Claudia Stolle

Atmospheric tides in the lower thermosphere play an important role in regulating upper‐atmospheric conditions relevant to space weather. However, their spatial and temporal variability remains poorly understood, apart from seasonal variations. Previous studies have shown that tides can be influenced by meteorological and solar conditions. This study clarifies the relative importance of the El Niño‐Southern Oscillation (ENSO), the Quasi‐Biennial Oscillation (QBO), the Northern and Southern Polar‐night Jet Oscillations (NPJO and SPJO), the Madden‐Julian Oscillation (MJO), and Lyman‐alpha (Ly) radiation to tidal variability in the lower thermosphere. Tides at 80–110 km are derived from hourly temperature and wind fields in the JAGUAR‐DAS Whole neutral Atmosphere Reanalysis (JAWARA) for the period September 2004–August 2025. Rotated empirical orthogonal function analysis is used to identify the dominant modes of de‐seasonalized tidal variability. The resulting principal component time series are used as daily indices of tidal activity and are compared with indices of ENSO, QBO, NPJO, SPJO, MJO, and Ly. Multiple linear regression analysis determines which tides exhibit statistically significant responses to these indices and quantifies their magnitudes. The most pronounced responses include those of the nonmigrating diurnal tide DE3 to ENSO (approximately 4 m in horizontal wind velocity), the migrating diurnal tide DW1 to QBO (∼10 m ), and the migrating semidiurnal tide SW2 to NPJO (∼12 m ) and SPJO (∼7 m ). Tidal responses to MJO and Ly are relatively weak and are therefore not identified with the same level of confidence.

The equatorial electrojet (EEJ) is a narrow band of zonal electric current flowing in the E‐region ionosphere within approximately latitude of the magnetic equator. At night, the EEJ is generally considered very weak because of low ionospheric conductivity. However, evidence in the literature suggests that strong EEJ currents might occur on the night side during geomagnetic storms. This paper presents observations of the nighttime EEJ during the January 2026 geomagnetic storm. During the storm main phase, the EEJ strengths estimated using the conventional two‐station method indicate the presence of intense westward EEJ currents (150–200 mA/m) in the Thailand and Philippine sectors during pre‐sunrise hours. Observations from a chain of low‐latitude magnetometers distributed across the Thailand sector further reveal the latitudinal structure of the ground magnetic field signatures associated with the nighttime westward EEJ, providing additional evidence for the presence of nighttime westward EEJ currents. The nighttime westward EEJ in the Thailand and Philippine sectors coincides with strong eastward EEJ (∼250 mA/m) in the Peruvian sector on the dayside, consistent with the influence of prompt penetration electric fields from high latitudes. Intensifications of the nighttime westward and daytime eastward EEJ are accompanied by enhanced asymmetric geomagnetic field disturbances at mid latitudes and equatorward expansion of auroral electrojet signatures.

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).

Ablation of re-entering satellites and rocket stages is expected to become a significant source of metals in the mesosphere, yet systematic observations remain limited so far. We present our initial Li atom observations between about 80 km and 100 km altitude using our lidar at Kühlungsborn, Germany (54°N, 12°E), covering a period between August 2024 and February 2025. The main source of the Li layer is still thought to be cosmic dust ablation. However, lithium is a crucial species for investigating anthropogenic impacts on the middle atmosphere because of its extensive use in the space industry. Our measurements revealed a column abundance mostly between 1x106 cm-2 and 5x106 cm-2. Initial simulations using the WACCM-Li model are in reasonable agreement with the observations, suggesting natural seasonal variability as the primary driver for the changes in Li abundance. Some of the observations in early 2025 showed, however, an unusually high abundance that cannot yet be explained by natural variation. A notable event occurred on February 19-20, 2025, at 00:21 UTC, with the detection of a Li cloud exhibiting densities ten times higher than typical, reaching up to ~30 atoms/cm³. Back-trajectory analysis with UA-ICON indicated the probed air mass originated from a location west of Ireland, coinciding with the atmospheric re-entry of a Falcon 9 upper stage. Simulations of the re-entry process revealed a beginning metal ablation of this rocket stage already around 100 km altitude due to its shallow entry angle. We will present the details of this case study as well as our observations of the typical Li layer. Furthermore, we will show first results of our new 3-channel multi-species lidar (MSL) that is set up to search for different species expected to be ablated by re-entering space debris, like Cu, Hf, AlO, etc., along observations of Li and (purely natural) Na.

The strongest ionospheric currents flow in general in the E‑region (~90-135 km) due to the high conductivities produced by dayside ionization. The solar quiet (Sq) current system arises from neutral winds pushing plasma across Earth’s magnetic field, generating electric fields and ionospheric currents. The strongest current at low latitude is the daytime equatorial electrojet (EEJ). While magnetic perturbations associated with these ionospheric currents are measured globally—both from ground-based observations and from low Earth orbit (LEO)—direct measurements of E‑region neutral winds remain extremely sparse. This gap limits our ability to quantify neutral wind variability on day-to-day timescales and hinders a full understanding of lower–upper atmospheric coupling and its influence on space weather phenomena such as neutral density and plasma variations. These challenges motivate the use of magnetic observations to better constrain neutral wind variability.In this presentation, we introduce atmospheric tides embedded in the neutral wind and their role in driving the wind dynamo. We illustrate how major tidal components contribute to the dynamo and the resulting magnetic signatures. We then present a data‑driven framework that combines ground-based magnetometer observations with ensemble modeling using the Thermosphere–Ionosphere–Electrodynamo General Circulation Model (TIEGCM) and an ionospheric electrodynamo model that simulates the full 3D current system and associated magnetic perturbations. This approach enables the estimation of hourly tidal variations at the TIEGCM lower boundary (~97 km altitude) and improves the representation of global EEJ variability. The simulation with improved winds is validated against LEO magnetic perturbation measurements, demonstrating that the agreement improves even in regions with limited data coverage. The results highlight the potential of magnetometer data to constrain tidal dynamics and enhance global modeling of equatorial electrodynamics.

A 10-fold enhancement of lithium atoms was detected at 96 km altitude by a resonance lidar at Kühlungsborn, Germany, approximately 20 hours after the uncontrolled re-entry of a Falcon 9 upper stage. The upper-atmospheric extension of the ICON general circulation model, nudged to ECMWF, was used to calculate winds. Backwards trajectories, including wind variability as measured by radar, traced air masses to the Falcon 9 re-entry path at 100 km altitude, west of Ireland. This study presents the first measurement of upper-atmospheric pollution resulting from space debris re-entry and the first observational evidence that the ablation of space debris can be detected by ground-based lidar. The analysis of geomagnetic conditions, atmospheric dynamics, and ionospheric measurements supports the claim that the enhancement was not of natural origin. Our findings demonstrate that identifying pollutants and tracing them to their sources is achievable, with significant implications for monitoring and mitigating space emissions in the atmosphere.

This study investigates the potential of localized total electron content (TEC) perturbation measurements, possibly associated with bottomside upwelling of the F‐layer, as precursors for forecasting ionospheric plasma irregularities, particularly the equatorial plasma bubbles (EPBs). We utilize TEC measurements from the Coherent Electromagnetic Radio Tomography (CERTO) onboard C/NOFS satellite, received by a GNU Radio Beacon Receiver (GRBR) at Phuket (8N, 98.32E; dip latitude N) to identify early signatures of the F‐layer upwelling in the evening sector, within the field‐of‐view of the Equatorial Atmosphere Radar (EAR) at Kototabang (0.2S, 100.3E, dip latitude S). Simultaneous occurrences of EPBs are monitored using the scanning capability of EAR, enabling a direct comparison between the observed TEC perturbations and the development of EPBs. Additionally, ionosonde measurements from Chumphon (10.5N, 99.4E; dip latitude N) are employed to substantiate these findings. The 445‐day analysis (2012–2014) under varying solar and geomagnetic conditions shows that while TEC perturbations often precede EPBs, not all lead to their development. EPB occurrence has been found to vary with perturbation amplitude, inferring that only certain perturbation strengths are conducive to EPB formation. Further, a receiver operating characteristic (ROC) curve analysis indicates that a TEC perturbation threshold of 5.65% yields a prediction accuracy of 96%, providing a lead time of 18–86 min. These findings demonstrate the feasibility of a satellite‐ground network comprising low‐inclination satellites with GRBR‐like receivers, sequentially traversing the same longitude sector at 30‐min intervals, for real‐time monitoring and forecasting of EPBs over a broad longitudinal sector.

A 10-fold enhancement of lithium atoms was detected at 96 km altitude by a resonance lidar at Kühlungsborn, Germany, approximately 20 hours after the uncontrolled re-entry of a Falcon 9 upper stage on 19 February 2025. The upper atmospheric extension of the ICON general circulation model nudged to the ECMWF operational analysis was used to calculate winds. Backwards trajectories, including wind variability as measured by a radar network, traced air masses to the Falcon 9 re-entry path at approximately 100 km altitude, west of Ireland. This study presents the first measurement of upper atmospheric pollution resulting from space debris re-entry and the first observational evidence that the ablation of space debris can be detected by ground-based lidar. The analysis of geomagnetic conditions, atmospheric dynamics, and ionospheric measurements strongly supports the claim that the enhancement was not of natural origin. Our findings demonstrate that identifying pollutants and tracing them to their sources is achievable, with significant implications for monitoring and mitigating space emissions in the atmosphere.

This study uses a 60‐year free‐run simulation by the upper atmospheric extension of the ICOsahedral Non‐hydrostatic (UA‐ICON) general circulation model to explore the influence of stratospheric polar vortex variability on the mesosphere and lower thermosphere (MLT). The Northern Annular Mode (NAM) index and the Southern Annular Mode (SAM) index are derived from the model output to represent the strengths of the polar vortices in the Northern Hemisphere (NH) and Southern Hemisphere (SH), respectively. During weak polar vortex events in the NH, there is an increase in zonal‐mean zonal winds in the MLT at the NH high latitudes and a warming of the lower thermosphere, accompanied by a cooling of the mesosphere. Conversely, the wind and temperature anomalies are reversed during strong NH polar vortex events. During weak polar vortex events in the SH, similar but generally weaker anomalies are observed in the corresponding hemisphere. This study also elucidates the response of the solar‐migrating semidiurnal tide (SW2) to variations in the strength of the polar vortices. A weak NH polar vortex is associated with an increase in SW2, while a strong NH vortex results in a decrease in SW2. The response of SW2 to changes in the SH polar vortex is similar, although considerably weaker. The NH polar vortex variability can explain around of the variability in the SW2 during NH winter. The SH polar vortex, however, accounts for only a small fraction of the variability (up to ) in SW2.