018–2019 sudden stratospheric warming (SSW) is simulated using a high‐resolution whole atmosphere model that includes interactive chemistry and constrained meteorology. The simulations are performed using a high‐resolution (∼0.25) configuration of the Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (WACCM‐X) with the meteorology constrained up to ∼10 hPa using ECMWF Reanalysis v5 (ERA5). The high‐resolution WACCM‐X simulations are compared to satellite and ground‐based observations as well as two whole atmosphere data assimilation systems. Based on these comparisons, the high‐resolution WACCM‐X simulations are shown to alleviate two long‐standing biases in low‐resolution (∼2) WACCM‐X: a westward wind bias in the mesosphere and lower thermosphere (MLT) at wintertime high‐latitudes, and insufficient downward transport of nitric oxide (NO) following SSWs. The high‐resolution simulations are also able to capture much of the day‐to‐day variability in MLT winds seen in meteor radar observations. The simulations represent the first meteorologically constrained high‐resolution whole atmosphere simulations with fully interactive chemistry, and demonstrate that high‐resolution whole atmosphere model simulations can significantly improve representation of dynamical and chemical variability in the middle and upper atmosphere during SSWs.

Specular meteor radars (SMRs) have been extensively used to investigate neutral winds in the mesosphere and lower thermosphere. Unlike other instruments, this type of radar has the advantage of operating continuously, regardless of the weather conditions. However, SMRs experience interruptions in their operation, which result in data gaps that can range from a few hours to several days, posing a challenge to continuous atmospheric analysis. These gaps, on the other hand, present an excellent opportunity to test and validate the predicting capabilities of advanced Machine Learning (ML) techniques for data imputation. In this study, we employ a robust three-step data imputation methodology to sequentially address different types of data gaps artificially introduced in the wind data from the MMARIA/SIMONe meteor radar networks in northern Germany and northern Norway. The three-step imputation protocol proceeds as follows: initially, isolated missing values are estimated using classical time-based interpolation methods. Subsequently, continuous missing values over a period, where concurrent data across neighboring heights are available, are addressed using traditional space-based machine learning methods, such as k-Nearest Neighbor (kNN) or Random Forest (RF). Finally, the most challenging gap type, continuous missing samples, defined as contiguous space-temporal data loss during a specified period, is predicted using a deep learning stepwise extrapolation model based on the Long Short-Term Memory (LSTM) network. The methodology is applied to a four-month period of multistatic SMR wind data encompassing the major sudden stratospheric warming (SSW) event of January 2024. Special attention will be given to comparing the predicted wind behavior against the observed wind data.

At Collm (51.3 degrees N, 13.0 degrees E) mesosphere/lower thermosphere (MLT) zonal and meridional winds have been measured for more than four decades using low-frequency spaced receiver measurements on 177, 225, and 270 kHz, and very high frequency meteor radar observations on 36.2 MHz. We analyse the combined time series of monthly mean horizontal winds at 90 km height from 1979 to 2024 with respect to long-term changes, and in particular to the effect of the 11-year solar cycle (SC). In the 1980s and 1990s there is a negative correlation with solar extreme ultraviolet proxies in spring and early summer, with a weaker jet in the lower thermosphere during solar maximum. This correspondence weakens after the year 2000. In winter, there is a weak positive effect towards stronger westerly winds during solar maximum. Together, the results suggest that solar forcing remains an important, season-dependent driver of mid-latitude MLT dynamics, but its expression is modulated by the recently weakened SCs 24-25, or modified by changing trends of forcing from below. These results are largely in agreement with partial reflection radar observations of mesospheric winds over Juliusruh (54.6 degrees N, 13.4 degrees E) at 3.18 MHz. We also compare them with decadal variations of gravity wave proxies, but these results are partly inconclusive.

The Northern Hemisphere stratospheric polar vortex (SPV) response to localized gravity wave (GW) forcing remains poorly understood, particularly in terms of its detailed morphology. Here, we investigated geometry-specific impacts of enhanced orographic GW drag in three hotspot regions, the Himalayas, Northwest America, and East Asia, using ensemble simulations with the high-top UA-ICON global circulation model. By classifying daily SPV geometries into ten distinct clusters with a novel unsupervised, shape-based hierarchical clustering framework, we isolated geometry-specific responses using the class contribution method. Our results show that all hotspot forcings consistently reduce planetary wave 1 (PW1) amplitude and induce a PW1-like displacement of the SPV core, though spatial patterns vary with hotspot location. This response manifests as negative geopotential height (GPH) anomalies within the forced region and positive anomalies to the north, indicating localized SPV edge mixing. The response is also sensitive to the forcing’s latitudinal position: the Himalayas, as the southernmost hotspot, produces a deepened vortex, while the more poleward Northwest America and East Asia forcings show similar patterns with greater intrusion of positive GPH anomalies into the vortex core. The forcing reduces PW1 amplitude both by shifting the frequency of specific clusters and altering the mean structure of the most frequent classes. Our results demonstrate that shape-based clustering combined with the class contribution framework can reveal robust, spatially coherent signals that might otherwise be masked by internal variability, providing a new perspective for understanding SPV variability and its predictability.

Calibration of instruments measuring the Earth's energy imbalance EEI as the difference of the total solar irradiance TSI and the total outgoing radiation of the Earth TOR requires precise, traceable TSI and TOR radiation standards with three congruent properties: spectral composition, power, and angular divergence. As there are no TSI and TOR standards available, EEI data should be considered estimates. To enable more accurate estimates, the proposed novel spectrometers are used. The innovative process behind it is called quasi-calibration and also compensates for the aging of the instruments. The data can be transferred to other instruments in space. SORACES allows the observation of spectral solar irradiance SSI and spectral outgoing radiation of the Earth SOR, which differ by about five orders of magnitude, with high statistical significance by the same detectors. It is equipped with a set of 16 compact Rowland spectrometers with 80 photomultiplier tubes (PMTs) and 32 radiation attenuators with transmissions from 10-1 to 10-5. The use of attenuators allows for a dynamic range of up to 12 orders of magnitude to be covered. The cadence of the spectra is one second. Based on the stability of the TSI data, quasi-calibrated measurement periods across a solar cycle are to be achieved. SORACES is intended to contribute time-stable estimated SOR data to climate research. By evaluating the spectral features of the data, annual changes in the global cover of the Earth's green biomass due to global warming are to be derived.

Having a comprehensive understanding of the ionosphere's irregular behavior and its response to solar activity is crucial for satellite communication and navigation applications. The sun's extreme ultraviolet (EUV) and ultraviolet (UV) radiation are the primary sources of energy for the Earth's thermosphere and ionosphere (TI). To understand the global response of TI parameters (e.g., O/N2, and the peak electron density (Nmax)) to changes in solar irradiance, various data have been used. These include the Global-Scale Observations of the Limb and Disk (GOLD) ultraviolet imaging spectrograph, solar radio flux F10.7, predictions from the Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) model, and International Global Navigation Satellite System Service total electron content maps (TEC). The comparison between these measurements shows that the CTIPe model successfully reproduces the behavior of the low- and mid-latitude ionosphere during both low and high solar activity. The study also investigated the delayed ionospheric TEC response against solar flux variations within the 27-day solar modulation. It was observed that the delay is less than one day, which was also confirmed in model simulations. Furthermore, the model simulations showed that the ionospheric time delay is significantly affected by various physical processes such as diffusion, photodissociation, solar and geomagnetic activities, and wave dynamics.

The Arctic Stratospheric Polar Vortex (SPV) exhibits significant interannual variability, characterized by major Sudden Stratospheric Warmings (SSWs) occurring approximately biennially and three Exceptionally Strong Vortex (ESV) events over recent decades, which are linked to springtime ozone depletion. This study investigates the dynamical and morphological characteristics such as the location, area and strength of the vortex edge. SPV over 45 extended winter seasons (September–May) from 1979 to 2023 in the Northern Hemisphere (NH) have been analysed using ERA5 reanalyses, focusing on the lower, middle, and upper stratosphere (850 K, 600 K, and 530 K, respectively). Additionally, two idealized experiments using the ICOsahedral Nonhydrostatic (ICON) general circulation model were conducted over a 30-year period, one with orographic waves turned off and the other with non-orographic waves disabled in addition to a control (CTL) run.The strength of the vortex edge increases more sharply with altitude compared to the vortex area, suggesting a stronger upper stratospheric vortex boundary that effectively resists tropospheric wave disturbances. Although vortex area recovery is observed during some SSW events, the strength of the vortex edge remains weak. Notably, no extreme events occurred between 1989 and 1995. The SPV center shows a pronounced latitudinal drift, moving away from the pole at an average rate of 14.31 km per year. Variability in the formation and deformation of the vortex is quantified across different stratospheric levels. Interannual variability of Polar Stratospheric Clouds (PSCs) and their relationship to SPV dynamics and ozone loss during late winter and early spring are also analyzed.The ICON-CTL simulation produces a smaller SPV area with a stronger vortex boundary compared to ERA5 reanalysis. Sensitivity experiments demonstrate a significantly smaller vortex area than the CTL. Non-orographic gravity waves play a critical role in modulating SPV dynamics in the NH by influencing wave-mean flow interactions. Their absence results in an earlier onset, delayed breakup, and a notably extended SPV duration, particularly in the upper stratosphere (850 K). PSC volumes in the CTL run align well with ERA5 observations but are slightly overestimated. Sensitivity experiments reveal higher PSC volumes relative to the CTL, with the absence of orographic waves leading to larger PSC volumes during late winter and early spring. This finding suggests the presence of strong, stable, and cold vortices under these conditions, which enhance Arctic ozone depletion, particularly when upward wave propagation is reduced.

Even though it is widely acknowledged that the stratospheric polar vortex (SPV) strengthens under stratospheric aerosol intervention (SAI), little is known about how the SPV's size, duration, location, and edge change under SAI compared to the present-day climate. Here, we address these issues using two large ensemble SAI simulations, namely GLENS (2060-2079) with extreme forcing and ARISE (2050-2069) with more moderate forcing. It is found that the wintertime Arctic and Antarctic stratospheric wind responses to SAI compared to the control (CTL) climate in GLENS (2060-2079) are roughly two times as large as in ARISE (2050-2069). While the zonal wind acceleration in ARISE (2050-2069) is hemispherically symmetric at 3-4 m s(-1) in the stratosphere of both hemispheres, the responses in GLENS (2060-2079) are hemispherically asymmetric, being two to three times larger in the Southern Hemisphere (SH, similar to 15 m s(-1)) compared to the Northern Hemisphere (NH). While the edge of the vortex in GLENS (2060-2079) intensifies under SAI, similar changes are not found in ARISE (2050-2069). Such intensification of the vortex edge in GLENS is limited to lower stratosphere levels and does not extend to greater heights (similar to 10 hPa). SAI has no discernible effect on the NH vortex morphology in ARISE simulations. However, the edge of the vortex intensifies in terms of Ertel's potential vorticity (EPV) gradient under SAI in the NH in GLENS. The greatest change that the SPV consistently shows under SAI in both GLENS and ARISE simulations is the SH spring vortex's behaviour. Under SAI, at 530 and 600 K, the vortex edge is weaker, its area is smaller, and it breaks up earlier than in the CTL runs.

We examine the variability of diurnal tide (DT), semidiurnal tide (SDT), and terdiurnal tide (TDT) amplitudes in the Arctic mesosphere and lower thermosphere (MLT) during and after sudden stratospheric warming (SSW) events using meteor radar data at three polar-latitude stations, Sodankyl & auml; (67.37 degrees N, 26.63 degrees E), Troms & oslash; (69.58 degrees N, 19.22 degrees E), and Svalbard (78.99 degrees N, 15.99 degrees E), as well as one station outside the polar vortex located at Collm (51.3 degrees N, 13 degrees E). By combining tidal amplitude anomalies with trace gas variations, induced by large-scale dynamical changes caused by the breaking of planetary waves, this study provides new observational insights into the variation of ozone and water vapor, transport, and tides at polar latitudes. We use short-wave (QRS) and long-wave (QRL) radiative heating and cooling rates simulated by the WACCM-X(SD) model to investigate the roles of polar ozone and water vapor in driving mesospheric tidal variability during SSWs in the polar regions. Our analysis reveals distinct tidal responses during SSW events. At the onset of SSWs, a significant negative anomaly in TDT amplitudes in zonal and meridional components is observed, with a decrease of 3 ms-1, approximately 25 % change compared to the mean TDT amplitude. Meanwhile, SDT shows a positive anomaly of 10 ms-1, with changes reaching up to 40 %, indicating an enhancement of tidal amplitude in both components. The DT amplitude exhibits a delayed enhancement, with a positive amplitude anomaly of up to 5 ms-1 in the meridional wind component, occurring approximately 20 d after the onset of SSWs. A similar but weaker effect is observed in the zonal wind component, with changes reaching up to 30 % in the zonal component and 50 % in the meridional wind component. We analyzed the contributions of ozone and water vapor to the short-wave heating and long-wave cooling before, during, and after the onset of SSW events. Our findings suggest that the immediate responses of SDT are most likely driven by dynamical effects accompanied by the radiative effects from ozone. Radiative forcing change during SSW likely plays a secondary role in DT changes but appears to be important 20 d after the event, particularly during the spring transition. Water vapor acts as a dynamical tracer in the stratosphere and mesosphere but has minimal radiative forcing, resulting in a negligible impact on tidal changes. This study presents the first comprehensive analysis of mesospheric tidal variability in polar regions during sudden stratospheric warmings (SSWs), examining and linking the significant role of trace gases and radiative effects in modulating tidal dynamics.

Time series of mesosphere/lower thermosphere half-hourly winds over Collm (51.3°N, 13.0°E) have been obtained from 1984 – 2008 by low frequency (LF) spaced receiver measurements and from 2004 to date by VHR meteor radar Doppler wind observations in the height range 82 – 97 km. From half-hourly differences of zonal and meridional winds, gravity wave (GW) proxies have been calculated that describe amplitude variations in the period range 1 – 3 hours. After applying corrections to account for instrumental differences, GW climatology and time series have been obtained. The mean GW activity in the upper mesosphere shows maximum amplitudes in summer, while in the lower thermosphere GWs maximize in winter. Positive/negative long-term trends are visible in winter/summer. Interannual and quasi-decadal variations of GW amplitudes are also visible, but these are intermittent.

A significant decreasing trend of Arctic stratospheric ozone has been observed since 2019, with the first reported ozone hole in the Arctic Stratospheric Polar Vortex (SPV) in 2020, raising concerns for humanity. This underlines that it is essential to develop an algorithm capable of predicting Arctic ozone levels, preferably using minimal computing resources. This study presents a novel approach for ozone prediction based on the morphological and dynamical properties of the SPV utilizing a explainable machine learning approach. XGBoost exhibits good agreement with the observations, achieving an $$R^2$$ score of 0.80 and a correlation of 0.91. The algorithm accurately predicts the daily and seasonal patterns of ozone variations. It successfully captures the pattern of the lowest recorded ozone levels in 2020, though it overestimates ozone values by approximately 20 Dobson units. Moreover, in some years the predicted ozone values also show a strong alignment with the observations. Notably, the algorithm relies solely on physics based features of the SPV to predict chemical ozone loss, demonstrating the potential of dynamical parameters in predicting the ozone variability. It could serve as a tool for projecting future Arctic ozone variability by utilizing input from climate models that lack interactive chemistry.

Continuous and reliable measurements of the mesosphere and lower thermosphere (MLT) are key to further the understanding of global atmospheric dynamics. Observations at horizontal scales of a few hundred kilometers (i.e., mesoscales) are particularly important since gravity waves have been recognized as the main drivers of various global phenomena, e.g., the pole-to-pole residual meridional circulation. Multistatic specular meteor radars are well suited to routinely probe the MLT at these scales. One way to accomplish this, is by investigating the momentum flux, horizontal divergence (del H & sdot;u) and relative vorticity ((del xu)z) estimated from the Doppler shifts measured by a radar network. Furthermore, the comparison between the horizontal divergence and the relative vorticity can be used to determine the relative importance of gravity waves (i.e., divergent motions) and strongly stratified turbulence (i.e., vortical motions). This work presents the first climatology of all these estimates together, as well as results on the probability distribution of the total momentum flux (TMF), and the comparison between del H & sdot;u and (del xu)z, obtained from almost 10 years of continuous measurements provided by two multistatic specular meteor radar networks: MMARIA/SIMONe Germany, covering an area of more than 200 km radius around (53 degrees N, 11 degrees E), and MMARIA/SIMONe Norway, which covers an area of similar size, but around (69 degrees N, 16 degrees E). Among others, our results indicate that at middle latitudes the horizontal divergence and the relative vorticity are balanced around summer mesopause altitudes, while the former dominates over the latter above similar to 90 km of altitude during parts of the fall transition. At high latitudes, the vortical motions dominate during late spring and early summer. Besides, the strongest 5 % of GWs contribute much more over northern Germany than over northern Norway, where the larger values of the excess-kurtosis indicate that the contribution from the small-amplitude GWs is also more significant at middle latitudes, especially during the summer. In other words, the TMF in the mesosphere and lower thermosphere over central Europe is considerably more intermittent at middle latitudes than at high latitudes.

The solar extreme ultraviolet (EUV) radiation drives the major ionization processes in the upper atmosphere. Its variability causes a related response in ionospheric observables. Especially of interest is the delayed response of electron density (Ne), integrated total electron content (TEC), and the density of major neutral and ionized species to the 27-d solar rotation period. But this solar signature is often influenced by underlying trends on shorter and longer time-scales. Therefore, this study examines the ionospheric response to a solar 27-d signature superposed with a long-term increase in solar EUV, showing that complex composition changes in the upper atmosphere influence the expected response significantly. Using high-resolution simulations of the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM), we compare two different 27-d solar rotation periods from the year 2014 with enhanced solar activity. This allows us to compare an almost ideal solar activity input with one that is superposed with an increase in solar activity. The main results show that the accumulation of ionized species O+ and O2+ in the lower ionosphere, especially up to the maximum density of ionized oxygen (O+) at about 230 km, is significantly affected by the long-term increase in solar activity. Nevertheless, the 27-d solar rotation period dominates the ionization in both, ideal and complex model run for altitudes above 230 km. Thus, our results are in good agreement with preceding studies and extend the study of the delayed ionospheric response to more complex cases.

The Arctic Stratospheric Polar Vortex (SPV) is known for its high interannual variability, with major Sudden Stratospheric Warmings (SSWs) occurring approximately every second year and with three Exceptionally Strong Vortex (ESV) events in the past decades, which are associated with springtime ozone depletion. Understanding the dynamical and morphological properties of the SPV is crucial for predicting these extreme events, and SPV variability in general. This study utilizes data from 45 Northern Hemisphere (NH) extended winter seasons, covering the period from September to May, at lower, middle and upper stratosphere heights. We explore the influence of different climate variability modes on the vortex’s dynamical properties. We introduced the SPV metrics, which provide a holistic overview of SPV intensity, and found a strong correlation (0.83) with the zonal wind. In February, March and April (FMA) of the 2019 NH winter, the climatological anomaly reached an all-time high of SPV strength, with record-low ozone due to an ESV, though its intensity did not extend to the upper stratosphere. Other ESV winters were 1996 and 2010. The EPV gradient increases more sharply with altitude than the area, indicating a stronger upper stratospheric vortex boundary that resists tropospheric wave disturbances. During some SSW events, the vortex area may recover, but the EPV gradient remains weak. The SPV center shows a significant poleward shift toward Eurasia at 14.31 km/year, linked to vortex dynamics. Minimal latitudinal displacement occurred during 1989–1995 (no extreme events), while greater shifts during 1998–2009 coincided with frequent SSWs. SPV metrics correlated with SPV position of (0.55) peak winter and (0.66) FMA. We quantify climatic variability and its role in extreme SPV events, highlighting the significant influence of the Quasi-Biennial Oscillation and Arctic Oscillation. Breakup timing, influenced by tropospheric waves, shows minor variations across levels. The vortex begins forming in the upper levels and dissipates progressively from the lower stratosphere. Notably, a statistically significant decreasing trend towards earlier vortex formation is seen in the upper stratosphere. We analysed the interannual variability of Polar Stratospheric Clouds and their relationship with SPV dynamics and associated ozone loss during late winter and early spring. We hypothesized that both SSWs and ESVs could potentially occur in a single NH winter in future.

Previous research has indicated that geomagnetic activity plays an important role in influencing the ionospheric delayed response to solar activity variations at the solar rotation time scale depending on solar activity conditions. In this study, we employed the Thermosphere-Ionosphere-Electrodynamic General Circulation Model to investigate the vertically resolved impact of geomagnetic activity on the ionospheric delay over the solar rotation period from 29 April to 25 May 2015. This time period was chosen due to its representative moderate solar and geomagnetic activity conditions. Our analysis revealed that the ionospheric delay increases with altitude due to geomagnetic activity and is more pronounced in the Southern Hemisphere than in the Northern Hemisphere. To further understand the underlying mechanisms responsible for the observed changes in ionospheric delay, we examined neutral species ( and ), their ratio , and neutral temperature. The results show that thermosphere-ionosphere composition varies both vertically and horizontally in response to geomagnetic activity, and that these composition changes contribute to vertical variations in ionospheric delay.

The mesosphere and lower thermosphere (MLT) comprise a highly variable region that forms the transition region between the middle and upper atmosphere. The variability of this region is driven by atmospheric waves transporting energy and momentum from the lower and middle atmosphere to MLT altitudes. These waves cover a wide range of temporal (minutes to days) and spatial (kilometers to planetary) scales. The upward propagation of atmospheric gravity waves and tides is one of the key processes at all latitudes that alters the state of the ionosphere–thermosphere system, and their vertical propagation depends crucially on the background mean winds. The TIMED Doppler Interferometer (TIDI) on board the Thermosphere-Ionosphere-Mesosphere-Energetics and Dynamics (TIMED) satellite observes neutral winds at the MLT using airglow emissions. We establish a TIDI mean wind climatology, compare our results with existing climatologies derived from local meteor radar observations, and discuss similarities and differences depending on local time and geographical latitude.

Gravity waves (GWs) are a major yet poorly constrained driver of middle-atmosphere dynamics. Using the high-top UA-ICON global circulation model, we conducted a set of six-member ensemble simulations in which orographic GW drag was selectively intensified over three Northern Hemisphere hotspots identified from observational and modeling studies – e.g., Himalayas (HI), Northwest America (NA), and East Asia (EA) – to assess their long-term dynamical impacts on the stratosphere. The imposed forcing generated distinctive vertical–horizontal drag structures in each region, yet produced a coherent hemispheric response. Resolved waves compensated the local drag through compensation mechanisms. In all three cases, added westward momentum suppressed upward and equatorward propagation of planetary waves, particularly of wavenumber 1, strengthening westerlies in the upper stratosphere–mesosphere. The frequency of sudden stratospheric warmings remained unchanged in the HI and NA experiments, but increased notably in EA, while the ratio of split to displacement events was unaffected. These results highlight the sensitivity of stratospheric variability to non-zonal GW forcing and underscore the importance of improving our understanding of GW–climate interactions. The simulation dataset presented here offers a valuable resource for future studies on gravity wave–induced variability in the climate system.

This study utilizes meteor radar observations gathered over nine years at two longitudes and 52°N latitude to explore planetary-scale waves in mesospheric winds. By analyzing zonal wavenumbers across various time scales—specifically multi-day, near-24-hour, 12-hour, and 8-hour periods—we were able to distinguish normal modes (NMs) from other planetary waves (PWs), identify migrating and non-migrating tides, and uncover a range of novel nonlinear interactions.Our statistical analysis revealed that multi-day oscillations were predominantly associated with NMs, which exhibit distinct seasonality in both period and wavenumber, and show a statistical correlation with sudden stratospheric warmings (SSWs). Notably, April featured a prominent 6-day NM (zonal wavenumber 1), followed by a dominance of 4- and 2-day NMs (wavenumbers 2 and 3, respectively) through June. From July to October, we observed peaks in 2-, 4-, and 6-day NMs (zonal wavenumbers 3, 2, and 1, respectively).Our insights into seasonal variations are based on observational determinations of frequency and zonal wavenumber, in contrast to satellite observations that often use fixed frequencies and wavenumbers to fit individual waves. The statistical link between NMs and SSWs provides significant input to the ongoing debate on this topic. Additionally, for the first time, we identified frequency and zonal wavenumber matching in over ten secondary waves resulting from nonlinear interactions among NMs (16-, 10-, and 6-day), tides (diurnal, semidiurnal, and terdiurnal, both migrating and non-migrating), and stationary planetary waves (SPWs).Among these interactions, three novel categories were identified: (1) interactions between terdiurnal tides and planetary waves, (2) interactions between stationary and traveling planetary waves, and (3) interactions between non-migrating tides and planetary waves. These interactions with SPWs help explain our finding that the amplitudes of non-migrating tides exceed those of the corresponding migrating tides, particularly evident in the winter diurnal tide and the summer terdiurnal tide. These non-migrating signatures stand out as notable exceptions, as migrating components generally dominate diurnal, semidiurnal, and terdiurnal tides throughout most of the year.

The Arctic stratospheric polar vortex (SPV) exhibits strong interannual variability due to the large landmass in the Northern Hemisphere (NH), which also enhances the generation of orographic and non-orographic gravity waves (GWs). In this study, two idealized experiments with the ICOsahedral Nonhydrostatic (ICON) model over a 30-year period were analyzed. One experiment involved turning off orographic waves (NO_SSO), while the other one involved turned off non-orographic waves (NO_NON).The NO_NON experiment exhibits a significantly smaller vortex area than the control simulation (ICON-CTL) and is also smaller than in the NO_SSO experiment at the same levels. In both experiments, the SPV is located more poleward compared to ICON-CTL, with the vortex center in NO_SSO being closest to the pole. The NO_SSO experiment demonstrates stronger and more stable vortices during late winter and early spring, while the NO_NON experiment shows a smaller vortex area and a shorter lifespan. The NO_NON experiment shows the highest variability in SPV breakup days.The Polar Stratospheric Cloud (PSC) volumes in the ICON-CTL run are mainly consistent with ERA5, although they are slightly overestimated. The sensitivity experiments reveal higher PSC volumes compared to ICON-CTL, with NO_SSO maintaining significantly larger volumes during late winter and early spring. The ICON-CTL run included two exceptionally strong vortex (ESV) events over the 30-year period, while NO_NON recorded none; and NO_SSO showed an unprecedented frequency of 13 ESV events during the same period.

At Collm ($51.3^{\circ} \mathrm{N}, \text{1 3. 0}^{\circ} \text{E}$) mesosphere/lower thermosphere (MLT) wind measurements have been performed for more than four decades using low-frequency spaced receiver and very high frequency meteor radar observations. We analyse the combined time series with respect to long-term changes, and in particular to the effect of the $\text{1 1}$-year solar cycle. In the 1980s and 1990s there is a negative correlation with solar extreme ultraviolet proxies in spring and early summer, with a weaker lower thermospheric jet during solar maximum. This correspondence weakens after the year 2000. In winter, there is a weak positive effect towards stronger westerly winds during solar maximum. Together, the results suggest that solar forcing remains an important, season-dependent driver of mid-latitude MLT dynamics, but its expression is modulated by the recently muted solar cycles 24-25. We compare these results with partial reflection radar observations of mesospheric winds over Juliusruh $\left(54.6^{\circ} \mathrm{N}, 13.4^{\circ} \mathrm{E}\right)$ and also compare them with decadal variations of gravity wave proxies.