Carrington Rotation Research Articles

Exploring Spatial and Temporal Patterns in the Debrecen Solar Faculae Database: Part II

In this study, utilizing data from the Solar Dynamics Observatory/Helioseismic and Magnetic Imager–Debrecen Faculae Data Catalogue, we investigated solar facula distribution over timescales much larger than the individual lifetimes of faculae. We aimed to better comprehend the behavior of the Sun’s global magnetic field, where faculae play a role as markers. (1) Along the latitudinal direction, we observed the following in the appearance of faculae. (i) Short-term periods with the Carrington rotation (27.3 days) and some of its harmonics (approximately 13.5 and 9 day periods) are identified. In the northern hemisphere, there is also a faint 7 day period. (ii) We also identified longer periods. These longer periods, approximately between 150–300 and 300–500 days, exhibit a diminishing trend from the solar equator to the poles in both hemispheres. (2) Analyzing the distribution and evolution of the longitudinal coordinates of the faculae, we identified two pairs of active longitudes that are separated by 180° from each other.

The Challenge of Predicting the Solar Wind Speed near Sunspot Minimum

By applying potential-field source-surface and potential-field current-sheet extrapolations to photospheric field maps from three different observatories, we predict the solar wind speed at Earth for several Carrington rotations during 2018–2021 and compare the results with in situ observations. The predicted speeds are taken to be inversely correlated with the rate of flux-tube expansion inside the source surface, located at a heliocentric distance of 2.5 R ⊙. The results often differ markedly from one observatory to another and are very sensitive to the latitudinal position of the ecliptic relative to the narrow belt of slow wind that surrounds the source-surface neutral line. Our main conclusions are that (1) the magnetograph measurements themselves are a major source of uncertainty in solar wind predictions; (2) these uncertainties are especially large near solar minimum, when Earth is located near the rapid transition between slow and fast wind that occurs on either side of the heliospheric current sheet; (3) comparison of the derived open field regions with observed coronal holes provides a strong, underutilized constraint on wind speed predictions; and (4) the observed polarity of the interplanetary magnetic field provides another important constraint on the location of the source region.

Magnetic connectivity from the Sun to the Earth with MHD models. I. Impact of the magnetic modelling on connectivity validation

The magnetic connectivity between the Sun and the Earth is crucial to our understanding of the solar wind and space weather events. However, establishing this connectivity is challenging because of the lack of direct observations, which explains the need for reliable simulations. The method most often used to make such measurements over the last few years is the two-step ballistic method, but it has many free parameters that can affect the final result. Thus, we want to provide a connectivity method based on self-consistent magnetohydrodynamics (MHD) models. To this end, we combined the COCONUT coronal model with the EUHFORIA heliospheric model to compute the magnetic field lines from the Earth to the Sun. We then developed a way to quantify both the spatial and temporal uncertainty associated with this computation. To validate our method, we selected four cases already studied in the literature and associated with high-speed-stream events coming from unambiguous coronal holes visible on the disk. We always find a partial overlap with the assumed CH of origin. The extent of this overlap is 19<!PCT!> for event 1, 100<!PCT!> for event 2, 45<!PCT!> for event 3, and 100<!PCT!> for event 4. We looked at the polarity at Earth over the full Carrington rotation to better understand these results. We find that, on average, MHD simulations provide a very good polarity estimation, showing 69<!PCT!> agreement with real data for event 1, 36<!PCT!> for event 2, 68<!PCT!> for event 3, and 69<!PCT!> for event 4. For events 1 and 3, we can then explain the mixed results by the spatial and temporal uncertainty. An interesting result is that, for MHD models, minimum-activity cases appear to be more challenging because of the multiple recurrent crossings of the HCS, while maximum-activity cases appear easier because of the latitudinal extent of the HCS. A similar result was also found with Parker Solar Probe data in another study. We demonstrate that it is possible to use MHD models to compute magnetic connectivity and that this approach provides results of equal quality to those from the two-step ballistic method, with additional possibilities for improvements as the models integrate more critical physics.

Solar differential rotation coefficients fitted from synoptic magnetic maps

ABSTRACT Based on the consecutive synoptic magnetic maps, we devise a new method to calculate the solar differential rotation coefficients. This method is very easy to implement and has a high accuracy. Firstly, based on the two-term or three-term differential rotation formula, we simulate a synoptic map CR$_{n}$ evolves one Carrington Rotation (CR) time only under the effect of the differential rotation, and thereby a stretched synoptic map CR$_{n*}$ is obtained. Then, through searching the maximum covariance between the maps CR$_{n*}$ and CR$_{n+1}$ by the grid search method, the rotation coefficients can be determined. Based on the synoptic maps of CRs 1625 to 2278 (during the years 1975–2023), the two-term coefficients A and B for latitude region between $\pm 40^{\circ }$ are calculated. The rotation coefficient B shows an obvious 11-yr period. From the time series of B, we find that the Sun usually rotates more differentially in the rising phases of the sunspot cycles than in the falling phases. Moreover, the strong magnetic field corresponds to an increasing of B (note that B has a negative sign) or decreasing of differential. The evolutionary trend of B also indicates that there are several years until the maximum value of B will be reached in solar cycle 25, and the coefficient B will be still in the rising phase in the few coming years. The two-term rotation coefficients for the two hemispheres are also calculated separately, and in the studied time-scale, the largest N–S asymmetry of the rotation rate appeared in October 2007.

Refinement of Global Coronal and Interplanetary Magnetic Field Extrapolations Constrained by Remote-sensing and In Situ Observations at the Solar Minimum

Solar magnetic fields are closely related to various physical phenomena on the Sun, which can be extrapolated with different models from photospheric magnetograms. However, the open flux problem (OFP), the underestimation of the magnetic field derived from the extrapolated model, is still unsolved. To minimize the impact of the OFP, we propose three evaluation parameters to quantitatively evaluate magnetic field models and determine the optimal free parameters in the models by constraining the coronal magnetic fields and the interplanetary magnetic fields (IMFs) with real observations. Although the OFP still exists, we find that magnetic field lines traced from the coronal models effectively capture the intricate topological configurations observed in the corona, including streamers and plumes. The OFP is lessened by using the Helioseismic and Magnetic Imager synoptic map instead of the Global Oscillation Network Group daily synoptic maps, and the potential field source surface + potential field current sheet (PFSS+PFCS) model instead of the current sheet source surface (CSSS) model. For Carrington Rotation 2231 at the solar minimum, we suggest that the optimal parameters for the PFSS+PFCS model are R ss = 2.2–2.5 R ☉ and R scs = 10.5–14.0 R ☉, as well as for the CSSS model, are R cs = 2.0–2.4 R ☉, R ss = 11.0–14.7 R ☉, and a = 1.0 R ☉. Despite the IMFs at 1 au being consistent with the measurements by artificially increasing the polar magnetic fields, the IMFs near the Sun are still underestimated. The OFP might be advanced by improving the accuracy of both the weak magnetic fields and polar magnetic fields, especially considering magnetic activities arising from interplanetary physical processes.

Validation of Simulated Statistical Characteristics of Magnetosphere‐Ionosphere Coupling in Global Geospace Simulations Over an Entire Carrington Rotation

AbstractWe study the statistical features of magnetosphere‐ionosphere (M‐I) coupling using a two‐way M‐I model, the GT configuration of the Multiscale Atmosphere Geospace Environment (MAGE) model. The M‐I coupling characteristics, such as field‐aligned current, polar cap potential, ionospheric Joule heating, and downward Alfvénic Poynting flux, are binned according to the interplanetary magnetic field clock angles over an entire Carrington Rotation event between 20 March and 16 April 2008. The MAGE model simulates similar distributions of field‐aligned currents compared to empirical Weimer/AMPS models and Iridium observations and reproduces the Region 0 current system. The simulated convection potential agrees well with the Weimer empirical model and displays consistent two‐cell patterns with SuperDARN observations, which benefit from more extensive data sets. The Joule heating structure in MAGE is generally consistent with both empirical Cosgrove and Weimer models. Moreover, our model reproduces Joule heating enhancements in the cusp region, as presented in the Cosgrove model and observations. The distribution of the simulated Alfvénic Poynting flux is consistent with that observed by the FAST satellite in the dispersive Alfvén wave regime. These M‐I coupling characteristics are also binned by the Kp indices, indicating that the Kp dependence of these patterns in the M‐I model is more effective than the empirical models within the Carrington Rotation. Furthermore, the MAGE simulation exhibits an improved M‐I current‐voltage relation that closely resembles the Weimer model, suggesting that the updated global model is significantly improved in terms of M‐I coupling.

Prediction of Solar Coronal Structures Using Fourier Neural Operators Based on the Solar Photospheric Magnetic Field Observation

AbstractThis paper constructs the structures of the solar corona (SC) using Fourier neural operators (FNO) based on solar photospheric magnetic field observation. The purpose is to learn the mapping between two infinite‐dimensional function spaces, which takes the photospheric magnetic field as input and the magnetohydrodynamic (MHD) solar wind plasma parameters as output, from a finite collection of input‐output pairs. The FNO‐SC model is established using MHD simulated results of 36 Carrington rotations (CRs) from 2008, 2009, and 2020. The performance of the FNO‐SC model is tested for 6 CRs during various phases of the solar activity such as descending, minimum, and ascending phases to generate the 3D structures of the SC. With the MHD simulations as references, the average structure similarity index measure (SSIM) value for the magnetic field topology from 1 to 3Rs is around 0.88. From 1 to 20Rs, the SSIM values for the number density and radial speed surpass 0.9. Relative to OMNI observations, the mean absolute percentage error for the radial speed generated from the FNO‐SC model does not exceed 0.25. These results indicate that the FNO‐SC model effectively captures the solar coronal structures typical of the periods investigated, by recovering the MHD simulations as well as the observations. The FNO‐SC model is further trained with enriched data from the maximum phase to assess the capability of modeling such a situation. The FNO‐SC model costs 48.7 s for a single CR prediction, and thus facilitates real‐time space weather forecasting.

Investigating the effects of numerical algorithms on global magnetohydrodynamics simulations of solar wind in the inner heliosphere

This paper explores the effects of numerical algorithms on global magnetohydrodynamics simulations of solar wind (SW) in the inner heliosphere. To do so, we use sunRunner3D, a 3-D magnetohydrodynamics model that employs the boundary conditions generated by CORHEL and the PLUTO code to compute the plasma properties of the SW with the ideal magnetohydrodynamics approximation up to 1.1 AU in the inner heliosphere. Mainly, we define three different combinations of numerical algorithms based on their diffusion level. This diffusion level is related to the way of solving the magnetohydrodynamics equations using the finite volume formulation, and, therefore, we set in terms of the divergence-free condition methods, Riemann solvers, variable reconstruction schemes, limiters, and time-steeping algorithms. According to the simulation results, we demonstrate that sunRunner3D reproduces global features of Corotating Interaction Regions observed by Earth-based spacecraft for a set of Carrington rotations that cover a period that lays in the late declining phase of solar cycle 24, independently of the numerical algorithms. Moreover, statistical analyses between models and in-situ measurements show reasonable agreement with the observations, and remarkably, the high diffusive method matches better with in-situ data than low diffusive methods.

Using sunRunner3D to interpret the global structure of the heliosphere from in-situ measurements

Understanding the large-scale three-dimensional structure of the inner heliosphere, while important in its own right, is crucial for space weather applications, such as forecasting the time of arrival and propagation of coronal mass ejections (CMEs). This study uses sunRunner3D (3D), a 3-D magnetohydrodynamic (MHD) model, to simulate solar wind (SW) streams and generate background states. SR3D employs the boundary conditions generated by CORona-HELiosphere (CORHEL) and the PLUTO code to compute the plasma properties of the SW with the MHD approximation up to 1.1 AU in the inner heliosphere. We demonstrate that SR3D reproduces global features of Corotating Interaction Regions (CIRs) observed by Earth-based spacecraft (OMNI) and the Solar TErrestial RElations Observatory (STEREO)-A for a set of Carrington rotations (CRs) that cover a period that lays in the late declining phase of solar cycle 24. Additionally, we demonstrate that the model solutions are valid in the corotating and inertial frames of references. Moreover, a comparison between SR3D simulations and in-situ measurements shows reasonable agreement with the observations, and our results are comparable to those achieved by Predictive Science Inc.'s Magnetohydrodynamic Algorithm outside a Sphere (MAS) code. We have also undertaken a comparative analysis with the Space Weather Adaptive Simulation Framework for Solar Wind (SWASTi-SW), a PLUTO physics-based model, to evaluate the precision of various initial boundary conditions. Finally, we discuss the disparities in the solutions derived from inertial and rotating frames.

Solar Wind Driven from GONG Magnetograms in the Last Solar Cycle

In a previous study, Huang et al. used the Alfvén Wave Solar atmosphere Model, one of the widely used solar wind models in the community, driven by ADAPT-GONG magnetograms to simulate the solar wind in the last solar cycle and found that the optimal Poynting flux parameter can be estimated from either the open field area or the average unsigned radial component of the magnetic field in the open field regions. It was also found that the average energy deposition rate (Poynting flux) in the open field regions is approximately constant. In the current study, we expand the previous work by using GONG magnetograms to simulate the solar wind for the same Carrington rotations and determine if the results are similar to the ones obtained with ADAPT-GONG magnetograms. Our results indicate that similar correlations can be obtained from the GONG maps. Moreover, we report that ADAPT-GONG magnetograms can consistently provide better comparisons with 1 au solar wind observations than GONG magnetograms, based on the best simulations selected by the minimum of the average curve distance for the solar wind speed and density.

ASTRONOMICAL SIGNALS IN THE BRIGHTEST FIREBALLS THAT FALL ON EARTH

In this work a wavelet spectral study of a time series of brightest fireballs is presented. The wavelet analysis shows that are two solar periodicities around 27 and 13.5 days. These periodicities have been associated to Carrington rotation and lunar motions and indicate that both Solar and Lunar rotations could have an influence on the brightest fireballs fall on Earth. A third periodicity around 2.5 days was also identified in almost all spectra but it could be a harmonic of those periods.

Assessing the Performance of the ADAPT and AFT Flux Transport Models Using In Situ Measurements from Multiple Satellites

The launches of Parker Solar Probe (Parker) and Solar Orbiter (SolO) are enabling a new era of solar wind studies that track the solar wind from its origin at the photosphere, through the corona, to multiple vantage points in the inner heliosphere. A key ingredient for these models is the input photospheric magnetic field map that provides the boundary condition for the coronal portion of many heliospheric models. In this paper, we perform steady-state, data-driven magnetohydrodynamic (MHD) simulations of the solar wind during Carrington rotation 2258 with the Grid GAMERA model. We use the ADAPT and AFT flux transport models and quantitatively assess how well each model matches in situ measurements from Parker, SolO, and Earth. We find that both models reproduce the magnetic field components at Parker quantitatively well. At SolO and Earth, the magnetic field is reproduced relatively well, though not as well as at Parker, and the density is reproduced extremely poorly. The velocity is overpredicted at Parker, but not at SolO or Earth, hinting that the Wang–Sheeley–Arge (WSA) relation, fine-tuned for Earth, misses the deceleration of the solar wind near the Sun. We conclude that AFT performs quantitatively similarly to ADAPT in all cases, and that both models are comparable to a purely WSA heliospheric treatment with no MHD component. Finally, we trace field lines from SolO back to an active region outflow that was observed by Hinode/EIS, and which shows evidence of elevated charge state ratios.

Reconstruction of Carrington Rotation Means of Open Solar Flux over the Past 154 Years

We generate reconstructions of signed open solar flux (OSF) for the past 154 years using observations of geomagnetic activity. Previous reconstructions have been limited to annual resolution, but this is here increased by a factor of more than 13 by using averages over Carrington rotation (CR) intervals. We use two indices of geomagnetic activity, the homogeneous aa index, aaH, and the IDV(1d) index; a combination of the two is fitted to OSF estimates from near-Earth interplanetary satellite data. For 1995 – 2022, these are corrected for excess flux (i.e. orthogardenhose flux and switchbacks) using strahl electrons. For 1970 – 2022, we also use the absolute values of the radial component of the near-Earth interplanetary magnetic field 〈|〈Br〉τ|〉CR\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}${\\langle }|{\\langle }B_{r}{\\rangle }_{\ au }|{\\rangle }_{CR}$\\end{document}, where the excess flux is allowed for by adopting the optimum averaging interval τ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}${\ au }$\\end{document} of 20 h. However, in the interval 1970 – 1995, data gaps in the interplanetary data are a serious problem. The errors that these missing data cause in CR averages of OSF are evaluated by synthetically masking data for CRs that have a full complement, using the same number and time series of data gaps as for the CR in question. Given the potential for missing data to generate large errors, we use the near-continuous 1995 – 2022 data to derive the best-fit combination of the geomagnetic data and employ the 1970 – 1995 data for testing in which we can readily allow for the errors caused by data gaps. Errors caused by inaccuracies in the geomagnetic data are shown to be considerably smaller than the uncertainties due to the polynomial fitting. It is shown that the new reconstructions are consistent with the previous annual estimates and that there is considerable variability in the OSF values from one CR to the next; in particular, in high-activity solar cycles, there can be individual CRs in which the OSF exceeds that for adjacent CRs by a factor as large as two.

Numerical MHD models of stream interaction regions (SIRs) and corotating interaction regions (CIRs) using sunRunner3D: comparison with observations

ABSTRACT In this work, we present numerical simulations of Stream Interaction Regions (SIRs) and Corotating Interaction Regions (CIRs) using the sunrunner3d tool that employs as a coronal model the boundary conditions obtained by corhel/mas with the pluto code that describes the global 3D structure of the solar wind using the magnetohydrodynamics (MHD) approach in the inner heliosphere. Specifically, we selected a set of SIRs and CIRs observed by the Parker Solar Probe (PSP) and STEREO-A (STA) missions during the Carrington rotations (CRs) 2207 to 2210 and CRs from 2020 to 2022. In order to describe the dynamics of the plasma that constitutes the solar wind background conditions for the selected CRs, we solve the ideal MHD equations in an inertial frame of reference, managing the solar rotation by rotating the boundary values in ϕ (longitude) at a rate corresponding to the sidereal rotation rate of the solar equator. We show that our results using sunrunner3d can globally reproduce the plasma parameters, such as radial velocity, number proton density, and radial magnetic field strength of these large-scale structures, observed by PSP and STA at distances near the Sun and around 1 au, respectively. These results allow exploring the global evolution of SIRs/CIRs in the inner heliosphere using sunrunner3d.

Near-real-time 3D Reconstruction of the Solar Coronal Parameters Based on the Magnetohydrodynamic Algorithm outside a Sphere Using Deep Learning

For the first time, we generate solar coronal parameters (density, magnetic field, radial velocity, and temperature) on a near-real-time basis by deep learning. For this, we apply the Pix2PixCC deep-learning model to three-dimensional (3D) distributions of these parameters: synoptic maps of the photospheric magnetic field as an input and the magnetohydrodynamic algorithm outside a sphere (MAS) results as an output. To generate the 3D structure of the solar coronal parameters from 1 to 30 solar radii, we train and evaluate 152 distinct deep-learning models. For each parameter, we consider the data of 169 Carrington rotations from 2010 June to 2023 February: 132 for training and 37 for testing. The key findings of our study are as follows: First, our deep-learning models successfully reconstruct the 3D distributions of coronal parameters from 1 to 30 solar radii with an average correlation coefficient of 0.98. Second, during the solar active and quiet periods, the AI-generated data exhibits consistency with the target MAS simulation data. Third, our deep-learning models for each parameter took a remarkably short time (about 16 s for each parameter) to generate the results with an NVIDIA Titan XP GPU. As the MAS simulation is a regularization model, we may significantly reduce the simulation time by using our results as an initial configuration to obtain an equilibrium condition. We hope that the generated 3D solar coronal parameters can be used for the near-real-time forecasting of heliospheric propagation of solar eruptions.

Simulating Compressive Stream Interaction Regions during Parker Solar Probe’s First Perihelion Using Stream-aligned Magnetohydrodynamics

We used the stream-aligned magnetohydrodynamics (SA-MHD) model to simulate Carrington rotation 2210, which contains Parker Solar Probe’s (PSP) first perihelion at 36.5 R ⊙ on 2018 November 6, to provide context to the in situ PSP observations by FIELDS and SWEAP. The SA-MHD model aligns the magnetic field with the velocity vector at each point, thereby allowing for clear connectivity between the spacecraft and the source regions on the Sun, without unphysical magnetic field structures. During this Carrington rotation, two stream interaction regions (SIRs) form, due to the deep solar minimum. We include the energy partitioning of the parallel and perpendicular ions and the isotropic electrons to investigate the temperature anisotropy through the compression regions to better understand the wave energy amplification and proton thermal energy partitioning in a global context. Overall, we found good agreement in all in situ plasma parameters between the SA-MHD results and the observations at PSP, STEREO-A, and Earth, including at PSP’s perihelion and through the compression region of the SIRs. In the typical solar wind, the parallel proton temperature is preferentially heated, except in the SIR, where there is an enhancement in the perpendicular proton temperature. This is further showcased in the ion cyclotron relaxation time, which shows a distinct decrease through the SIR compression regions. This work demonstrates the success of the Alfvén wave turbulence theory for predicting interplanetary magnetic turbulence levels, while self-consistently reproducing solar wind speeds, densities, and overall temperatures, including at small heliocentric distances and through SIR compression regions.

Synoptic maps from two viewpoints

Context. Over recent decades, various kinds of magnetic synoptic chart products have seen major improvements in observation cadence, resolution, and processing, but their creation is still limited by the 27.27 day rotation rate of the solar surface. Aims. Co-observation from a second vantage point away from the Earth–Sun line with SO/PHI enables the creation of combined magnetic synoptic maps from observation periods that are significantly shorter than a typical Carrington rotation, and therefore provides a data product with magnetic information that is temporally more consistent. Methods. We upgraded the SDO/HMI synoptic map pipeline in order for it to be compatible with SO/PHI observations at variable distances and a much lower and variable observation cadence. This enabled us to produce combined magnetic synoptic maps using SO/PHI data taken from the far side of the Sun. Results. We present a pipeline to produce combined magnetic synoptic maps from simultaneous SO/PHI and SDO/HMI observations. Depending on the orbital position of SO/PHI, our combined synoptic maps can be produced up to 13 days faster than any other comparable data product currently available. This strongly reduces the time-lag between the observations that are used to build the map and thereby provides a more consistent map of the magnetic field across the solar surface.

The differential rotation of the chromosphere and the quiet chromosphere in the falling and rising periods of a solar cycle

ABSTRACT The full-disc chromosphere was routinely monitored in the He i 10 830 Å line at the National Solar Observatory/Kitt Peak from 2004 November to 2013 March, and thereby, synoptic maps of He i line intensity from Carrington rotations 2032 to 2135 were acquired. They are utilized to investigate the differential rotation of the chromosphere and the quiet chromosphere during the one falling (descending part of solar cycle 23) period and the one rising (ascending part of solar cycle 24) period of a solar cycle. Both the quiet chromosphere and the chromosphere are found to rotate slower and have a more prominent differential rotation in the rising period of solar cycle 24 than in the falling period of solar cycle 23, and an illustration is offered.

A first rapid synoptic magnetic field map using SDO/HMI and SO/PHI data

Context. Traditionally, the observation time needed to build synoptic maps of the solar magnetic field is bound to the 27 days of a full Carrington rotation due to the single viewpoint from Earth. Aims. Our aim is to reduce this observation time to 13.5 days by combining magnetograms from two vantage points, 180° apart in longitude in the ideal case. Methods. We combined observations taken by the Polarimetric and Helioseismic Imager (SO/PHI) during the superior conjunction of the Solar Orbiter in February 2021 with data from the Helioseismic and Magnetic Imager (SDO/HMI) and constructed a synoptic map of the line-of-sight magnetic field of CR 2240. Resuls. The result is the first multi-view synoptic map using SDO/HMI and SO/PHI data from an observing period of only 16 days. Comparing the multi-view synoptic map to the standard synoptic map of SDO/HMI shows a significant amount of magnetic evolution between the dates on which the two instruments observed the same solar longitudes. The changed magnetic field was caught by the multi-view synoptic map but would have been missed by a standard synoptic map. Conclusions. Our results demonstrate that multi-view synoptic maps provide a new method to obtain a more instantaneous map of the magnetic field over the entire solar surface.

Spacecraft Floating Potential Measurements for the Wind Spacecraft

Analysis of 8,804,545 electron velocity distribution functions, observed by the Wind spacecraft near 1 au between 2005 January 1 and 2022 January 1, was performed to determine the spacecraft floating potential, ϕ sc. Wind was designed to be electrostatically clean, which helps keep the magnitude of ϕ sc small (i.e., ∼5–9 eV for nearly all intervals) and the potential distribution more uniform. We observed spectral enhancements of ϕ sc at frequencies corresponding to the inverse synodic Carrington rotation period with at least three harmonics. The two-dimensional histogram of ϕ sc versus time also shows at least two strong peaks, with a potential third, much weaker peak. These peaks vary in time, with the intensity correlated with solar maximum. Thus, the spectral peaks and histogram peaks are likely due to macroscopic phenomena like coronal mass ejections (solar cycle dependence) and stream interaction regions (Carrington rotation dependence). The values of ϕ sc are summarized herein and the resulting data set is discussed.