Solar Wind Conditions Research Articles

The He++/H+ Density Ratio Across Earth's Subsolar Magnetopause and Its Implications for the Presence of a Mass‐Dependent Reflection Coefficient

AbstractWhen magnetic reconnection is occurring at Earth's magnetopause, incident magnetosheath ions are either reflected or transmitted, and the likelihood of each outcome is quantified by the reflection coefficient. This statistical study reexamines the question of whether or not the reflection coefficient is mass dependent by observing the He++/H+ density ratio at magnetopause crossings. High‐resolution data from the Hot Plasma Composition Analyzer on board the Magnetospheric Multiscale spacecraft are used from its Mission Phase 1a. We analyze these new measurements of the relative changes in the He++/H+ density ratio across the boundary layers of the magnetopause for a restricted set of solar wind conditions. From this analysis, we conclude that, for southward IMF, the reflection coefficient has no dependence on mass.

Ultra-low-frequency waves in the ion foreshock of Mercury: a global hybrid modelling study

ABSTRACT We study the solar wind interaction with Mercury using a global three-dimensional hybrid model. In the analysed simulation run, we find a well-developed, dynamic Hermean ion foreshock ahead of the quasi-parallel bow shock under upstream solar wind and interplanetary magnetic field (IMF) conditions corresponding to the orbital perihelion of the planet. A portion of the incident solar wind ion flux is scattered back upstream near the quasi-parallel bow shock including both major solar wind ion species, protons and alphas. The scattered particles form the Hermean suprathermal foreshock ion population. A significant part of the suprathermal population is backstreaming with a velocity component towards the Sun in the near-foreshock at the planetocentric distance of few planetary radii in the plane of the IMF. The ion foreshock is associated with large-scale, oblique fast magnetosonic waves in the ultra-low-frequency (ULF) range convecting downstream with the solar wind. The ULF wave period is about 5 s in the analysed upstream condition case at Mercury, which corresponds to the 30-s foreshock waves at Earth when scaled by the IMF magnitude.

Quiet Time Structured Pc1 Waves Generated During Transient Foreshock

AbstractWe study two events of structured Pc1 waves (pearls) observed by CARISMA magnetometers during a period of quiet magnetic (Kp ~1) and solar wind conditions on 1 August 2008. Bursts of proton precipitations and electromagnetic ion‐cyclotron waves were simultaneously observed by NOAA/POES and GOES satellites at dayside. Apparent correspondence was found between ground pearl pulsations and magnetospheric compressions observed by GOES and THEMIS satellites. We have found the Pc1 wave splitting into very close subfrequencies (within 0.1 Hz) that can be explained by weak magnetospheric compressions. The compressions are caused by pressure pulses originated from transient foreshock and interplanetary magnetic field discontinuities observed upstream of the bow shock by the THEMIS‐C probe. Thus, the observed pearls are compression‐related Pc1 waves generated under transient foreshock conditions.

Dayside Magnetopause Reconnection: Its Dependence on Solar Wind and Magnetosheath Conditions

AbstractMagnetic reconnection permits topological rearrangements of the interplanetary and magnetospheric magnetic fields and the entry of solar wind mass, energy, and momentum into the magnetosphere. Thus, magnetic reconnection is a key issue to understand space weather. However, it has not been fully understood yet under which interplanetary/magnetosheath conditions magnetic reconnection takes place more effectively at the dayside magnetopause. In the present study 25 dayside magnetopause reconnection events are investigated using the “Time History of Events and Macroscale Interactions during Substorms” (THEMIS) satellite observations in order to find its dependence on solar wind and magnetosheath conditions. It is found that the reconnection electric field is proportional to the interplanetary electric field and inversely proportional to the solar wind‐Alfvén Mach number and that the reconnection outflow speed is proportional to the solar wind Alfvén speed and inversely proportional to the magnetosheath plasma beta. It is also shown that the range of magnetic shear angles for which magnetic reconnection should occur is restricted to large shears as the magnetosheath flow direction becomes more perpendicular to the direction of the local magnetopause normal vector. Since these results refer to fairly typical solar wind‐Alfvén Mach number condition, they may not necessarily apply to more extreme cases.

The Variation of Geomagnetic Storm Duration with Intensity

Variability in the near-Earth solar wind conditions can adversely affect a number of ground- and space-based technologies. Such space-weather impacts on ground infrastructure are expected to increase primarily with geomagnetic storm intensity, but also storm duration, through time-integrated effects. Forecasting storm duration is also necessary for scheduling the resumption of safe operating of affected infrastructure. It is therefore important to understand the degree to which storm intensity and duration are correlated. The long-running, global geomagnetic disturbance index, mathit{aa}, has recently been recalibrated to account for the geographic distribution of the component stations. We use this mathit{aa}_{H} index to analyse the relationship between geomagnetic storm intensity and storm duration over the past 150 years, further adding to our understanding of the climatology of geomagnetic activity. Defining storms using a peak-above-threshold approach, we find that more intense storms have longer durations, as expected, though the relationship is nonlinear. The distribution of durations for a given intensity is found to be approximately log-normal. On this basis, we provide a method to probabilistically predict storm duration given peak intensity, and test this against the mathit{aa}_{H} dataset. By considering the average profile of storms with a superposed-epoch analysis, we show that activity becomes less recurrent on the 27-day timescale with increasing intensity. This change in the dominant physical driver, and hence average profile, of geomagnetic activity with increasing threshold is likely the reason for the nonlinear behaviour of storm duration.

Jupiter's Dark Polar Region as Observed by the Hubble Space Telescope During the Juno Approach Phase

AbstractWe present an analysis of Jupiter's dark polar region, previously described as a crescent‐shaped region devoid of emission along the dawnside poleward of the main oval. Using ultraviolet images obtained by the Hubble Space Telescope between days of year 137 and 176, coupled with interplanetary data captured during the approach phase of the NASA Juno spacecraft, we examine the morphology and variability of the dark polar region and the influence of solar wind conditions on the region. We find that the dark polar region is more variable than previously thought and in particular shows significant variability during compressions of the magnetosphere by the solar wind. Duskward extensions of the dark polar region through the noon sector are often observed during periods of deep rarefaction in the solar wind, while a larger dark polar region width is observed nearer to local noon under solar wind compression. Intensity distributions of the dark polar region reveal a greater probability of lower emission intensity during deep rarefactions. Calculation of the magnetic flux associated with the dark polar region returns lower flux values than previous estimates of the total open flux at Jupiter. This may suggest that either the dark polar region does not account for the entirety of the open flux region, or the magnetotail is not composed of only open flux, as previously suggested.

Energetic charged particle measurements from Voyager 2 at the heliopause and beyond

The long-anticipated encounter by Voyager 2 (V2) of the region between the heliosphere and the very local interstellar medium (VLISM) occurred toward the end of 2018. Here, we report measurements of energetic (>28 keV) charged particles on V2 from the interface region between the heliosheath, dominated by heated solar wind plasma, and the VLISM, expected to contain cold non-solar plasma and the Galactic magnetic field. The number of particles of solar origin began a gradual decrease on 7 August 2018 (118.2 au), while those of Galactic origin (Galactic cosmic rays) increased ~20% in number over a period of a few weeks. An abrupt change occurred on 5 November when V2 was located at 119 au, with a decrease in the number of particles at energies of >28 keV and a corresponding increase in the number of Galactic cosmic rays of energy E > 213 MeV. This signature of the transition to the VLISM resembles, but is very different from, that observed on Voyager 1 at ~121.6 au, associated with the putative crossing of the heliopause some six years earlier. Measurements of energetic ions and electrons with the Low-Energy Charged Particle instrument on Voyager 2 are presented from the boundary of the heliosphere and from the interstellar medium. Voyager 2’s heliopause crossing bears some similarity to that of Voyager 1, despite differing solar wind conditions.

Storm-time mesoscale field-aligned currents and interplanetary parameters

Present paper studies Field aligned currents (FACs) estimated by employing Ampere's law to the magnetic field recorded by CHAMP satellite during 24 geomagnetic storms. Low-pass filtered FACs with a cutoff period of 20 s (scale size~150 km) are used to determine FAC range, which is defined as a peak-to-peak amplitude of FAC density. Thus we are considering only the strongest positive and negative FACs emerging either from Region 1, Region 2, Region 0, or substorm current wedge systems. It is known that the FACs significantly depend on the highly variable solar wind (SW) and interplanetary magnetic field (IMF) conditions and also on the processes internal to magnetospheric-ionospheric system such as substorm. The correlation analysis carried out here shows that sometimes the FAC range, correlates well with SymH, AsyH, AsyD, AL, am and Kp indices (>95% significance), but not always. The variation of the FAC range with magnetic local times shows distinctly different patterns during southward and northward IMF conditions, with peaks near dawn-dusk during southward IMF and near local noon-midnight during northward IMF. These results are in agreement with the earlier reports. However, the seasonal dependence reveals that the noon time peak is essentially associated with the summer season. We have determined a new parameter called ‘occurrence rate of FAC range ≥1 μA/m2’ and examined it under various solar wind and IMF conditions. It is found that the probability of FAC range ≥1 μA/m2 have a clear dependence on the clock angle, suggesting more frequent intensifications during southward IMF. Clear linear dependence on the cone angle demonstrates higher occurrence probability of FAC range ≥ 1 μA/m2 when the IMF is perpendicular to the Sun-Earth line (cone angle nearing 90°). All these results based on the newly defined parameters such as FAC range and probability of FAC range ≥1 μA/m2, for the storm time mesoscale FAC are consistent with the previous studies. The FAC ranges are found to have a linear dependence on the values of IMF BY, BYZ, BT and BZ, though saturation is apparent at higher values of the IMF parameters. FAC range shows distinctly different dependence for slow and fast solar wind, suggesting the importance of the composition and properties of SW in controlling the FAC strengths.

Kappa-Maxwellian Electrons and Bi-Maxwellian Protons in a Two-fluid Model for Fast Solar Wind

Abstract Modeling fast solar wind based on kinetic theory is an important task for scientists. In this paper, we present a two-fluid model for fast solar wind with anisotropic Kappa-Maxwellian electrons and Bi-Maxwellian protons. In the simulation, the energy exchange between the plasma particles and low-frequency Alfvén waves is considered. A set of eleven coupled equations is derived by applying the zeroth- to fourth-order moments of the Vlasov equation and the modified electromagnetic Maxwell equations. A characteristic of the Kappa distribution (indicated by κ index) is explicit in the equation for the parallel component of the electron heat flux (parallel to the ambient magnetic field line) and differs from the equation derived for the proton heat flux due to the different nature of the distributions. Within the large κ index, the equations for the two-fluid model tend to the equations obtained by the Maxwellian distribution. Using an iterated Crank–Nicolson method, the coupled equations are numerically solved for the fast solar wind conditions. We show that at (0.3–1) au from the Sun, the electron density, components of temperature, and components of heat flux follow the power-law behavior. We also showed that near the Earth, the flow speed (electron or proton) increases with decreasing κ. We concluded that through applying the small κ index (the non-Maxwellian distribution), the extraordinary nature of the solar atmosphere, with its temperature of several million kelvin for electrons, has been captured.

Particle-in-cell Simulations of the Whistler Heat-flux Instability in Solar Wind Conditions.

In collision-poor plasmas from space, e.g., solar wind or stellar outflows, the heat flux carried by the strahl or beaming electrons is expected to be regulated by the self-generated instabilities. Recently, simultaneous field and particle observations have indeed revealed enhanced whistler-like fluctuations in the presence of counter-beaming populations of electrons, connecting these fluctuations to the whistler heat-flux instability (WHFI). This instability is predicted only for limited conditions of electron beam-plasmas, and has not yet been captured in numerical simulations. In this Letter we report the first simulations of WHFI in particle-in-cell setups, realistic for the solar wind conditions, and without temperature gradients or anisotropies to trigger the instability in the initiation phase. The velocity distributions have a complex reaction to the enhanced whistler fluctuations conditioning the instability saturation by a decrease of the relative drifts combined with induced (effective) temperature anisotropies (heating the core electrons and pitch-angle and energy scattering the strahl). These results are in good agreement with a recent quasilinear approach, and support therefore a largely accepted belief that WHFI saturates at moderate amplitudes. In the anti-sunward direction the strahl becomes skewed with a pitch-angle distribution decreasing in width as electron energy increases, which seems to be characteristic of self-generated whistlers and not to small-scale turbulence.

Local Time Variation in the Large‐Scale Structure of Saturn's Magnetosphere

AbstractThe large‐scale structure of Saturn's magnetosphere is determined by internal and external factors, including the rapid planetary rotation rate, significant internal hot and cold plasma sources, and varying solar wind pressure. Under certain conditions the dayside magnetospheric magnetic field changes from a dipolar to more disk‐like structure, due to global force balance being approximately maintained during the reconfiguration. However, it is still not fully understood which factors dominantly influence this behavior, and in particular how it varies with local time. We explore this in detail using a 2‐D force‐balance model of Saturn's magnetodisk to describe the magnetosphere at different local time sectors. For model inputs, we use recent observational results that suggest a significant local time asymmetry in the pressure of the hot (>3 keV) plasma population, and magnetopause location. We make calculations under different solar wind conditions, in order to investigate how these local time asymmetries influence magnetospheric structure for different system sizes. We find significant day/night asymmetries in the model magnetic field, consistent with recent empirical studies based on Cassini magnetometer observations. We also find dawn‐dusk asymmetries in equatorial current sheet thickness, with the varying hot plasma content and magnetodisk radius having comparable influence on overall structure, depending on external conditions. We also find significant variations in magnetic mapping between the ionosphere and equatorial disk, and ring current intensity, with substantial enhancements in the night and dusk sectors. These results have consequences for interpreting many magnetospheric phenomena that vary with local time, such as reconnection events and auroral observations.

Global Solar Magnetic Field and Interplanetary Scintillations During the Past Four Solar Cycles

The extended minimum of Solar Cycle 23, the extremely quiet solar-wind conditions prevailing, and the mini-maximum of Solar Cycle 24 drew global attention and many authors have since attempted to predict the amplitude of the upcoming Solar Cycle 25, which is predicted to be the third successive weak cycle; it is a unique opportunity to probe the Sun during such quiet periods. Earlier work has established a steady decline, over two decades, in solar photospheric fields at latitudes above $45^{\circ}$ and a similar decline in solar-wind micro-turbulence levels as measured by interplanetary scintillation (IPS) observations. However, the relation between the photospheric magnetic fields and those in the low corona/solar-wind are not straightforward. Therefore, in the present article, we have used potential-field source-surface (PFSS) extrapolations to deduce global magnetic-fields using synoptic magnetograms observed with National Solar Observatory (NSO), Kitt Peak, USA (NSO/KP) and Solar Optical Long-term Investigation of the Sun (NSO/SOLIS) instruments during 1975-2018. Furthermore, we have measured the normalized scintillation index [m] using the IPS observations carried out at the Institute of Space Earth Environment Research (ISEE), Japan during 1983-2017. From these observations, we have found that, since the mid-1990s, the magnetic-field over different latitudes at 2.5 $\rm R_{\odot}$ and 10 $\rm R_{\odot}$(extrapolated using PFSS method) has decreased by $\approx 11.3-22.2 \%$. In phase with the declining magnetic-fields, the quantity m also declined by $\approx 23.6 \%$. These observations emphasize the inter-relationship between the global magnetic-field and various turbulence parameters in the solar corona and solar wind.

On the response of Martian Ionosphere to the Passage of a Corotating Interaction Region: MAVEN Observations

AbstractThe response of Martian ionosphere to the passage of corotating interaction region (CIR) of June 2015 is studied using observations from several instruments aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. An intense CIR arrived at Mars on 22 June 2015, during which the upstream solar wind and interplanetary magnetic field conditions were monitored by the Solar Wind Ion Analyzer (SWIA), Solar Wind Electron Analyzer (SWEA), Solar Energetic Particle (SEP), and Magnetometer (MAG) instruments aboard MAVEN. The CIR event was characterized by enhancements in solar wind density, velocity, and dynamic pressure, and increased and fluctuating interplanetary magnetic field and was associated with enhanced fluxes of Solar Energetic Particles. The Langmuir Probe and Waves (LPW) instrument onboard MAVEN provided the ionospheric observations such as electron density and electron temperature during this period. The dayside ionosphere is significantly compressed only near the peak of solar wind dynamic pressure enhancement (∼14 nPa). In contrast, on the nightside, the electron density remains depleted for a longer period of time. The electron temperatures are also enhanced during the period of electron depletion on the nightside. The Suprathermal and Thermal Ion Composition (STATIC) measurements show enhanced fluxes of suprathermal heavy ions in the Martian exosphere during CIR period, and evidences for enhanced tailward flow of these pickup ions. The analysis suggests that the nightside ionosphere is primarily controlled by the precipitating Solar Energetic Particles and pickup ions transported across the Martian terminator and depletes significantly when the heavy ion flux in the exosphere enhances.

Effect of Rapid Changes of Solar Wind Conditions on the Pickup Ion Velocity Distribution

AbstractWe performed the first systematic analysis of pickup ion (PUI) cutoff speed variations, across compression regions and due to fast fluctuations in solar wind (SW) speed and magnetic field strength. This study is motivated by the need to remove or correct for systematic effects on the determination of the interstellar flow longitude based on the longitudinal variation of the PUI cutoff. Using 2007–2014 STEREO A PLASTIC observations, we identified SW compression regions and accumulated the contained PUI velocity distributions in a superposed epoch analysis. The shift of the cutoff in velocity, interpreted as PUI energization, varies systematically across the compression region and increases approximately linearly with the speed gradient of the compression. Additionally, the shift remains positive into the negative speed gradient at the beginning of the rarefaction region. A similar response is found when PUI distributions are sorted according to the strength of fast fluctuations in SW speed, density, and magnetic field strength. These parameters remain high in the first part of the rarefaction region, suggesting a possible PUI energization through compressive turbulence. Based on these results, we removed the strongest compression regions from the interstellar flow analysis, finding no significant change in direction or uncertainty. Thus, we have revealed the influence of adiabatic compression and compressive turbulence, increasing the PUI cutoff energy, and we have demonstrated that the determination of the interstellar inflow direction via analysis of PUI distributions is robust for a multiyear data set, even in the presence of SW interaction regions.

Propagation properties of foreshock cavitons: Cluster observations

Foreshock cavitons are transient phenomena observed in the terrestrial foreshock region. They are characterized by a simultaneous depression of magnetic field magnitude and plasma density, which are bounded with enhancements of these two parameters and surrounded by ultralow frequency (ULF) waves. Previous studies focused on the interplanetary magnetic field (IMF) conditions, solar wind (SW) conditions, and the growth of the foreshock waves related to the generation of foreshock cavitons. Previously, a multipoint spacecraft analysis method using Cluster data was applied to analyze only two foreshock cavitons, and this method did not consider uncertainties. In this study, multipoint spacecraft analysis methods, including the timing method, the minimum directional derivative (MDD) method, and the spatiotemporal difference (STD) method are applied to determine the velocity in both spacecraft and solar wind frames. The propagation properties show good agreement with previous results from simulations and observations that most cavitons move sunward in the solar wind frame, with the velocities larger than the Alfven speed. The propagation properties of foreshock cavitons support the formation mechanism of cavitons in previous simulations, which suggested that cavitons are formed due to the nonlinear evolution of compressive ULF waves. We find that there is clear decreasing trend between the size of cavitons and their velocity in the solar wind frame. In addition, the timing method considering errors has been applied to study the evolution properties by comparing the velocities with errors of the leading and trailing edges, and we identify three stable cavitons and one contracting caviton, which has not been studied before. Most cavitons should remain stable when they travel toward the Earth’s bow shock. The relationship between the size of foreshock cavitons and their distance from the bow shock is also discussed.

GUMICS-4 analysis of interplanetary coronal mass ejection impact on Earth during low and typical Mach number solar winds

Abstract. We study the response of the Earth's magnetosphere to fluctuating solar wind conditions during interplanetary coronal mass ejections (ICMEs) using the Grand Unified Magnetosphere-Ionosphere Coupling Simulation (GUMICS-4). The two ICME events occurred on 15–16 July 2012 and 29–30 April 2014. During the strong 2012 event, the solar wind upstream values reached up to 35 particles cm−3, speeds of up to 694 km s−1, and an interplanetary magnetic field of up to 22 nT, giving a Mach number of 2.3. The 2014 event was a moderate one, with the corresponding upstream values of 30 particles cm−3, 320 km s−1 and 10 nT, indicating a Mach number of 5.8. We examine how the Earth's space environment dynamics evolves during both ICME events from both global and local perspectives, using well-established empirical models and in situ measurements as references. We show that on the large scale, and during moderate driving, the GUMICS-4 results are in good agreement with the reference values. However, the local values, especially during high driving, show more variation: such extreme conditions do not reproduce local measurements made deep inside the magnetosphere. The same appeared to be true when the event was run with another global simulation. The cross-polar cap potential (CPCP) saturation is shown to depend on the Alfvén–Mach number of the upstream solar wind. However, care must be taken in interpreting these results, as the CPCP is also sensitive to the simulation resolution.

Properties of Stream Interactions and Their Associated Shocks near 1.52 au: MAVEN Observations

Abstract The measurements from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft are analyzed for the basic properties of solar wind stream interaction regions (SIRs) and their associated shocks at 1.52 au, as well as the evolution of SIRs from 1 to 1.52 au. A total of 149 SIRs are identified during the period from 2014 October to 2018 November, and 126 SIRs with high-quality data are selected for this study. The average occurrence rate of SIRs at 1.52 au is 36.3 yr−1, which is comparable to but slightly higher than that (32.4 yr−1) at 1 au, meaning that most SIRs are well formed at 1 au. The average duration of SIRs at 1.52 au is about 37.0 hr, comparable to that at 1 au (36.73 hr), indicating that SIRs have not yet expanded more rapidly as they are convected to 1.52 au. The maximum magnetic field strength and pressure of SIRs decrease significantly from 1 to 1.52 au. The shock association rates of SIRs increase from 20.3% to 33.3% or higher as SIRs evolve from 1 to 1.52 au. The forward shocks tend to occur twice more frequently than the reverse shocks. About 75% of shocks at 1.52 au are quasi-perpendicular shocks. The strength of the shocks becomes weaker and the average shock speed remains almost unchanged from 1 to 1.52 au. These results will help us understand the solar wind conditions at Mars and their potential impact on the Martian space environment.

The Variation of Resonating Magnetospheric Field Lines With Changing Geomagnetic and Solar Wind Conditions

AbstractStanding ultralow frequency waves redistribute energy and momentum around the Earth's magnetosphere. The eigenfrequencies of these standing waves can be measured by applying the cross‐phase technique to ground magnetometer data. To make a detection, the flux tubes in the vicinity of the magnetometers must all be driven at their local eigenfrequencies by a source with a sufficient frequency width. Therefore, successful measurement of the local eigenfrequencies indicates that a broadband source is exciting the flux tubes. We have analyzed 10 years of magnetometer data with an automated cross‐phase algorithm and used correlations with the OMNI data set to understand under what conditions broadband excitation occurs and how the conditions affect the eigenfrequency values. This is the largest such survey of its kind to date. We found that lower eigenfrequencies at higher latitudes (L>5) and higher eigenfrequencies at lower latitudes (L<4) were excited under different conditions. It was also possible to directly compare the first and third harmonics at midlatitudes. The lower eigenfrequencies were excited during more disturbed conditions, and we suggest that these harmonics are driven by solar wind pressure pulses or the Kelvin‐Helmholtz instability at the magnetopause. The higher eigenfrequencies were excited when the magnetosphere was relatively quiet, and we suggest that the cause was waves generated upstream of the Earth's bow shock. The eigenfrequencies were observed to decrease in the middle magnetosphere during disturbed intervals. This is because the intensification of the ring current weakens the magnetic field. Variations in magnetic local time and latitude were also investigated.

The Lunar Paleo‐Magnetosphere: Implications for the Accumulation of Polar Volatile Deposits

AbstractAnalyses of lunar samples suggest the Moon once possessed a dynamo from ~4.25 Ga until perhaps as recently as 1 Ga, with surface field strengths between ~5 and 100 μT. While the exact timing, strength, and structure of these paleomagnetic fields are not precisely known, such relatively strong fields imply that the Moon also likely possessed a magnetosphere. Here, we present hybrid plasma simulations of the structure and morphology of the putative lunar “paleo‐magnetosphere” for varying surface field strengths and orientations, using ambient solar wind conditions representative of the early Sun. The presence of the paleo‐magnetosphere reduces total solar wind fluxes to the lunar surface overall yet, for a spin‐aligned dynamo, increases the relative solar wind flux to the lunar polar regions. In turn, the paleo‐magnetosphere may have altered the rate of volatile accretion to the Moon over its history.

The dynamo-wind feedback loop : Assessing their non-linear interplay

AbstractThough generated deep inside the convection zone, the solar magnetic field has a direct impact on the Earth space environment via the Parker spiral. It strongly modulates the solar wind in the whole heliosphere, especially its latitudinal and longitudinal speed distribution over the years. However the wind also influences the topology of the coronal magnetic field by opening the magnetic field lines in the coronal holes, which can affect the inner magnetic field of the star by altering the dynamo boundary conditions. This coupling is especially difficult to model because it covers a large variety of spatio-temporal scales. Quasi-static studies have begun to help us unveil how the dynamo-generated magnetic field shapes the wind, but the full interplay between the solar dynamo and the solar wind still eludes our understanding.We use the compressible magnetohydrodynamical (MHD) code PLUTO to compute simultaneously in 2.5D the generation and evolution of magnetic field inside the star via an α-Ω dynamo process and the corresponding evolution of a polytropic coronal wind over several activity cycles for a young Sun. A multi-layered boundary condition at the surface of the star connects the inner and outer stellar layers, allowing both to adapt dynamically. Our continuously coupled dynamo-wind model allows us to characterize how the solar wind conditions change as a function of the cycle phase, and also to quantify the evolution of integrated quantities such as the Alfvén radius. We further assess the impact of the solar wind on the dynamo itself by comparing our results with and without wind feedback.