Magnetic Field Observations Research Articles

The Distribution of Small‐Scale Irregularities in the E‐Region, and Its Tendency to Match the Spectrum of Field‐Aligned Current Structures in the F‐Region

AbstractWe associate new data from icebear, a coherent scatter radar located in Saskatchewan, Canada, with scale‐dependent physics in the ionosphere. We subject the large‐scale icebear 3D echo patterns (treated as 2D point clouds) to a data analysis technique hitherto never applied to the ionosphere, a technique that is widely applied in cosmological red‐shift surveys to characterize the spatial clustering of galaxies. The technique results in a novel method to calculate the spatial power spectral density of the greater ionospheric irregularity field. We compare results from this method to in‐situ plasma density and magnetic field observations from the Swarm mission. We show that there is a remarkable similarity between echo clustering spectra in the E‐region and the field‐aligned current structuring spectrum observed in the F‐region: a clear and characteristic preferred scale (5 km) both in the E‐ and F‐region spectra. We discuss the possibility that this represents evidence of an energy injection into the ionospheric irregularity field via energetic particle precipitation, but offer alternative interpretations with wider connotations for the ionosphere‐magnetosphere system. These findings open new and promising avenues of research for the study of the location of ionospheric scatter echoes with 3D information. It constitutes a novel way to consider the pattern of ionospheric irregularities over wide fields of view when there is an abundance of radar echoes, which allows for the analysis of radar data as point clouds.

Estimation of Turbulent Proton and Electron Heating Rates via Landau Damping Constrained by Parker Solar Probe Observations

The heating of ions and electrons due to turbulent dissipation plays a crucial role in the thermodynamics of the solar wind and other plasma environments. Using magnetic field and thermal plasma observations from the first two perihelia of the Parker Solar Probe, we model the relative heating rates as a function of the radial distance, magnetic spectra, and plasma conditions, enabling us to better characterize the thermodynamics of the inner heliosphere. We employ the Howes et al. steady-state cascade model, which considers the behavior of turbulent, low-frequency, wavevector-anisotropic, critically balanced Alfvénic fluctuations that dissipate via Landau damping to determine proton-to-electron heating rates Q p /Q e . We distinguish ion cyclotron frequency circularly polarized waves from low-frequency turbulence and constrain the cascade model using spectra constructed from the latter. We find that the model accurately describes the observed energy spectrum from over 39.4% of the intervals from Encounters 1 and 2, indicating the possibility for Landau damping to heat the young solar wind. The ability of the model to describe the observed turbulent spectra increases with the ratio of thermal-to-magnetic pressure, β p , indicating that the model contains the necessary physics at higher β p . We estimate high magnitudes for the Kolmogorov constant which is inversely proportional to the nonlinear energy cascade rate. We verify the expected strong dependency of Q p /Q e on β p and the consistency of the critical balance assumption.

Interaction of solar jets with filaments: Triggering of large-amplitude filament oscillations

Context. Large-amplitude oscillations (LAOs) are often detected in filaments. Using multi-wavelength observations, their origin can be traced back to the interaction with eruptions and jets. Aims. We present two different case studies as observational evidence in support of 2.5D numerical magnetohydrodynamics (MHD) experiments that show that the LAOs in the filament channels can be initiated by solar jets. Methods. We use longitudinal magnetic field observations using the Helioseismic Magnetic Imager to study the evolution of the filament channels. The LAOs in the filaments are analysed using two techniques. The first is time-distance diagnostics with extreme-ultraviolet (EUV) and Hα datasets. In the second method, the oscillations in different parts of the filaments are examined using Fourier analysis of the brightness variations of all pixels in Hα observations. Results. In the two studied events, we can identify a quadrupolar configuration with an X-point at the top of the parasitic region suggestive of a classical null-point. The X-point evolves into a flat structure suggestive of a breakout current sheet. A reconnection flow emanates from this structure, leading to a jet that propagates along the filament channel. In both cases, we can identify the quiescent and eruptive phases of the jet. The triggered LAOs have periods of around 70–80 min and are damped after a few oscillations. The minimum magnetic field intensity inferred with seismology for the filament turns out to be around 30 Gauss. Conclusions. We conclude that the two case studies are consistent with a recently published numerical model in which the LAOs are initiated by jets. The relationship between the onset of the jet and filament oscillations is straightforward for the first case but is less clear for the second case. In the second event, although there is some evidence for a relationship, we cannot rule out other possibilities such as activity unrelated to the null-point or changes in the magnetic structure of the filament. Both jets are associated with very weak flares that did not launch any EUV waves. Therefore, a role of EUV waves in triggering the filament oscillations can be eliminated for these two cases.

A statistical study of the compressible energy cascade rate in solar wind turbulence: Parker solar probe observations

We investigated incompressible and compressible magnetohydrodynamic (MHD) energy cascade rates in the solar wind at different heliocentric distances. We used in situ magnetic field and plasma observations provided by the Parker Solar Probe mission and exact relations in fully developed turbulence. To estimate the compressible cascade rate, we applied two recent exact relations for compressible isothermal and polytropic MHD turbulence, respectively. Our observational results show a clear increase in the absolute value of the compressible and incompressible cascade rates as we get closer to the Sun. Moreover, we obtained an increase in both isothermal and polytropic cascade rates with respect to the incompressible case as compressibility increases in the plasma. Further discussion about the relation between the compressibility and the heliocentric distance is carried out. Furthermore, we compared both exact relations as compressibility increases in the solar wind, and although we note a slight trend to observe larger cascades using a polytropic closure, we obtained essentially the same cascade rate in the range of compressibility observed. Finally, we investigated the signed incompressible and compressible energy cascade rates and its connection with the real cascade rate.

On the determination and interpretation of the lithospheric induced magnetisation

We present a new technique for reducing the uncertainties inherent in the interpretation of lithospheric magnetic field observations over the Earth. This technique, without involving iterations, provides an improved estimate of the depth-integrated magnetic susceptibility of the crust as compared to previous approaches. Departing from the normal practice of using observations at specific locations, we model directly Gauss coefficients of the lithospheric magnetic field and use an a-priori initial lithospheric thickness model to circumvent magnetic annihilators (i.e. magnetisation distributions that cannot be determined from magnetic data since they have no impact on the lithospheric magnetic field). Of the several initial magnetic layer models tested, we prefer the model where magnetic thickness is based on the Moho or the regional estimate of the Curie depth when it is shallower than the Moho because it is physically reasonable and produces the fewest artefacts. The method is applied to a recent high-degree lithospheric magnetic field model called LCS-1 derived from CHAMP and Swarm magnetic satellite data. The technique is appropriate for regions where induced magnetisation dominates over remanent magnetisation. We show that high degrees of the final depth-integrated magnetic susceptibility variation are dependent only on the corresponding high degrees of the LCS-1 magnetic field model. Thus, the depth-integrated magnetic susceptibility variation is an important quantity derived in the study which enables readily qualitative interpretation of regional geology.

Hourly Periodic Variations of Ultralow‐Frequency (ULF) Waves in Jupiter's Magnetosheath

AbstractPeriodic variations are widely identified in the Jovian system, varying from 10 s of seconds to several days or even longer. These processes are strongly influenced by solar wind conditions, planetary rotation and Io's volcanic activity. Ultralow‐frequency (ULF) waves at 10 s of minutes, which are the typical time scale of field‐line resonance, are considered as a crucial process in driving the Jovian energy circulation. The longer time‐scale periodicities are likely associated with global mass circulation. In this study, we focus on multihour variations of the ULF wave energy, which are difficult to identify within the magnetosphere due to the rapid planetary rotation modulation. Using the magnetic field observations from Juno and Galileo in Jupiter's magnetosheath, we found multiple significant multihour periodicities, widely distributed from 2 to 10 hr, peaked at different values from case to case. The most common periodicities were between 3 and 5 hr, existing in both the dawn and dusk sides. These common periodicities are likely associated with the energy transport from the inside to the magnetosheath.

Preliminary Modeling of Magnetized Sprite Streamers on Jupiter Following Juno's Observations of Possible Transient Luminous Events

AbstractThe first observation of possible transient luminous events (TLEs) on Jupiter was reported recently. Whereas initiation of elves on Jupiter has been theoretically studied before, the possibility of sprite streamer inception on Jupiter has not been investigated yet. Here we critically review the literature concerned with TLEs on Jupiter. Subsequently, we report on development of a numerical model for modeling of magnetized streamers in presence of Jupiter's strong magnetic field. The model utilizes the knowledge provided by recent observations of Jupiter's lightning and magnetic field by the Juno spacecraft. It is demonstrated that sprite streamer inception under realistic atmospheric conditions on Jupiter is possible.

An Ancient Martian Dynamo Driven by Hemispheric Heating: Effect of Thermal Boundary Conditions

Magnetic field observations from the MGS, MAVEN, and InSight missions reveal that a dynamo was active in Mars’s early history. One unique feature of Mars’s magnetic crustal field is its hemispheric dichotomy, where magnetic fields in the southern hemisphere are much stronger than those in the northern hemisphere. Here we use numerical dynamo simulations to investigate the potential hemispheric nature of Mars’s ancient dynamo. Previous studies show that a hemispheric heat flux perturbation at the core–mantle boundary could result in either a stable hemispherical magnetic field or a constantly reversing field, depending on choices of parameters used in those models. These two scenarios lead to different implications for the origin of crustal fields. Here we test the dynamo sensitivity to varying hemispheric heat flux perturbations at the core–mantle boundary in a broader parameter regime to understand whether a hemispheric dynamo is likely for early Mars. We find that features of the dynamo change from stable, hemispheric magnetic fields to reversing, hemispheric fields, with increasing hemispheric heat flux perturbations at the core–mantle boundary. We also find that magnetic fields powered by bottom heating are more stable and transition from a nonreversing, hemispheric magnetic field to a multipolar field at higher hemispheric heat flux perturbations, while the transition happens at a much lower heat flux perturbation for magnetic fields powered by internal heating.

Changes of Magnetic Energy and Helicity in Solar Active Regions from Major Flares

Magnetic free energy powers solar flares and coronal mass ejections, and the buildup of magnetic helicity might play a role in the development of unstable structures that subsequently erupt. To better understand the roles of energy and helicity in large flares and eruptions, we have characterized the evolution of magnetic energy and helicity associated with 21 X-class flares from 2010 to 2017. Our sample includes both confined and eruptive events, with 6 and 15 in each category, respectively. Using the Helioseismic and Magnetic Imager vector magnetic field observations from several hours before to several hours after each event, we employ (a) the Differential Affine Velocity Estimator for Vector Magnetograms to determine the photospheric fluxes of energy and helicity, and (b) nonlinear force-free field extrapolations to estimate the coronal content of energy and helicity in source-region fields. Using superposed epoch analysis, we find, on average, the following: (1) decreases in both magnetic energy and helicity, in both photospheric fluxes and coronal content, that persist for a few hours after eruptions, but no clear changes, notably in relative helicity, for confined events; (2) significant increases in the twist of photospheric fields in eruptive events, with twist uncertainties too large in confined events to constrain twist changes (and lower overall twist in confined events); and (3) on longer timescales (event time +12 hr), replenishment of free magnetic energy and helicity content to near preevent levels for eruptive events. For eruptive events, magnetic helicity and free energy in coronal models clearly decrease after flares, with the amounts of decrease proportional to each region’s pre-flare content.

Evidence for Magnetic Reconnection at Ganymede's Upstream Magnetopause During the PJ34 Juno Flyby

AbstractJuno made a close flyby of Ganymede and flew through its magnetosphere on 7 June 2021, including an outbound crossing of Ganymede's upstream magnetopause. We present plasma and magnetic field observations near the upstream magnetopause from Juno's Jovian Auroral Distributions Experiment (JADE) and magnetometer. JADE observed enhanced electron fluxes, including field‐aligned electrons accelerated up to 2–3 keV/q, some having bidirectional pitch angle distributions, as Juno crossed Ganymede's magnetopause. Energy enhancements of cold protons and heavy ions originating from Ganymede were also observed on approach to the magnetopause. We interpret the presence of accelerated, field‐aligned electrons as indicating that magnetic reconnection is occurring on magnetic field lines that connect the spacecraft to Ganymede's magnetopause at that time. Counter‐streaming electrons observed on both sides of the magnetopause suggest the presence of multiple reconnection sites, both north and south of the spacecraft.

Ultraviolet spectropolarimetry: investigating stellar magnetic field diagnostics

Magnetic fields are important for stellar photospheres and magnetospheres, influencing photospheric physics and sculpting stellar winds. Observations of stellar magnetic fields are typically made in the visible, although infrared observations are becoming common. Here we consider the possibility of directly detecting magnetic fields at ultraviolet (UV) wavelengths using high resolution spectropolarimetry, specifically considering the capabilities of the proposed Polstar mission. UV observations are particularly advantageous for studying wind resonance lines not available in the visible, but they can also provide many photospheric lines in hot stars. Detecting photospheric magnetic fields using the Zeeman effect and Least Squares Deconvolution is potentially more effective in the UV due to the much higher density of strong lines. We investigate detecting magnetic fields in the magnetosphere of a star using the Zeeman effect in wind lines, and find that this could be detectable at high S/N in an O or B star with a strong magnetic field. We consider detecting magnetic fields using the Hanle effect in linear polarization, which is complementary to the Zeeman effect, and could be more sensitive in photospheric lines of rapid rotators. The Hanle effect can also be used to infer circumstellar magnetism in winds. Detecting the Hanle effect requires UV observations, and a multi-line approach is key for inferring magnetic field properties. This demonstrates that high resolution spectropolarimetry in the UV, and the proposed Polstar mission, has the potential to greatly expand our ability to detect and characterize magnetic fields in and around hot stars.

Auroral Field‐Aligned Current Signatures in Jupiter's Magnetosphere: Juno Magnetic Field Observations and Physical Modeling

AbstractWe analyze magnetic data obtained during northern high‐altitude traversals of Jovian middle magnetosphere (MM) field lines during the first 10 inbound data‐taking passes of the Juno spacecraft for azimuthal field perturbations associated with magnetosphere‐ionosphere coupling currents. Full traversals across the MM region occur on all 10 passes at radial distances ∼7 to 16 RJ (T1 traversals), followed in four cases by reversed traversals (T2) at ∼4 to 7 RJ. Signatures of upward field‐aligned currents were observed in all cases, closely collocated with the statistical main auroral oval when mapped along field lines to the ionosphere. Two T1 sheets carry currents ∼10 MA per radian of azimuth in ionospheric colatitudinal layers ∼1.2°, closely comparable with the ∼8.5 MA rad−1 theoretical model value of Cowley et al. (2008, https://doi.org/10.5194/angeo-26-4051-2008). The other T1 sheets typically carry half this current ∼5.1 MA rad−1 in layers half the width ∼0.56°, thus with comparable current densities ∼425 nA m−2. The T2 currents are smaller ∼3.4 MA rad−1 with current densities ∼120 nA m−2, a difference that may relate to locations on opposite sides of the main oval as reflected in near‐contemporaneous ultraviolet observations, though ionospheric field strengths are not greatly different. Comparison with northern near‐periapsis currents observed inside ∼2 RJ on the same passes by Kotsiaros et al. (2019, https://doi.org/10.1038/s41550-019-0819-7) yields a cross‐correlation coefficient ∼0.7 with our T1 currents, though Kotsiaros et al.’s mean current value of ∼3.8 MA rad−1 is somewhat less than our overall mean T1 value ∼6.2 MA rad−1. The differences may have spatial, temporal, or methodological origins.

Reconstructing solar magnetic fields from historical observations

Context. We apply our recently developed method to reconstruct synoptic maps of the photospheric magnetic field from observations of chromospheric plages and the magnetic polarity of sunspots. Here, we apply the method to an extended time interval from 1915 to 1985. Aims. Systematic magnetographic observations of the solar photospheric magnetic field were initiated as recently as the 1970s and the lack of earlier observations limits our ability to study and understand the long-term evolution of the Solar global field. This study is aimed at creating synoptic maps of magnetic fields for the pre-magnetograph era and using these maps as input for modern simulation models to investigate the long-term (centennial) evolution of the Sun’s global magnetic fields. Methods. We reconstructed active Solar regions by identifying chromospheric plages from Ca II K line synoptic maps and assigning magnetic polarities based on the observed polarity of sunspots. We used a surface flux transport (SFT) model to simulate the evolution of the photospheric magnetic field from the reconstructed active regions. We used the potential field source surface (PFSS) model to determine the amount of open magnetic flux from the reconstruction and from magnetographic observations. We also reconstructed the coronal field during two eclipses and compared the result with eclipse drawings. Results. We successfully reconstructed the photospheric magnetic field from 1915 to 1985. The number and total magnetic flux of the reconstructed active regions shows a realistic cyclic behavior that mostly follows the evolution of the sunspot number, even on relatively short timescales. The polar field strengths of cycles 19 and 20 do not reflect the evolution of the sunspot number very accurately, which may be related to problems related to the calcium data during cycle 19 and the long data gap during cycle 20. The polarity of polar fields and the amount of open field both at high and low latitudes all demonstrate the expected cyclic behavior. The agreement of the modeled coronal structure with eclipse drawings in 1922 and 1923 is fair.

Magnetic Evidence for an Extended Hydrogen Exosphere at Mercury

AbstractRemote observations by the Mariner 10 and MErcury Surface, Space ENvironment, GEophysics, and Ranging (MESSENGER) spacecraft have shown the existence of hydrogen in the exosphere of Mercury. However, to date the hydrogen number densities could only be estimated indirectly from exospheric models, based on the remotely observed Lyman‐α radiances for atomic H, and the detection threshold of the Mariner 10 occultation experiment for molecular H2. Here, we show the first on‐site determined altitude‐density profile of atomic H, derived from in situ magnetic field observations by MESSENGER. The results reveal an extended H exosphere with densities that are ∼1–2 orders of magnitude larger than previously predicted. Using an exospheric model that reproduces the H altitude‐density profile allows us to constrain the so far unknown H2 density at the surface, which is ∼2–3 orders of magnitude smaller than previously assumed. These findings demonstrate the importance of (a) in situ measurements supporting remote observations of Mercury's exosphere that will be realized in the near future by the BepiColombo mission and (b) that dissociation processes play a crucial role in Mercury's exosphere.

Forecasting changes of the magnetic field in the United Kingdom from L1 Lagrange solar wind measurements

Extreme space weather events can have large impacts on ground-based infrastructure important to technology-based societies. Machine learning techniques based on interplanetary observations have proven successful as a tool for forecasting global geomagnetic indices, however, few studies have examined local ground magnetic field perturbations. Nowcast and forecast models which predict the magnitude of the horizontal geomagnetic field, |BH|, and its time derivative, dBHdt, at ground level would be valuable for assessing the potential space weather hazard. We attempt to predict the variation of the magnetic field at the three United Kingdom observatories (Eskdalemuir, Hartland and Lerwick) driven by L1 solar wind parameters. The horizontal magnetic field component and its time derivative are predicted from solar wind plasma and interplanetary magnetic field observations using Long Short-Term Memory (LSTM) networks and hybrid Convolutional Neural Network-LSTM models. A 5-fold grid search cross-validation is used for tuning the hyperparameters in each model. Forecasts were made with 5, 15 and 30-min lead times. Models were trained and validated with geomagnetic storm-only data from 1997 to 2016; their outputs were evaluated with the 7–9th September 2017 storms. The forecast models are only able to predict the directly driven parts of geomagnetic storms (not the substorms) and LSTM models generally perform best. We find the |BH| 15- and 30-min forecasts at Lerwick and Eskdalemuir have some predictive power. The 5-min |BH| forecast as well as all the dBHdt models for Eskdalemuir and all the Hartland models were found to have little or no predictive power. This suggests that the machine learning models have better forecasting power at higher latitude (closer to the auroral zones), where the ground magnetic variation field is larger and during storm onset, which is directly driven by changes in the solar wind.

The characteristics of flare- and CME-productive solar active regions

Solar flares and coronal mass ejections (CMEs) cause immediate and adverse effects on the interplanetary space and geospace. In an era of space-based technical civilization, the deeper understanding of the mechanisms that produce them and the construction of efficient prediction schemes are of paramount importance. The source regions of flares and CMEs exhibit some common morphological characteristics, such as δ-spots, filaments and sigmoids, which are associated with strongly sheared magnetic polarity inversion lines, indicative of the complex magnetic configurations that store huge amounts of free magnetic energy and helicity. The challenge is to transform this empirical knowledge into parameters/predictors that can help us distinguish efficiently between quiet, flare-, and CME-productive (eruptive) active regions. This paper reviews these efforts to parameterize the characteristics of eruptive active regions as well as the importance of transforming new knowledge into more efficient predictors and including new types of data. Magnetic properties of active regions were first introduced when systematic ground-based observations of the photospheric magnetic field became possible and the relevant research was boosted by the provision of near real time, uninterrupted, high-quality observations from space, which allowed the study of large, statistically significant samples. Nonetheless, flare and CME prediction still faces a number of challenges. The magnetic field information is still constrained at the photospheric level and accessed only from one vantage point of observation, thus there is always need for better predictors; the dynamic behavior of active regions is still not fully incorporated into predictions; the inherent stochasticity of flares and CMEs renders their prediction probabilistic, thus benchmark sets are necessary to optimize and validate predictions. To meet these challenges, researchers have put forward new magnetic properties, which describe different aspects of magnetic energy storage mechanisms in active regions and offer the opportunity of parametric studies for over an entire solar cycle. This inventory of features/predictors is now expanded to include information from flow fields, transition region and coronal spectroscopy, data-driven modeling of the coronal magnetic field, as well as parameterizations of dynamic effects from time series. Further work towards these directions may help alleviate the current limitations in observing the magnetic field of higher atmospheric layers. In this task, fundamental and operational research converge, with promising results which could stimulate the development of new missions and lay the ground for future exploratory studies, also profiting from and utilizing the long anticipated observations of the new generation of instruments.

Radial and Local Time Variations in the Thickness of Jupiter's Magnetospheric Current Sheet

AbstractThe magnetic field observations from the Galileo, Ulysses, Voyager 1 and 2, and Pioneer 10 and 11 spacecraft are analyzed to understand the structures and thickness of the Jovian magnetospheric current sheet. Using a new technique that can determine the motion of the spacecraft relative to the current sheet, we have built the first global map of the thickness of the Jovian magnetospheric current sheet. We show that the current sheet thickness in Jupiter's magnetosphere is not equal everywhere but changes systematically with both radial distance and local time. The extremely thin dawnside current sheet appears to be linked to the stresses imposed by the solar wind on the open magnetic flux housed in the lobes of the magnetosphere in that sector. We also show evidence of a mostly closed magnetosphere in the dusk sector. We show that the current sheet thickness asymmetries likely arise from a field and plasma convection system set up by the reconnection of the interplanetary magnetic field with that of Jupiter.

Validation of the DSCOVR Spacecraft Mission Space Weather Solar Wind Products

AbstractIn this paper, we present a statistical validation of the Deep Space Climate Observatory (DSCOVR) solar wind data in the operational space weather archive. The DSCOVR observations of the interplanetary magnetic field (IMF), solar wind velocity, density, and temperature were hourly averaged and compared to measurements from NASA's Advanced Composition Explorer (ACE) and Wind spacecraft. Hourly averages, in general, show good correlations between the satellites for the IMF, solar wind velocity Geocentric Solar Ecliptic (GSE) vx‐component, and density. During the period covered by this study (spanning from late July 2016, when DSCOVR went operational, to the end of 2020), the DSCOVR products show no clear evidence of permanent degradation. However, for plasma parameters, there were periods of disagreement with ACE and Wind. The correlation coefficients (Pearson's r) calculated over the entire study period were similar or the same between DSCOVR versus Wind and DSCOVR versus ACE. For comparisons between DSCOVR and Wind, the IMF Bx and By GSE r were 0.94 and 0.96, respectively, while r for the IMF GSE Bz‐component was 0.88. For solar wind velocity, r was found to be 0.96 for the GSE vx‐component, compared with 0.30 for vy and 0.33 for vz. For density, r was found to be 0.84. DSCOVR density observations tend to overestimate compared to Wind values when the solar wind densities are low (below ∼5/cc), while the agreement between the two spacecraft on IMF measurements tends to increase with decreasing spatial separation.

LatHyS global hybrid simulation of the BepiColombo second Venus flyby

Plasma and magnetic field observations by BepiColombo during its 2nd Venus flyby in August 10, 2021 have been examined and compared with the newly developed global hybrid simulation LatHyS for the Venusian environment. The LatHyS-Venus simulation was first validated by a comparison with Venus Express observations obtained during average solar wind conditions, before it was applied to the BepiColombo flyby using as inputs solar wind parameters measured upstream of Venus by Solar Orbiter. The simulation confirms that BepiColombo passed through the stagnation region of Venus, which supports the results obtained by data analysis. In addition, we have sampled the plasma parameters along the BepiColombo trajectory and constructed the energy spectrum for two species, i.e., protons of both solar wind and planetary origins, and planetary oxygen ions, and discussed the possible effects due to the limited field of views of the plasma instruments onboard BepiColombo. The most intense observational features are properly captured in the LatHyS-Venus simulation, which show that the model is a powerful tool for interpreting and understanding in-situ data obtained from the instruments with a limited field of views. The estimated ion escape for protons and oxygen ions at Venus during the BepiColombo flyby is of the order of ∼ 10 24 ions/s, which is the same order of magnitude compared to the estimation from Venus Express observations at the solar minimum. 1) We have developed the global hybrid simulation for the Venusian environment. 2) Observations by BepiColombo during its 2nd Venus flyby in August 10, 2021 have been examined. 3) The possible effects due to the limited field of views of the plasma instruments onboard BepiColombo have been discussed by sampling plasmas in the simulation domain.

Nature of helicity injection in non-erupting solar active regions

ABSTRACT Using time-sequence vector magnetic field and coronal observations from Solar Dynamics Observatory, we report the observations of the magnetic field evolution and coronal activity in four emerging active regions (ARs). The ARs emerge with leading polarity being the same as for the majority of ARs in a hemisphere of solar cycle 24. After emergence, the magnetic polarities separate each other without building a sheared polarity inversion line. In all four ARs, the magnetic fields are driven by foot point motions such that the sign of the helicity injection (dH/dt) in the first half of the evolution is changed to the opposite sign in the later part of the observation time. This successive injection of opposite helicity is also consistent with the sign of mean force–free twist parameter (αav). Further, the EUV light curves off the ARs in 94 Å and GOES X-ray flux reveal flaring activity below C-class magnitude. Importantly, the white-light coronagraph images in conjunction with the AR images in Atmospheric Imaging Assembly (AIA) 94 Å delineate the absence of associated Coronal Mass ejections (CMEs) with the studied ARs. These observations imply that the ARs with successive injection of opposite sign magnetic helicity are not favourable to twisted flux rope formation with excess coronal helicity, and therefore are unable to launch CMEs, according to recent reports. This study provides the characteristics of helicity flux evolution in the ARs referring to the conservative property of magnetic helicity and more such studies would help to quantify the eruptive capability of a given AR.