Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The physical mechanisms that produce the slow solar wind are still highly debated. <jats:italic>Parker Solar Probe</jats:italic>’s (<jats:italic>PSP</jats:italic>’s) second solar encounter provided a new opportunity to relate in situ measurements of the nascent slow solar wind with white-light images of streamer flows. We exploit data taken by the <jats:italic>Solar and Heliospheric Observatory</jats:italic>, the <jats:italic>Solar TErrestrial RElations Observatory</jats:italic> (<jats:italic>STEREO</jats:italic>), and the Wide Imager on Solar Probe to reveal for the first time a close link between imaged streamer flows and the high-density plasma measured by the Solar Wind Electrons Alphas and Protons (SWEAP) experiment. We identify different types of slow winds measured by <jats:italic>PSP</jats:italic> that we relate to the spacecraft’s magnetic connectivity (or not) to streamer flows. SWEAP measured high-density and highly variable plasma when <jats:italic>PSP</jats:italic> was well connected to streamers but more tenuous wind with much weaker density variations when it exited streamer flows. <jats:italic>STEREO</jats:italic> imaging of the release and propagation of small transients from the Sun to <jats:italic>PSP</jats:italic> reveals that the spacecraft was continually impacted by the southern edge of streamer transients. The impact of specific density structures is marked by a higher occurrence of magnetic field reversals measured by the FIELDS magnetometers. Magnetic reversals are associated with much stronger density variations inside than outside streamer flows. We tentatively interpret these findings in terms of magnetic reconnection between open magnetic fields and coronal loops with different properties, providing support for the formation of a subset of the slow wind by magnetic reconnection.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Solar Probe Cup (SPC) is a Faraday cup instrument on board NASA’s <jats:italic>Parker Solar Probe</jats:italic> (<jats:italic>PSP</jats:italic>) spacecraft designed to make rapid measurements of thermal coronal and solar wind plasma. The spacecraft is in a heliocentric orbit that takes it closer to the Sun than any previous spacecraft, allowing measurements to be made where the coronal and solar wind plasma is being heated and accelerated. The SPC instrument was designed to be pointed directly at the Sun at all times, allowing the solar wind (which is flowing primarily radially away from the Sun) to be measured throughout the orbit. The instrument is capable of measuring solar wind ions with an energy between 100 and 6000 V (protons with speeds from 139 to 1072 km s<jats:sup>−1</jats:sup>). It also measures electrons with an energy/charge between 100 and 1500 V. SPC has been designed to have a wide dynamic range that is capable of measuring protons and alpha particles at the closest perihelion (9.86 solar radii from the center of the Sun) and out to 0.25 au. Initial observations from the first orbit of <jats:italic>PSP</jats:italic> indicate that the instrument is functioning well.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>On 2019 April 5, while the <jats:italic>Parker Solar Probe</jats:italic> was at its 35 solar radius perihelion, the data set collected at 293 samples/s contained more than 10,000 examples of spiky electric-field-like structures with durations less than 200 milliseconds and amplitudes greater than 10 mV m<jats:sup>−1</jats:sup>. The vast majority of these events were caused by plasma turbulence. Defining dust events as those with similar, narrowly peaked, positive, and 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 dust events expected from other techniques. Defining time domain structures (TDS) as those with opposite polarity signals in the opposite antennas resulted in finding 238 clear TDS events which, after correcting for the detection efficiency, resulted in an estimated 500–1000 TDS events on this day. The TDS electric fields were bipolar, as expected for electron holes. Several events were found at times when the magnetic field was in the plane of the two measured components of the electric field such that the component of the electric field parallel to the magnetic field was measured. One example of significant parallel electric fields shows the negative potential that classified them as electron holes. Because the TDS observation rate was not uniform with time, it is likely that there were local regions below the spacecraft with field-aligned currents that generated the TDS.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this work, we present the first results from the flux angle (FA) operation mode of the Faraday Cup instrument on board the <jats:italic>Parker Solar Probe</jats:italic> (<jats:italic>PSP</jats:italic>). The FA mode allows rapid measurements of phase space density fluctuations close to the peak of the proton velocity distribution function with a cadence of 293 Hz. This approach provides an invaluable tool for understanding kinetic-scale turbulence in the solar wind and solar corona. We describe a technique to convert the phase space density fluctuations into vector velocity components and compute several turbulence parameters, such as spectral index, residual energy, and cross helicity during two intervals when the FA mode was used in <jats:italic>PSP</jats:italic>’s first encounter at 0.174 au distance from the Sun.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The first two orbits of the <jats:italic>Parker Solar Probe</jats:italic> spacecraft have enabled the first in situ measurements of the solar wind down to a heliocentric distance of 0.17 au (or 36 <jats:inline-formula> <jats:tex-math> <?CDATA ${R}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsab60a3ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>). Here, we present an analysis of this data to study solar wind turbulence at 0.17 au and its evolution out to 1 au. While many features remain similar, key differences at 0.17 au include increased turbulence energy levels by more than an order of magnitude, a magnetic field spectral index of −3/2 matching that of the velocity and both Elsasser fields, a lower magnetic compressibility consistent with a smaller slow-mode kinetic energy fraction, and a much smaller outer scale that has had time for substantial nonlinear processing. There is also an overall increase in the dominance of outward-propagating Alfvénic fluctuations compared to inward-propagating ones, and the radial variation of the inward component is consistent with its generation by reflection from the large-scale gradient in Alfvén speed. The energy flux in this turbulence at 0.17 au was found to be ∼10% of that in the bulk solar wind kinetic energy, becoming ∼40% when extrapolated to the Alfvén point, and both the fraction and rate of increase of this flux toward the Sun are consistent with turbulence-driven models in which the solar wind is powered by this flux.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Integrated Science Investigation of the Sun (IS⊙IS) suite on board NASA’s <jats:italic>Parker Solar Probe</jats:italic> (<jats:italic>PSP</jats:italic>) observed six distinct enhancements in the intensities of suprathermal-through-energetic (∼0.03–3 MeV nucleon<jats:sup>−1</jats:sup>) He ions associated with corotating or stream interaction regions (CIR or SIR) during its first two orbits. Our results from a survey of the time histories of the He intensities, spectral slopes, and anisotropies and the event-averaged energy spectra during these events show the following: (1) In the two strongest enhancements, seen at 0.35 and 0.85 au, the higher-energy ions arrive and maximize later than those at lower energies. In the event seen at 0.35 au, the He ions arrive when <jats:italic>PSP</jats:italic> was away from the SIR trailing edge and entered the rarefaction region in the high-speed stream. (2) The He intensities either are isotropic or show sunward anisotropies in the spacecraft frame. (3) In all events, the energy spectra between ∼0.2 and 1 MeV nucleon<jats:sup>−1</jats:sup> are power laws of the form ∝<jats:italic>E</jats:italic> <jats:sup>−2</jats:sup>. In the two strongest events, the energy spectra are well represented by flat power laws between ∼0.03 and 0.4 MeV nucleon<jats:sup>−1</jats:sup> modulated by exponential rollovers between ∼0.4 and 3 MeV nucleon<jats:sup>−1</jats:sup>. We conclude that the SIR-associated He ions originate from sources or shocks beyond <jats:italic>PSP</jats:italic>’s location rather than from acceleration processes occurring at nearby portions of local compression regions. Our results also suggest that rarefaction regions that typically follow the SIRs facilitate easier particle transport throughout the inner heliosphere such that low-energy ions do not undergo significant energy loss due to adiabatic deceleration, contrary to predictions of existing models.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>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, <jats:inline-formula> <jats:tex-math> <?CDATA $\epsilon =\langle \delta n\rangle /\langle n\rangle $?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsab65bdieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, at the effective turbulence scale length. Here, we analyzed 30 type III bursts detected by <jats:italic>Parker Solar Probe</jats:italic> (<jats:italic>PSP</jats:italic>). For the first time, we retrieved type III burst decay times, <jats:inline-formula> <jats:tex-math> <?CDATA ${\tau }_{{\rm{d}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsab65bdieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, between 1 and 10 MHz thanks to an unparalleled temporal resolution of <jats:italic>PSP</jats:italic>. 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 <jats:italic>Solar TErrestrial RElations Observatory</jats:italic> (<jats:italic>STEREO</jats:italic>) 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 <jats:italic>PSP</jats:italic> observations and Monte Carlo simulations, we predict relative density fluctuations, <jats:italic>ϵ</jats:italic>, at the effective turbulence scale length at radial distances between 2.5 and 14 <jats:inline-formula> <jats:tex-math> <?CDATA ${R}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsab65bdieqn3.gif" xlink:type="simple" /> </jats:inline-formula> to range from 0.22 to 0.09. Finally, we calculated relative density fluctuations, <jats:italic>ϵ</jats:italic>, measured in situ by <jats:italic>PSP</jats:italic> at a radial distance from the Sun of 35.7 <jats:inline-formula> <jats:tex-math> <?CDATA ${R}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsab65bdieqn4.gif" xlink:type="simple" /> </jats:inline-formula> during perihelion #1, and perihelion #2 to be 0.07 and 0.06, respectively. It is in a very good agreement with previous <jats:italic>STEREO</jats:italic> predictions (<jats:inline-formula> <jats:tex-math> <?CDATA $\epsilon =0.06\mbox{--}0.07$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsab65bdieqn5.gif" xlink:type="simple" /> </jats:inline-formula>) obtained by remote measurements of radio sources generated at this radial distance.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Wide-field Imager for Solar PRobe (WISPR) obtained the first high-resolution images of coronal rays at heights below 15 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub> when the <jats:italic>Parker Solar Probe</jats:italic> (<jats:italic>PSP</jats:italic>) was located inside 0.25 au during the first encounter. We exploit these remarkable images to reveal the structure of coronal rays at scales that are not easily discernible in images taken from near 1 au. To analyze and interpret WISPR observations, which evolve rapidly both radially and longitudinally, we construct a latitude versus time map using the full WISPR data set from the first encounter. From the exploitation of this map and also from sequential WISPR images. we show the presence of multiple substructures inside streamers and pseudostreamers. WISPR unveils the fine-scale structure of the densest part of streamer rays that we identify as the solar origin of the heliospheric plasma sheet typically measured in situ in the solar wind. We exploit 3D magnetohydrodynamic models, and we construct synthetic white-light images to study the origin of the coronal structures observed by WISPR. Overall, including the effect of the spacecraft relative motion toward the individual coronal structures, we can interpret several observed features by WISPR. Moreover, we relate some coronal rays to folds in the heliospheric current sheet that are unresolved from 1 au. Other rays appear to form as a result of the inherently inhomogeneous distribution of open magnetic flux tubes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Switchbacks (rotations of the magnetic field) are observed on the <jats:italic>Parker Solar Probe</jats:italic>. Their evolution, content, and plasma effects are studied in this paper. The solar wind does not receive a net acceleration from switchbacks that it encountered upstream of the observation point. The typical switchback rotation angle increased with radial distance. Significant Poynting fluxes existed inside, but not outside, switchbacks, and the dependence of the Poynting flux amplitude on the switchback radial location and rotation angle is explained quantitatively as being proportional to (<jats:italic>B</jats:italic> sin(<jats:italic>θ</jats:italic>))<jats:sup>2</jats:sup>. The solar wind flow inside switchbacks was faster than that outside due to the frozen-in ions moving with the magnetic structure at the Alfvén speed. This energy gain results from the divergence of the Poynting flux from outside to inside the switchback, which produces a loss of electromagnetic energy on switchback entry and recovery of that energy on exit, with the lost energy appearing in the plasma flow. Switchbacks contain 0.3–10 Hz waves that may result from currents and the Kelvin–Helmholtz instability that occurs at the switchback boundaries. These waves may combine with lower frequency magnetohydrodynamic waves to heat the plasma.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In the first orbit of the <jats:italic>Parker Solar Probe</jats:italic> (<jats:italic>PSP</jats:italic>), in situ thermal plasma and magnetic field measurements were collected as close as 35 <jats:italic>R</jats:italic> <jats:sub>Sun</jats:sub> from the Sun, an environment that had not been previously explored. During the first orbit of <jats:italic>PSP</jats:italic>, the spacecraft flew through a streamer blowout coronal mass ejection (SBO-CME) on 2018 November 11 at 23:50 UT as it exited the science encounter. The SBO-CME on November 11 was directed away from the Earth and was not visible by L1 or Earth-based telescopes due to this geometric configuration. However, <jats:italic>PSP</jats:italic> and the <jats:italic>STEREO</jats:italic> <jats:italic>-A</jats:italic> spacecraft were able to make observations of this slow (<jats:italic>v</jats:italic> ≈ 380 km s<jats:sup>−1</jats:sup>) SBO-CME. Using the <jats:italic>PSP</jats:italic> data, <jats:italic>STEREO</jats:italic>-<jats:italic>A</jats:italic> images, and Wang–Sheeley–Arge model, the source region of the CME is found to be a helmet streamer formed between the northern polar coronal hole and a mid-latitude coronal hole. Using the YGUAZU-A model, the propagation of the CME is traced from the source at the Sun to <jats:italic>PSP</jats:italic>. This model predicts the travel time of the flux rope to the <jats:italic>PSP</jats:italic> spacecraft as 30 hr, which is within 0.33 hr of the actual measured arrival time. The in situ Solar Wind Electrons Alphas and Protons data were examined to determine that no shock was associated with this SBO-CME. Modeling of the SBO-CME shows that no shock was present at <jats:italic>PSP</jats:italic>; however, at other positions along the SBO-CME front, a shock could have formed. The geometry of the event requires in situ and remote sensing observations to characterize the SBO-CME and further understand its role in space weather.</jats:p>