Mesosphere Research Articles

Tailored accelerometer calibration by POD for thermospheric density retrieval with GRACE and GRACE-FO

The density of the upper atmosphere can be determined by orbit and accelerometer data from low Earth orbit satellites as insitu measurements along the orbit. One main challenge therein is the estimation of physical accelerometer calibration parameters, meaning that these parameters should not absorb other effects and model deficiencies in the Precise Orbit Determination (POD) process. The accelerometers of all geodetic satellites like GRACE and GRACE-FO are affected by time dependent bias and scale factors. Therefore a calibration of the data is indispensable.A dynamic POD based physical accelerometer calibration is developed for the complete GRACE and GRACE-FO missions. We investigate different parametrization strategies and utilize different observation data, as the accurate inter-satellite ranging additionally to GPS orbit data. For the estimation parameters we distinguish between offset and scale, furthermore, cross-track and radial directions are significantly less sensitive than along-track and require a different evaluation. For the offset, constant and time dependent parameters are investigated. Furthermore, a continuous offset calibration over arc boundaries is implemented and tested. The sensitivity of the scale factor is lower, although, in contrast to the offset, it increases with higher total accelerations. This means that it needs to be estimated over longer time periods. We investigate periods between three hours and one month as well as results from Gravity Field Recovery (GFR). Monthly scale factors give valuable results, at least for x-axis and when the Solar activity is not very low. Nevertheless, we also estimate weighted constant scale factors from the monthly results and use these in a subsequent POD, giving more realistic offset results for most periods and cross-track and radial directions.From the used background models in the POD, Earth’s gravitational model has a noticeable influence on the estimated calibration parameters, especially the scale factors. We utilized several different models. Results with monthly ITSG solutions are distinctly better than the ones with the time dependent GOCO06s model.We show that the validation with usual metrics, like post-fit POD residuals, is not able to reflect the quality of the different estimated calibration parameters. For a quantitative validation we introduce an approach based on the modeled non-gravitational accelerations. Therefore, the uncertainty of the models is evaluated first. The influence of main error sources in the models is assessed and propagated to the results.We compare our scale parameters to available references and the complete calibration to TU Delft’s latest results. Finally we show the effect of different calibration options on the retrieved density.The estimated calibration parameters and non-gravitational accelerations for the whole GRACE and GRACE-FO missions are available on our data server www.zarm.uni-bremen.de/zarm_daten.

The Response of the Venusian Upper Atmosphere During the Passage of Interplanetary Coronal Mass Ejections

The Response of the Venusian Upper Atmosphere During the Passage of Interplanetary Coronal Mass Ejections

A new hybrid deep neural network for multiple sites PM2.5 forecasting

Many studies have confirmed that fine particulate matter (PM2.5) poses significant hazards to both human health and the ecological environment. Predicting future trends in PM2.5 concentrations is crucial for preventing air pollution hazards to human health. However, current machine learning-based forecasting models often focus on specific regions or sites, resulting in poor spatial generalization performance. To address this issue, this study utilizes ERA5 meteorological reanalysis data, MERRA2 assimilated aerosol optical depth (AOD) data, and ground pollutant monitoring site data to construct a three-dimensional dataset. A novel hybrid deep neural network model (D_GAT) is proposed to simultaneously forecast the future 72h PM2.5 concentration trends for all sites in China. The D_GAT model combines the advantages of a graph attention network and a long short-term memory neural network, which can effectively aggregate spatial information between sites and simulate the spatial transport process and time series change characteristics of pollutant particles. Moreover, the proposed calculation method for attention scores quantified based on the actual pollutant propagation characteristics, combined with the upper atmosphere pollution transport process represented by AOD, can better express the pollution contributions of different neighboring sites to the predicted central site. Experimental results show that, compared to four other baseline models, the novel model achieves an average R2 of 0.732 for all sites in 72-h prediction, which is the highest among the five models, and the prediction accuracy of 72h is also in the forefront compared with the current similar research. The RMSE and MAE are 14.63 μg/m3 and 9.49 μg/m3, respectively, which are 2–4 μg/m3 lower than the other four baseline models, indicating that it has higher reliability and can achieve the goal of timely prediction and early warning. Overall, the new model is an effective tool for multiple sites generalization forecasting.

Spectral deconvolution approach for Beryllium-7 detection: Evaluating soil redistribution with NaI(Tl) detectors

Beryllium-7 is a cosmogenic radionuclide produced in the upper atmosphere through the spallation of cosmic rays and falls to Earth mainly by wet deposition. Given its short half-life (53 days) and strong adsorption to the clay present in the soil, 7Be inventory can be evaluated to obtain information about soil redistribution over periods of up to 6 months. By performing these measurements, one can infer the efficiency of soil management and conservation procedures. The isotope presence is measured using gamma-ray spectrometry to detect its decay emission, specifically a photon with an energy of 477.6 keV. Since other isotopes found in soil emit photons with similar energies, it is common to use High-Purity Germanium (HPGe) detectors due to their high energy resolution. However, these detectors are expensive and require cryogenic cooling during operation. An alternative is the Thallium-Activated Sodium Iodide (NaI(Tl)) detector, which is less costly and does not require cryogenic cooling, but has poorer resolution and cannot separate the emissions from 228Ac (463.0 keV), 7Be, and 208Tl (510.7 keV). This work aims to apply spectral deconvolution to quantify 7Be in soil samples collected from an agricultural mega-parcel situated on a hill slope and evaluate the soil redistribution experienced within. The activities of the interfering isotopes were quantified using other emissions, and the results were used to calculate the corresponding area in the desired region of the spectra. From this, 7Be activities were calculated and compared with the HPGe results to validate the deconvolution technique. The calculated activities for the three radioisotopes showed similar correspondence between the two detectors, indicating that the applied method is adequate for evaluating soil redistribution at lower costs. The calculated net soil deposition was 36.4 ± 6.4 kgm−2 for the NaI(Tl) detector and 26.4 ± 7.9 kgm−2 for the HPGe detector during the evaluated period. Furthermore, these results suggest that a similar approach can be applied to quantify other isotopes using NaI(Tl) detectors as an alternative to HPGe detectors.

Effect of atmospheric density stratification on the generation of water waves by wind

The critical level instability mechanism for the generation of water waves by wind is re-examined for the situation when the atmosphere is density stratified. The density stratification is confined to the middle and upper atmosphere and then two cases are investigated. In case (A) no internal gravity waves are generated in the upper atmosphere and the effect of the density stratification is very small. In case (B) vertically propagating internal gravity waves form in the upper atmosphere and travel to infinity causing an energy loss, thus inhibiting the critical level instability in the lower atmosphere. Both cases are examined quantitatively for a logarithmic wind shear profile.

Simulation of a cold spell in Guangdong-Hong Kong-Macao Greater Bay Area with WRF: Sensitivity to PBL schemes

The selection of the planetary boundary layer (PBL) parameterisation schemes is crucial for the simulation of local meteorology, especially under extreme weather events. A suitable PBL scheme is one of the key conditions to accurately reproduce the real weather conditions. In this study, the performance of all the three available PBL schemes that can be coupled with the multi-layer urban canopy model in the Weather Research and Forecasting (WRF) model: Yonsei University (YSU), Mellor-Yamada-Janjic (MYJ), and Bougeault-Lacarrere (BL), is evaluated for a cold spell event with Guangdong-Hong Kong-Macao Greater Bay Area (GBA) as the study region. It is found that accurate prediction of the strength of the vertical mixing and the change in wind speeds over the upper atmosphere is critical for reproducing the nighttime temperatures during the cold spell. The simulations of the BL scheme are consistent with observations that wind speeds do not vary much during daytime and nighttime, thus exhibiting strong vertical mixing and slowing down the near-surface temperature decrease during nighttime. The MYJ and YSU schemes cause significant underestimation of the nighttime 2-m temperature due to significant overestimation of the nighttime upper-air wind speeds, which leads to more heat transport through horizontal advection and hinders vertical mixing and convective activities. The results confirm that selection of a suitable PBL scheme can effectively reduce the uncertainty of the simulation results, and the coupling of the BL scheme with the multi-layer urban canopy model can better simulate the cold spell events occurring in the GBA, which also provides valuable references for the simulation of other similar coastal cities.

Tracing the Transport and Residence Times of Atmospheric Microplastics Using Natural Radionuclides.

While atmospheric microplastics are known to be transported over long distances, their residence times and transport processes lack clarity. This study utilized natural radionuclides 7Be, 210Pb, and 210Po to explore the transport of atmospheric microplastics in Tianjin, a coastal city in Northern China. Microplastic concentrations ranged from 0.03 to 0.13 particles m-3 over the course of a year. The proportion of microplastic fragments in winter was significantly higher than that in other seasons, with median microplastic sizes in autumn and winter being larger than those in spring and summer. The atmospheric microplastic surface was rough, exhibiting irregular pores and multiple depressions and cracks. Microplastics experienced vertical mixing with the upper atmosphere in April and August and were influenced by rainfall in July. The residence time of atmospheric particles ranged from 9.47 to 22.85 days throughout the year, with an average of 14.41 days. The peak residence time of atmospheric particulates in November may be correlated with increased 210Po levels from coal consumption. Their prolonged atmospheric presence and rough surface allow microplastics to act as carriers for various chemical pollutants, underscoring the complexity and potential risks associated with their presence in the atmosphere.

GOLD Observations of the Merging of the Southern Crest of the Equatorial Ionization Anomaly and Aurora During the 10 and 11 May 2024 Mother's Day Super Geomagnetic Storm

AbstractUsing NASA's Global‐scale Observations of the Limb and Disk (GOLD) imager, we report nightside ionospheric changes during the G5 super geomagnetic storm of 10 and 11 May 2024. Specifically, the nightside southern crest of the Equatorial Ionization Anomaly (EIA) was observed to merge with the aurora near the southern tip of South America. During the storm, the EIA southern crest was seen moving poleward as fast as 450 m/s. Furthermore, the aurora extended to mid‐latitudes reaching the southern tips of Africa and South America. The poleward shift of the equatorial ionospheric structure and equatorward motion of the aurora means there was no mid‐latitude ionosphere in this region. These observations offer unique insights into the ionospheric response to extreme geomagnetic disturbances, highlighting the complex interplay between solar activity and Earth's upper atmosphere.

Augmented Four‐Dimensional Mesosphere and Lower Thermosphere Wind Field Reconstruction via the Physics‐Informed Machine Learning Approach HYPER

AbstractThe mesosphere and lower thermosphere (MLT) is a fluid framework whose multiscale dynamics is determined by a superposition of non‐linear processes and by the interplay of gravity waves and turbulent motions. A thorough comprehension of this atmospheric region requires substantial observational infrastructure, needed to resolve and disentangle its complex dynamics. State‐of‐the‐art observational methods struggle to accurately capture mesoscale dynamics due to the inherent difficulty to perform observations at MLT altitudes. A majority of the observational methods rely on assumptions such as homogeneity, smoothness of the prognostic fields, or zero vertical wind velocities, which may not hold in the upper atmosphere at the mesoscales. In this study, we introduce a novel machine learning‐based approach HYPER (HYdrodynamic Point‐wise Environment Reconstructor), designed to characterize MLT dynamics. HYPER utilizes a physics‐informed neural network to project sparse Doppler meteor detections into four‐dimensional time‐series arrays containing the Cartesian components of the velocity field. This method combines meteor radar observations with the physics prescribed by the Navier‐Stokes equations. The validation of HYPER was conducted through a series of benchmarks on numerical data and the application of our algorithm on actual meteor radar observations, all of which yielded realistic approximations of the reconstructed physical fields. This innovative approach represents a significant step toward an accurate characterization of the MLT dynamics, overcoming the limitations of existing methods, and providing valuable insights into the behavior of this poorly accessible region of the atmosphere.

Seasonal Variation of Saturn's Lyα Brightness

We examine Saturn’s nonauroral (dayglow) emissions at Lyα observed by the Cassini/Ultraviolet Imaging Spectrograph (UVIS) instrument from 2003 until 2017, to constrain meridional and seasonal trends in the upper atmosphere. We separate viewing geometry effects from trends driven by atmospheric properties, by applying a multivariate regression to the observed emissions. The Lyα dayglow brightnesses depend on the incident solar flux, solar incidence angle, emission angle, and observed latitude. The emissions across latitudes and seasons show a strong dependence with solar incidence angle, typical of resonantly scattered solar flux and consistent with no internal source such as electroglow. We observe a bulge in Lyα brightnesses that shifts with the summer season from the southern to the northern hemisphere. We estimate atomic hydrogen optical depths above the methane homopause level for dayside disk observations (2004–2016) by comparing observed Lyα emissions to a radiative transfer model. We model emissions from resonantly scattered solar flux and a smaller but significant contribution by scattered photons from the interplanetary hydrogen (IPH) background. During the northern summer, inferred hydrogen optical depths steeply decrease with latitude toward the winter hemisphere from a northern hemisphere bulge, as predicted by a 2D seasonal photochemical model. The southern hemisphere mirrors this trend during its summer. However, inferred optical depths show substantially more temporal variation between 2004 and 2016 than predicted by the photochemical model. We benchmark our brightness values by comparing observed IPH Lyα emissions from Cassini/UVIS in 2006 with a model of the IPH emissions. Cassini/UVIS observations agree well with the modeled IPH background.

A Technique for Retrieving the Exospheric Number Density Distribution from Pickup Ion Ring Distributions

Ion pickup by the solar wind is ubiquitous in space plasma. Because pickup ions are originally produced by ionization of an exospheric neutral atmosphere, their measurements contain information on the exospheric neutral abundance. Here we established a method to retrieve exospheric number densities, by analyzing the ion velocity distribution functions of pickup ions measured by the Mars Atmosphere and Volatile EvolutioN spacecraft. We successfully retrieved exospheric oxygen density distributions at altitudes ranging from 1000 to 10,000 km around Mars except for the vicinity of the bow shock. This method can be applied to other space missions to study the upper atmosphere of planets, moons, and other small bodies in our solar system, where pickup ions exist.

Probing atmospheric escape through metastable He I triplet lines in 15 exoplanets observed with SPIRou

For several years, the metastable helium triplet line has been successfully used as a tracer to probe atmospheric escape in transiting exoplanets. This absorption in the near-infrared (1083.3 nm) can be observed from the ground using high-resolution spectroscopy, providing new constraints on the mass-loss rate and the temperature characterizing the upper atmosphere of close-in exoplanets. The aim of this work is to search for the He triplet signature in 15 transiting exoplanets – ranging from super-Earths to ultrahot Jupiters – observed with SPIRou, a high-resolution (R ~ 70 000) near-infrared spectropolarimeter at the CFHT, in order to bring new constraints or to improve existing ones regarding atmospheric escape through a homogeneous study. We developed a full data processing and analysis pipeline to correct for the residual telluric and stellar contributions. We then used two different 1D models based on the Parkerwind equations and nonlocal thermodynamic equilibrium (NLTE) radiative transfer to interpret the observational results. We confirm published He triplet detections for HAT-P-11 b, HD 189733 b, and WASP-69 b. We tentatively detect the signature of escaping He in HD 209458 b, GJ 3470 b, and WASP-76 b. We report new constraints on the mass-loss rate and temperature for our three detections and set upper limits for the tentative and nondetections. We notably report improved constraints on the mass-loss rate and temperature of the escaping gas for TOI-1807 b, and report a nondetection for the debated atmospheric escape in GJ 1214 b. We also conducted the first search for the He signature in GJ 486 b since its discovery and report a nondetection of the He triplet. Finally, we studied the impact of important model assumptions on our retrieved parameters, notably the limitations of 1D models and the influence of the H/He ratio on the derived constraints.

On the Response of the Transition Region and the Corona to Rapid Excursions in the Chromosphere

Spicules are the thin hair/grass-like structures that are prominently observed at the chromospheric solar limb. It is believed that fibrils and rapid blueshifted and redshifted excursions (RBEs and RREs; collectively referred to as REs) correspond to on-disk counterparts of type I spicules and type II spicules, respectively. Our investigation focuses on observing the response of these REs alongside similar spectral features in the chromosphere, transition region (TR), and corona, utilizing space–time plots derived from coordinated observations from the Swedish 1 m Solar Telescope/Hα, Interface Region Imaging Spectrograph (IRIS), and Solar Dynamics Observatory. Our analysis reveals upflowing REs, promptly reaching temperatures characteristic of the TR and corona, indicating a multithermal nature. Similarly, downflowing features exhibiting similar spectral signatures over the disk display plasma motion from the corona to chromospheric temperatures, demonstrating a multithermal nature. In addition to distinct upflows and downflows, we observe sequential upflow and downflow along the same path, depicting a distinctive parabolic trajectory in space–time plots of observations sampling TR and various coronal passbands. Similar to isolated upflows and downflows, these REs also exhibit a multithermal nature throughout their trajectory. Furthermore, our results reveal a more intricate motion of the REs in which both upflow and downflow coexist at the same spatial location. On a different note, our analysis, utilizing coordinated IRIS spectral observations, shows spatiotemporal redshifts/downflows in both the TR and chromosphere, suggesting that at least subsets of the strong redshifts/downflows observed in TR temperature spectra result from the return from the upper atmosphere flow of plasma in the form of bundles of spicules or features exhibiting similar spectra.

Bridging Model–Data Discrepancies in Mars’ Dayside Ionosphere: Exploring Varying Reaction Rate Coefficients

Measurements of concentrations of neutral and ion species in the upper atmosphere of Mars by the Neutral Gas and Ion Mass Spectrometer (NGIMS) on board the Mars Atmosphere and Volatile EvolutioN mission have served as model input and/or for comparison with model output in numerous earlier studies of the Martian dayside ionosphere. While many models reproduce the altitudinal density profiles of key ion species within a factor of a few, it has proven challenging to achieve a level of agreement within tens of percent for multiple ion species over a wide range of altitudes. We explore means to overcome this issue while keeping with a reduced chemical model and utilizing the assumptions of photochemical equilibrium and that the NGIMS data are devoid of any measurement errors. We entertain, for instance, the idea that the rate coefficient for the charge-transfer reaction between CO2+ and O may vary with altitude as a result of a pressure-controlled internal energy distribution of the CO2+ population.

Unraveling the untwisting process and upward mass transfer of a twisted prominence driven by vortex motion

Solar filaments or prominences are common features in the Sun's atmosphere that contain cool chromospheric material suspended within the hot corona. However, the intricate topology of these structures and the mechanisms driving their instability and upward material transfer are not well understood. Investigating these issues is essential for gaining insight into the fundamental laws that govern solar activity. This study is to analyze a specific twisted prominence observed on February 10, 2021, and to explore its dynamics, including stability, motion, and material transfer. The study also aims to propose a mechanism, based on the K\'arm\'an Vortex Street instability, to explain the destabilization of the prominence. The study utilizes high-resolution H$_ alpha $ observations from the 1-m New Vacuum Solar Telescope and space-borne observations from the Solar Dynamics Observatory. These observations capture the characteristics and behavior of the twisted prominence. We analyzed the data to investigate the equilibrium state, subsequent destabilization, vortex motion, oscillations, resonations, untwisting, and upward mass loading of the prominence. We also detected and measured the speeds of outflows surrounding the prominence. The study reveals that the observed twisted prominence exhibited a stretched and twisted structure at its apex, distinguishing it from familiar cloudy prominences. Following a period of more than 30 hours in equilibrium, the prominence underwent destabilization, leading to a series of dynamic phenomena, such as vortex motion, oscillations, resonations, untwisting, and the upward transfer of mass. Consequently, material from the top of the prominence was carried upward and deposited into the overlying magnetic arcades. Noteworthy, outflows surrounding the prominence were characterized by speeds exceeding 40 km s$^ Based on these findings, we propose, for the first time, a mechanism rooted in the K\'arm\'an Vortex Street instability to explain the destabilization of the prominence. The estimated typical Strouhal Number of 0.23pm 0.06, which is related to vortex shedding, falls within the expected range for the K\'arm\'an Vortex Street effect, as predicted by simulations. These discoveries provide new insights into the dynamics and fundamental topology of solar prominences and reveal a previously unknown mechanism for mass loading into the upper atmosphere.

Influence of the Sun on the night side of the Earth

Solar radiation breaks hydrogen bonds between water molecules, which prevents their self-organization and destroys water clusters. This may be accounted for by the influence of muons which are generated in the upper atmosphere by the solar wind. Muon flux is anisotropic and changes direction depending on the position of the Sun in the sky. For this reason, the rate of hydrolysis of triethyl phosphite in acetonitrile depends on geometric shape of the reaction solution, its position in space and changes during the day. For example, in three 5 mm NMR-tubes directed North-South, East-West and Vertically the distributions of the rates of this reaction are always different in the daytime. At noon, when the Sun is at its zenith, the rates are considerably higher in the horizontal tubes, and at sunrise and sunset when the Sun shines along the East-West line the rate is higher in the vertical tube. One might assume that at night when the Sun irradiates the opposite side of the Earth, this phenomenon should disappear, and the reaction rates should be the same in all directions. However, it turned out that at midnight the distribution of hydrolysis rates in multidirectional NMR-tubes is the same as at noon. This may indicate that on the night side of the Earth the influence of the Sun is inducing the appearance of some radiation vertically from underground. This phenomenon requires detailed study in different places on the Earth.

The Impact of Polar Vortex Strength on the Longitudinal Structure of the Noontime Mid-Latitude Ionosphere and Thermosphere

Ground-based ionospheric, CHAMP/STAR, and GOCE satellite neutral density ρ observations under deep solar minimum conditions were used to find whether there is a dependence of longitudinal variations on polar vortex strength. Ionospheric stations at fixed-dipole geomagnetic Φ ≈ 38° and geographic φ ≈ 40°N latitudes located in ‘near-pole’ and ‘far-from-pole’ longitudinal sectors were used in the analysis. No significant longitudinal NmF2 (electron concentration in the F2-layer maximum) dependence on the polar vortex strength was revealed. Geomagnetic control was shown to be responsible for the observed longitudinal NmF2 variations. Satellite-observed longitudinal variations in neutral density did not show any visible reaction to the polar vortex strength. However, the impact of sudden stratospheric warming (SSW) on the upper atmosphere is strong enough to change the neutral density longitudinal distribution. The impact of SSW shows a global occurrence and ‘works’ within 3–5 days in geographic coordinates in the vicinity of the SSW peak. Atomic oxygen values retrieved under ‘strong’ and ‘weak’ polar vortex strengths confirm the results obtained on longitudinal variations in NmF2 and ρ. In conclusion, no visible effects related to ‘strong’ or ‘weak’ polar vortex strengths have been revealed in either NmF2 or satellite neutral density longitudinal variations. Alternatively, such effects may be very small and therefore cannot be confirmed experimentally.

The Preparation Phase of the 2022 ML 5.7 Offshore Fano (Italy) Earthquake: A Multiparametric–Multilayer Approach

This paper presents an analysis of anomalies detected during the preparatory phase of the 9 November 2022 ML = 5.7 earthquake, occurring approximately 30 km off the coast of the Marche region in the Adriatic Sea (Italy). It was the largest earthquake in Italy in the last 5 years. According to lithosphere–atmosphere–ionosphere coupling (LAIC) models, such earthquake could induce anomalies in various observable variables, from the Earth’s surface to the ionosphere. Therefore, a multiparametric and multilayer approach based on ground and satellite data collected in each geolayer was adopted. This included the revised accelerated moment release method, the identification of anomalies in atmospheric parameters, such as Skin Temperature and Outgoing Longwave Radiation, and ionospheric signals, such as Es and F2 layer parameters from ionosonde measurements, magnetic field from Swarm satellites, and energetic electron precipitations from NOAA satellites. Several anomalies were detected in the days preceding the earthquake, revealing that their cumulative occurrence follows an exponential trend from the ground, progressing towards the upper atmosphere and the ionosphere. This progression of anomalies through different geolayers cannot simply be attributed to chance and is likely associated with the preparation phase of this earthquake, supporting the LAIC approach.

Selecting the best solar EUV proxy for long-term timescale applications

Solar EUV proxies are a solution to the difficulties in obtaining solar EUV time series covering extended periods or during times without measurements available. Despite being very similar at interannual and decadal timescales, proxies are not identical. The upper atmosphere, highly sensitive to this spectral range, can serve as a “witness” of solar EUV variations to help selecting the best proxy. Its choice can be critical depending on the problem we are trying to solve through the proxy implementation and on the nature of the proxies’ non-identical part variation. We analyze the best proxy selection process whose outcome depends on the method and on the physics knowledge we have of the system. This study aims to contribute and highlight certain critical aspects of selection methodologies. A case where this issue becomes critical is upper atmosphere long-term trends’ estimation in order to detect the increasing greenhouse gas effect along the last decades.

Exoplanet Aeronomy: A Case Study of WASP-69 b’s Variable Thermosphere

Aeronomy, the study of Earth’s upper atmosphere and its interaction with the local space environment, has long traced changes in the thermospheres of Earth and other solar system planets to solar variability in the X-ray and extreme-ultraviolet (collectively, XUV) bands. Extending comparative aeronomy to the short-period extrasolar planets may illuminate whether stellar XUV irradiation powers atmospheric outflows that change planetary radii on astronomical timescales. In recent years, near-IR transit spectroscopy of metastable Hei has been a prolific tracer of high-altitude planetary gas. We present a case study of exoplanet aeronomy using metastable Hei transit observations from Palomar Observatory's Wide Field InfraRed Camera and follow-up high-energy data from the Neil Gehrels Swift Observatory that were taken within 1 month of the WASP-69 system, a K-type main-sequence star with a well-studied hot Jupiter companion. Supplemented by archival data, we find that WASP-69's X-ray flux in 2023 was less than 50% of what was recorded in 2016 and that the metastable Hei absorption from WASP-69 b was lower in 2023 versus past epochs from 2017 to 2019. Via atmospheric modeling, we show that this time-variable metastable Hei signal is in the expected direction given the observed change in stellar XUV, possibly stemming from WASP-69's magnetic activity cycle. Our results underscore the ability of multiepoch, multiwavelength observations to paint a cohesive picture of the interaction between an exoplanet’s atmosphere and its host star.