arXiv subjects

Tamas I. Gombosi

Publications and source records attributed to Tamas I. Gombosi.

At least 19 recordsLinked to original sources

arXiv2026

Counterintuitive Magnetic Connectivity and Energetic Particle Flux Differences among Nearby Spacecraft During the 2023 February 24 Solar Energetic Particle Event

For solar energetic particles (SEPs), it is generally expected that observers magnetically closer to the eruption source region exhibit higher particle intensities than those poorly connected to the eruption site. However, the 2023 February 24 SEP event departs from this simple picture: Earth and STA, near 1 au, are nominally better connected to the source region, whereas Solar Orbiter (SolO), at 0.77 au but less favorably connected, observed SEP fluxes more than an order of magnitude higher. This difference cannot be simply explained by nominal magnetic connectivity or radial scaling of SEP fluxes alone. To investigate this behavior, we perform a global magnetohydrodynamic simulation of the associated coronal mass ejection (CME) using the Alfvén Wave Solar-atmosphere Model-Realtime (AWSoM-R). The simulation reveals that the CME flux rope originates close to a coronal streamer and as it propagates and expands, the CME-driven shock is effectively distorted, developing into two distinct flanks with different strengths. Although the three spacecraft are separated by only $\lesssim$30$^{\circ}$ in heliolongitude, their magnetic footpoints differ by $\gtrsim$50$^{\circ}$ in longitude because of a nearby stream interaction region. Specifically, Earth and STA connect to a weaker shock region, while SolO connects to the shock nose with a higher compression ratio and more efficient particle acceleration. We further simulate SEPs using the Multiple-Field-Line Advection Model for Particle Acceleration (M-FLAMPA) coupled with AWSoM-R, obtaining results that reproduce the observed flux differences among the three spacecraft, demonstrating that this counterintuitive behavior results from their connections to different regions of the inhomogeneous CME-driven shock.

physics.space-ph↗

arXiv2026

The Effects of Energy Conservation in Simulating Solar Eruptions

Strict energy conservation is, perhaps, the most basic principle in all physics, but has proven to be difficult to satisfy in numerical simulations of solar eruptions. The Alfvén Wave Solar atmosphere Model (AWSoM) is used to perform a rigorous comparison of CME simulations whose only difference is the use of a conservative vs. non-conservative scheme for the energy equation. A simple, symmetric active region is assumed for the initial magnetic field. As expected, the different numerical schemes result in very different plasma thermal energy, but surprisingly, we also find a factor $>2$ difference in the final kinetic energy, with the energy substantially larger in the energy-conservative scheme. The increase in thermal energy is comparable to the increase in kinetic energy in the conservative simulation. Our analysis reveals that the flare reconnection and increase of kinetic energy terminate earlier with the non-conservative scheme. We conclude that the plasma thermodynamics plays a critical role in the flare reconnection, with the thermal pressure gradient in the current sheet slowing down the reconnection. Our results imply that using strict energy-conservative numerics is critical for space weather modeling of CMEs and for understanding the CME energy budget partitioning.

astro-ph.SR↗

arXiv2026

Simulating the Solar Corona with Multiple Solar Photospheric Magnetic Maps during the 8 April 2024 Total Solar Eclipse

The 8 April 2024 total solar eclipse (TSE) provides a unique opportunity to study the solar corona. This work presents our simulations of the solar corona at the time of the eclipse based on magnetohydrodynamic (MHD) modeling performed with the Alfvén Wave Solar atmosphere Model (AWSoM) in the Space Weather Modeling Framework, developed at the University of Michigan. We performed multiple simulations based on photospheric magnetic maps from four sources, i.e., ADAPT-GONG, Lockheed Martin ESFAM-HMI, HipFT-HMI, and NSO-NRT-HMI maps. Our study focuses on how differences in the magnetic field maps affect the coronal magnetic field structure and coronal heating properties in the simulation. The synthesized observables show remarkable differences due to the distinct magnetic coronal topologies, which stem from the different local magnetic flux distributions. We analyze the properties of the open magnetic flux regions of the models. We also study the coronal heating rate in the models. The total volume integrated heating rate yields a difference of $20\%$ across the models. The results also show that the differential emission measure in the high-temperature regions is sensitive to the magnetic field maps. Our findings underscore the importance of comprehensive photospheric magnetic field data in improving future solar coronal models.

astro-ph.SR↗

arXiv2026

Effects of the Background Magnetic Field on Flux Rope Eruptions

Solar eruptive events are generally believed to involve magnetic flux ropes (MFR), formed either in the pre-eruptive phase of the event or during the eruption itself. These MFR eruptions exhibit significant complexity and variations due to the interplay of the physical mechanisms involved, in particular magnetic reconnection and ideal instabilities. This work considers the effect of the background magnetic field on the nature of eruptions with pre-existing MFRs. We used a new MHD model to simulate the whole MFR eruption process, including the pre-eruptive stage and the initiation. Three simulations were performed, all of which used an identical bipolar active region, but with different background magnetic fields in the three cases. The simulations resulted in two successful eruptions (CMEs) and one failed eruption (a confined flare). We analyzed the energetics and the acceleration of the MFR in detail, and found a transition to a rapid exponential rise phase in two of the simulations. We also calculated the criterion for the torus instability and the timing of the breakout and flare reconnections. Our results show that the rapid exponential rise phase is likely due to breakout reconnection. We conclude that a background field antiparallel to the active-region field lowers the magnetic free-energy threshold for eruption; but, does not guarantee a successful eruption. We also found that an antiparallel background field leads to faster flare reconnection, but of shorter duration. Our findings underscore the importance of the background magnetic field in understanding CMEs.

astro-ph.SR↗

arXiv2026

Simulated Operational Testing of the Prototype Implementation of the SOFIE Model: The 2025 Space Weather Prediction Testbed Exercise

The CLEAR Space Weather Center of Excellence's solar energetic particle (SEP) model, SOlar wind with FIeld lines and Energetic particles (SOFIE), was run and evaluated on-site during the Space Weather Prediction Testbed (SWPT) exercise at the National Oceanic and Atmospheric Administration's Space Weather Prediction Center (NOAA/SWPC) in May 2025. As a physics-based SEP model, SOFIE simulates the acceleration and transport of energetic particles by the coronal mass ejection (CME)-driven shock in the solar corona and inner heliosphere, and has been validated against historical events. However, questions remain regarding whether a physics-based model, traditionally considered computationally expensive, could meet operational needs. The SWPT exercise offered a valuable opportunity to evaluate SOFIE under simulated operational conditions. On-site interactive feedback from SWPC forecasters, Space Radiation Analysis Group (SRAG) console operators, Community Coordinated Modeling Center (CCMC) personnel, and Moon-to-Mars Space Weather Analysis Office (M2M SWAO) analysts led to significant strategic improvements in the model configuration. The simulation grid was optimized by combining a coarser background grid with higher-resolution regions along the CME path and toward Earth, reducing computational cost without compromising accuracy. In this work, we present the simulated operational performance of SOFIE and its capability to predict SEP fluxes significantly faster than real time. During the SWPT exercise, SOFIE completed a 4-day SEP simulation within 5 hours using 1,000 central processing unit cores, although the earliest SEP forecast was obtained a few hours after CME onset. This marks a milestone in demonstrating SOFIE's operational usefulness and robustness to support future human space exploration.

astro-ph.SR↗

arXiv2025

Physics-Based Simulation of the 2013 April 11 Solar Energetic Particle Event

Solar energetic particles (SEPs) can pose hazardous radiation risks to both humans and spacecraft electronics in space. Numerical modeling based on first principles offers valuable insights into the underlying physics of SEPs and provides synthetic observables for SEPs at any time and location in the inner heliosphere. In this work, we present a numerical scheme, which conserves the number of particles based on integral relations for Poisson brackets \citep{sokolov2023high}, to solve the kinetic equation for particle acceleration and transport processes. We implement this scheme within the Space Weather Modeling Framework, developed at the University of Michigan. In addition, we develop a new shock-capturing tool to study the coronal mass ejection-driven shock originating from the low solar corona. These methodological advancements are applied to conduct a comprehensive study of a historical SEP event on April 11, 2013. Multi-spacecraft observations, including SOHO, SDO, GOES and ACE near Earth, and STEREO-A/B, are used for model--data comparison and validation. We show synthetic observables, including extreme ultraviolet and white-light images, proton time--intensity profiles, and energy spectra, and discuss their differences and probable explanations compared to observations. Our simulation results demonstrate the application of the Poisson bracket scheme with a particle solver to simulating a historical SEP event. We also show the capability of extracting the complex shock surface using our shock-capturing tool and understand how the complex shock surface affects the particle acceleration process.

astro-ph.SR↗

arXiv2025

Physics-Based Forecasting of Tomorrow's Solar Wind at 1 AU

Inspired by the concept of relativity of simultaneity used in the theory of special relativity, a new approach is proposed to simulate future solar wind conditions at any point in the inner solar system. An important distinctive feature of the proposed approach is that the simulation in the solar corona is driven by hourly updated solar magnetograms and is continuously simulated in nearly real time. The model for the inner heliosphere is based on time transformation to a boosted frame of reverence (or spacetime coordinate system) in which the current state of the solar wind at the solar corona -- inner heliosphere boundary and future states of the solar wind are simultaneous. The predictive capability for tomorrow's parameters of the ambient solar wind at 1 AU is achieved by simulating them simultaneously with the current observations of the solar magnetic field, the time offset being due to the use of boosted frame. We derive the modified governing equations for both hydrodynamics and magnetohydrodynamics and present a new numerical algorithm that solves the modified governing equations. The proposed method enables an efficient numerical implementation and thus a significantly longer forecast time than traditional solution methods. In the numerical test for transient propagation, the boosted solution for the CME-driven shock arrival at 1AU is 16 hours ahead of the solution at the solar corona -- inner heliosphere boundary.

astro-ph.SR↗

arXiv2024

Interaction between a Coronal Mass Ejection and Comet 67P/Churyumov-Gerasimenko

The interaction between a Coronal Mass Ejection (CME) and a comet has been observed several times by in-situ observations from the Rosetta Plasma Consortium (RPC), which is designed to investigate the cometary magnetosphere of comet 67P/Churyumov-Gerasimenko (CG). Goetz et al. (2019) reported a magnetic field of up to 300 nT measured in the inner coma, which is among the largest interplanetary magnetic fields observed in the solar system. They suggested the large magnetic field observations in the inner coma come from magnetic field pile-up regions, which are generated by the interaction between a CME and/or corotating interaction region and the cometary magnetosphere. However, the detailed interaction between a CME and the cometary magnetosphere of comet CG in the inner coma has not been investigated by numerical simulations yet. In this manuscript, we will use a numerical model to simulate the interaction between comet CG and a Halloween class CME and investigate its magnetospheric response to the CME. We find that the plasma structures change significantly during the CME event, and the maximum value of the magnetic field strength is more than 500nT close to the nucleus. Virtual satellites at similar distances as Rosetta show that the magnetic field strength can be as large as 250nT, which is slightly less than what Goetz et al. (2019) reported.

astro-ph.EP↗

arXiv2023

Volatiles in the H$_2$O and CO$_2$ ices of comet 67P/Churyumov-Gerasimenko

ESA's Rosetta spacecraft at comet 67P/Churyumov-Gerasimenko (67P) was the first mission that accompanied a comet over a substantial fraction of its orbit. On board was the ROSINA mass spectrometer suite to measure the local densities of the volatile species sublimating from the ices inside the comet's nucleus. Understanding the nature of these ices was a key goal of Rosetta. We analyzed the primary cometary molecules at 67P, namely H$_2$O and CO$_2$, together with a suite of minor species for almost the entire mission. Our investigation reveals that the local abundances of highly volatile species, such as CH$_4$ and CO, are reproduced by a linear combination of both H$_2$O and CO$_2$ densities. These findings bear similarities to laboratory-based temperature programmed desorption experiments of amorphous ices and imply that highly volatile species are trapped in H$_2$O and CO$_2$ ices. Our results do not show the presence of ices dominated by these highly volatile molecules. Most likely, they were lost due to thermal processing of 67P's interior prior to its deflection to the inner solar system. Deviations in the proportions co-released with H$_2$O and CO$_2$ can only be observed before the inbound equinox, when the comet was still far from the sun and the abundance of highly volatile molecules associated with CO$_2$ outgassing were lower. The corresponding CO$_2$ is likely seasonal frost, which sublimated and lost its trapped highly volatile species before re-freezing during the previous apparition. CO, on the other hand, was elevated during the same time and requires further investigation.

astro-ph.EP↗

arXiv2022

Large-Scale Spatial Cross-Calibration of Hinode/SOT-SP and SDO/HMI

We investigate the cross-calibration of the Hinode/SOT-SP and SDO/HMI instrument meta-data, specifically the correspondence of the scaling and pointing information. Accurate calibration of these datasets gives the correspondence needed by inter-instrument studies and learning-based magnetogram systems, and is required for physically-meaningful photospheric magnetic field vectors. We approach the problem by robustly fitting geometric models on correspondences between images from each instrument's pipeline. This technique is common in computer vision, but several critical details are required when using scanning slit spectrograph data like Hinode/SOT-SP. We apply this technique to data spanning a decade of the Hinode mission. Our results suggest corrections to the published Level 2 Hinode/SOT-SP data. First, an analysis on approximately 2,700 scans suggests that the reported pixel size in Hinode/SOT-SP Level 2 data is incorrect by around 1%. Second, analysis of over 12,000 scans show that the pointing information is often incorrect by dozens of arcseconds with a strong bias. Regression of these corrections indicates that thermal effects have caused secular and cyclic drift in Hinode/SOT-SP pointing data over its mission. We offer two solutions. First, direct co-alignment with SDO/HMI data via our procedure can improve alignments for many Hinode/SOT-SP scans. Second, since the pointing errors are predictable, simple post-hoc corrections can substantially improve the pointing. We conclude by illustrating the impact of this updated calibration on derived physical data products needed for research and interpretation. Among other things, our results suggest that the pointing errors induce a hemispheric bias in estimates of radial current density.

astro-ph.SR↗

arXiv2021

Refractory elements in the gas phase for comet 67P/Churyumov-Gerasimenko

Results. We found that gas-phase silicon was present throughout the Rosetta mission. Furthermore, the presence of sodium and iron atoms near the comet's perihelion confirms that sputtering cannot be the sole release process for refractory elements into the gas phase. Nickel was found to be below the detection limit. The search for parent species of any of the identified gas phase refractories has not been successful. Upper limits for a suite of possible fragment species (SiH, SiC, NaH, etc.) of larger parent and daughter species have been obtained. Furthermore, Si did not exhibit the same drop in signal as do common cometary gases when the spacecraft is pointed away from the nucleus. The combined results suggest that a direct release of elemental species from small grains on the surface of the nucleus or from small grains in the surrounding coma is a more likely explanation than the previous assumption of release via the dissociation of gaseous parent molecules.

astro-ph.EP↗

arXiv2021

Fast and Accurate Emulation of the SDO/HMI Stokes Inversion with Uncertainty Quantification

The Helioseismic and Magnetic Imager (HMI) onboard NASA's Solar Dynamics Observatory (SDO) produces estimates of the photospheric magnetic field which are a critical input to many space weather modelling and forecasting systems. The magnetogram products produced by HMI and its analysis pipeline are the result of a per-pixel optimization that estimates solar atmospheric parameters and minimizes disagreement between a synthesized and observed Stokes vector. In this paper, we introduce a deep learning-based approach that can emulate the existing HMI pipeline results two orders of magnitude faster than the current pipeline algorithms. Our system is a U-Net trained on input Stokes vectors and their accompanying optimization-based VFISV inversions. We demonstrate that our system, once trained, can produce high-fidelity estimates of the magnetic field and kinematic and thermodynamic parameters while also producing meaningful confidence intervals. We additionally show that despite penalizing only per-pixel loss terms, our system is able to faithfully reproduce known systematic oscillations in full-disk statistics produced by the pipeline. This emulation system could serve as an initialization for the full Stokes inversion or as an ultra-fast proxy inversion. This work is part of the NASA Heliophysics DRIVE Science Center (SOLSTICE) at the University of Michigan, under grant NASA 80NSSC20K0600E, and has been open sourced.

astro-ph.SR↗

arXiv2021

SynthIA: A Synthetic Inversion Approximation for the Stokes Vector Fusing SDO and Hinode into a Virtual Observatory

Both NASA's Solar Dynamics Observatory (SDO) and the JAXA/NASA Hinode mission include spectropolarimetric instruments designed to measure the photospheric magnetic field. SDO's Helioseismic and Magnetic Imager (HMI) emphasizes full-disk high-cadence and good spatial resolution data acquisition while Hinode's Solar Optical Telescope Spectro-Polarimeter (SOT-SP) focuses on high spatial resolution and spectral sampling at the cost of a limited field of view and slower temporal cadence. This work introduces a deep-learning system named SynthIA (Synthetic Inversion Approximation), that can enhance both missions by capturing the best of each instrument's characteristics. We use SynthIA to produce a new magnetogram data product, SynodeP (Synthetic Hinode Pipeline), that mimics magnetograms from the higher spectral resolution Hinode/SOT-SP pipeline, but is derived from full-disk, high-cadence, and lower spectral-resolution SDO/HMI Stokes observations. Results on held-out data show that SynodeP has good agreement with the Hinode/SOT-SP pipeline inversions, including magnetic fill fraction, which is not provided by the current SDO/HMI pipeline. SynodeP further shows a reduction in the magnitude of the 24-hour oscillations present in the SDO/HMI data. To demonstrate SynthIA's generality, we show the use of SDO/AIA data and subsets of the HMI data as inputs, which enables trade-offs between fidelity to the Hinode/SOT-SP inversions, number of observations used, and temporal artifacts. We discuss possible generalizations of SynthIA and its implications for space weather modeling. This work is part of the NASA Heliophysics DRIVE Science Center (SOLSTICE) at the University of Michigan under grant NASA 80NSSC20K0600E, and will be open-sourced.

astro-ph.IM↗

arXiv2021

What Sustained Multi-Disciplinary Research Can Achieve: The Space Weather Modeling Framework

MHD-based global space weather models have mostly been developed and maintained at academic institutions. While the "free spirit" approach of academia enables the rapid emergence and testing of new ideas and methods, the lack of long-term stability and support makes this arrangement very challenging. This paper describes a successful example of a university-based group, the Center of Space Environment Modeling (CSEM) at the University of Michigan, that developed and maintained the Space Weather Modeling Framework (SWMF) and its core element, the BATS-R-US extended MHD code. It took a quarter of a century to develop this capability and reach its present level of maturity that makes it suitable for research use by the space physics community through the Community Coordinated Modeling Center (CCMC) as well as operational use by the NOAA Space Weather Prediction Center (SWPC).

physics.space-ph↗

arXiv2020

Threaded-Field-Lines Model for the Low Solar Corona Powered by the Alfven Wave Turbulence

We present an updated global model of the solar corona, including the transition region. We simulate the realistic tree-dimensional (3D) magnetic field using the data from the photospheric magnetic field measurements and assume the magnetohydrodynamic (MHD) Alfvén wave turbulence and its non-linear dissipation to be the only source for heating the coronal plasma and driving the solar wind. In closed field regions the dissipation efficiency in a balanced turbulence is enhanced. In the coronal holes we account for a reflection of the outward propagating waves, which is accompanied by generation of weaker counter-propagating waves. The non-linear cascade rate degrades in strongly imbalanced turbulence, thus resulting in colder coronal holes. The distinctive feature of the presented model is the description of the low corona as almost-steady-state low-beta plasma motion and heat flux transfer along the magnetic field lines. We trace the magnetic field lines through each grid point of the lower boundary of the global corona model, chosen at some heliocentric distance, $R=R_{b}\sim1.1\ R_\odot$ well above the transition region. One can readily solve the plasma parameters along the magnetic field line from 1D equations for the plasma motion and heat transport together with the Alfvén wave propagation, which adequately describe physics within the heliocentric distances range, $R_{\odot}<R<R_{b}$, in the low solar corona. By interfacing this threaded-field-lines model with the full MHD global corona model at $r=R_{b}$, we find the global solution and achieve a faster-than-real-time performance of the model on $\sim200$ cores.

astro-ph.SR↗

arXiv2020

CHO-bearing molecules in Comet 67P/Churyumov-Gerasimenko

In 2004, the Rosetta spacecraft was sent to comet 67P/Churyumov-Gerasimenko for the first ever long-term investigation of a comet. After its arrival in 2014, the spacecraft spent more than two years in immediate proximity to the comet. During these two years, the ROSINA Double Focusing Mass Spectrometer (DFMS) onboard Rosetta discovered a coma with an unexpectedly complex chemical composition that included many oxygenated molecules. Determining the exact cometary composition is an essential first step to understanding of the organic rich chemistry in star forming regions and protoplanetary disks that are ultimately conserved in cometary ices. In this study a joint approach of laboratory calibration and space data analysis was used to perform a detailed identification and quantification of CHO-compounds in the coma of 67P/Churyumov-Gerasimenko. The goal was to derive the CHO-compound abundances relative to water for masses up to 100 u. For this study, the May 2015 post-equinox period represent the best bulk abundances of comet 67P/Churyumov-Gerasimenko. A wide variety of CHO-compounds were discovered and their bulk abundances were derived. Finally, these results are compared to abundances of CHO-bearing molecules in other comets, obtained mostly from ground-based observations and modelling.

astro-ph.EP↗

arXiv2020

Predicting solar flares with machine learning: investigating solar cycle dependence

A deep learning network, Long-Short Term Memory (LSTM) network, is used in this work to predict whether the maximum flare class an active region (AR) will produce in the next 24 hours is class $Γ$. We considered $Γ$ are $\ge M$, $\ge C$ and any flare class. The essence of using LSTM, which is a recurrent neural network, is its capability to capture temporal information of the data samples. The input features are time sequences of 20 magnetic parameters from SHARPs - Space-weather HMI Active Region Patches. We analyzed active regions from June 2010 to Dec 2018, using the Geostationary Operational Environmental Satellite (GOES) X-ray flare catalogs and label the data samples with identified ARs in the GOES X-ray flare catalogs. Our results (i) shows consistent skill scores with recently published results using LSTMs and better than the previous work using single time input (eg. DeFN) (ii) The skill scores from the model show essential differences when different years of data was chosen for training and testing.

astro-ph.SR↗

arXiv2019

Elemental and molecular abundances in comet 67P/Churyumov-Gerasimenko

Comets are considered to be some of the most pristine and unprocessed solar system objects accessible to in-situ exploration. Investigating their molecular and elemental composition takes us on a journey back to the early period of our solar system and possibly even further. In this work, we deduce the bulk abundances of the major volatile species in comet 67P/Churyumov-Gerasimenko, the target of the European Space Agency's Rosetta mission. The basis are measurements obtained with the ROSINA instrument suite on board the Rosetta orbiter during a suitable period of high outgassing near perihelion. The results are combined with both gas and dust composition measurements published in the literature. This provides an integrated inventory of the major elements present in the nucleus of 67P/Churyumov-Gerasimenko. Similar to comet 1P/Halley, which was visited by ESA's Giotto spacecraft in 1986, comet 67P/Churyumov-Gerasimenko also shows near-solar abundances of oxygen and carbon, whereas hydrogen and nitrogen are depleted compared to solar. Still, the degree of devolatilization is lower than that of inner solar system objects, including meteorites and the Earth. This supports the idea that comets are among the most pristine objects in our solar system.

astro-ph.EP↗