In this study we examine the radial dependence of the inertial and dissipation range indices, as well as the spectral break separating the inertial and dissipation range in power density spectra of interplanetary magnetic field fluctuations using {\it Parker Solar Probe} data from the fifth solar encounter between $\sim$0.1 and $\sim$0.7 au. The derived break wavenumber compares reasonably well with previous estimates at larger radial distances and is consistent with gyro-resonant damping of Alfvénic fluctuations by thermal protons. We find that the inertial scale power law index varies between approximately -1.65 and -1.45. This is consistent with either the Kolmogorov (-5/3) or Iroshnikov-Kraichnan (-3/2) values, has a very weak radial dependence with a possible hint that the spectrum becomes steeper closer to the Sun. The dissipation range power law index, however, has a clear dependence on radial distance (and turbulence age), decreasing from -3 near 0.7 au (4 days) to -4 [$\pm$0.3] at 0.1 au (0.75 days) closer to the Sun.
Understanding the magnetic connections from the Sun to interplanetary space is crucial for linking in situ particle observations with the solar source regions of the particles. A simple connection along the large-scale Parker spiral magnetic field is made complex by the turbulent random-walk of field lines. In this paper, we present the first analytical model of heliospheric magnetic fields where the dominant 2D component of the turbulence is transverse to the Parker spiral. The 2D wave field is supplemented with a minor wave field component that has asymptotically slab geometry at small and l…
The Parker Solar Probe (PSP) primary mission extends seven years and consists of 24 orbits of the Sun with descending perihelia culminating in a closest approach of ($\sim 9.8~R_\odot$). In the course of these orbits PSP will pass through widely varying conditions, including anticipated large variations of turbulence properties such as energy density, correlation scales and cross helicities. Here we employ global magnetohydrodynamics simulations with self-consistent turbulence transport and heating \citep{usmanov2018} to preview likely conditions that will be encountered by PSP, by assuming su…
The turbulent magnetic fields of a large set of fast solar wind streams measured onboard ACE and STEREO A and B are analyzed in an effort to identify the effects of the turbulence-level broad variations on the orientations of the local, time-averaged magnetic fields. The power level of turbulence, roughly defined as the power in the transverse field fluctuations normalized to the medium-scale average background field, tightly orders the location of the peaks in the probability distribution functions (PDFs) of the angles between local fields and Parker spiral. As a result, the broad variations …
Simulation results from a global magnetohydrodynamic model of the solar corona and solar wind are compared with Parker Solar Probe (PSP) observations during its first five orbits. The fully three-dimensional model is based on Reynolds-averaged mean-flow equations coupled with turbulence transport equations. The model includes the effects of electron heat conduction, Coulomb collisions, turbulent Reynolds stresses, and heating of protons and electrons via a turbulent cascade. Turbulence transport equations for average turbulence energy, cross helicity, and correlation length are solved concurre…
Parker Solar Probe (PSP) routinely observes magnetic field deflections in the solar wind at distances less than 0.3 au from the Sun. These deflections are related to structures commonly called 'switchbacks' (SBs), whose origins and characteristic properties are currently debated. Here, we use a database of visually selected SB intervals - and regions of solar wind plasma measured just before and after each SB - to examine plasma parameters, turbulent spectra from inertial to dissipation scales, and intermittency effects in these intervals. We find that many features, such as perpendicular stoc…
The scaling of the turbulent spectra provides a key measurement that allows to discriminate between different theoretical predictions of turbulence. In the solar wind, this has driven a large number of studies dedicated to this issue using in-situ data from various orbiting spacecraft. While a semblance of consensus exists regarding the scaling in the MHD and dispersive ranges, the precise scaling in the transition range and the actual physical mechanisms that control it remain open questions. Using the high-resolution data in the inner heliosphere from Parker Solar Probe (PSP) mission, we fin…
We use \emph{Parker Solar Probe} (\emph{PSP}) in-situ measurements to analyze the characteristics of solar wind turbulence during the first solar encounter covering radial distances between $35.7R_\odot$ and $41.7R_\odot$. In our analysis we isolate so-called switchback (SB) intervals (folded magnetic field lines) from non-switchback (NSB) intervals, which mainly follow the Parker spiral field. Using a technique based on conditioned correlation functions, we estimate the power spectra of Elsasser, magnetic and bulk velocity fields separately in the SB and NSB intervals. In comparing the turbul…
The Parker or field line tangling model of coronal heating is investigated through long-time high-resolution simulations of the dynamics of a coronal loop in cartesian geometry within the framework of reduced magnetohydrodynamics (RMHD). Slow photospheric motions induce a Poynting flux which saturates by driving an anisotropic turbulent cascade dominated by magnetic energy and characterized by current sheets elongated along the axial magnetic field. Increasing the value of the axial magnetic field different regimes of MHD turbulence develop with a bearing on coronal heating rates. In physical …
Using the Parker Solar Probe data taken in the inner heliosphere, we investigate the power and spatial anisotropy of magnetic-field spectra at kinetic scales (i.e., around sub-ion scales) in solar wind turbulence in the inner heliosphere. We find that strong anisotropy of magnetic spectra occurs at kinetic scales with the strongest power in the perpendicular direction with respect to the local magnetic field (forming an angle theta_B with the mean flow velocity). The spectral index of magnetic spectra varies from -3.2 to -5.8 when the angle theta_B changes from 90 to 180 (or 0) deg, indicating…
Characterization of compressible fluctuations in solar wind streams dominated by balanced and imbalanced turbulence: Parker Solar Probe, Solar Orbiter and Wind observations
The University of Texas at Austin（德克萨斯大学奥斯汀分校）
研究通过分析Wind、Solar Orbiter和Parker Solar Probe的数据，探讨太阳风中压缩性波动的尺度依赖性和与等离子体β值及径向距离的关系，揭示压缩性波动在太阳风加速和加热中的作用。
We make use of the Parker Solar Probe (PSP) data to explore the nature of solar wind turbulence focusing on the Alfvénic character and power spectra of the fluctuations and their dependence on distance and context (i.e. large scale solar wind properties), aiming to understand the role that different effects such as source properties, solar wind expansion, stream interaction might play in determining the turbulent state. We carry out a statistical survey of the data from the first five orbits of PSP with a focus on how the fluctuation properties at the large, MHD scales, vary with different sol…
Observations from Parker Solar Probe's first five orbits are used to investigate the helioradial evolution of probability density functions (PDFs) of fluctuations of magnetic field components, between \(\sim 28\) - 200 \(\rs\). Transformation of the magnetic field vector to a local mean-field coordinate system permits examination of anisotropy relative to the mean magnetic field direction. Attention is given to effects of averaging-interval size. It is found that PDFs of the perpendicular fluctuations are well approximated by a Gaussian function, with the parallel fluctuations less so: kurtose…
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…
The solar wind, a continuous flow of plasma from the sun, not only shapes the near Earth space environment but also serves as a natural laboratory to study plasma turbulence in conditions that are not achievable in the lab. Starting with the Mariners, for more than five decades, multiple space missions have enabled in-depth studies of solar wind turbulence. Parker Solar Probe (PSP) was launched to explore the origins and evolution of the solar wind. With its state-of-the-art instrumentation and unprecedented close approaches to the sun, PSP is starting a new era of inner heliospheric explorati…
A wavelet-based model of magnetic turbulence over a Parker spiral field
Istituto per la Scienza e la Tecnologia dei Plasmi, Consiglio Nazionale delle Ricerche（等离子体科学与技术研究所，意大利国家研究委员会）；Dipartimento di Fisica, Università della Calabria（卡塔尼亚大学物理系）；Istituto Nazionale di Astrofisica, sede di Cosenza（意大利国家天体物理学研究所，科森扎分部）
We examine the radial evolution of correlation lengths perpendicular (\(λ_C^{\perp}\)) and parallel (\(λ_C^{\parallel}\)) to the magnetic-field direction, computed from solar wind magnetic-field data measured by Parker Solar Probe (PSP) during its first eight orbits, Helios 1, Advanced Composition Explorer (ACE), WIND, and Voyager 1 spacecraft. Correlation lengths are grouped by an interval's alignment angle; the angle between the magnetic-field and solar wind velocity vectors (\(Θ_{\rm BV}\)). Parallel and perpendicular angular channels correspond to angles \(0^{\circ}~<~Θ_{\rm BV}~<~40^{\cir…
The Parker Solar Probe mission provides a unique opportunity to characterize several features of the solar wind at different heliocentric distances. Recent findings have shown a transition in the inertial range spectral and scaling properties around 0.4-0.5 au when moving away from the Sun. Here we provide, for the first time, how to reconcile these observational results on the radial evolution of the magnetic and velocity field fluctuations with two scenarios drawn from the magnetohydrodynamic theory. The observed breakdown is the result of the radial evolution of magnetic field fluctuations …
Direct evidence of an inertial-range turbulent energy cascade has been provided by spacecraft observations in heliospheric plasmas. In the solar wind, the average value of the derived heating rate near 1 au is $\sim 10^{3}\, \mathrm{J\,kg^{-1}\,s^{-1}}$, an amount sufficient to account for observed departures from adiabatic expansion. Parker Solar Probe (PSP), even during its first solar encounter, offers the first opportunity to compute, in a similar fashion, a fluid-scale energy decay rate, much closer to the solar corona than any prior in-situ observations. Using the Politano-Pouquet third-…
From the the solar photosphere to the outer heliosphere, the Sun's plasma properties are fluctuating with a broad range of temporal and spatial scales. In fact, a turbulent cascade of energy from large to small scales is a frequently invoked explanation for heating the corona and accelerating the solar wind. NASA's Parker Solar Probe (PSP) is expected to revolutionize our understanding of coronal heating and magnetohydrodynamic (MHD) turbulence by performing in situ sampling closer to the Sun than any other prior space mission. This research note presents theoretical predictions for some prope…
NASA's Parker Solar Probe (Parker) spacecraft reached its first perihelion of 35.7 solar radii on November 5th, 2018. To aid in mission planning, and in anticipation of the unprecedented measurements to be returned, in late October, we developed a three-dimensional magnetohydrodynamic (MHD) solution for the solar corona and inner heliosphere, driven by the then available observations of the Sun's photospheric magnetic field. Our model incorporates a wave-turbulence-driven (WTD) model to heat the corona. Here, we present our predictions for the structure of the solar corona and the likely {\it …
The solar corona and young solar wind may be characterized by critical surfaces -- the sonic, Alfvén, and first plasma-$β$ unity surfaces -- that demarcate regions where the solar wind flow undergoes certain crucial transformations. Global numerical simulations and remote sensing observations offer a natural mode for the study of these surfaces at large scales, thus providing valuable context for the high-resolution in-situ measurements expected from the soon-to-be-launched Parker Solar Probe (PSP). The present study utilizes global three-dimensional magnetohydrodynamic simulations of the sola…
We examine Alfvén Wave Solar atmosphere Model (AWSoM) predictions of the first Parker Solar Probe (PSP) encounter. We focus on the 12-day closest approach centered on the 1st perihelion. AWSoM (van der Holst et al., 2014) allows us to interpret the PSP data in the context of coronal heating via Alfvén wave turbulence. The coronal heating and acceleration is addressed via outward-propagating low-frequency Alfvén waves that are partially reflected by Alfvén speed gradients. The nonlinear interaction of these counter-propagating waves results in a turbulent energy cascade. To apportion the wave d…
Effects of Alfvénicity on the Compressible Energy Cascade in Magnetohydrodynamic Solar Wind Turbulence: Evidence from Parker Solar Probe, Solar Orbiter, and WIND observations
Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales（布宜诺斯艾利斯大学，理学院）；CONICET – Universidad de Buenos Aires, Instituto de Física Interdisciplinaria y Aplicada (INFINA)（阿根廷国家科学研究委员会–布宜诺斯艾利斯大学，交叉与应用物理研究所）；Department of Physics, The University of Texas at Austin（德克萨斯大学奥斯汀分校，物理系）；Department of Astronomy, University of Maryland, College Park（马里兰大学帕克分校，天文学系）；Planetary Magnetospheres Laboratory, NASA Goddard Space Flight Center（NASA戈达德太空飞行中心，行星磁层实验室）
We present a first theoretical modeling of joint Parker Solar Probe (PSP) - Metis/Solar Orbiter (SolO) quadrature observations Telloni et al 2022c. The combined observations describe the evolution of a slow solar wind plasma parcel from the extended solar corona ($3.5-6.3$ R$_\odot$) to the very inner heliosphere (23.2 R$_\odot$). The Metis/SolO instrument remotely measures the solar wind speed finding a range from $96-201$ kms$^{-1}$, and PSP measures the solar wind plasma in situ, observing a radial speed of 219.34 kms$^{-1}$. We find theoretically and observationally that the solar wind spe…
Small-scale magnetic flux ropes (SFRs) are a type of structures in the solar wind that possess helical magnetic field lines. In a recent report (Chen & Hu 2020), we presented the radial variations of the properties of SFR from 0.29 to 8 au using in situ measurements from the Helios, ACE/Wind, Ulysses, and Voyager spacecraft. With the launch of the Parker Solar Probe (PSP), we extend our previous investigation further into the inner heliosphere. We apply a Grad-Shafranov-based algorithm to identify SFRs during the first two PSP encounters. We find that the number of SFRs detected near the Sun i…
Observations of Transition from Imbalanced to Balanced Kinetic Alfvénic Turbulence
Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）；Space Sciences Laboratory, University of California, Berkeley（加州大学伯克利分校空间科学实验室）；Physics Department, University of California, Berkeley（加州大学伯克利分校物理系）；School of Physics and Electronic Sciences, Changsha University of Science and Technology（长沙理工大学物理与电子科学学院）；LPC2E, CNRS, CNES, University of Orléans（奥尔良大学CNRS/CNES LPC2E研究中心）；International Space Science Institute (ISSI)（国际空间科学研究所）；University of California, Berkeley（加州大学伯克利分校）
Radio waves are strongly scattered in the solar wind, so that their apparent sources seem to be considerably larger and shifted than the actual ones. Since the scattering depends on the spectrum of density turbulence, better understanding of the radio wave propagation provides indirect information on the relative density fluctuations $ε=\langleδn\rangle/\langle n\rangle$ at the effective turbulence scale length. Here, we have analyzed 30 type III bursts detected by Parker Solar Probe (PSP). For the first time, we have retrieved type III burst decay times $τ_{\rm{d}}$ between 1 MHz and 10 MHz t…
Switchbacks are widely acknowledged phenomena observed by the Parker Solar Probe and appear to occur in patches. Previous studies focused on the fluctuations at the magnetic reversals. However, the nature of the fluctuations inside the switchbacks remains unknown. Here we utilize the magnetic field data and plasma data measured by the Parker Solar Probe in the first four encounters. We investigate the fluctuations in the switchback intervals of 100 s with BR>0 at every instant and compare them to the fluctuations in the nonswitchback intervals of 100 s with theta_RB>160o at every instant. We c…
The Parker Solar Probe (PSP) observed an interplanetary coronal mass ejection (ICME) event during its first orbit around the sun, among many other events. This event is analyzed by applying a wavelet analysis technique to obtain the reduced magnetic helicity, cross helicity, and residual energy, the first two of which are magnetohydrodynamics (MHD) invariants. Our results show that the ICME, as a large scale magnetic flux rope, possesses high magnetic helicity, very low cross helicity, and highly negative residual energy, thus pointing to a magnetic fluctuation dominated structure. Using the s…
During the Parker Solar Probe's (PSP) first perihelion pass, the spacecraft reached within a heliocentric distance of \(\sim 37~R_\odot\) and observed numerous magnetic and flow structures characterized by sharp gradients. To better understand these intermittent structures in the young solar wind, an important property to examine is their degree of correlation in time and space. To this end, we use the well-tested Partial Variance of Increments (PVI) technique to identify intermittent events in FIELDS and SWEAP observations of magnetic and proton-velocity fields (respectively) during PSP's fir…
On April 5, 2019, while the Parker Solar Probe was at its 35 solar radius perihelion, the data set collected at 293 samples/sec contained more than 10,000 examples of spiky electric-field-like structures having durations less than 200 milliseconds and amplitudes greater than 10 mV/m. The vast majority of these events was caused by plasma turbulence. Defining dust events as those having similar, narrowly peaked, positive, single-ended signatures, resulted in finding 135 clear dust events, which, after correcting for the low detection efficiently, resulted in an estimate consistent with the 1000…
We report analysis of sub-Alfvénic magnetohydrodynamic (MHD) perturbations in the low-\b{eta} radial-field solar wind using the Parker Solar Probe spacecraft data from 31 October to 12 November 2018. We calculate wave vectors using the singular value decomposition method and separate the MHD perturbations into three types of linear eigenmodes (Alfvén, fast, and slow modes) to explore the properties of the sub-Alfvénic perturbations and the role of compressible perturbations in solar wind heating. The MHD perturbations there show a high degree of Alfvénicity in the radial-field solar wind, with…
Knowing the lengthscales at which turbulent fluctuations dissipate is key to understanding the nature of weakly compressible magnetohydrodynamic turbulence. We use radio wavelength interferometric imaging observations which measure the extent to which distant cosmic sources observed against the inner solar wind are scatter-broadened. We interpret these observations to determine that the dissipation scales of solar wind density turbulence at heliocentric distances of 2.5 -- 20.27 $R_{\odot}$ range from $\approx$ 13500 to 520 m. Our estimates from $\approx$ 10--20 $R_{\odot}$ suggest that the di…
We report small-scale magnetic flux ropes via the Parker Solar Probe in situ measurements during the first six encounters and present additional analyses to supplement our prior work in Chen et al. 2021. These flux ropes are detected by the Grad-Shafranov-based algorithm with the duration and scale size ranging from 10 seconds to $\lesssim$1 hour and from a few hundred kilometers to 10$^{-3}$ au, respectively. They include both static structures and those with significant field-aligned plasma flows. Most structures tend to possess large cross helicity, while the residual energy distributes in …
Parker Solar Probe (PSP) entered a region of the sub-Alfvenic solar wind during encounter 8 and we present the first detailed analysis of low-frequency turbulence properties in this novel region. The magnetic field and flow velocity vectors were highly aligned during this interval. By constructing spectrograms of the normalized magnetic helicity, cross helicity, and residual energy, we find that PSP observed primarily Alfvenic fluctuations, a consequence of the highly field-aligned flow that renders quasi-2D fluctuations unobservable to PSP. We extend Taylor hypothesis to sub and super Alfveni…
We present an observational analysis of the electron thermal energy budget using data from Parker Solar Probe. We use the macroscopic moments, obtained from our fits to the measured electron distribution function, to evaluate the thermal energy budget based on the second moment of the Boltzmann equation. We separate contributions to the overall budget from reversible and irreversible processes. We find that an irreversible thermal energy source must be present in the inner heliosphere over the heliocentric distance range from 0.15 to 0.47 au. The divergence of the heat flux is positive at heli…
Solar wind turbulence is anisotropic with respect to the mean magnetic field. Anisotropy leads to ambiguity when interpreting in-situ turbulence observations in the solar wind because an apparent change in the measurements could be due either to the change of intrinsic turbulence properties or to a simple change of the spacecraft sampling direction. We demonstrate the ambiguity using the spectral index and magnetic compressibility in the inertial range observed by the Parker Solar Probe during its first seven orbits ranging from 0.1 to 0.6 AU. To unravel the effects of the sampling direction, …
Observations by the Parker Solar Probe mission of the solar wind at about 35.7 solar radii reveal the existence of whistler wave packets with frequencies below 0.1 f/fce (20-80 Hz in the spacecraft frame). These waves often coincide with local minima of the magnetic field magnitude or with sudden deflections of the magnetic field that are called switchbacks. Their sunward propagation leads to a significant Doppler frequency downshift from 200-300 Hz to 20-80 Hz (from 0.2 f/fce to 0.5 f/fce). The polarization of these waves varies from quasi-parallel to significantly oblique with wave normal an…
The Taylor microscale is a fundamental length scale in turbulent fluids, representing the end of fluid properties and onset of dissipative processes. The Taylor microscale can also be used to evaluate the Reynolds number in classical turbulence theory. Although the solar wind is weakly collisional, it approximately behaves as a magnetohydrodynamic (MHD) fluid at scales larger than the kinetic scale. As a result, classical fluid turbulence theory and formalisms are often used to study turbulence in the MHD range. Therefore, a Taylor microscale can be used to estimate an effective Reynolds numbe…
The fourth orbit of Parker Solar Probe (PSP) reached heliocentric distances down to 27.9 Rs, allowing solar wind turbulence and acceleration mechanisms to be studied in situ closer to the Sun than previously possible. The turbulence properties were found to be significantly different in the inbound and outbound portions of PSP's fourth solar encounter, likely due to the proximity to the heliospheric current sheet (HCS) in the outbound period. Near the HCS, in the streamer belt wind, the turbulence was found to have lower amplitudes, higher magnetic compressibility, a steeper magnetic field spe…
Parallel Diffusion Coefficient of Energetic Charged Particles in the Inner Heliosphere from the Turbulent Magnetic Fields Measured by Parker Solar Probe
One of the most striking observations made by Parker Solar Probe during its first solar encounter is the omnipresence of rapid polarity reversals in a magnetic field that is otherwise mostly radial. These so-called switchbacks strongly affect the dynamics of the magnetic field. We concentrate here on their macroscopic properties. First, we find that these structures are self-similar, and have neither a characteristic magnitude, nor a characteristic duration. Their waiting time statistics shows evidence for aggregation. The associated long memory resides in their occurrence rate, and is not inh…
To understand the nonlinear dynamics of the Parker scenario for coronal heating, long-time high-resolution simulations of the dynamics of a coronal loop in cartesian geometry are carried out. A loop is modeled as a box extended along the direction of the strong magnetic field $B_0$ in which the system is embedded. At the top and bottom plates, which represent the photosphere, velocity fields mimicking photospheric motions are imposed. We show that the nonlinear dynamics is described by different regimes of MHD anisotropic turbulence, with spectra characterized by intertial range power laws who…
Waiting time distributions of solar flares and {\sl coronal mass ejections (CMEs)} exhibit power law-like distribution functions with slopes in the range of $α_τ \approx 1.4-3.2$, as observed in annual data sets during 4 solar cycles (1974-2012). We find a close correlation between the waiting time power law slope $α_τ$ and the {\sl sunspot number (SN)}, i.e., $α_τ$ = 1.38 + 0.01 $\times$ SN. The waiting time distribution can be fitted with a Pareto-type function of the form $N(τ) = N_0$ $(τ_0 + τ)^{-α_τ}$, where the offset $τ_0$ depends on the instrumental sensitivity, the detection threshold…
