Shirsh Lata Soni

Solar radio bursts (SRBs) provide key diagnostics of energetic electron propagation and coronal magnetic field structures. Among them, J- and U-type bursts are particularly valuable for tracing electron motion along closed magnetic loops, yet they remain less explored than type III bursts in open field lines. Using high-resolution dynamic spectra from the e-CALLISTO network, we analyzed a total of 38 SRB events (J-type 18 events and U-type 20 events) observed during the ascending phase of Solar Cycle 25, from June 2020 to December 2024, to characterize their spectral morphology, frequency drift, and magnetic connectivity. Complementary, Solar Dynamic Observatory/Helioseismic Magnetic Imager (SDO/HMI), Potential-Field Source-Surface Models (PFSS) extrapolations, and SDO/Atmospheric Imaging Assembly (AIA) extreme ultraviolet (EUV) imaging have been used to identify associated active regions and loop geometries. Approximately 30% of the events occurred without associated flares, indicating that small-scale reconnections can also produce SRBs. Application of the Newkirk density model yielded that the drift-rate analysis reveals broadly similar descending branches for J- and U-type SRBs but subtle asymmetries in ascending branches; steeper drift in J-type and smoother drift in U-type, indicating differences in electron propagation and density structuring between low-lying and extended closed coronal loops. For 19 of 38 events, constrained by the PFSS upper boundary (2.5 Rs), the loop heights inferred from the Newkirk model agree with PFSS within ±0.5 Rs, although PFSS tends to underestimate more extended structures. These results demonstrate the diagnostic potential of J- and U-type SRBs for probing electron propagation and closed magnetic structures in the solar corona.

The SunRISE Ground Radio Lab (GRL) at the University of Michigan develops and deploys Long Wavelength Array (LWA) antennas operating over 40–160 MHz to support low-frequency radio heliophysics and student training. This paper presents the scientific and educational outcomes of a dual-site observing campaign conducted during the 8 April 2024, total solar eclipse, which provided a valuable natural laboratory to investigate rapid, eclipse-driven ionospheric variability driven by the sudden reduction of solar extreme ultraviolet (EUV) and X-ray input. LWA systems were deployed at Upland, Indiana, located along the path of totality, and at Peach Mountain Observatory, Michigan, which experienced approximately 95% solar obscuration. The dynamic spectra at both sites were dominated by persistent and intermittent narrowband features consistent with radio-frequency interference, while the integrated intensity curves showed complex, nonmonotonic variability that did not follow eclipse obscuration in a simple manner. At Upland, the intensity minimum occurred before eclipse onset and was followed by a gradual increase through the eclipse interval. At Peach Mountain, the signal exhibited smaller and more irregular variations during and after maximum obscuration. These results indicate that the measured radio intensity reflects the combined influence of evolving solar-disk and coronal emission, ionospheric propagation, background variability, and residual interference rather than eclipse geometry alone. Complementary GNSS-derived total electron content measurements near Upland showed eclipse-associated F-region variability of approximately 5–8 TECU. Because the LWA and GNSS observations probe different ionospheric regions and physical processes, the two datasets are interpreted as complementary rather than directly equivalent diagnostics. Beyond the scientific observations, the campaign integrated undergraduate and master’s students into antenna deployment, calibration, real-time monitoring, data processing, and scientific communication, providing practical experience in field-based heliophysics research and public outreach.

A key process in solar‐terrestrial interactions is magnetic reconnection at the magnetopause. In addition to in situ observations of plasma entry at the magnetopause, some of the important global aspects of magnetic reconnection are addressed using plasma observations in the Earth's magnetospheric cusp region. Ions injected at the magnetopause are subject to a time‐of‐flight effect, which results in distinctive ion‐energy dispersions observed in the cusp. The shape of these ion dispersions is analyzed and linked with predictions of the magnetopause reconnection location from the maximum magnetic shear model to determine the plasma entry points at the magnetopause. This study determines how those plasma entry locations affect the observed cusp ion dispersion profiles. This study uses first observations from the Analyzers for Cusp Ions (ACIs) onboard the Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites spacecraft.

Interacting coronal mass ejections (CMEs) result in complex heliospheric structures that can dramatically enhance their geoeffectiveness compared with isolated events. A striking example of such complex structures is that of the Mother’s Day event, which occurred during 2024 May 10–14, leading to the strongest geomagnetic storm in decades. It was driven by at least 10 interacting CMEs accompanied by flare and filament eruptions from the solar western hemisphere. We aim to understand its solar and heliospheric origins, variations in plasma and magnetic characteristics, and predict its geoeffectiveness. Furthermore, we focus on bringing to the community the challenges and limitations faced during the modelling of such a complex, yet important, environment. We use multipoint remote observations of CMEs and employ different methods to estimate their speeds and geometry. These parameters drive the 3D magnetohydrodynamic simulations of CME evolution and heliospheric propagation in the framework of the EUHFORIA model. The best-performing simulation reproduced the storm’s arrival time and peak intensity with a lead of ∼2 hr, and estimated the storm strength with about 70% accuracy. This work underscores the requirements and challenges involved in accurately modelling extreme events. The major bottleneck was to constrain the CME input parameters that dictate the accuracy of the data-driven simulations. Predicting the impacts of the complex heliospheric structures during this event required the modeling of the CME–CME interactions accurately. As a community, we need to invest more in observational infrastructure while improving the speed and accuracy of our MHD forecasting models.

Magnetic switchbacks are large-amplitude fluctuations in the interplanetary magnetic field, and appear frequently in the near-Sun solar wind explored recently by Parker Solar Probe: these new observations have prompted many new studies into their properties and origins. Here, we first review what is known about how switchbacks evolve as they travel away from the Sun: both in terms of their expansion-driven growth and their decay due to various processes like turbulence, reconnection, dispersion, parametric instability, and interaction with interplanetary shocks. We then review the current state of knowledge on how switchbacks impact the physics of the solar wind as a whole: in terms of the turbulent cascade, acceleration and heating of the wind, modification of the open solar flux and scattering of energetic particles. Finally, we suggest future studies to further our understanding of switchback evolution and impacts on the heliosphere.

We present observations from two consecutive TRACERS‐2 orbits through the northern low‐altitude cusp. During the first crossing, TRACERS‐2 observed reversed cusp ion dispersion and sunward convection, consistent with magnetopause reconnection tailward of the cusp during this northward IMF interval. Simultaneous THEMIS‐D observations at the equatorial magnetopause show heated magnetosheath plasma captured on closed field lines, with similar particle spectra as in the low‐altitude cusp, indicating that reconnection indeed occurred tailward of the cusp and in both hemispheres. When TRACERS‐2 traversed the northern cusp again, 95 min later, the IMF was dominated by a negative B _X component. Despite the different IMF conditions, TRACERS‐2 recorded nearly the same cusp signatures as before, that is, reversed ion dispersion and sunward convection. The observations indicate that tailward‐of‐cusp reconnection can occur for both northward and B _X ‐dominated IMF and that these distinct IMF geometries can produce remarkably similar plasma and field signatures in the low‐altitude cusp.

The Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites (TRACERS) mission observes electron energy‐latitude dispersion at the equatorward edge of the magnetospheric cusp, and high‐cadence Analyzer for Cusp Electrons (ACE) measurements resolve the dispersed edge. The inverse velocity dispersion (low energy before high energy) encountered by TRACERS as it travels southward through the northern cusp rules out pure energy‐time dispersion from nearby injections or Alfvén wave‐driven acceleration. TRACERS observes electron dispersion at the equatorward edge of the northern cusp roughly half of the time for southward interplanetary magnetic field (IMF), and almost never for northward IMF. The TRACERS measurements therefore provide strong observational support for the hypothesis that the observed electron dispersion results from dayside magnetic reconnection and plasma convection, much like the ion dispersion that commonly extends across the cusp. Observations of multiple electron dispersions and electron steps suggest fine‐scale spatial and/or temporal variability in magnetic reconnection.

Magnetic switchbacks are fluctuations in the solar wind in which the interplanetary magnetic field sharply deflects away from its background direction so as to create folds in magnetic field lines while remaining of roughly constant magnitude. The magnetic field and velocity fluctuations are extremely well correlated in a way corresponding to Alfvénic fluctuations propagating away from the Sun. For a background field which is nearly radial this causes an outwardly propagating jet to form. Switchbacks and their characteristic velocity jets have recently been observed to be nearly ubiquitous by Parker Solar Probe with in situ measurements in the inner heliosphere within 0.3 AU. Their prevalence, substantial energy content, and potentially fundamental role in the dynamics of the outer corona and solar wind motivate the significant research efforts into their understanding. Here we review the in situ measurements of these structures (primarily by Parker Solar Probe). We discuss how they are identified and measured, and present an overview of the primary observational properties of these structures, both in terms of individual switchbacks and their collective arrangement into “patches”. We identify both properties for which there is a strong consensus and those that have limited or qualified support and require further investigation. We identify and collate several open questions and recommendations for future studies.

Magnetic switchbacks are fluctuations in the solar wind in which the interplanetary magnetic field sharply deflects away from its background direction so as to create folds in magnetic field lines while remaining of roughly constant magnitude. The magnetic field and velocity fluctuations are extremely well correlated in a way corresponding to Alfvénic fluctuations propagating away from the Sun. For a background field which is nearly radial this causes an outwardly propagating jet to form. Switchbacks and their characteristic velocity jets have recently been observed to be nearly ubiquitous by Parker Solar Probe with in situ measurements in the inner heliosphere within 0.3 AU. Their prevalence, substantial energy content, and potentially fundamental role in the dynamics of the outer corona and solar wind motivate the significant research efforts into their understanding. Here we review the in situ measurements of these structures (primarily by Parker Solar Probe). We discuss how they are identified and measured, and present an overview of the primary observational properties of these structures, both in terms of individual switchbacks and their collective arrangement into ``patches''. We identify both properties for which there is a strong consensus and those that have limited or qualified support and require further investigation. We identify and collate several open questions and recommendations for future studies.

We present an unprecedented simulation of how two large-scale heliospheric transients—a coronal mass ejection (CME) and a corotating stream interaction region—collide, producing a dramatic increase in the complexity of the CME due to formation of mesoscale flux ropes. These structures are captured for the first time by a numerical simulation using high-resolution numerical grids. The circumstances that lead to the formation of these complex structures occur during solar maximum. At the time of the solar maximum taken for this study, 2014 September, the heliospheric current sheet is vertically inclined running over the poles, allowing the CME to impact a preceding slow-fast stream interaction region. The simulation is performed with the Alfvén Wave Solar Atmosphere Model (or AWSoM), with which we initiate a fast CME from active region (AR) 12158 by applying a Gibson–Low magnetic flux rope. Magnetic reconnection within the leading extremity of the CME results in the formation of mesoscale flux ropes, which contain sufficiently strong magnetic fields (∼30 nT) to affect planetary magnetospheres. Finally, we use a tetrahedral configuration of four virtual probes, corresponding to the Space Weather Investigation Frontier mission concept, to show that the mission can uniquely resolve the spatial characteristics and temporal evolution of reconnecting current sheets within the CME, as well as the resulting mesoscale structures.