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Quasi-steady emission from repeating fast radio bursts can be explained by magnetar wind nebulae

Thu, 01 Jan 2026 00:00:00 GMT

Title: Quasi-steady emission from repeating fast radio bursts can be explained by magnetar wind nebulae Authors: Bhattacharya, Mukul Abstract: Among more than 1000 known fast radio bursts (FRBs), only five sources – FRBs 20121102A, 20190520B, 20201124A, 20240114A, and 20190417A –have confirmed associations with persistent radio sources. The observed quasi-steady emission is consistent with synchrotron radiation from a composite of magnetar wind nebula and supernova (SN) ejecta. Using a phenomenological model that incorporates simplified treatments of the nebular dynamics and particle acceleration, we compute the synchrotron flux by solving kinetic equations for energized electrons, accounting for electromagnetic cascades of electron positron pairs interacting with nebular photons. Within the framework of our model, the rotation-powered scenario requires a young neutron star (NS) with age tage ≈ 20yr , dipolar magnetic field Bdip ≈ (3–5) × 1012 G and initial spin period Pi ≈ 1 . 5–3ms in an ultra-stripped SN progenitor to account for emissions from FRBs 20121102A and 20190520B. In contrast, FRB 20201124A requires tage ≈ 10yr , Bdip ≈ 5 . 5 × 1013 G, and Pi ≈ 10ms in a conventional core-collapse SN progenitor. For the magnetar- flare-powered model, NS aged tage ≈ 25 / 40yr in a USSN progenitor and tage ≈ 12 . 5yr in a CCSN progenitor explains theobserved flux for FRB 20121102A/20190520B and FRB 20201124A, respectively. Finally, we estimate a minimum NS age tage , min ∼ 1–3yr based on the near-source plasma contribution to observed DM, and tage , min ∼ 6 . 5–10yr from the absence of radio signal attenuation. © The Author(s) 2025. Published by Oxford University Press on behalf of Royal Astronomical Society.

A Machine Learning-Based Framework for Bias Correction of Doppler Weather Radar Observations

Thu, 01 Jan 2026 00:00:00 GMT

Title: A Machine Learning-Based Framework for Bias Correction of Doppler Weather Radar Observations Authors: Tyagi, Vaibhav; Das, Saurabh Abstract: Radar constant miscalibration is one of the major sources of uncertainty in the radar-derived rainfall products. The traditional bias correction techniques often struggle to account for the non-stationary and nonlinear nature of bias. This study proposes a novel machine learning-based framework using the XGBoost algorithm to model reflectivity bias as a function of ground radar (GR) and space radar (SR) reflectivity differences, along with radar geometrical parameters (range, azimuth, and elevation). Furthermore, a strategy for near real-time bias correction is proposed based on an ensemble approach that combines an offline-pretrained model with an adaptive online learning component, incrementally updating the output as new data becomes available. This allows the model to adapt to evolving bias patterns over time. The results indicate that the proposed technique consistently outperforms the traditional iterative method. The results point towards its potential in reducing bias in near real-time for improved quantitative precipitation estimation (QPE) and other applications. © 2004-2012 IEEE.

Characteristic behavior of SAR arc, STEVE and Red-Green arc during HILDCAA events

Thu, 01 Jan 2026 00:00:00 GMT

Title: Characteristic behavior of SAR arc, STEVE and Red-Green arc during HILDCAA events Authors: Datta, Abhirup Abstract: Using 630.0 nm all-sky airglow imagers at Athabasca (Canada), Kapuskasing (Canada) and Nyr(Formula presented) l(Formula presented) (Finland), we present the first statistical analysis of the Stable Auroral Red (SAR) arcs, STEVE, and Red-Green (RG) arcs during High-Intensity Long-Duration Continuous AE Activity (HILDCAA) events from 2011 to 2019. These optical phenomena are unique and relatively faint subauroral optical phenomena observed in the Earth’s upper atmosphere at subauroral latitudes. We discovered 25 subauroral optical phenomena (SAR arc, STEVE, and Red-Green arc) after analyzing all-sky images taken over the 9-years period. The arc detachments from the auroral oval typically occur in the premidnight sector, indicating ring current ion drift to the dusk sector. Out of total 12 HILDCAA events, from 2011 to 2019, more than 90 % were accompanied by at least one of these auroras. We also found that the auroras occurring during these HILDCAA events tends to happen predominantly during midnight hours. The occurrence rate of these auroras found to be much higher during HILDCAA events reaching to approximately 45 %, compared to previous statistical studies, including non–HILDCAA times. © 2026 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Atmospheric Impact of Typhoon Hagibis: A Multi-Layer Investigation of Stratospheric and Ionospheric Responses

Thu, 01 Jan 2026 00:00:00 GMT

Title: Atmospheric Impact of Typhoon Hagibis: A Multi-Layer Investigation of Stratospheric and Ionospheric Responses Authors: Datta, Abhirup Abstract: We investigate the multi-layer atmospheric impacts of Typhoon Hagibis (2019), which formed on 6 October, tracked across 12–35° N and 135–155° E, and made landfall on 12 October over the Izu Peninsula, central Honshu, Japan. We present a multi-layer study that involves the troposphere, stratosphere and upper ionosphere to examine the thermodynamic and electromagnetic coupling between these layers due to such extreme weather conditions. Using ERA5 reanalysis, we identify pronounced stratospheric temperature perturbations, elevated atmospheric gravity wave (AGW) potential energy, substantial spatiotemporal variability in the zonal (U) and meridional (V) wind components, relative humidity, and specific rainwater content throughout the cyclone’s evolution. Quantitatively, AGW potential energy increased from background levels of <5 J kg−1 to >40 J kg−1 near the cyclone core, while tropospheric wind anomalies reached (Formula presented.) –40 m s−1, accompanied by relative humidity values exceeding 90% and specific rainwater content up to (Formula presented.) kg kg−1, indicative of vigorous moist convection and strong vertical energy transport. The ionospheric response, derived from GPS-based Total Electron Content (TEC) at 10 Japanese IGS stations, reveals vertical TEC (VTEC) perturbations whose amplitudes and temporal evolution vary systematically with GPS-station-to-typhoon-eye distance, including clear enhancements and reductions around the closest-approach day. These signatures indicate a measurable ionospheric response to cyclone-driven atmospheric forcing under geomagnetically quiet conditions, confirming that Hagibis produced vertically coupled disturbances linking stratospheric AGW activity with ionospheric electron density variability. © 2026 by the authors.