Perturbations in the solar wind caused by space weather drivers can have a significant impact on the magnetosphere and subsequently on the ionosphere, producing global geomagnetic effects. Understanding and characterizing these responses requires a detailed study of magnetosphere-ionosphere (MI) coupling under varying space weather forcing conditions. In this study, we present global 3D magnetohydrodynamic (MHD) simulations with a two-way coupled MI coupling module to study the impact of a solar wind density pulse on the spatial and temporal profiles of ionospheric field-aligned currents (FACs) under northward interplanetary magnetic field (IMF) conditions. The pulse compresses and relaxes the magnetosphere, generating Alfv & eacute;nic disturbances that manifest as alternating polarity FACs on the ionosphere. We find that the MI response is also significantly modulated by the IMF clock angle. For small, non-zero IMF nT, FAC profiles show the largest enhancement and enable prompt penetration electric fields (PPEF). The IMF case shows weaker, symmetric enhancements, while a higher IMF nT creates a dominant convection cell that suppresses oscillatory currents, yielding diffuse and delayed responses. FACs intensify rapidly within min after impact, consistent with Alfv & eacute;n wave travel time from magnetosphere to ionosphere. We compare our model results with relevant observations from AMPERE, which exhibit similar responses under comparable solar wind forcing. This demonstrates that, even under northward IMF conditions, compressive solar wind forcing can induce substantial ionospheric disturbances, with the IMF component modulating the nature of this response.

Understanding the spatial coherence of solar wind plasma and magnetic field properties is essential for interpreting multi-spacecraft observations and for characterizing the large-scale structure of heliospheric transients. In this study, we quantify the spatial correlation of six key solar wind parameters—interplanetary magnetic field components, bulk flow speed, proton number density, and the alpha-to-proton abundance ratio—using simultaneous measurements from the ACE and Wind spacecraft as a function of their instantaneous separation distance. The analysis is performed separately for intervals of background solar wind, Interplanetary Coronal Mass Ejections (ICMEs), and Stream Interaction Regions (SIRs). The decay of the Pearson correlation coefficient with distance is modeled using an exponential function to infer characteristic de-correlation length scales. We find that the bulk solar wind speed is the most spatially coherent parameter in all regimes, while plasma composition exhibits the weakest coherence. Magnetic field coherence shows strong dependence on solar wind structure: ICMEs display near-unity correlations and the largest magnetic coherence scales, consistent with organized, flux-rope-like configurations, whereas SIRs exhibit reduced coherence—particularly in the north–south magnetic field component—reflecting compressed and turbulent plasma. The background solar wind exhibits intermediate behavior, with large-scale coherence in bulk plasma properties but shorter coherence lengths in magnetic fluctuations. These results provide a quantitative framework for distinguishing solar wind structures based on their spatial coherence properties and have important implications for multi-point solar wind studies and space weather applications.

Understanding turbulence in interplanetary coronal mass ejections is fundamental to space plasma research and critical for assessing the impact of space weather on geospace. Turbulence governs energy cascade, plasma heating, magnetic reconnection, and solar wind magnetosphere coupling, thereby influencing both ICME evolution and geoeffectiveness. While previous event-based and statistical studies have examined ICME turbulence and its radial evolution in great detail, no significant measurements of ICME magnetic turbulence at a specific vantage point have been made using multiple observatories separated azimuthally. Here, we present the first multipoint analysis of MHD turbulence across ICME plasma regions, using four spacecraft at the Sun-Earth L1 point, separated by 80 RE along the dawn-dusk direction. Previous studies reveal that ICME shocks, sheaths, and magnetic clouds are highly non-uniform, with strong azimuthal variability. Using high-resolution magnetic field observations from ISRO's Aditya-L1, NASA's Wind and ACE, and NOAA's DSCOVR, we analyze turbulence associated with the 10th October 2024 solar storm, which triggered the second-strongest geomagnetic storm of solar cycle 25. Our results reveal significant variability and differing turbulence maturity across small separations, supported by analysis of field-aligned and perpendicular magnetic field cascades, indicating strong anisotropies. Sheath turbulence is substantially modified by shock induced energy injection. Evidence of compressible turbulence and plasma energization at the flux rope interaction region indicates that internal processes, such as magnetic reconnection, strongly influence ICME plasma evolution, highlighting pronounced spatial variability in turbulence and plasma states observed by multiple L1 monitors near Earth and underscoring their potential role in space weather impacts.

The influence of collisional age (A_c) on the alpha-to-proton temperature ratio (T_α/T_p) has been explored in the past. However, the modulation of this ratio with respect to the solar cycle has remained unexplored so far. We show solar-cycle modulation of T_α/T_p and A_c using nearly three decades of in-situ observations from Wind spacecraft across distinct solar wind speed regimes and solar activity phases. Our results reveal that in the slow solar wind with velocity <400 km s^-1, where A_c happens to be typically >1, the ratio T_α/T_p stays close to unity. This suggests frequent Coulomb collisions efficiently iron out temperature differences. In contrast, the fast wind with velocity >500 km s^-1, where A_c happens to be typically <1, mass-proportional heating is most pronounced, with T_α/T_p often exceeding 4. The intermediate speed regime (400-500 km s^-1) represents a gradual transition between the slow and fast wind populations in terms of their solar-cycle dependence. This behavior reflects the changing dominance of high-speed streams from polar coronal holes during minima to denser slow wind during maxima. These results suggest that mass-proportional ion heating at 1 AU is not solely governed by local collisional physics but is significantly modulated by the solar cycle dependent variations in the solar wind sources.

The Aditya-L1 mission, India’s first dedicated solar observatory at the first Lagrange point of the Sun-Earth system, carries the Solar Wind Ion Spectrometer (SWIS) as part of the Aditya Solar Wind Particle Experiment (ASPEX) payload suite. Even before settling down at the Halo orbit, AL1-ASPEX-SWIS has been delivering nearly continuous in situ measurements of solar wind ion spectra. Moments of the velocity distribution function (VDFs) have been calculated to derive the solar wind bulk parameters like density, bulk speed, temperature etc. Through this work, we evaluate the performance of AL1-ASPEX-SWIS through comparisons with contemporaneous measurements from the Wind and DSCOVR spacecrafts. A detailed case study of the 07 August 2024 interplanetary coronal mass ejection (ICME) is presented where sharp transitions in bulk speed, thermal speed, and number density were well-aligned with independent observations, confirming the instrument’s capability in capturing dynamic solar wind features. Spectral analysis of kinetic fluctuations revealed a well-defined inertial range with a spectral slope consistent with magnetohydrodynamic (MHD) turbulence. Additionally, a 17-month statistical comparison (January 2024–May 2025) shows strong agreement in bulk velocity ( R^2 ≈ 0.94 with Wind), with expected variability in thermal speed and density due to inter-instrument differences. These results confirm the scientific utility of AL1-ASPEX-SWIS in monitoring both transient events and long-term solar wind conditions.

There has been long-standing controversy regarding the origin and transport of short-lived energetic ion events observed upstream of the Earth's bow shock. In this work, by adopting a unique method, we study the characteristics of 152 upstream ion events observed by the Suprathermal Energetic Particles (STEP) instrument on board the Wind satellite during 2012-2017. These events are selected manually based on rise and fall of H and 4He intensities. During nearly 80% of the selected upstream events, the local interplanetary magnetic field appears to be nearly radial. Using the multidirectional measurement capability of the STEP, we compare the 4He/H and CNO/H ratios as well as the spectral indices of H, 4He, and CNO in the Earth-facing sectors with those seen in the Sun-facing sectors. This exercise is repeated by applying 10-120 minute lags on the ion intensities measured in the Sun-facing sectors of the instrument. It is found that the composition ratios are well correlated, thus confirming that the origin of the ions seen in the opposite-facing directions is the same. Surprisingly, we find that the spectra measured in the Earth-facing sectors are generally softer during majority of the events as compared to those measured in the Sun-facing sectors, with the mean softening in H, 4He, and CNO spectra in the solar wind frame varying between similar to 0.877 and 1.0, similar to 1.068-1.116, and similar to 1.4-1.939, respectively. We propose that scattering due to processes like cross-field diffusion could be responsible for producing the harder spectra in the Sun-facing sectors.

The inner to middle solar corona is a key region for solar wind generation. Akatsuki’s radio occultation measurementsduring five consecutive solar conjunctions from 2016 to 2022 provided a continuous dataset to study the accelerationof the solar wind between 3 and 11 solar radii (R⊙) within the lower-middle corona. These events occurred during the minima of solar cycles 24 and 25. Frequency fluctuation spectra revealed turbulence spectral indices between 0.2 and0.4, indicating an underdeveloped cascade. A positive correlation was found between the spectral index and sunspotnumber, suggesting modulation of coronal turbulence by the solar activity cycle. Plasma flow speeds estimated fromDoppler shifts ranged from 100 to 400 km/s, consistent with fast solar wind streams emerging from coronal holes.These results provided new insights on the nature of turbulence and wind acceleration in the low corona during solar minimum.

The interaction between interplanetary coronal mass ejection (ICME) structures can alter the geoeffectiveness of the ICME events in myriad ways. Many aspects of these interaction processes are not well understood. Using the energy spectra measured in two mutually orthogonal top-hat analyzers (THA-1 and 2), which are part of the Solar Wind Ion Spectrometer subsystem of the Aditya Solar Wind Particle EXperiment (ASPEX) on board India’s Aditya-L1 mission, we gain insights into intricate features of ICME–ICME interactions during the 2024 May solar event. We report here an unprecedented two-orthogonal-plane perspective of ICME–ICME interactions for the first time from the L1 point. The investigation reveals a special interaction region formed by the propagation of the forward shock driven by complex ejecta in the preceding ICME. The interaction causes the formation of a downstream region spanning over 13 hr, which propagates in the interplanetary medium. The observations reveal that this region serves as a site for proton and alpha particle energization, and the particles within this region get distributed from one plane to the other. The presence of forward shock and particle energization is confirmed by the energetic particle flux measurements by the SupraThermal and Energetic Particle Spectrometer of ASPEX. These observations provide an unprecedented perspective on how solar wind ions become energized and distributed in an ICME–ICME interaction region.

Understanding turbulence in interplanetary coronal mass ejections (ICMEs) is fundamental to space plasma research and critical for assessing the impact of space weather on geospace. Turbulence governs the energy cascade, plasma heating, magnetic reconnection, and solar wind-magnetosphere coupling, thereby influencing both ICME evolution and geoeffectiveness. While previous event-based and statistical studies have examined ICME turbulence and its radial evolution in great detail, no significant measurements of ICME magnetic turbulence at a single vantage point from multiple observatories separated azimuthally have been reported. Here, we present the first multipoint analysis of magnetohydrodynamic turbulence across ICME plasma regions using four spacecraft at the Sun-Earth L1 point, separated by approximate to 80RE (mesoscale) along the dawn-dusk direction. Using high-resolution magnetic field observations from ISRO's Aditya-L1, NASA's Wind and ACE, and NOAA's DSCOVR, we analyze turbulence associated with the 2024 October 10 solar storm, which triggered the second-strongest geomagnetic storm of Solar Cycle 25. Our results reveal significant variability and differing turbulence maturity across small separations, supported by analyses of field-aligned and perpendicular magnetic field cascades, indicating strong anisotropies. Sheath-region turbulence is substantially modified by shock-induced energy injection. Evidence of compressible turbulence and plasma energization in the flux-rope interaction region indicates that internal processes, such as magnetic reconnection, strongly influence ICME plasma evolution. These findings highlight pronounced spatial variability in turbulence and plasma states observed by multiple L1 monitors near Earth and underscore their potential role in space weather impacts.

The origin, acceleration, and anisotropy of suprathermal ions in the interplanetary medium during quiet time have remained poorly understood issues in solar wind physics. Using measurements (in the energy range of 0.12−1.33 MeV n ^−1 ) by the four detectors that are part of the Supra-Thermal and Energetic Particle Spectrometer (STEPS) of Aditya Solar Wind Particle Experiment (ASPEX) on board the Aditya L1 spacecraft, we address the variations in spectral indices with directions in shorter durations during 2024 January–November, which coincides with the maximum phase of Solar Cycle 25. Three out of four detectors on STEPS—Parker Spiral, Intermediate, Earth Pointing—are in one plane, while the fourth detector—North Pointing—is in a mutually orthogonal plane. The derived spectral indices are found to be −1.99 ± 0.06 regardless of directions, suggesting directionally near isotropic behavior during quiet times. It is also shown that the influence of the Compton–Getting effect is negligible in this assessment of directional isotropy. This result has important ramifications as directional isotropy is assumed while solving the Parker transport equation to explain the acceleration of energetic particles. Further analysis of elemental abundance ratios ( ^3 He/ ^4 He, Fe/O, and C/O) during the same quiet times obtained from the Ultra Low Energy Isotope Spectrometer on board the Advanced Composition Explorer spacecraft suggests possible contributions from the leftover ions from the previous solar energetic particle events in the quiet time suprathermal ion pool.

The Solar Wind Ion Spectrometer (SWIS) instrument is a part of the Aditya Solar Wind Particle Experiment (ASPEX), one of the three in situ observation instruments on board India’s Aditya-L1 spacecraft. SWIS comprises two Top-Hat analysers (THA-1 and THA-2), which have a 360∘ angular coverage in the ecliptic plane and in the plane perpendicular to the ecliptic plane, respectively, with opening angles of ± 1.5^∘ . Both are electrostatic scanning instruments designed to measure the flux, the energy distribution and the angular distribution of the solar wind particles, covering the energy range of 0.1 – 20.0 keV with a 5 s cadence and 8

Electrified Medium Scale Traveling Ionospheric Disturbances (EMSTIDs) is one of the prominent plasma structures that affect the propagation of high frequency radio waves. Overall, seasonal variation and propagation characteristics of the EMSTIDs are widely reported in literature. However, the effects of substorms on the formation and dissipation of the EMSTIDs are not well explored. In the present study, on a moderately geomagnetically active night of 26 October 2019 (Ap = 24), the airglow imager over Hanle (32.7 degrees N, 78.9 degrees E; Mlat. similar to 24.1 degrees N), India recorded the evolution and decay of an EMSTID in the O(1D) 630.0 nm airglow images in between 13.3 UT and 15.8 UT. In addition, during the same time, a steep rise and fall of the virtual base height of the ionospheric F-layer were also recorded by a nearby digisonde over New Delhi (28.70 degrees N, 77.10 degrees E; Mlat. similar to 20.2 degrees N). The most important aspect of the event was the occurrence of the two consecutive substorms in between 13.3 UT and 15.8 UT. To the best of our knowledge, this is the first of its kind study where we report the role of interplanetary electric field (IEF) and substorm induced electric fields on the evolution and decay of the EMSTID. Therefore, this investigation provides evidence that space weather induced prompt electric field perturbations can alter the state of the ionosphere already affected by EMSTID. (c) 2025 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

During its earth-bound phase of the Aditya-L1 spacecraft of India, the Supra-Thermal and Energetic Particle Spectrometer (STEPS) of the Aditya Solar wind Particle EXperiment (ASPEX) was operated whenever the orbit was above 52000 km during 11 - 19 September 2023. This phase of operation provided measurements of energetic ions (with energies 0.1–2 MeV) in the magnetosphere, magnetosheath, and interplanetary medium. Three interplanetary coronal mass ejections (ICME) hit the magnetosphere during this period. This provided opportunity to examine the relative roles of ICME-generated solar energetic particles (SEPs) and substorm generated energetic ions on the magnetosphere. We approach this objective by detailed spectral analyses of energetic ion fluxes measured by two units of ASPEX-STEPS. We identify three distinctly different conditions of the north-south component of the interplanetary magnetic field (IMF B_z = 0, > 0, and < 0) and use the derived spectral indices to understand this relative role. By combining these with the simultaneous energetic ion flux variations from the Advanced Composition Explorer (ACE) around the Sun-Earth first Lagrangian (L1) point and the Geostationary Operational Environmental Satellite (GOES) in the Earth's magnetosphere, we show that the polarity of IMF B_z influences the energetic ion spectra in the magnetosphere by modulating the interplay of the ICME-generated SEP with the energetic particles generated inside the magnetosphere by substorms. Interestingly, ASPEX-STEPS observations also indicate towards directional anisotropy based on spectral indices. This suggests spatially inhomogeneous mixing of energetic ions coming from different source processes.

In the present-day context, small satellites and their constellations consisting of varying sizes (nano, micro, pico satellites) are being favored for remote sensing and in situ probing of the heliosphere and terrestrial magnetosphere-ionosphere system. We introduce a mission concept aimed at concurrently observing Earth's northern and southern auroral ovals while conducting in situ measurements of particles, fields, and temperature. The mission concept consists of two small satellites, each having an identical auroral X-ray imager, an in situ particle detector, a magnetometer pair, and an electron temperature analyzer onboard in an elliptical polar orbit (400X1000 km ). This mission would assist the space weather community in primarily answering important questions about the formation, morphology, and hemispherical asymmetries that we observe in the X-ray aurora, the fluxes of precipitating particles, Solar Energetic Particles, currents, and cusp dynamics. Once realized, this would be the first dedicated twin spacecraft mission of such kind to simultaneously study hemispheric asymmetries of solar-wind magnetosphere coupling. This study reveals the intricacies of the mission concept, encompassing orbital details, potential payloads, and its underlying scientific objectives. By leveraging the capabilities of small satellites, this mission concept is poised to make significant contributions to space weather monitoring and research.

Coronal Mass Ejections (CMEs) are key to solar eruptions and geomagnetic storms, heavily influenced by their interaction with solar wind streams. Accurately predicting CME trajectories and impacts hinges on understanding how they evolve within ambient solar wind. Despite numerous qualitative studies, a detailed quantitative analysis of these interactions, crucial for predicting CME behavior, remains elusive, primarily due to the challenges in isolating CMEs from the solar wind. In the initial segment of the presentation, I'll introduce a newly developed MHD model, SWASTi, offering fresh insights into CME-SW interaction through simulation. Developed on the PLUTO code framework, SWASTi integrates a modified WSA relation for setting initial solar wind conditions and features two CME modules: a basic non-magnetized cone CME and an advanced flux rope CME. I'll also discuss a passive scalar tracing approach, developed for isolating CME structures in the heliosphere and analyzing their interactions with stream interaction regions. Following this, I'll delve into an in-depth analysis of CME interactions with variable ambient solar wind and the resulting effects on their evolution. Our approach involves two distinct setups: the 'real case', utilizing the standard SWASTi-CME flux rope model, and the 'synthetic case', a controlled scenario with uniform solar wind speed to examine CME behavior without SIR interference. The synthetic case, acting as a benchmark, allows us to measure the impact of solar wind variability on CME characteristics, contrasting it with findings from the real case. To conclude, the presentation will highlight our research's key outcomes, encompassing both qualitative and quantitative dimensions. These include examining the deformation of the CME front, and the evolution of thermal, kinetic, and magnetic pressures. Additionally, I will discuss the dynamic nature and implications of the drag force exerted on CMEs. We observed that the volume of CME follows a non-fractal power-law expansion over time, eventually reaching a balanced state.

We suggest that the next era of Heliophysics should focus on the Sun-Heliosphere and Geospace as each a system-of-systems, and recommend a coordinated, deliberate, worldwide scientific effort to answer long-standing questions that will remain unanswered without a unified program. Many of the biggest unanswered science questions that remain across Heliophysics center around the interconnectivity of the different physical systems and the role of mesoscale dynamics in modulating, regulating, and controlling that interconnected behavior. Heliophysics has made key progress understanding both the large-scale dynamics and the microphysical processes that occur in these dynamic systems. Such understanding grew out of a systematic approach to study both limits of the system, from global, with the coordinated missions of the International Solar Terrestrial Physics (ISTP) program, to micro, with largely uncoordinated (albeit coincident) missions such as Cluster, Time History of Events and Macroscale Interactions during Substorms (THEMIS), Van Allen Probes, Magnetospheric Multiscale (MMS), Parker Solar Probe, and Solar Orbiter. We suggest that the international Heliophysics community should embark on a grand program to study these system-of-systems holistically, with coordinated, multipoint measurements. We particularly recommend an emphasis on resolving the mesoscale dynamics that links micro to global, and a whole-of-science approach that includes ground-based measurements and advanced numerical modeling. In effect, we propose a mesoscale ISTP type program that would consist of a system of Great Observatories capable of revealing the connections among systems from the solar interior to the top of Earth's atmosphere. The paradigm and specific approaches outlined in this paper could serve as a strategic imperative and overarching theme that binds our Solar and Space Physics communities together under a common scientific objective. By its very nature, the type of program we argue for would be large, with several coordinated elements, and international in scope. It would include space-borne missions and coordinated ground-based observatories, artificial intelligence/machine learning (AI/ML) methods of analyzing large and complex datasets, and next-generation numerical modeling. The need to coordinate and integrate these different elements is independent of any specific mission implementation. Hence, we suggest the Heliophysics community organize around an ISTP-type program, ISTPNext, with associated Heliophysics "Great Observatories".

Stream interaction regions (SIRs) are often thought to be responsible for the generation of suprathermal population in the interplanetary medium. Even though the source is the same, wide variations in the spectral indices of suprathermal populations are observed at 1 au during SIRs. This poses a significant uncertainty in understanding the generation of suprathermal ion populations by SIRs and indicates an interplay of multiple source mechanisms. By analyzing variations in suprathermal ^4 He, O, and Fe for 20 SIR events recorded by STEREO-A during 2007–2014, we find that the spectral indices of these elements vary in the range of 2.06–4.08, 1.85–4.56, and 2.11–4.04 for 19 events. However, in one special case, all three suprathermal elements show nearly identical (∼1.5) spectral indices. We describe possible mechanisms that might cause significant variations in the spectral indices of suprathermal particles. More importantly, we show the possible role of merging and/or contraction of small-scale magnetic islands near 1 au in producing nearly identical spectral indices for three different elements with different first ionization potentials and mass-to-charge ratios. The occurrence of these magnetic islands near 1 au also supports the minimal modulation in the spectral indices of these particles. We also suggest that a possible solar flare may have played a role in generating these magnetic islands near the heliospheric current sheet.

On 3 July 2021, an X1.5 solar flare from the National Oceanic and Atmospheric Administration solar Active Region AR12838 (24 degrees N, 88 degrees W) occurred at 14:18 UT, peaked at 14:29 UT, and decayed at 14:34 UT. The study of this X1.5 solar flare is significant due to its unique geomagnetic crochet feature at high latitudes and its effective signature on Earth. The study examined X-rays, the extreme ultraviolet spectrum, ionospheric equivalent current (IEC), and geomagnetic field components. The study reveals a sudden increase in IEC during the X1.5 flare episode, forming a zonal current region and producing a geomagnetic crochet signature in geomagnetic field components at high latitudes (50 degrees-80 degrees N) along the 11 degrees-26 degrees E longitude sector during the flare peak time. All three geomagnetic field components show different sensitivity to the solar flare effect (sfe), and the amplitude and phase of the geomagnetic crochet across latitudes (for a given longitude) are consistent with the variations in the IEC. The present study is the first to appraise geomagnetic crochets of low magnitude (8-40 nT) and short duration (10-15 min) at high latitudes, particularly in the polar cusp region, during the X-class limb flare. The X1.5 solar flare at 14:18 UT on 3 July 2021, occurred in a newly formed solar active region AR12838 (24 degrees N, 88 degrees W) on the sun. The current study analyses the solar flare effect (sfe) signature at high latitude induced by an X1.5 flare, and compares the results from previous paper of Yamauchi et al. (2020, ). However, while that paper reported geomagnetic crochet of high amplitude (200 nT) and long duration (similar to 2 hr), the present work reports geomagnetic crochet of small amplitude (40 nT) and short duration (similar to 15 min). The current study is unique regarding observations of geomagnetic crochet in the polar cusp region. An X1.5-class solar flare was recorded on 3 July 2021, from the newly emerged solar active region NOAA AR12838 over the solar limb The current study examines the solar flare effect at high latitude magnetometer stations, an aspect that has not been extensively studied Unique signatures of Cusp geomagnetic crochet of small amplitude and short duration are observed

The hemispheric differences in the impact of the geomagnetic storms of June 2015 and December 2015 are investigated. A meridional chain of ground observatories along 95 degrees E +/- 10 degrees E (conjugate point-GNSS receiver/Ionosonde), satellite in -situ measurements (SWARM/ COSMIC/C-NOFS), and Total Electron Content maps are utilized. Symmetric negative (positive) effects were noted during the main phase of the June (December) storm but hemispheric asymmetry was manifested during the recovery phase. The quiet time hemispheric asymmetry was reversed during both storms with positive TEC effects on the winter side. Differential VTEC and NmF2 responses exhibited seasonal variation. On 23 June 2015, the VTEC enhancements in the southern low latitude were large and consistent in contrast to the weak response in NmF2. In contrast, during the December storm, the NmF2 depletion in southern low latitude was more severe than the corresponding depletion in VTEC. The topside density/TEC enhancement in the southern low latitude recorded by SWARM was much higher than 300 % during the morning of 23 June. The SWARM Ne/TEC profile as well as the ground GPS TEC map showed a third latitudinal maximum around -45 degrees dip angle of field lines in southern low latitudes on 23 June, in addition to the conventional EIA crests. Similarly, an early morning maximum was recorded at + 45 degrees dip (northern hemisphere) on 21 December. The hmF2 measured by the southern hemisphere ionosonde and COSMIC satellite showed an anomalously higher altitude of the F2-layer on 23 June while C/NOFS recorded equator-ward meridional flow velocity. The reversal of the hemispheric asymmetry and the additional storm time transient maximum on the winter side is attributed to the equator-ward winds surge in the winter hemisphere due to storm time heating of the polar region. (c) 2023 COSPAR. Published by Elsevier B.V. All rights reserved.