Nonlinear Analysis of Radial Evolution of Solar Wind in the Inner Heliosphere
<p>The electrons in the solar wind exhibit an interesting kinetic substructure with many important implications for the overall energetics of the plasma in the heliosphere. We are especially interested in the formation and evolution of the electron strahl, a field-aligned beam of superthermal electrons, in the heliosphere. We develop a kinetic transport equation for typical heliospheric conditions based on a Parker-spiral geometry of the magnetic field. We present the results of our theoretical model for the radial evolution of the electron velocity distribution function (VDF) in the solar wind. We study the effects of the adiabatic focusing of energetic electrons, wave-particle interactions, and Coulomb collisions through a generalized kinetic equation for the electron VDF. We compare and contrast our results with the observed effects in the electron VDFs from space missions that explore the radial evolution of electrons in the inner heliosphere such as Helios, Parker Solar Probe, and Solar Orbiter.</p>
Evolution of the MHD turbulence properties in the inner heliosphere with the PSP/SolO alignment data
<p>Radial alignments between pairs of spacecraft is the only way to observationally investigate the turbulent evolution of the solar wind as it expands throughout interplanetary space. On September 2020 Parker Solar Probe (PSP) and Solar Orbiter (SolO) were nearly perfectly radially aligned, with PSP orbiting around its perihelion at 0.1 au (and crossing the nominal Alfv&#233;n point) and SolO at 1 au. PSP/SolO joint observations of the same solar wind plasma allow the extraordinary and unprecedented opportunity to study how the turbulence properties of the solar wind evolve in the inner heliosphere over the wide distance of 0.9 au. The radial evolution of (i) the MHD properties (such as radial dependence of low- and high-frequency breaks, compressibility, Alfv&#233;nic content of the fluctuations), (ii) the polarization status, (iii) the presence of wave modes at kinetic scale as well as their distribution in the plasma instability-temperature anisotropy plane are just few instances of what can be addressed. Of furthest interest is the study of whether and how the cascade transfer and dissipation rates evolve with the solar distance, since this has great impact on the fundamental plasma physical processes related to the heating of the solar wind. In this talk I will present some of the results obtained by exploiting the PSP/SolO alignment data.</p>
The evolution of inverted magnetic fields through the inner heliosphere
ABSTRACT Local inversions are often observed in the heliospheric magnetic field (HMF), but their origins and evolution are not yet fully understood. Parker Solar Probe has recently observed rapid, Alfvénic, HMF inversions in the inner heliosphere, known as ‘switchbacks’, which have been interpreted as the possible remnants of coronal jets. It has also been suggested that inverted HMF may be produced by near-Sun interchange reconnection; a key process in mechanisms proposed for slow solar wind release. These cases suggest that the source of inverted HMF is near the Sun, and it follows that these inversions would gradually decay and straighten as they propagate out through the heliosphere. Alternatively, HMF inversions could form during solar wind transit, through phenomena such velocity shears, draping over ejecta, or waves and turbulence. Such processes are expected to lead to a qualitatively radial evolution of inverted HMF structures. Using Helios measurements spanning 0.3–1 au, we examine the occurrence rate of inverted HMF, as well as other magnetic field morphologies, as a function of radial distance r, and find that it continually increases. This trend may be explained by inverted HMF observed between 0.3 and 1 au being primarily driven by one or more of the above in-transit processes, rather than created at the Sun. We make suggestions as to the relative importance of these different processes based on the evolution of the magnetic field properties associated with inverted HMF. We also explore alternative explanations outside of our suggested driving processes which may lead to the observed trend.
<div> <div>The 4th encounter (~30 Rs away from the sun) of the Parker Solar Probe (PSP) is a great opportunity to observe the radial evolution of the solar wind from the inner heliosphere to the near-earth environment when the sun, PSP, and the earth are quasi-radial aligned. Similar features of the solar wind are observed from both PSP and Wind (at 1 au) measurements. The accelerating-solar-wind model could be more suitable than the constant speed model for the observation, which means the solar wind is still accelerating from 30 Rs to 1 au. Both PSP and Wind measure the co-existence of the Alfvenic and compressive fluctuations in the solar wind. The correlated radial velocity (dVR), proton density (dn) and temperature (dT) fluctuations indicate the nature of the compressive fluctuations are outward-propagating slow waves. However, dn and dB is not correlated from PSP, but correlated from Wind, which indicates the propagating direction of the slow waves is changed. Comparing the radial evolution of the energies of both Alfvenic and compressive fluctuations with the WKB model, we find the observed energy decays slower than the theoretical prediction, which indicates an extra energy injection during the solar wind propagation.</div> 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--></p>
<p>The first four orbits of Parker Solar Probe (PSP) consists of many observations of stream interaction regions (SIRs), which form when fast solar wind streams overtake slower solar wind. While it is known that SIRs accelerate ions in the heliosphere and can trigger geomagnetic storms, the temporal and radial evolution of SIRs is still an active topic of research. During the first four orbits of PSP, SIRs were observed by PSP at small heliospheric distances, as well as at 1 au by the Advanced Composition Explorer (ACE), Wind, and Solar Terrestrial Relations Observatory (STEREO) missions. These SIRs are observed not only at different heliospheric distances, but also at different points in the temporal development of the stream interface. Through analyzing the various SIRs together, insight can be gained in regards to the spatial and temporal evolution of SIR characteristics, as well as to the mechanisms of particle acceleration and transport along the SIR interface. The general characteristics of SIRs observed by PSP during the first four orbits are presented, and an in-depth comparison of a few of the SIR events is conducted to further analyze the evolution of SIR streams in the inner heliosphere. These observations show examples of a fast solar wind stream steepening into an SIR, with evidence of locally accelerated particles via compressive mechanisms at the interface distinguishable from observations of particles likely accelerated at shocks formed at larger heliospheric distances.</p>
<p>Local inversions, or &#8216;switchbacks&#8217;, in the heliospheric magnetic field (HMF) have recently been identified as prominent features in the inner heliosphere through observations by Parker Solar Probe. These inversions coincide with spikes in radial velocity, and have been interpreted as possibly being the result of jets originating in the corona. While magnetic inversions with similar properties to these jets have also been observed by Helios around its perihelion of ~0.3 AU, inversions with a range of properties and scales have long been studied at distances of 1 AU and beyond. The processes which form the inversions seen outside of 0.3 AU, and whether they are a result of solar wind formation in the solar corona or the transport of solar wind through the heliosphere, are not clear. We present a statistical study on the occurrence of inverted heliospheric magnetic field using Helios 1 observations spanning heliocentric distances 0.3&#8212;1 AU. The evolution of inversion occurrence allows us to identify probable locations in the heliosphere where inversions may be produced. Based on these results, we make suggestions as to which processes are most likely responsible for inverted HMF observed between 0.3 and 1 AU.</p>
ABSTRACT A strong correlation between speed and proton temperature has been observed, across many years, on hourly averaged measurements in the solar wind. Here, we show that this relationship is also observed at a smaller scale on intervals of a few days, within a single stream. Following the radial evolution of a well-defined stream of coronal-hole plasma, we show that the temperature–speed (T–V) relationship evolves with distance, implying that the T–V relationship at 1 au cannot be used as a proxy for that near the Sun. We suggest that this behaviour could be a combination of the anticorrelation between speed and flux-tube expansion factor near the Sun and the effect of a continuous heating experienced by the plasma during the expansion. We also show that the cooling index for the radial evolution of the temperature is a function of the speed. In particular, T⊥ in faster wind, although higher close to the Sun, decreases more quickly with respect to slower wind, suggesting that it has less time to interact with the mechanism(s) able to heat the plasma. Finally, we predict the expected T–V relationship in fast streams closer to the Sun with respect to the Helios observations, which Parker Solar Probe will explore in the near future.
