pynasonde: An open-source Python library for ionosonde data processing

12 hr Forecast of the SYM-H Index under Strong Southward Interplanetary Magnetic Field Conditions Using Deep Learning

Magnetic reconnection, a universal process governing energy release in astrophysical plasmas, has long been studied as a key phenomenon in magnetized planets. However, its drivers and impacts in unmagnetized bodies remain poorly understood. Despite the detection of magnetic reconnection in the near Venusian magnetotail over a decade ago, the physical mechanism enabling this process in a non-intrinsic magnetic field environment has remained unresolved. Here, we present a global magnetohydrodynamic simulation of Venusian magnetotail reconnection, providing a plausible explanation for this phenomenon. We demonstrate that reconnection is triggered by the compression of the draped interplanetary magnetic field following an interplanetary shock, a mechanism previously associated with terrestrial dynamics. Our results reproduce characteristic reconnection signatures at approximately 1.72 Venus radii down the tail and delineate the formation of three-dimensional magnetic structures consistent with reconnection topologies. These findings highlight a physically plausible pathway by which dynamic pressure enhancement associated with an interplanetary shock may trigger magnetotail reconnection in unmagnetized plasma environments. While based on a single case, these results may provide a physical basis for understanding potential drivers of atmospheric evolution on rocky planets and exoplanets.

This study focuses on the dynamics of the subsolar position ( , in Earth radii ) of the magnetopause in response to events originating in corotating interaction regions (CIRs) during the declining phase of solar cycle 24. Based on analyses using the models developed by Shue et al. (1998), Liu et al. (2015) and Lin et al. (2010), we quantify the impact of mechanical and electromagnetic couplings on this boundary. We analyse these dynamics based on the north–south component of the interplanetary magnetic field ( Bz, in nT ), the total interplanetary magnetic field strength ( B, in nT ), the dynamic pressure of the solar wind (Pd, in nPa ), and the magnetic pressure (Pm, in nPa ). Additionally, we consider the normalised solar wind–magnetosphere coupling index (N), derived from the Newell et al. (2007) function and scaled by a normalisation factor of 10⁻⁴. Analysis of the temporal profiles across the different phases of the CIR storms studied reveals progressive and oscillatory variations in the magnetopause's subsolar position ( ). Our results reveal significant compressions, with a reduction in Ro amplitude ranging from 0.9 Re to 5 Re . The main minimum Ro reached during these CIR events studied is 6.4 Re , pushing the magnetopause below the geosynchronous orbit (6.6 Re ). The originality of this study lies in the joint application of cross-correlation, Granger causality, and Bootstrap, an approach that allows dissociating the information-contribution delay (Granger causality) from the time required for the maximum physical adjustment of Ro to the various constraints imposed by solar drivers. Granger causality analysis reveals that predictability is not always immediate: while it is instantaneous for certain drivers, it takes between 14 and 21 minutes for past values of to Pd improve the prediction of Ro during the CIR event of 27 March 2017, and 18 to 20 minutes for the intensity of the interplanetary magnetic field B in the event of 20 January 2016. Regarding physical adjustment, while the responses to and the coupling index (N) are immediate across all six events, the analysis reveals remarkable inertia in the other parameters. The adjustment to the Bz constraint took 33 min to reach its maximum during a specific event. In the six CIR events studied, the adjustment of Ro to the IMF B intensity constraint was slow, with delays ranging from 10 minutes to more than 2 hours (8 min to 130 min). These prolonged delays, particularly well captured by the Lin and Liu models, indicate a hysteresis effect and a slow, global reconfiguration of magnetospheric currents.

This study investigates the ionospheric and geomagnetic response to Coronal Mass Ejection forcing by analyzing Total Electron Content (TEC) distributions, the relationship between the Interplanetary Magnetic Field (IMF) Bz component and the solar-wind convective electric field (Ey), and the temporal evolution of key geospace parameters during disturbed periods. TEC data derived from GNSS-based Global Ionospheric Maps were used to examine spatial variations and storm-time anomalies in ionospheric electron density. Concurrent solar-wind and IMF measurements obtained from the OMNI dataset were used to compute Ey and assess its correlation with IMF-Bz through statistical and scatter-plot analyses. Time-series plots of Dst, IMF-Bz, solar-wind speed, density, and Ey were constructed to identify the coupling between solar-wind drivers and geomagnetic activity. The results demonstrate that strong southward IMF-Bz enhances Ey, which in turn intensifies geomagnetic disturbances indicated by Dst reductions. Corresponding TEC enhancements and depletions reveal significant restructuring of the ionosphere during storm main and recovery phases. This integrated approach provides improved understanding of solar-wind–magnetosphere–ionosphere coupling and the dynamic behavior of ionospheric TEC under varying geospace conditions. The enhancements and disturbances in the solar wind field due to combined co-rotating interaction region (CIR) and CH HSS influences likely resulted in isolated periods of G1 storm levels late on 23 March and isolated G4 storm levels on 24 March. The Dst index value showed a sudden commencement with a sudden increase to 24nT and then decreased continuously to -163nT on March 24, 2023, which is the largest storm so far in solar cycle 25. The IMF-Bz developed a prolonged and significant southward component reaching a minimum of about -20 nT at 03:00 UT, which corresponds to the peak of the minimum Dst index of -163 nT. Solar wind pressure shows a jump from 1.83 nPa on March 22, 2023, to 14.79 nPa on March 23, 2023. Rapid increases in solar wind dynamic pressure compress the Earth’s magnetosphere and rapidly restructure the electrodynamics within. The enhancement of TEC towards the southern hemisphere high latitude was observed. On March 24, 2023, an enhanced spatial distribution of TEC coverage is over the globe. These all evidences might be the result of the geomagnetic storms.

Abstract The cusp region plays a crucial role in the interaction between the solar wind and the Earth's magnetosphere, where solar wind particles can enter the magnetosphere directly. This study reports that the cusp boundary exhibits a twisting structure, which intensifies with increasing altitude, as demonstrated by global magnetohydrodynamic (MHD) simulations. It is further revealed that the dawn‐dusk component of the interplanetary magnetic field (IMF) significantly influences the degree of cusp twisting. This effect can be attributed to the tilt of the magnetic reconnection X‐line and the subsequent tilt of the plasma flow directions, modulated by the IMF . Moreover, the relationship between the cusp twisting deformations at different altitudes and the magnitude of the IMF is quantitatively analyzed across the entire cusp region based on systematic MHD simulation runs. A remarkable enhancement in the twisting angle is indicated with increasing IMF and altitude, varying from 0 to 7.6. The orientation of the cusp twisting follows that of the magnetotail and current sheet dynamics reported in previous studies, implying that the cusp twisting reported here is an essential part of the global effect of non‐zero IMF on the dayside magnetopause.

The interaction between the solar wind and the atmosphere of Venus leads to the formation of an induced magnetosphere, within which pronounced dawn–dusk asymmetries are observed in magnetic field pileup and ion transport. These asymmetries are known to depend on the orientation of the interplanetary magnetic field (IMF), but the underlying physical mechanisms governing this dependence remain incompletely understood. The aim of this study was to investigate how different IMF orientations influence magnetic field pileup, mathrm O ^+ ion distribution, and horizontal plasma transport in the induced magnetosphere of Venus, and to identify the dominant electromagnetic forces responsible for the resulting dawn–dusk asymmetries. We employed a multi-fluid magnetohydrodynamic (MHD) model to simulate the solar wind–Venus interaction under different IMF orientations. The model was used to analyze the spatial distribution of magnetic field strength, mathrm O ^+ ion number density, horizontal velocity, and ion flux. In addition, individual electromagnetic force components, including the motional electric field, the ambipolar electric field force, and the boldsymbol J B force, were quantitatively examined. The simulations show that when the IMF is not perpendicular to the solar wind flow, the dawnside, corresponding to the hemisphere toward which the IMF points in the simulation setup, exhibits stronger magnetic field pileup and enhanced horizontal plasma transport than the duskside. This dawn–dusk asymmetry weakens when the IMF orientation approaches perpendicularity to the solar wind. Force analysis reveals that the boldsymbol J B force is the primary driver of the asymmetric plasma transport. The magnetic field component normal to the planetary surface displays opposite signs on the dawn and dusksides, generating horizontal magnetic gradients and oppositely directed current density systems, which in turn produce asymmetric boldsymbol J B forces. These results demonstrate that the radial magnetic field structure and the resulting boldsymbol J B force play a critical role in controlling dawn–dusk asymmetries in plasma transport within Venus’ induced magnetosphere. The findings highlight the importance of electromagnetic forces, particularly the boldsymbol J B force, in shaping the structure and dynamics of the solar wind–Venus interaction under varying IMF orientations.

Abstract Using high‐time‐resolution Super Dual Auroral Radar Network (SuperDARN) radar data, we investigated the dynamic evolution of ionospheric convection under various conditions, including an interplanetary magnetic field (IMF) southward turning, a substorm onset, quasi‐steady southward IMF, and Pc5 ultra‐low frequency (ULF) waves. The SuperDARN high‐resolution convection revealed that during an IMF southward turning, convection enhancements form narrow, transient flow channels in the polar cap rather than broad, uniform flows, with velocity peaks moving equatorward and crossing the nightside open‐closed boundary. These flow peaks are linked to poleward boundary intensifications. The convection response was nearly simultaneous across latitudes. During a substorm onset, enhanced equatorward flow across the polar cap boundary preceded auroral onset, suggesting that flow observations may be a more sensitive indicator of pre‐onset conditions than auroral data. Under quasi‐steady southward IMF, both aurora and plasma velocity show significant unsteady behavior, with flow channels moving equatorward beyond the extent of their corresponding auroral streamers. For Pc5 ULF waves, the data reveal fine‐scale velocity structures within larger poleward‐moving enhancements, which correspond to breaks in the ULF magnetic field. This study emphasizes that high‐time‐resolution convection observations are essential for accurately capturing the rapid evolution of ionospheric convection, which is often underestimated using conventional lower‐resolution methods.

Context. Switchbacks–transient, large-angle deflections of the interplanetary magnetic field–pervade the solar wind, yet their origin remains disputed. Current ex situ theories, notably coronal jets and interchange reconnection, are typically tested on day-scale intervals. Aims. We aim to establish a connection between switchbacks and ex situ theories on solar-cycle timescales. Methods. We exploited 27 years of continuous in situ measurements from ACE, Wind, and STEREO-A/B at 1 au, complemented by synoptic remote-sensing data from SDO, to examine the solar-cycle modulation of switchback occurrence and to test whether ex situ scenarios (coronal jets and interchange reconnection) play a dominant role in such long-term modulation. Results. The switchback occurrence rate correlates strongly with Alfvénicity ( cc = 0.70 ± 0.04) and shows no solar-maximum preference (independent of the sunspot number, cc = 0.13 ± 0.05). Coronal jets affect switchbacks only indirectly via modulation of the solar wind speed. Multi-spacecraft consensus confirms that a stable, Alfvénicity-dependent process governs switchback variability, rather than episodic surface drivers. In addition, these results are robust to the deflection threshold of switchbacks. These findings impose quantitative constraints on theories of solar-wind turbulence and the transport of magnetic energy from the Sun to interplanetary space.

Abstract Fast forward interplanetary shocks (FFs) are one of the primary drivers of space weather events. This study presents an automated detection algorithm for FFs based on a multilayer perceptron model, utilizing in situ measurements of interplanetary magnetic fields and solar wind plasma from the Wind spacecraft at 1 AU. The training data set was constructed using FF events from the Harvard‐Smithsonian Center for Astrophysics (CfA) shock list between 1995 and 2019, while the testing data set comprised FF events from a combined catalog of the CfA and Helsinki University shock lists from 2020 to 2024. During the testing period, the method identified 169 FFs, of which 83 matched entries in the existing catalog. Among the remaining 86 uncatalogued events, 67 satisfied the Rankine‐Hugoniot (R‐H) jump conditions, confirming them as novel shocks not previously recorded. Using direct comparison with the composite CfA/Helsinki catalog, the model achieves a recall of 80.58%. Since some apparent false positives in this direct comparison are later supported as physically consistent shocks by the R‐H checks, the combined evaluation against the expanded benchmark yields a recall of 81.62% with false alarm rate = 10.65%. This approach provides a robust tool for the classification and study of interplanetary shock properties, thus enhancing the capability for space weather forecasting.

ABSTRACT When the interplanetary magnetic field (IMF) changes towards its final orientation, induction within the Moon enhances the magnetic field beneath the lunar surface but outside the conductive interior. This enhanced magnetic field compresses the solar wind near the lunar terminator, forming limb compression structures. Using three-dimensional, time-dependent magnetohydrodynamic simulations, we systematically explore how the lunar core radius, core conductivity, and the amplitude of the IMF variation influence these limb compression structures. Our findings demonstrate that a larger core radius, higher core conductivity, and a larger magnetic field change result in a stronger induced magnetic field and more pronounced limb compression. However, when core conductivity exceeds 0.1 S m−1, further increases in the core conductivity have minimal impact. These simulation results serve as a forward-modelling study that lays the groundwork for future efforts to constrain the lunar interior stratification under conditions of external magnetic field perturbations by combining numerical modeling with spacecraft observations.

Abstract The influence of the right ascension of the ascending node (RAAN) of a Mars orbiter on magnetic connectivity to Jupiter along Parker-spiral interplanetary magnetic field lines is examined. A highly elliptical Mars orbit (400 × 76,000 km, inclination 54°) referenced from the Tianwen-3 mission concept is adopted to evaluate the geometric accessibility of Jovian electrons using a dual-criteria connectivity metric based on heliolongitude footpoint matching and detector field-of-view alignment. A parametric sweep of RAAN from 0° to 360° reveals two symmetric connectivity windows separated by ∼180°, with mean per-orbit connectivity duty cycles of approximately 4%–6% depending on solar wind speed. The results demonstrate that orbital-plane orientation acts as a primary geometric control on Jovian magnetic accessibility at Mars orbit. This geometric framework provides a simple method for assessing potential observation opportunities for energetic particle detectors in planetary orbit and highlights the importance of orbital-plane configuration in heliospheric observation strategies.

Abstract Extreme conditions during storms profoundly alter the evolution of equatorial plasma bubbles (EPBs), yet the key dynamics remains poorly understood. We document the rapid expansion, contraction, and decay of super EPBs in South America during the 12 November 2025 storm with Interplanetary Magnetic Field (IMF) Bz/By magnitude exceeding ∼50 nT. These EPBs expanded to ∼37° magnetic latitude with pronounced hemispheric and longitudinal asymmetries and westward tilt. Notably, the equatorial ionization anomaly (EIA) crests retracted into an X‐pattern during suppression. We suggest that eastward prompt penetration electric fields (PPEF) driven by strong IMF Bz caused the rapid expansion, while fast equatorward winds (peaking at 488 m/s vs. typically ∼<100 m/s) together with westward PPEF triggered EIA merging and EPB decay. The entire EPB lifecycle unfolded within 3 hrs, considerably faster than previously reported events. Our findings reveal storm‐time mechanisms shaping the low‐latitude ionosphere under extreme conditions and advance understanding crucial for space weather prediction.

Abstract The interplanetary magnetic field (IMF) measured near Earth can be up to 2 times greater than that derived from models using remote solar observations. We investigate this discrepancy by modeling the IMF using a potential field source surface (PFSS) model using synoptic maps of the photospheric magnetic field from 2010 May to 2024 April. Five types of radial field synoptic maps are used in this work: the B r synoptic maps from vector magnetic field data, the M r synoptic maps from the line-of-sight field data, the rescaled M r synoptic maps rescaled from the M r maps by a center-to-limb distance dependent rescaling factor of B r / M r , and composite and rescaled composite synoptic maps comprised of a combination of strong-field pixels from the B r maps and the rest from either the original M r or rescaled M r maps. The modeled IMFs from all five types of synoptic maps agree with each other well in the solar maximum phase, when they are about 2 times smaller than in situ measurements. The IMF calculated from the B r and both composite and rescaled composite synoptic maps match well with in situ observations during solar minimum from 2017 to 2022. The IMF values modeled from both the M r and rescaled M r synoptic maps are still significantly smaller in this time interval. This suggests that (1) the B r maps represent the radial field better than the M r ; and (2) the PFSS model is appropriate to model the heliospheric magnetic field in solar minimum, but has limitations when used near solar maximum.

Abstract – In the study a geomagnetic storm forecasting data mining model is created with the help of key solar wind and interplanetary magnetic field (IMF) parameters that are optimized based on their features. The suggested model makes use of high-resolution solar wind plasma and IMF measurements retrieved in the OMNI database, and the disturbance storm time (Dst) index is used as the main measure of the strength of geomagnetic storms. A strategy of feature optimization is adopted to determine the most geoeffective parameters to predict the computational efficiency and reliability of predictive power, such as solar wind speed, proton density, total vertical magnetic field strength and southward component of IMF (Bz). Weakly correlated and redundant features are automatically removed in order to simplify the model without decreasing forecast accuracy. An optimized feature subset is then applied to the data to form a predictive model based on data mining that has the potential to learn the nonlinear relationships between the upstream solar wind conditions and geomagnetic response. The performance of the models is measured by standard statistical measures and compared to non-optimized baseline models. These findings indicate that the proposed methodology has a better forecasting accuracy at a much lower cost of computation, thus it can be used in near real-time space weather forecasting. The results indicate that feature selection is also vital in space weather prediction and that the majority of the geomagnetic disturbances are due to IMF orientation and solar wind dynamics. The suggested model offers a stable and effective framework of the operational geomagnetic storm forecasting and leads to the creation of well-grounded data-driven space weather forecasting systems. Keywords: Geomagnetic storms, Space weather forecasting, Data mining, Feature optimization, Solar wind, Interplanetary magnetic field, Dst index.

Abstract The offset between Earth's magnetic and rotational axes introduces a diurnal dependence in the high‐latitude EUV exposure of the northern hemisphere (NH) and southern hemisphere (SH). This variation raises the question: Does the Universal Time (UT) of geomagnetic storm onset impact its geospace consequences? To address this question, we used the Multiscale Atmosphere‐Geospace Environment (MAGE) model to simulate the 10 October 2024, geomagnetic storm—the year's second strongest (SYM‐H minimum of −346 nT). Since the storm occurred near equinox, we did not expect, but found, significant interhemispheric asymmetries in magnetosphere‐ionosphere‐thermosphere (M‐I‐T) coupling parameters such as the cross‐polar cap potential, hemispherically integrated field‐aligned current, and hemispheric power of electron precipitation. Controlled simulations show that interplanetary magnetic field (IMF) and solar wind have negligible effects on these asymmetries, whereas the EUV variation arising from the diurnal dipole tilt produces noticeable interhemispheric differences. Coincidentally, during this storm, IMF B z turned southward when the SH was tilted toward the Sun, and it maintained this orientation for 12 hr. A controlled simulation with storm onset shifted by 12 hr exhibits a substantial reduction in interhemispheric asymmetry. Differences in integrated Joule heating power and the SML/SMU indices also occurred with the shifted onset, underscoring the importance of UT in stormtime magnetosphere‐ionosphere coupling.

Abstract The interaction between a turbulent plasma flow, such as the solar or stellar wind, and a magnetic field acting as an obstacle is a common phenomenon in space and astrophysical plasmas. The Earth's magnetosphere is formed precisely as a result of this interaction, and there is extensive evidence suggesting that the geomagnetic tail behaves like a turbulent wake behind an obstacle. Unlike an ordinary wake, the geomagnetic tail is divided into a plasma sheet, filled with dense, turbulent plasma, and tail lobes filled with rarefied, quasi-laminar plasma. The interaction between the turbulent plasma sheet and the inner magnetosphere is crucial for understanding key magnetospheric processes such as geomagnetic storms and substorms. Meanwhile, variations in solar wind density, velocity, and the interplanetary magnetic field (IMF) simultaneously affect plasma conditions in both the plasma sheet and the inner magnetosphere, although through different and not yet fully understood mechanisms. In this work, data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission are used to analyze the influence of the IMF and solar wind dynamic pressure on eddy diffusion within the plasma sheet. 
Our results indicate that eddy diffusion coefficients increase with a southward orientation of the IMF and can intensify by more than an order of magnitude under high values of the solar wind dynamic pressure. Both of these factors contribute to an increase in the plasma beta parameter within the plasma sheet, leading to a shift of the transition zone between turbulent and quasi-laminar plasmas towards Earth.

Abstract Cloud formation is due to a combination between water uptake and aerosol distribution and characteristics. Globally, the state of the terrestrial atmosphere is influenced by solar activity and galactic cosmic rays through the global electric circuit. This paper investigates the possible link between cloud cover and solar proxies, namely sunspot number (SSN), solar/plasma wind speed (PWS), and the associated interplanetary electric and magnetic fields (IEF, IMF), respectively, for two solar cycles. The seasonal variation on possible links is also investigated. Each solar driver may influence the atmospheric electricity, thus cloud formation and cloud cover. The study uses the first long-term cloud database, as provided by the International Satellite Cloud Climatology Project (ISCCP), since these data had sufficient time for validation and are ready to use as such. Solar proxies were taken from NASA’s OMNIWeb database, from measurements with instruments onboard several spacecraft with geocentric orbits. Cloud types were individually considered, and global distribution of cloud cover was analyzed. The study reveals that the cloud cover response to changes in various solar indicator depends on local conditions, and varies with season. E.g., high clouds cover exhibited anticorrelation with IEF in January on large areas, while low cloud cover was moderately positively correlated with PWS on extended regions in July.

Abstract Flux transfer events (FTEs) transport solar wind energy and plasma into the Earth's magnetosphere. Their topological twisting features can be described by magnetic helicity, a crucial quantity for understanding the large‐scale magnetic field structure and evolution. The interplanetary magnetic field (IMF) orientation significantly influences the properties and global behaviors of FTEs. Recent observations revealed the relation between FTE formation and helicity sign and its dependence on IMF orientations. However, the detailed characteristics of FTE helicity magnitude and its relations with FTE evolution as influenced by IMF orientation are still poorly understood. Using global MHD simulations with different IMF clock angles arctan( B y / B z ), we designed a novel method to calculate FTE helicity magnitude for the first time and investigated its relations with other FTE properties. We find that magnetic helicity has positive correlations with the FTE core field and lifetime. The helicity and lifetime are the largest when IMF has comparable B y and B z , implying that as IMF turns from near‐purely southward to duskward, the helicity and lifetime first increase as a function of increasing B y / B z but then decrease once B y / B z exceeds a threshold. This is attributed to the increasing magnetic tension force generated by the FTE core field, which can suppress kink instability or straighten the flux rope depending on the IMF orientation regime. Interplanetary magnetic field B y generally controls FTE helicity signs, with exceptions occurring when IMF B y is small even without the Hall effect. These findings enhance our understanding of global‐scale FTE structures and evolution, aiding interpretation of future satellite data such as SMILE and TRACERS.

Abstract We apply a hybrid model (kinetic ions, fluid electrons) to provide context for MErcury Surface Space ENvironment, GEochemistry, and Ranging (MESSENGER) observations of Disappearing Dayside Magnetosphere (DDM) events at Mercury. Such events have been observed on four occasions and are caused by Coronal Mass Ejections completely removing the dayside magnetopause (MP) through erosion and compression. We investigate how different Interplanetary Magnetic Field (IMF) orientations, resulting in different reconnection rates, influence Mercury's magnetosphere under these extreme conditions. The model uses constant upstream conditions and the highest ram pressure reported for any DDM event to date. Our results are: (a) Under DDM conditions, a bow shock forms above Mercury's low‐latitude surface for northward or duskward IMF orientation. (b) However, when the IMF points southward, the solar wind impacts unhindered onto the equatorial dayside surface, and a shock develops only at high latitudes. In this case, the IMF is antiparallel to the dayside planetary field, and any closed field lines in the upstream hemisphere are eroded through reconnection. Hence, despite the favorable IMF orientation, no return plasma flow forms: protons largely travel along the outer flanks of the MP toward downstream. (c) The wakeside draping pattern seen during a DDM event in 2013 is consistent with a drop in upstream pressure by at least while MESSENGER passed through the magnetotail. The observed neutral sheet position suggests that the IMF changed from duskward to dawnward orientation during the spacecraft's passage through the magnetosphere. (d) Magnetotail twisting may have caused the southward displacement of the neutral sheet observed during the 2013 event.