High Altitude Observatory

Abstract. We investigate the impacts of increased CO2 concentration on migrating diurnal tide (DW1). A future climate simulation is conducted using a WACCM-X model, with surface CO2 levels increasing according to the RCP8.5 scenario. The DW1 (1,1) mode, a propagating tide peaking near the equator, exhibits a statistically significant positive trend in a range of 20–70 km, and a significant negative trend in a range of 90–110 km. The positive trend is likely driven by a reduction in atmospheric density in the mesosphere and enhanced equatorial convective activity, while the negative trend appears in the mesosphere, which overwhelms the positive trend. Two potential mechanisms may explain the negative trend. First, increasing CO2 enhances mesospheric stability, reducing tidal vertical wavelengths. In our simulation, equatorial temperatures around ∼50–70 km become cooler than those in ∼70–90 km. This strong cooling could be linked to CO2 mixing and transport, as well as the contraction of the mesospheric ozone layer due to atmospheric descent induced by CO2-driven cooling. Second, stronger convective activity intensifies gravity wave generation, increasing gravity wave diffusion in the mesosphere. This strong convective activity also likely intensifies the tide below ∼70 km. While our positive DW1 trend is consistent with McLandress and Fomichev (2006), the negative trend in the lower thermosphere contrasts with their results. This discrepancy might arise because their model used a time-independent diffusion coefficient, whereas WACCM-X accounts for CO2-driven changes in gravity wave diffusion. The negative trend is confirmed in SABER observation for the last two decades, while the positive trend is not verified.

We discuss the requirements, concepts, simulations, implementation, and calibration of two dual Fabry-Perot (FPI)-based imaging spectropolarimeters, CRISP and CHROMIS, at the Swedish 1-m Solar Telescope, and CRISP2, which is under construction. These instruments are optimised for a large field of view and high cadence at the expense of a moderate spectral resolution, and use a combination of a high-resolution and a low-resolution etalon together with an order-sorting prefilter to define the bandpass. The overall design is made robust and stable by tailoring the low-resolution etalon reflectivity to accommodate expected cavity errors from both etalons, by using a compact optical design that eliminates the need for folding mirrors, and enclosing the entire system within a single container sealed by lenses. By using a telecentric design based on lenses rather than mirrors, image degradation by the FPI system is negligible, as shown in a previous publication, and the throughput of the system is maximised. The initial alignment, and maintaining that alignment over time, is greatly simplified. Moreover, the telecentric design allows the full calibration and/or modelling of essential system parameters to be carried out without interfering with the optical set-up or the cameras. We also discuss briefly the polarimeters developed for CRISP and CHROMIS. The high performance of CRISP and CHROMIS has been demonstrated in an earlier publication through measurements of the granulation contrast and comparisons with similar measurements simultaneously made through broadband continuum filters. Here, we focus on the aspects of the design that are central to enabling high performance and robustness, but also discuss the calibration and processing of the data, and use a few examples of processed data to demonstrate the achievable image and data quality. We put forward a proposal for a similar conceptual design for the European Solar Telescope and conclude by discussing potential problems of the proposed approach to designs of this type. Some aspects of these FPI systems may also be of interest outside the solar community.

Abstract Cold plasma distribution in the ionosphere‐plasmasphere system governs wave‐particle interactions, plasma energization and loss, and radio wave propagation. A longstanding observational gap at altitudes 800–8,000 km has largely prevented studying the coupled dynamics of the two regions. Here, we show that observations by JAXA's Arase mission can bridge this gap. Electron densities inferred from the upper hybrid resonance frequencies measured by Arase are highly consistent with radio occultation profiles from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) mission, with a median difference of 5%. Using the combined COSMIC‐Arase data set, we provide a convenient way to reconcile the two regions in empirical models based on the analytical Chapman function inversion for scale height. Our results enable studying fundamental questions about the ionosphere‐plasmasphere coupling, their transition, and life cycle of cold plasma in near‐Earth space.

Abstract We present the long‐term trends of the Arctic stratospheric polar vortex (SPV) using the Modern Era Retrospective Research analysis for Research and Application‐2 (MERRA‐2) reanalysis data, and assess its impact on the mesosphere and lower thermosphere (MLT) using Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (SD‐WACCM‐X) simulations. Our findings reveal that the SPV showed a weakening trend from 1980 until the early 2000s, but a strengthening trend after the 2000s. This change is attributed to the weakening of the planetary wave (PW) activities, particularly the wavenumber‐1, which can be driven by long‐term Arctic surface changes. A strong link has been found between the observed PWs activity and the increasing sea surface temperature (SST) over/nearby the Barents‐Kara Sea before early 2000s and over the Central North Pacific region after the 2000s. Furthermore, we observe that the SPV trend influences the zonal mean zonal winds and migrating solar semidiurnal tide (SW2) in the MLT. The SW2 exhibits a ∼13%/decade positive trend from 1980 to the early 2000s and a ∼14%/decade negative trend after 2000s. These results provide evidence of the impact of Arctic surface variabilities, including sea‐ice, on the MLT dynamics, especially SW2 tide.

With the widespread deployment of high-voltage and ultra-high-voltage transmission lines, composite insulators play a vital role in modern power systems. However, prolonged service leads to material aging, and the current lack of standardized, quantitative methods for evaluating silicone rubber degradation poses significant challenges for condition-based maintenance. To address this measurement gap, we propose a novel aging assessment framework that integrates Fourier Transform Infrared (FTIR) spectroscopy with a measurement-oriented ensemble learning model. FTIR is utilized to extract absorbance peak areas from multiple aging-sensitive functional groups, forming the basis for quantitative evaluation. This work establishes a measurement-driven framework for aging assessment, supported by information-theoretic feature selection to enhance spectral relevance. The dataset is augmented to 4847 samples using linear interpolation to improve generalization. The proposed model employs k-nearest neighbor (KNN), Support Vector Machine (SVM), Random Forest (RF), and Gradient-Boosting Decision Tree (GBDT) within a two-tier ensemble architecture featuring dynamic weight allocation and a class-balanced weighted cross-entropy loss. The model achieves 96.17% accuracy and demonstrates strong robustness under noise and anomaly disturbances. SHAP analysis confirms the resistance to overfitting. This work provides a scalable and reliable method for assessing silicone rubber aging, contributing to the development of intelligent, data-driven diagnostic tools for electrical insulation systems.

Scattering polarization signals offer unique diagnostics of the physical conditions in the solar atmosphere, in particular magnetic fields via the Hanle effect. However, their spatial structure remains poorly constrained due to the difficulty of achieving a high spatial resolution and polarimetric sensitivity simultaneously. We present the first direct observation of sub-arcsecond structuring in the linear scattering polarization of the photospheric Sr i 4607,Å line near the solar disk center (μ = 0.74), obtained with the Visible Spectro-Polarimeter (ViSP) at the Daniel K. Inouye Solar Telescope (DKIST). The data achieve about ∼0 resolution with 30,s integration and sufficient sensitivity to detect fine-scale patterns in the total linear polarization, which are evident in Sr i but absent in a nearby Fe i line that is simultaneously observed. Since this Fe i line is more Zeeman-sensitive than the Sr i 4607,Å,, this disparity confirms that the signals in the Sr i 4607,Å line arise from scattering. These data provide the first spatially resolved two-dimensional maps of photospheric scattering polarization at sub-arcsecond scales, enabled by the capabilities of a 4-meter solar telescope.

Abstract We present a case study of a moderate geomagnetic storm, which exhibits an abrupt relativistic enhancement in the heart of the radiation belt accompanied by low‐latitude purple auroral emission. The relativistic enhancement occurs on a timescale of tens of minutes and reaches MeV energies deep within the inner magnetosphere. The enhancement is concurrent with mesoscale purple patches which protrude below the pre‐existing auroral oval. We analyze the event using a novel combination of observational data sets and physics‐based modeling. This includes multispectral auroral imaging, dosimeter data from the Global Positioning System constellation, auroral transport modeling, and global geospace modeling. Our analysis reveals the cause of both the radiation belt enhancement and purple emission to be direct, mesoscale injections of electrons reaching relativistic energies. Finally, we show that these injections are most likely caused by near‐Earth reconnection which produces deeply depleted entropy bubbles capable of trapping and transporting energetic particles into the inner magnetosphere.

BackgroundThe progression of type 2 diabetes (T2D) is driven by pancreatic β-cell dysfunction and loss, yet current therapies fail to address this core pathophysiology.MethodsWe implemented an integrative pipeline combining genetic and functional data to prioritize T2D targets. We leveraged genome-wide association study (GWAS) and protein quantitative trait loci (pQTL) summary data to infer causal associations between circulating proteins and disease risk. Phenome-wide association studies were conducted to evaluate pleiotropy and potential off-target effects. Single-cell RNA-seq was used to delineate cell-type-specific expression and identify biological pathways associated with candidate genes. Lead candidates were then validated by molecular docking and functional assays.FindingsMendelian randomization and colocalization analyses prioritized 14 circulating proteins with causal links to T2D, nine of which shared strong causal variants (PPH4 > 0.8). Phenome-wide association studies (PheWAS) excluded off-target effects for 2 candidates (HP and SVEP1). Among the remaining 7 candidates (ENG, GOLM1, GSTA1, HIBCH, PAM, PLXND1, and PTN), PAM (peptidylglycine α-amidating monooxygenase) was found to be expressed in over 80% of β-cells, as revealed by single-cell RNA-sequencing. Moreover, genes co-expressed with PAM were functionally clustered in pathways related to insulin secretion and protein processing. Notably, PAM expression was significantly downregulated in islets of diabetic mice. Molecular docking simulations identified a high-affinity interaction between PAM and oleic acid (OA), a metabolite linked to β-cell function. Strikingly, pharmacological PAM inhibition in INS1 β-cells induced deficits in cell proliferation and survival that were unresponsive to OA supplementation, underscoring PAM’s indispensable role in β-cell integrity.Interpretation This study positions PAM as a clinically relevant therapeutic target for T2D, offering new opportunities for β-cell preservation therapies and diagnostic biomarker development.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12967-025-07086-x.

Subauroral polarization streams (SAPS) are a latitudinally narrow band of intense westward plasma flows just equatorward of the auroral oval in the dusk-to-midnight ionosphere. SAPS are frequently observed by radars and satellites during geomagnetically active times. SAPS are produced when the downward Region-2 current is closed through the subauroral region of low ionospheric conductivity and a strong poleward electric field is established to ensure current continuity. SAPS are a manifestation of the strong coupling between the magnetosphere ionosphere and thermosphere. In this study, we employ the high-resolution Multiscale Atmosphere-Geospace Environment (MAGE) model developed by the NASA DRIVE Science Center for Geospace Storms (CGS) to simulate the SAPS effects on the global thermosphere-ionosphere system during the 17 March 2013 geomagnetic storm. MAGE can self-consistently generate SAPS and simulate their effects. In the SAPS channel, two processes occur to affect the thermosphere and ionosphere state, the first one is the intense frictional heating to the ionospheric plasma and atmospheric neutrals and the other one is the strong ion drag that changes the neutral winds. Our MAGE numerical experiments show that thermospheric temperature and wind circulation are modulated by the SAPS, and the SAPS effects are transmitted globally to affect the behavior of the entire thermosphere and ionosphere system during the storm. With SAPS included in MAGE simulations ionospheric total electron content and electron densities are enhanced in the afternoon sector at middle and high latitudes. This provides a strong source of ionization for the high-latitude convection pattern to transport the plasma into the polar cap to facilitate the occurrence and strengthening of polar cap tongue of ionization.