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 show evidence of aggregation. The associated long memory resides in their occurrence rate, and is not inherent to the background fluctuations. Interestingly, the spectral properties of inertial range turbulence differ inside and outside of switchback structures; in the latter the 1/f range extends to higher frequencies. These results suggest that outside of these structures we are in the presence of lower-amplitude fluctuations with a shorter turbulent inertial range. We conjecture that these correspond to a pristine solar wind.
Measurements of the near-Sun solar wind by the Parker Solar Probe have revealed the presence of large numbers of discrete Alfvénic impulses with an anti-sunward sense of propagation. These are ...similar to those previously observed near 1 au, in high speed streams over the Sun's poles and at 60 solar radii. At 35 solar radii, however, they are typically shorter and sharper than seen elsewhere. In addition, these spikes occur in "patches" and there are also clear periods within the same stream when they do not occur; the timescale of these patches might be related to the rate at which the spacecraft magnetic footpoint tracks across the coronal hole from which the plasma originated. While the velocity fluctuations associated with these spikes are typically under 100 km s−1, due to the rather low Alfvén speeds in the streams observed by the spacecraft to date, these are still associated with large angular deflections of the magnetic field-and these deflections are not isotropic. These deflections do not appear to be related to the recently reported large-scale, pro-rotation solar wind flow. Estimates of the size and shape of the spikes reveal high aspect ratio flow-aligned structures with a transverse scale of 104 km. These events might be signatures of near-Sun impulsive reconnection events.
NASA's Van Allen Probes observed significant, long‐lived fluxes of inner belt electrons up to ∼1 MeV after geomagnetic storms in March and June 2015. Reanalysis of Magnetic Electron Ion Spectrometer ...(MagEIS) data with improved background correction showed a clearer picture of the relativistic electron population that persisted through 2016 and into 2017 above the Fennell et al. (2015, https://doi.org/10.1002/2014gl062874) limit. The intensity and duration of these enhancements allow estimation of decay timescales for comparison with simulated decay rates and theoretical lifetimes. We compare decay timescales from these data and DREAM3D simulations based on them using geomagnetic activity‐dependent pitch angle diffusion coefficients derived from plasmapause‐indexed wave data (Malaspina et al., 2016, https://doi.org/10.1002/2016gl069982, 2018, https://doi.org/10.1029/2018gl078564) and phase space densities derived from MagEIS observations. Simulated decay rates match observed decay rates more closely than the theoretical lifetime due to significantly nonequilibrium pitch angle distributions in simulation and data. We conclude that nonequilibrium effects, rather than a missing diffusion or loss process, account for observed short decay rates.
Plain Language Summary
Earth's radiation belts are influenced by a wide variety of source and loss processes, so it is difficult to model and forecast its evolution or predict its effects on spaceborne assets. Decay timescales for loss processes are essential to understanding this balance, but the theoretical predictions for these timescales in the inner radiation belt can exceed the observed decay times by an order of magnitude or more. We have observed and simulated an exceptional period of radiation belt injection and decay to understand this discrepancy. We have found that changes in the wave properties due to geomagnetic activity can account for the difference: changes in the equilibrium distribution associated with the wave environment result in consistent refilling of non‐equilibrium modes that decay much faster than the equilibrium mode.
Key Points
DREAM3D simulations of Earth's inner electron belt, based on Van Allen Probes observations, are carried out to evaluate model decay rates
Pitch angle diffusion using coefficients reflecting geomagnetic activity demonstrates realistic decay rates
Decay rates extracted with a Random Sample Consensus‐based algorithm from modeled and observed fluxes agree, while theoretical lifetimes are too long
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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, a better understanding of the radio wave propagation provides indirect information on the relative density fluctuations, , at the effective turbulence scale length. Here, we analyzed 30 type III bursts detected by Parker Solar Probe (PSP). For the first time, we retrieved type III burst decay times, , between 1 and 10 MHz thanks to an unparalleled temporal resolution of PSP. We observed a significant deviation in a power-law slope for frequencies above 1 MHz when compared to previous measurements below 1 MHz by the twin-spacecraft Solar TErrestrial RElations Observatory (STEREO) mission. We note that altitudes of radio bursts generated at 1 MHz roughly coincide with an expected location of the Alfvén point, where the solar wind becomes super-Alfvénic. By comparing PSP observations and Monte Carlo simulations, we predict relative density fluctuations, ϵ, at the effective turbulence scale length at radial distances between 2.5 and 14 to range from 0.22 to 0.09. Finally, we calculated relative density fluctuations, ϵ, measured in situ by PSP at a radial distance from the Sun of 35.7 during perihelion #1, and perihelion #2 to be 0.07 and 0.06, respectively. It is in a very good agreement with previous STEREO predictions ( ) obtained by remote measurements of radio sources generated at this radial distance.
Heat transport in the solar corona and wind is still a major unsolved astrophysical problem. Because of the key role played by electrons, the electron density and temperature(s) are important ...prerequisites for understanding these plasmas. We present such in situ measurements along the two first solar encounters of the Parker Solar Probe, between 0.5 and 0.17 au from the Sun, revealing different states of the emerging solar wind near the solar activity minimum. These preliminary results are obtained from a simplified analysis of the plasma quasi-thermal noise (QTN) spectrum measured by the Radio Frequency Spectrometer (FIELDS). The local electron density is deduced from the tracking of the plasma line, which enables accurate measurements, independent of calibrations and spacecraft perturbations, whereas the temperatures of the thermal and suprathermal components of the velocity distribution, as well as the average kinetic temperature, are deduced from the shape of the plasma line. The temperature of the weakly collisional thermal population, similar for both encounters, decreases with the distance as R−0.74, which is much slower than adiabatic. In contrast, the temperature of the nearly collisionless suprathermal population exhibits a virtually flat radial variation. The 7 s resolution of the density measurements enables us to deduce the low-frequency spectrum of compressive fluctuations around perihelion, varying as f−1.4. This is the first time that QTN spectroscopy is implemented with an electric antenna length not exceeding the plasma Debye length. As PSP will approach the Sun, the decrease in the Debye length is expected to considerably improve the accuracy of the temperature measurements.
The available magnetic field data from the terrestrial magnetosphere, solar wind and planetary magnetospheres exceeds over 106 hours. Identifying plasma waves in these large data sets is a time ...consuming and tedious process. In this Paper, we propose a solution to this problem. We demonstrate how self‐organizing maps (SOMs) can be used for rapid data reduction and identification of plasma waves in large data sets. We use 72,000 fluxgate and 110,000 search coil magnetic field power spectra from the Magnetospheric Multiscale Mission (MMS1) and show how the SOM sorts the power spectra into groups based on their shape. Organizing the data in this way makes it very straightforward to identify power spectra with similar properties and therefore this technique greatly reduces the need for manual inspection of the data. We suggest that SOMs offer a time effective and robust technique, which can significantly accelerate the processing of magnetic field data and discovery of new wave forms.
Key Points
We develop a robust method to classify large data sets of power spectra of magnetic field
The technique significantly reduces the need for time consuming manual inspection of the data and allows the discovery of new wave forms
The classification technique can be used to categorize plasma waves based on frequency, amplitude and bandwidth
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We compare magnetic field measurements taken by the FIELDS instrument on board Parker Solar Probe (PSP) during its first solar encounter to predictions obtained by potential field source surface ...(PFSS) modeling. Ballistic propagation is used to connect the spacecraft to the source surface. Despite the simplicity of the model, our results show striking agreement with PSP's first observations of the heliospheric magnetic field from ∼0.5 au (107.5 R ) down to 0.16 au (35.7 R ). Further, we show the robustness of the agreement is improved both by allowing the photospheric input to the model to vary in time, and by advecting the field from PSP down to the PFSS model domain using in situ PSP/Solar Wind Electrons Alphas and Protons measurements of the solar wind speed instead of assuming it to be constant with longitude and latitude. We also explore the source surface height parameter (RSS) to the PFSS model, finding that an extraordinarily low source surface height (1.3-1.5 R ) predicts observed small-scale polarity inversions, which are otherwise washed out with regular modeling parameters. Finally, we extract field line traces from these models. By overlaying these on extreme ultraviolet images we observe magnetic connectivity to various equatorial and mid-latitude coronal holes, indicating plausible magnetic footpoints and offering context for future discussions of sources of the solar wind measured by PSP.
Magnetic Field Kinks and Folds in the Solar Wind Tenerani, Anna; Velli, Marco; Matteini, Lorenzo ...
The Astrophysical journal. Supplement series,
02/2020, Volume:
246, Issue:
2
Journal Article
Peer reviewed
Open access
Parker Solar Probe (PSP) observations during its first encounter at 35.7 R have shown the presence of magnetic field lines that are strongly perturbed to the point that they produce local inversions ...of the radial magnetic field, known as switchbacks. Their counterparts in the solar wind velocity field are local enhancements in the radial speed, or jets, displaying (in all components) the velocity-magnetic field correlation typical of large amplitude Alfvén waves propagating away from the Sun. Switchbacks and radial jets have previously been observed over a wide range of heliocentric distances by Helios, Wind, and Ulysses, although they were prevalent in significantly faster streams than seen at PSP. Here we study via numerical magnetohydrodynamics simulations the evolution of such large amplitude Alfvénic fluctuations by including, in agreement with observations, both a radial magnetic field inversion and an initially constant total magnetic pressure. Despite the extremely large excursion of magnetic and velocity fields, switchbacks are seen to persist for up to hundreds of Alfvén crossing times before eventually decaying due to the parametric decay instability. Our results suggest that such switchback/jet configurations might indeed originate in the lower corona and survive out to PSP distances, provided the background solar wind is sufficiently calm, in the sense of not being pervaded by strong density fluctuations or other gradients, such as stream or magnetic field shears, that might destabilize or destroy them over shorter timescales.
Abstract
A database of in situ dust impact detections made by the Parker Solar Probe spacecraft is created to facilitate studies of interplanetary dust dynamics in the inner heliosphere. A ...standardized dust detection methodology is established and tested for validity. Individual impact detections are included in the database, and are used to derive dust impact rates. Impact rates are corrected for effects related to high-amplitude plasma waves and undercounting due to finite detection window duration. These corrections suggest that: (i) most dust impacts on Parker Solar Probe are consistent with a random process; and (ii) the true dust impact rate may be ∼50% greater than the impact rate determined using uncorrected data for certain portions of the orbit, especially near perihelion.
Statistical properties of low‐frequency plasmaspheric hiss Malaspina, David M.; Jaynes, Allison N.; Hospodarsky, George ...
Journal of geophysical research. Space physics,
August 2017, 2017-08-00, 20170801, Volume:
122, Issue:
8
Journal Article
Peer reviewed
Plasmaspheric hiss is an important wave mode for the dynamics of inner terrestrial magnetosphere plasma populations. It acts to scatter high‐energy electrons out of trapped orbits about Earth and ...into the atmosphere, defining the inner edge of the radiation belts over a range of energies. A low‐frequency component of hiss was recently identified and is important for its ability to interact with higher‐energy electrons compared to typically considered hiss frequencies. This study compares the statistical properties of low‐ and high‐frequency plasmaspheric hiss in the terrestrial magnetosphere, demonstrating that they are statistically distinct wave populations. Low‐frequency hiss shows different behavior in frequency space, different spatial localization (in magnetic local time and radial distance), and different amplitude distributions compared to high‐frequency hiss. The observed statistical properties of low‐frequency hiss are found to be consistent with recently developed theories for low‐frequency hiss generation. The results presented here suggest that careful consideration of low‐frequency hiss properties can be important for accurate inclusion of this wave population in predictive models of inner magnetosphere plasma dynamics.
Key Points
Low‐ and high‐frequency plasmaspheric hiss are found to be statistically distinct wave populations
Low‐ and high‐frequency hiss wave power have different spatial and frequency distributions
Proper statistical treatment of low‐frequency hiss is important for predictive models of particle loss by hiss in the inner magnetosphere
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