Advances in Space Research最新文献

{"title":"Remote sensing role in assessing the changes of LULC and LST during war on Gaza","authors":"Zahraa Zawawi ,&nbsp;Iman khudiesh ,&nbsp;Ayah Helal","doi":"10.1016/j.asr.2026.01.043","DOIUrl":"10.1016/j.asr.2026.01.043","url":null,"abstract":"<div><div>The Gaza Strip, located in Palestine, consists of five governorates including North Gaza, Gaza, Deir el-Balah, Khan Younis, and Rafah. The region has experienced several major wars, including those in 2008, 2009, 2012, 2014, 2020, and most recently in 2023, which began on October 7, 2023. These repeated wars have had a devastating impact on the Gaza Strip, particularly on land use and land cover, both of which have been significantly altered over time. This study examines how frequent wars between 2005 and 2024 have transformed the landscape, with a specific focus on changes in land use and land cover and their relationship with Land Surface Temperature (LST). The research relies on remote sensing data from Landsat satellites (Landsat 4–5 TM, Landsat 7 ETM+, and Landsat 8–9 OLI/TIRS), in combination with the Boolean AND tool and Geographic Information System (GIS) technology, to conduct a spatial analysis of these changes. The results reveal widespread destruction in both urban and agricultural areas, which has contributed to a substantial increase in LST. In most cases, LST increases ranged from 5 to 10°C; however, following the 2023 war, the increase was considerably higher, reaching between 5 and 18°C. The loss of agricultural land is particularly alarming, as it disrupts local food production and results in unusually high LST levels, thereby intensifying environmental stress. The study shows the severe and long-term environmental consequences of war on Gaza’s land and climate.</div></div>","PeriodicalId":50850,"journal":{"name":"Advances in Space Research","volume":"77 6","pages":"Pages 6832-6854"},"PeriodicalIF":2.8,"publicationDate":"2026-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147388079","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Quantification of oxygen production from solar pyrolysis of lunar regolith","authors":"Jack Robinot ,&nbsp;Sylvain Rodat ,&nbsp;Stéphane Abanades ,&nbsp;Eric Bêche ,&nbsp;Alexis Paillet ,&nbsp;Aidan Cowley","doi":"10.1016/j.asr.2026.02.003","DOIUrl":"10.1016/j.asr.2026.02.003","url":null,"abstract":"<div><div>The extraction of oxygen from lunar regolith is a critical step toward enabling sustainable human presence on the Moon, reducing reliance on Earth-based resupply. Among various proposed in-situ resource utilization (ISRU) methods, solar vacuum pyrolysis offers a promising, reagent-free approach by leveraging the Moon’s natural vacuum, abundant regolith and solar energy resources. Conventional oxygen extraction techniques, such as carbothermal reduction or molten salt electrolysis, require imported reactants, posing challenges for long-term lunar operations. Here, we demonstrate that concentrated solar pyrolysis under low vacuum can efficiently extract oxygen from EAC-1 lunar regolith simulant while simultaneously producing metallic byproducts. Using concentrated solar energy with a maximum flux of 4.8 MW/m² under low vacuum conditions at 10 mbar, we extracted 35 mg of oxygen, corresponding to a mass yield of 1.05 %. This represents 2.47 % of the total oxygen available in the regolith simulant recovered as gaseous oxygen. These values provide the first ever quantification of oxygen production from regolith solar pyrolysis. Moreover, process intensification routes are further identified. These findings indicate that oxygen production occurs in distinct stages, with early release during regolith melting, followed by sustained extraction at higher temperatures. This study also suggests that fractional separation of metals might be possible, proposing a potential pathway for in-situ metal refining on the Moon. Solar vacuum pyrolysis requires no consumable or reductants and operates under conditions naturally available on the lunar surface, enhancing its feasibility for large-scale ISRU applications. This work provides new insights into solar vacuum pyrolysis as a process for lunar oxygen extraction and metal separation. These results reinforce the strategic importance of ISRU for enabling long-duration lunar missions, reducing Earth-based supply dependency, and laying the groundwork for autonomous life support, construction, and fuel production using local resources.</div></div>","PeriodicalId":50850,"journal":{"name":"Advances in Space Research","volume":"77 6","pages":"Pages 7373-7386"},"PeriodicalIF":2.8,"publicationDate":"2026-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147387679","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"LLM-KGFP: A chain-of-thought-driven knowledge graph planner for autonomous rover operations in lunar polar shadowed regions","authors":"HongRun Chen ,&nbsp;Li Yang ,&nbsp;Long Sun ,&nbsp;HaoQing Yu","doi":"10.1016/j.asr.2026.01.031","DOIUrl":"10.1016/j.asr.2026.01.031","url":null,"abstract":"<div><div>Permanently shadowed regions (PSRs) at the lunar south pole present formidable challenges for autonomous planetary exploration, owing to their extreme environmental conditions and significant operational uncertainty. These constraints severely undermine the effectiveness of conventional planning methods, particularly for long-horizon, multi-step robotic tasks. Traditional planning methods, such as Hierarchical Task Networks (HTN) or Model Predictive Control (MPC), rely heavily on predefined task models and rigid rule-based policies, which struggle to adapt to the evolving and unstructured nature of PSR environments.To address these challenges, we propose a novel Task and Motion Planning (TAMP) framework that combines high-level reasoning with low-level motion planning using large language models (LLMs). By leveraging the strong reasoning, semantic interpretation, and generalization capabilities of LLMs, our framework facilitates robust and flexible rover–ground collaborative planning, enabling autonomous operations in highly constrained environments. Specifically, we introduce the Knowledge Graph Feedback Planner with Chain-of-Thought Reasoning for Autonomous Space Systems (LLM-KGFP), which integrates a structured local knowledge base with Chain-of-Thought (CoT) prompting to enhance the LLM’s symbolic reasoning and adaptability in complex environments such as PSRs.Through extensive simulation experiments conducted in a high-fidelity lunar south pole environment, we demonstrate that LLM-KGFP significantly improves both planning accuracy and adaptability. Compared to existing baselines, LLM-KGFP achieves a 62.15 % improvement in task success rate, and a 48.16 % increase in performance when handling semantically ambiguous task instructions. These results underscore the potential of LLM-guided TAMP frameworks to advance intelligent, context-aware autonomous planning, bridging high-level reasoning with low-level execution to enhance decision-making in future planetary rover missions.</div></div>","PeriodicalId":50850,"journal":{"name":"Advances in Space Research","volume":"77 6","pages":"Pages 7406-7423"},"PeriodicalIF":2.8,"publicationDate":"2026-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147387684","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"CMEGNets: A self-supervised framework for coronal mass ejection detection & region segmentation","authors":"Besma Guesmi ,&nbsp;Jinen Daghrir ,&nbsp;David Moloney ,&nbsp;Jose Luis Espinosa-Aranda ,&nbsp;Elena Hervas-Martin","doi":"10.1016/j.asr.2026.01.061","DOIUrl":"10.1016/j.asr.2026.01.061","url":null,"abstract":"<div><div>The detection and analysis of coronal mass ejections (CMEs) rely on robust segmentation of LASCO C2 and C3 coronagraph images. We introduce CMEGNets, a novel self-supervised framework that eliminates the need for manual annotations by leveraging contrastive pre-training and iterative pseudo-label generation. First, we pretrain a lightweight backbone using instance discrimination on large volumes of unlabelled LASCO data. Next, we derive statistical pseudo-masks via unsupervised clustering of feature activations, which in turn supervise fine-tuning of a U-Net segmentation head. Finally, a small set of expert-verified masks refines the network in a semi-supervised loop. On the LASCO C2 benchmark, CMEGNets achieves 99 % classification accuracy between CME and non-CME frames and a 95 % Dice coefficient for CME region segmentation. Moreover, our method reduces the annotation effort by more than 80 %. These results demonstrate that CMEGNets effectively produce expert-quality coherent segmentations while avoiding costly manual labelling.</div></div>","PeriodicalId":50850,"journal":{"name":"Advances in Space Research","volume":"77 6","pages":"Pages 7455-7483"},"PeriodicalIF":2.8,"publicationDate":"2026-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147387685","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Meteoroid streams and associations based on radar observations at the Hisar Astronomical Observatory in January 1970","authors":"M. Narziev,&nbsp;H.F. Khujanazarov","doi":"10.1016/j.asr.2026.01.021","DOIUrl":"10.1016/j.asr.2026.01.021","url":null,"abstract":"<div><div>Based on the data of radiants, velocities, and orbital elements of 2743 meteors measured using the radio direction-finding and timing method at the Hisar Astronomical Observatory from January 1 to 16, 1970, and from January 18 to 31, 1970, the identification of meteoroids into meteoroid streams and associations was carried out in three stages: (a) graphical; (b) by velocities; and (c) applying the Southworth-Hawkins and Jopek criteria. As a result, from 279 clusters of radiants identified by the graphical method, 109 groups were actually obtained and identified as meteoroid streams and associations. Among them, 67 correspond to known meteoroid streams, while 42 are candidates for new meteoroid streams or associations.</div><div>For all meteor showers and associations, data on radiant coordinates, velocities, orbital elements, as well as average values of mass and density of meteoroids are provided. The average masses of meteoroids in the groups range from 4.4 × 10^–4 to 1.7 × 10^–1 g, and the densities range from 0.3 to 6.4 g/cm³.</div></div>","PeriodicalId":50850,"journal":{"name":"Advances in Space Research","volume":"77 6","pages":"Pages 7484-7493"},"PeriodicalIF":2.8,"publicationDate":"2026-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147387686","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Atmospheric tide amplitudes and their dependence on QBO and ENSO phases: insights from MUAM ensemble simulations","authors":"A.V. Koval ,&nbsp;K.A. Didenko ,&nbsp;T.S. Ermakova ,&nbsp;S. Eswaraiah ,&nbsp;A.S. Fadeev ,&nbsp;E.N. Savenkova ,&nbsp;A.V. Shnaider ,&nbsp;A.V. Sokolov","doi":"10.1016/j.asr.2026.01.047","DOIUrl":"10.1016/j.asr.2026.01.047","url":null,"abstract":"<div><div>This study examines the dependence of tide amplitudes in the upper atmosphere on long-period tropical oscillations, specifically the Quasi-Biennial Oscillation (QBO) of zonal wind in the equatorial stratosphere and the El Niño–Southern Oscillation (ENSO). Numerical simulations of global atmospheric circulation are performed with the nonlinear mechanistic Middle and Upper Atmosphere Model (MUAM) for different combinations of QBO/ENSO phases. The structures of migrating and non-migrating diurnal and semidiurnal tides are calculated. The analysis focuses on boreal winter (January–February), when planetary waves (PWs) reach peak activity and contribute to the nonlinear generation of non-migrating tides. The results demonstrate, in particular, that the migrating diurnal westward propagating tide (DW1) is amplified during the westerly QBO phase (wQBO) and under La Niña conditions. For the semidiurnal migrating tide (SW2), ENSO effects are found to be more pronounced than those of the QBO. During El Niño, the tide’s amplitude decreases in the equatorial region while increasing to the North and South of it, regardless of the QBO phase. Changes in non-migrating tides differ from those of migrating tides with similar periods, which is attributed to the altered wave activity of the stationary PW with zonal wave number 1 (SPW1). The effect of strengthening/weakening of non-migrating diurnal westward propagating tide (DW2) generation for different combinations of QBO/ENSO is demonstrated explicitly by considering the terms responsible for the nonlinear interaction of PW1 and DW1 in the balance equation of perturbed potential enstrophy. Idealized simulations isolating the effects of QBO and ENSO, allowed for the differentiation of the influences of these two oscillations. Such separation is difficult with observational data, where limited time series restrict sample size and reduce statistical power to distinguish between these closely related phenomena.</div></div>","PeriodicalId":50850,"journal":{"name":"Advances in Space Research","volume":"77 6","pages":"Pages 7300-7315"},"PeriodicalIF":2.8,"publicationDate":"2026-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147387887","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Refined dual-horizon peridynamics model for step-path failure analysis of rock slope","authors":"Yu Bai ,&nbsp;Mingyu Yu ,&nbsp;Hao Luo ,&nbsp;Ning Guo ,&nbsp;Yanan Wang ,&nbsp;Jiayun Han ,&nbsp;Jiajun Zhang ,&nbsp;Shida Liu ,&nbsp;Xinlei Han ,&nbsp;Ning Luo ,&nbsp;Hu Zhang ,&nbsp;Yanan Zhang","doi":"10.1016/j.asr.2026.01.068","DOIUrl":"10.1016/j.asr.2026.01.068","url":null,"abstract":"<div><div>The step-path failure is a typical unstable mode of rock slope caused by the crack propagation and coalescence of discontinuous interfaces. To simulate the complex and destructive process of step-path failure in rock slopes, a refined dual-horizon bond-based peridynamics (BB PD) model is presented. The calculation efficiency is improved via nonuniform discretization. The potential failure zone is meshed with dense grids, and the other region is meshed with sparse grids. By using the peridynamic differential operator, the force density vector is redefined, and the requirement for surface correction is removed. The accuracy of the current approach is verified by comparing the deformation of the slope under quasi-static loading and failure of granite under blasting loading with other numerical methods. Then the progressive damage process for step-path failure of rock slope under quasi-static and dynamic loading is analyzed, respectively. The behavior of crack initiation, propagation, bifurcation, and coalescence can be captured by the new tool. The simulation results are in good agreement with other numerical method calculation results. The numerical method developed in this study provides a new calculation tool with high accuracy and efficiency for understanding the step-path failure of rock slopes.</div></div>","PeriodicalId":50850,"journal":{"name":"Advances in Space Research","volume":"77 6","pages":"Pages 6990-7001"},"PeriodicalIF":2.8,"publicationDate":"2026-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147388045","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The effect of magnetic field dissipation in the inner heliosheath: reconciling global heliosphere model and voyager data","authors":"Sergey D. Korolkov ,&nbsp;Igor I. Baliukin ,&nbsp;Merav Opher","doi":"10.1016/j.asr.2026.01.018","DOIUrl":"10.1016/j.asr.2026.01.018","url":null,"abstract":"<div><div>Global ideal magnetohydrodynamic models of the heliosphere typically predict a greatly exaggerated magnetic field pile-up in the inner heliosheath (IHS), the region between the termination shock and heliopause. However, Voyager 1 and 2 observations show only a gradual increase throughout this region. This mismatch is largely attributed to the simplified assumption of a unipolar solar magnetic field in many global models, which neglects the complex, folded structure of the heliospheric current sheet (HCS). The IHS, especially at low heliolatitudes, contains these compressed sector boundaries, widely considered prime locations for magnetic dissipation via reconnection. To align global model simulations with observations without incurring the prohibitive computational cost of resolving the kinetic-scale current sheet, this work introduces a phenomenological term into the magnetic field induction equation. This term captures the macroscopic effect of magnetic energy dissipation due to unresolved HCS dynamics. It is designed to mitigate the artificial magnetic pile-up, preserve the topological integrity of the magnetic field lines, and avoid explicit magnetic diffusion. This study demonstrates that incorporating a phenomenological dissipation term into global heliospheric models helps to resolve the longstanding discrepancy between simulated and observed magnetic field profiles in the IHS. The proposed mechanism reduces exaggerated magnetic energy (converts it into thermal energy), aligns model output with Voyager measurements of both magnetic field and proton density, and produces the outward shift in termination shock position and a reduction of the IHS thickness. We found that the characteristic time for magnetic field dissipation of about 6 years provides improved agreement with Voyager data in the IHS.</div></div>","PeriodicalId":50850,"journal":{"name":"Advances in Space Research","volume":"77 6","pages":"Pages 7443-7454"},"PeriodicalIF":2.8,"publicationDate":"2026-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147387682","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ionospheric reconstruction from LEO-GNSS, LEO-PNT, and ground-GNSS using an information-filter","authors":"Lucas Schreiter ,&nbsp;Andreas Brack ,&nbsp;Benjamin Männel ,&nbsp;Harald Schuh","doi":"10.1016/j.asr.2026.01.078","DOIUrl":"10.1016/j.asr.2026.01.078","url":null,"abstract":"<div><div>This paper presents a theoretical study on ionospheric reconstruction using GNSS data obtained from Low Earth Orbit (LEO) satellites in a PNT (Position, Navigation, and Timing) configuration, where the LEO satellites not only receive but also transmit GNSS signals, which can be tracked by ground or mobile receivers. The study is intended to pave the way for incorporating slant Total Electron Content (TEC) data from ESA’s upcoming LEO-PNT into ionospheric reconstructions. We generate synthetic slant TEC for three observation scenarios: Ground-GNSS, ground-LEO, and LEO-GNSS links. As ground-truth, the IRI-20 model with the Ozhogin plasmasphere extension is used. An inversion to recover the electron density from slant TEC observations is performed using an Extended Kalman Filter (EKF) in the information-filter formulation for all possible combinations of observation scenarios. As the LEO constellation, we will utilize existing LEO satellites that were available in May 2020, including Swarm, COSMIC-2, GRACE-FO, Jason-3, Sentinel-1, Sentinel-2, and Sentinel-3, as well as several Spire satellites. They cover a variety of altitudes between 400 km and 1350 km. For this study, we assume they could transmit dual-frequency GNSS-like signals like a PNT mission, which is not the case for any of the satellites mentioned. We only consider relative slant TEC to be insensitive to calibration biases that may reach a few TEC units. Given a real global ground-station network, LEO and GNSS satellites, we show that 15-min reconstruction solutions, only containing ground stations, cannot compete with solutions including LEO satellites. Furthermore, our results show that the joint use of LEO-POD (Precise Orbit Determination Antenna) and LEO-PNT (RMSE at 500 km: <span><math><mrow><mn>0.95</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>-</mo><mn>4</mn></mrow></msup><mspace></mspace><msup><mrow><mtext>cm</mtext></mrow><mrow><mo>-</mo><mn>3</mn></mrow></msup></mrow></math></span>) provides superior performance compared to configurations where either is substituted by ground-based GNSS (ground-GNSS and PNT: <span><math><mrow><mn>4.03</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>-</mo><mn>4</mn></mrow></msup><mspace></mspace><msup><mrow><mtext>cm</mtext></mrow><mrow><mo>-</mo><mn>3</mn></mrow></msup></mrow></math></span>; Gound-GNSS and POD <span><math><mrow><mn>1.18</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>-</mo><mn>4</mn></mrow></msup><mspace></mspace><msup><mrow><mtext>cm</mtext></mrow><mrow><mo>-</mo><mn>3</mn></mrow></msup></mrow></math></span>). We also show that the reconstruction error roughly doubles when radio occultation measurements are omitted. The dependency of the error on the distribution of the ground stations is also shown. Areas with only a few or no ground stations show the lowest correlation between IRI-20 and the reconstructions, e.g., near Point Nemo, where the correlation drops to 0.5.</div></div>","PeriodicalId":50850,"journal":{"name":"Advances in Space Research","volume":"77 6","pages":"Pages 7240-7256"},"PeriodicalIF":2.8,"publicationDate":"2026-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147387503","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Impact of nighttime foF2 enhancement at Juliusruh on ionospheric trend estimation and model accuracy","authors":"Bruno S. Zossi ,&nbsp;Franco D. Medina ,&nbsp;Trinidad Duran ,&nbsp;Dario J. Zamora ,&nbsp;Ana G. Elias","doi":"10.1016/j.asr.2026.01.048","DOIUrl":"10.1016/j.asr.2026.01.048","url":null,"abstract":"<div><div>The last two solar minima, around 2008 and 2019, were exceptionally low, with ionospheric electron densities even lower than expected. An irregular variation among the last three minima is observed in data from Juliusruh ionospheric station. Annual mean data indicates that the F2-layer critical frequency (foF2) during nighttime was slightly higher during the deep minima of 2008/2019 compared to the 1996 minimum, despite the lower solar activity levels. This implies a deviation from the expected direct association between foF2 and solar EUV proxies. This effect is more noticeable in winter during the post-midnight enhancement; however, the irregular behavior is sufficient to affect the annual mean, possibly affecting long-term trend estimations using the linear regression method. The enhanced plasmaspheric flux expected to be more noticeable, relative to the background ionization, during lower solar activity may lead to stronger nighttime ionization than that expected from the direct effect of solar activity. These findings suggest that long-term ionospheric trend estimations and models require revision to incorporate nighttime enhancement effects and dependence on solar activity levels during minima, improving accuracy in regions influenced by such phenomena.</div></div><div><h3>Plain language summary</h3><div>The ionosphere, a region of the upper atmosphere that contains charged particles and affects radio communications, is strongly influenced by solar extreme-ultraviolet (EUV) radiation that varies with solar activity. Thus, ionospheric parameters usually show a linear relationship with solar activity level. However, during the last two unusually quiet solar activity minima, around 2008 and 2019, nighttime measurements at Juliusruh, a mid-latitude station, revealed unexpected behavior. The maximum electron density was higher than during the previous, less quiet solar minimum around 1996. This increase occurs at night during a process known as “nighttime enhancement,” which refers to a rise in ionospheric electron density after sunset and is more pronounced during winter. Because this effect appears toward the end of long-term observation records, it can bias estimates of long-term trends in foF2, a key ionospheric parameter that measures the ionospheric maximum electron density. One possible explanation is an increased flow of charged particles from the plasmasphere, a region above the ionosphere that is populated by the up flow of ionospheric plasma during the day and that acts as a nighttime source of ionization. This process can produce higher electron densities than expected from solar EUV radiation alone. Current ionospheric models, which are partly based on observations and empirical relationships, do not reproduce this behavior. Our results indicate that both long-term trend estimates and models should be revised to account for nighttime enhancement effects during periods of low solar activity.</div></div>","PeriodicalId":50850,"journal":{"name":"Advances in Space Research","volume":"77 6","pages":"Pages 7316-7323"},"PeriodicalIF":2.8,"publicationDate":"2026-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147387888","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}