Francesco Pecora, William H. Matthaeus, Antonella Greco
et al.
Spatiotemporal correlation of magnetic field fluctuations is investigated using the Magnetospheric Multiscale mission in the terrestrial magnetosheath. The first observation of the turbulence propagator in space emerges through analysis of more than a thousand intervals. Results show clear features of spatial and spectral anisotropy, leading to a distinct behavior of relaxation times in the directions parallel and perpendicular to the mean magnetic field. Full space-time investigation of the Taylor hypothesis reveals a scale-dependent anisotropy of magnetosheath fluctuations that can be compared to the effect of flow propagation on spacecraft frame time decorrelation rates as well as with Eulerian estimates. The turbulence propagator reveals that the amplitudes of the perpendicular modes decorrelate according to sweeping or Alfvénic propagation mechanisms. The decorrelation time of parallel modes instead does not depend on the parallel wavenumber, which could be due to resonant interactions. Through direct observation, this study provides unprecedented insight into the space-time structure of turbulent space plasmas, while giving critical constraints for theoretical and numerical models.
Forrest Mozer, Oleksiy Agapitov, Stuart Bale
et al.
On November 6, 2024, the Parker Solar Probe flew past Venus to make the first accurate electric field measurement in the nightside Venusian magnetosphere. To achieve this result, the electric field antennas were current biased in a way never before experienced by an electric field detector. This biasing requirement, that the positive bias current in the Venus shadow be about equal to the electron thermal current, is discussed and illustrated. About one minute of useful electric f ield data in the eight-minute nightside magnetosphere crossing was obtained, during which the only feature observed was a few Hz signal. This result, along with the magnetic field measurements, showed that there were few if any electromagnetic waves, such as low-frequency electromagnetic turbulence or whistlers, in the nightside crossing. Instead, a few Hertz, purely electrostatic signal was found. This suggests that the interaction of the solar wind with an unmagnetized body having an ionosphere may be different from that of previously studied magnetized bodies. In the sunlit flanks, many electromagnetic wave modes were observed. These results describe the first step in the proper technique for future measurements of electric fields in shadow.
AbstractMuch of the longitude/local time dependence of the thermosphere is controlled by non‐migrating tides. Observations of semidiurnal (12‐hr) tides between 120 and 200 km altitude, that is, the middle thermosphere, are rare owing to the lack of systematic measurements in this region. Since late 2018, the Global‐scale Observations of the Limb and Disk (GOLD) Mission has provided unique measurements of thermospheric disk temperature and the column density ratio of atomic oxygen to molecular nitrogen ratio (ΣO/N2) from geostationary orbit. In this paper, we present an approach to deduce the strongest semidiurnal non‐migrating tides in the middle thermosphere by adapting the method of Krier et al. (2021, https://doi.org/10.1029/2021ja029563) that deduces diurnal non‐migrating tides in simultaneous observations of temperature and ΣO/N2 made by GOLD. Testing of this approach suggests that the principal sources of uncertainties in the derived semidiurnal non‐migrating tides are the limitation on the longitudes sampled, such that uncertainties are higher for tides with longer horizontal wavelength, and contamination of the local time sums by stationary planetary waves, which causes amplitudes to be overestimated. Our approach is applied to GOLD data during solstice conditions in 2019–2021. Comparison to models yield disagreements which are likely due to uncertainties intrinsic to the method and/or misrepresentation of tidal dynamics in the models. These results are the first observations of semidiurnal non‐migrating tides in the middle thermosphere from a geostationary observational platform.
Francesco Pecora, Francesco Pucci, Francesco Malara
et al.
Plasma turbulence involves complex, nonlinear interactions of electromagnetic fields and charged particles across multiple scales. Studying these phenomena in space plasmas, like the solar wind, is facilitated by the intrinsic scale separations and the availability of in situ spacecraft observations. However, the single-point or single-scale configurations of current spacecraft limit our understanding of many properties of the turbulent solar wind. To overcome these limitations, multipoint measurements spanning a range of characteristic scales are essential. This paper prepares for the enhanced measurement capabilities of upcoming multispacecraft missions by demonstrating that higher-order statistics, specifically kurtosis, as a baseline for intermittency can be accurately measured. Using synthetic turbulent fields with adjustable intermittency levels, we achieve scale separations analogous to those in the solar wind and apply these techniques to the planned trajectories of the HelioSwarm mission. This approach promises significant advancements in our understanding of plasma turbulence.
AbstractLarge‐amplitude stationary electron‐acoustic (EA) waves are studied, which are developed into the shocklets with the passage of time in an unmagnetized non‐isothermal plasma. The latter comprises two groups of electrons; namely the hot and cool electrons that are distinctly characterized by different electron densities and temperatures. On an EA timescale, the cool electrons behave as fluid, while non‐isothermal hot electrons obey the vortex‐like trapped distribution in the background of immobile ions. The nonlinear fluid equations are solved together both analytically and numerically within the framework of diagonalization matrix technique. Various parameters such as the free hot‐to‐trapped hot electron temperature ratio (β), the cool electron density ratio (α), and the cool‐to‐hot electron temperature ratio (σ) are numerically analyzed for dayside auroral zone plasma, showing a significant modification of solitary and shocklet structures. The plasma model is also applied to the electron diffusion region at the earth magnetopause, revealing the potential excitations depending significantly on the trapping parameter. These findings are important for understanding the nonlinear properties and steepening effects of the EA waves, especially in auroral zone and electron diffusion regions of earth's magnetosphere, where different types of electron populations are observed.
AbstractA prominent feature of the interaction between a planetary moon and its magnetospheric environment is the formation of a wake cavity in the downstream hemisphere, characterized by a significant decrease of the incident plasma density. Using an analytical model of Triton's sub‐Alfvénic interaction with Neptune's magnetosphere, we demonstrate that this moon's wake may be rotated away from its downstream hemisphere into a region that would be accessible to the undisturbed upstream flow. Due to the strong tilt of Neptune's magnetospheric field and the low Alfvénic Mach number of the plasma, one of Triton's Alfvén wings can penetrate into the upstream region and intercept the impinging plasma long before it reaches the moon. The interaction with this upstream wing causes the flow to be deflected toward Triton at a steep angle before being absorbed, thereby generating a wake cavity that is significantly displaced with respect to the moon's geometric plasma shadow. Along the downstream‐facing wing, the flow is deflected away from Triton and therefore unable to refill the displaced wake. Since the ionospheric Pedersen conductance greatly exceeds the Alfvén conductance, this asymmetric flow deflection is particularly intense at Triton: when the plasma encounters the wings, it is channeled toward or away from the moon along the axes of the wing tubes. The deflection of the streamlines away from their upstream direction peaks in the range of plasma parameters found along Triton's orbit. Therefore, the displaced wake may be a persistent feature of this moon's plasma interaction and observable during future flybys.
AbstractThe response of the Mars ionosphere to changes in solar irradiance is an important aspect of how conditions on Mars are shaped by our dynamic Sun. Changes in the composition of ionospheric plasma with changes in solar irradiance will affect how the ionosphere mediates the interaction of the neutral atmosphere with the surrounding space environment. Here we use MAVEN ion and neutral density measurements acquired at low (Deep Dip 8) and high (Deep Dip 2) solar irradiance conditions to determine how ion and neutral densities change when the ionizing solar irradiance doubles. We find that the neutral composition does not change significantly when examined at fixed total neutral number density. Furthermore, we find that and O+ densities increase by a factor of 2, but densities increase by a factor of 1.5. The relative abundance of decreases as solar irradiance increases. These results are explained by straightforward theoretical considerations of changes in ion production and loss rates. However, a photochemical model fails to reproduce these results with its default set of inputs. Consistent with previous modeling efforts, densities are over‐predicted. Acceptable model–data agreement requires significant adjustments to important model inputs, such as reduction in irradiance by 15%, reduction in CO2 density by a factor of 2, and increase in O density by a factor of 2. These large adjustments are suggestive of the need for improvements to the state of Mars ionosphere models based on MAVEN inputs rather than issues with the underlying data.
Accurate forecasting of the solar wind has grown in importance as society becomes increasingly dependent on technology that is susceptible to space weather events. This work describes an inner boundary condition for ambient solar wind models based on tomography maps of the coronal plasma density gained from coronagraph observations, providing a novel alternative to magnetic extrapolations. The tomographical density maps provide a direct constraint of the coronal structure at heliocentric distances of 4 to 8Rs, thus avoiding the need to model the complex non-radial lower corona. An empirical inverse relationship converts densities to solar wind velocities which are used as an inner boundary condition by the Heliospheric Upwind Extrapolation (HUXt) model to give ambient solar wind velocity at Earth. The dynamic time warping (DTW) algorithm is used to quantify the agreement between tomography/HUXt output and in situ data. An exhaustive search method is then used to adjust the lower boundary velocity range in order to optimize the model. Early results show up to a 32% decrease in mean absolute error between the modelled and observed solar wind velocities compared to that of the coupled MAS/HUXt model. The use of density maps gained from tomography as an inner boundary constraint is thus a valid alternative to coronal magnetic models, and offers a significant advancement in the field given the availability of routine space-based coronagraph observations.
Abstract In the publication Troshichev et al. (2006) ( https://doi.org/10.1029/2005JA011402 ) on the polar cap (PC) indices, PCN and PCS, an error was made by using components of the interplanetary magnetic field (IMF) in their geocentric solar ecliptic (GSE) representation instead of the prescribed geocentric solar magnetospheric (GSM) representation for calculations of index scaling parameters. The mistake has caused a trail of incorrect relations and wrong conclusions extending since 2006 up to now (2020) which should be discontinued, for instance, by issuing a corrigendum note from the authors. The present contribution explains the error and discusses in an extended example its consequences for one of the publications that have referred to the invalid scaling parameter set. Further investigations reported here of the PC index versions recommended by the International Association for Geomagnetism and Aeronomy (IAGA) indicate occurrences of similar problems in the present derivation of index scaling parameters.
Rohit Chhiber, William H. Matthaeus, Trevor A. Bowen
et al.
High time-resolution solar wind magnetic field data is employed to study statistics describing intermittency near the first perihelion (~35.6 Rs) of the Parker Solar Probe mission. A merged dataset employing two instruments on the FIELDS suite enables broadband estimation of higher order moments of magnetic field increments, with five orders established with reliable accuracy. The duration, cadence, and low noise level of the data permit evaluation of scale dependence of the observed intermittency from the inertial range to deep subproton scales. The results support multifractal scaling in the inertial range, and monofractal but non-Gaussian scaling in the subproton range, thus clarifying suggestions based on data near Earth that had remained ambiguous due to possible interference of the terrestrial foreshock. The physics of the transition to monofractality remains unclear but we suggest that it is due to a scale-invariant population of current sheets between ion and electron inertial scales; the previous suggestion of incoherent kinetic-scale wave activity is disfavored as it presumably leads to re-Gaussianization which is not observed.
R. D. Strauss, C. van der Merwe, C. Diedericks
et al.
Neutron monitors have been the premier ground-based instruments for monitoring the near-Earth cosmic ray flux for more than 70 years. It is essential to continue with such measurements in order to extend this unique long-term time series. Moreover, with the recent interest of the aviation industry to space weather effects, and especially the radiation risk posed by solar energetic particles and galactic cosmic rays, it is vital to extend the current neutron monitor network in order to provide near-real-time measurements to the space weather community. In this paper we discuss a new electronics system that was retrofitted to the SANAE neutron monitor in Antarctica. We present initial results from this system, featuring very high temporal resolution and discuss the techniques applied to the data analysis. Based on these successful upgrades, we are confident that this system can be used to rejuvenate the aligning neutron monitor network, and even possibly to revive some of the decommissioned instruments.
Muon detectors and neutron monitors were recently installed at Syowa Station, in the Antarctic, to observe different types of secondary particles resulting from cosmic ray interactions simultaneously from the same location. Continuing observations will give new insight into the response of muon detectors to atmospheric and geomagnetic effects. Operation began in February, 2018 and the system has been stable with a duty-cycle exceeding 94%. Muon data shows a clear seasonal variation, which is expected from the atmospheric temperature effect. We verified successful operation by showing that the muon and neutron data are consistent with those from other locations by comparing intensity variations during a space weather event. We have established a web page to make real time data available with interactive graphics (http://polaris.nipr.ac.jp/~cosmicrays/).
AbstractWe constrain the diagnostic potential of ion energy spectrograms to identify signatures of water vapor plumes in the thermal plasma environment of Jupiter's moon Europa. For this purpose, we apply a hybrid model of Europa's Alfvénic plasma interaction to calculate the perturbations of the flow and the electromagnetic fields near the moon for various plume locations on its surface, combined with different sets of magnetospheric upstream conditions (corresponding to different distances between Europa and the center of Jupiter's plasma sheet). The model output is used to generate synthetic time series for the count rates of the observable thermal ion population as a function of energy along several hypothetical spacecraft trajectories as well as for the Galileo E26 flyby. We demonstrate that the observability of characteristic plume signatures depends strongly on the viewing direction of the detector. Most surprisingly, for certain plume locations, a particle detector facing away from Europa captures more clearly discernible signatures of a plume passage than a detector looking into the direction of the moon. This puzzling result is caused by the deflection of magnetospheric and plume ions near Europa's Alfvén wings as well as a “contamination” of the spectrograms by cold plasma from the moon's global exosphere. The signature of the plume crossed during E26 is most clearly visible for a detector orientation that simultaneously captures the cold plume ions and a portion of the incident magnetospheric ion population. The results of this study will facilitate the planning of synergistic measurements during upcoming missions to Europa.
Justyna M. Sokół, D. J. McComas, M. Bzowski
et al.
The solar wind (SW) and the extreme ultraviolet (EUV) radiation modulate fluxes of interstellar and heliospheric particles inside the heliosphere both in time and in space. Understanding this modulation is necessary to correctly interpret measurements of particles of interstellar origin inside the heliosphere. We present a revision of heliospheric ionization rates and provide the Sun-Heliosphere Observation-based Ionization Rates (SHOIR) model based on the currently available data. We calculate the total ionization rates using revised SW and solar EUV data. We study the in-ecliptic variation of the SW parameters, the latitudinal structure of the SW speed and density, and the reconstruction of the photoionization rates. The revision most affects the SW out of the ecliptic plane during solar maximum and the estimation of the photoionization rates, the latter due to a change of the reference data. The revised polar SW is slower and denser during the solar maximum of solar cycle (SC) 24. The current estimated total ionization rates are higher than the previous ones for H, O, and Ne, and lower for He. The changes for the in-ecliptic total ionization rates are less than 10% for H and He, up to 20% for O, and up to 35% for Ne. Additionally, the changes are not constant in time and vary as a function of time and latitude.
Binzheng Zhang, Peter A. Delamere, Zhonghua Yao
et al.
Jupiter's bright persistent polar aurora and Earth's dark polar region indicate that the planets' magnetospheric topologies are very different. High-resolution global simulations show that the reconnection rate at the interface between the interplanetary and jovian magnetic fields is too slow to generate a magnetically open, Earth-like polar cap on the timescale of planetary rotation, resulting in only a small crescent-shaped region of magnetic flux interconnected with the interplanetary magnetic field. Most of the jovian polar cap is threaded by helical magnetic flux that closes within the planetary interior, extends into the outer magnetosphere and piles-up near its dawnside flank where fast differential plasma rotation pulls the field lines sunward. This unusual magnetic topology provides new insights into Jupiter's distinctive auroral morphology.
Jorge Amaya, Romain Dupuis, Maria Elena Innocenti
et al.
One of the goals of machine learning is to eliminate tedious and arduous repetitive work. The manual and semi-automatic classification of millions of hours of solar wind data from multiple missions can be replaced by automatic algorithms that can discover, in mountains of multi-dimensional data, the real differences in the solar wind properties. In this paper we present how unsupervised clustering techniques can be used to segregate different types of solar wind. We propose the use of advanced data reduction methods to pre-process the data, and we introduce the use of Self-Organizing Maps to visualize and interpret 14 years of ACE data. Finally, we show how these techniques can potentially be used to uncover hidden information, and how they compare with previous manual and automatic categorizations.
AbstractEntire fields of science, most notably in astrophysics, rely on line‐of‐sight observations. In planetary science and heliophysics, the techniques of soft X‐ray and energetic neutral atom imaging also produce line‐of‐sight measurements. An important question is whether the geometry of the surface, for example, the magnetopause, can be reconstructed using only line‐of‐sight observations from a single spacecraft. Under a broad range of conditions, the peak emission corresponds to the tangent to the boundary surface, such as the planetary surface or magnetopause, the so‐called limb brightening phenomenon. Thus, line‐of‐sight observations frequently provide information concerning the tangent to the surfaces being observed. We present an algorithm to reconstruct the cross section of the magnetopause using line‐of‐sight soft X‐ray observations (and, in principle, energetic neutral atom observations). The algorithm successfully reconstructs the cross section of the magnetopause in the orbit plane. The three‐dimensional magnetopause structure can be recovered from observations by a spacecraft whose orbit precesses around the magnetosphere.
The mechanisms underlying cytoplasmic pH (pHi) regulation in rat thymic lymphocytes were studied using trapped fluorescein derivatives as pHi indicators. Cells that were acid-loaded with nigericin in choline+ media recovered normal pHi upon addition of extracellular Na+ (Nao+). The cytoplasmic alkalinization was accompanied by medium acidification and an increase in cellular Na+ content and was probably mediated by a Nao+/Hi+ antiport. At normal [Na+]i, Nao+/Hi+ exchange was undetectable at pHi greater than or equal to 6.9 but was markedly stimulated by internal acidification. Absolute rates of H+ efflux could be calculated from the Nao+-induced delta pHi using a buffering capacity of 25 mmol X liter-1 X pH-1, measured by titration of intact cells with NH4+. At pHi = 6.3, pHo = 7.2, and [Na+]o = 140 mM, H+ extrusion reached 10 mmol X liter-1 X min-1. Nao+/Hi+ exchange was stimulated by internal Na+ depletion and inhibited by lowering pHo and by addition of amiloride (apparent Ki = 2.5 microM). Inhibition by amiloride was competitive with respect to Nao+. Hi+ could also exchange for Lio+, but not for K+, Rb+, Cs+, or choline+. Nao+/Hi+ countertransport has an apparent 1:1 stoichiometry and is electrically silent. However, a small secondary hyperpolarization follows recovery from acid-loading in Na+ media. This hyperpolarization is amiloride- and ouabain-sensitive and probably reflects activation of the electrogenic Na+-K+ pump. At normal Nai+ values, the Nao+/Hi+ antiport of thymocytes is ideally suited for the regulation of pHi. The system can also restore [Na+]i in Na+-depleted cells. In this instance the exchanger, in combination with the considerable cytoplasmic buffering power, will operate as a [Na+]i- regulatory mechanism.
The shape of the solar wind bubble within the interstellar medium, the so-called heliosphere, has been explored over six decades. As the Sun moves through the surrounding partially-ionized medium, neutral hydrogen atoms penetrate the heliosphere, and through charge-exchange with the supersonic solar wind, create a population of hot pick-up ions (PUIs). The Termination Shock (TS) crossing by Voyager 2 (V2) data demonstrated that the heliosheath (HS) (the region of shocked solar wind) pressure is dominated by suprathermal particles. Here we use a novel magnetohydrodynamic model that treats the freshly ionized PUIs as a separate fluid from the thermal component of the solar wind. Unlike previous models, the new model reproduces the properties of the PUIs and solar wind ions based on the New Horizon and V2 spacecraft observations. The PUIs charge exchange with the cold neutral H atoms of the ISM in the HS and are quickly depleted. The depletion of PUIs cools the heliosphere downstream of the TS, "deflating" it and leading to a narrower HS and a smaller and rounder shape, in agreement with energetic neutral atom observations by the Cassini spacecraft. The new model, with interstellar magnetic field orientation constrained by the IBEX ribbon, reproduces the magnetic field data outside the HP at Voyager 1(V1). We present the predictions for the magnetic field outside the HP at V2.
In the early days of 2017 September, an exceptionally energetic solar active region AR12673 aroused great interest in the solar physics community. It produced four X class flares, more than 20 CMEs and an intense geomagnetic storm, for which the peak value of the Dst index reached up to -142nT at 2017 September 8 02:00 UT. In this work, we check the interplanetary and solar source of this intense geomagnetic storm. We find that this geomagnetic storm was mainly caused by a shock-ICME complex structure, which was formed by a shock driven by the 2017 September 6 CME propagating into a previous ICME which was the interplanetary counterpart of the 2017 September 4 CME. To better understand the role of this structure, we conduct the quantitative analysis about the enhancement of ICME's geoeffectiveness induced by the shock compression. The analysis shows that the shock compression enhanced the intensity of this geomagnetic storm by a factor of two. Without shock compression, there would be only a moderate geomagnetic storm with a peak Dst value of -79 nT. In addition, the analysis of the proton flux signature inside the shock-ICME complex structure shows that this structure also enhanced the solar energetic particles (SEPs) intensity by a factor of ~ 5. These findings illustrate that the shock-ICME complex structure is a very important factor in solar physics study and space weather forecast.