ST1.5

To date, Parker Solar Probe has completed ten solar encounters and measured a wealth of in-situ data down to heliocentric distances of ~13 solar radii. This data provides a novel opportunity to investigate the near-Sun environment and understand the young slow solar wind. Typically, the slow solar wind observed in the inner heliosphere is split into an Alfvenic and a non-Alfvenic component. The Alfvenic slow wind is thought to originate from overexpanded coronal hole field lines, whereas the non-Alfvenic slow wind could originate from active regions, transient events, or reconnection at the tips of helmet streamers. In this work, we find structures associated with non-Alfvenic slow wind in the low latitude wind measured by Parker Solar Probe. We identify at least two distinct types of structure using magnetic field magnitude, electron pitch angle distributions, and electron number density. After statistically analysing these structures, with a focus on their plasma properties, shape, and location with respect to the heliospheric current sheet, we link them to solar origins. We find structures that are consistent with the plasma blobs seen previously in remote sensing observations.

How to cite: Woolley, T., Matteini, L., Horbury, T. S., Bale, S. D., Laker, R., Woodham, L. D., and Stawarz, J. E.: Linking In-situ Magnetic and Density Structures in the Low Latitude Slow Solar Wind to Solar Origins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-565, https://doi.org/10.5194/egusphere-egu22-565, 2022.

We report observations of <100 keV/nucleon suprathermal (ST) H, He, O, and Fe ions in association with three separate crossings of the heliospheric current sheet that occurred near perhelia during PSP encounters 7, 8, and 9. In particular, we compare and contrast the ST ion time-intensity profiles, velocity dispersion, pitch-angle distributions, spectral forms, and maximum energies during the three HCS crossings. We find that these unique ST observations are remarkably different in each case, with those during E07 posing the most serious challenges for existing models of ST ion production in the inner heliosphere. In contrast, the ISOIS observations during E08 appear to be consistent with a scenario in which ST ions escape out of the reconnection exhausts into the separatrix layers after getting accelerated up to ~50-100 keV/nucleon by HCS-associated magnetic reconnection-driven processes. Finally, ST ions during the E09 HCS crossing have properties that are somewhat similar to those seen during both E07 and E08 crossings, with ion intensities being higher outside the exhausts and the separatrices, but significant intensity increases are also observed inside the reconnection exhausts. We discuss these new observations in terms of local versus remote acceleration sources as well as in terms of expectations of existing ST ion production and propagation, including reconnection-driven and diffusive acceleration in the inner heliosphere.

How to cite: Desai, M. and the the Parker Solar Probe ISOIS, FIELDS & SWEAP Teams: Suprathermal Ion Observations Associated with the Heliospheric Current Sheet Crossings during Parker Solar Probe Encounters 7, 8, and 9, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1353, https://doi.org/10.5194/egusphere-egu22-1353, 2022.

Near-f_ce harmonic waves are prevalent in the high-frequency electric field spectrum during Parker Solar Probe's (PSP) close encounters with the Sun. These waves are electrostatic and tend to occur in regions of a relatively stable magnetic field with low broadband magnetic fluctuation levels. We show that the emissions of near-f_ce harmonic waves are strongly connected to the magnetic field direction. We express the magnetic field direction in terms of spherical angles, where θ_B is the elevation angle and φ_B is the azimuthal angle. Then, we show that near-f_ce harmonics emissions occur when the magnetic field points in a narrow angular range, bounded by 80° ≤ θ_B ≤ 100° and 10° ≤ φ_B ≤ 30°, in most of the cases. We also show that the influence of magnetic field direction on near-f_ce harmonic waves goes down to the shortest time scales the FIELDS instrument can access. These results suggest that cross-scale interaction might play an essential role in the dynamics of the near-f_ce harmonics measured by PSP at small radial distances from the Sun. It may also provide important clues about the origin of these waves and their role at the early stages of solar wind evolution.

How to cite: F. Tigik, S., Vaivads, A., and M. Malaspina, D.: The emission of near-fce harmonic waves at small radial distances from the Sun, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3195, https://doi.org/10.5194/egusphere-egu22-3195, 2022.

We investigate the polarization of Langmuir waves observed by the Time Domain Sampler (TDS) module of the Radio and Plasma Waves instrument on Solar Orbiter during several extensive Type III burst events. During its two-year-long cruise phase, Solar orbiter often crossed the source region of the Type III radio emission and observed the Langmuir waves generated by solar energetic electrons. The waves are known to exhibit complex modulation and often non-trivial elliptical polarization which sometimes rapidly changes on the timescales of tens of milliseconds. We show that the observed waveforms are typically composed of multiple sub-packets with a relatively short coherence length. We investigate the correlation between the polarization of the waves, simultaneously observed energetic electrons beams and other plasma properties.

How to cite: Soucek, J., Bandara, S., Pisa, D., Santolik, O., Maksimovic, M., Chust, T., Khotyaintsev, Y., Vecchio, A., Kretzschmar, M., Wimmer-Schweingruber, R., Berger, L., Rodriquez-Pacheco, J., and Gomez-Herrero, R.: Polarization of Langmuir waves observed by RPW-TDS instrument on Solar Orbiter during Type III radio bursts, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3859, https://doi.org/10.5194/egusphere-egu22-3859, 2022.

Following their presence during Parker Solar Probe’s (PSP) first encounter, switchbacks have become an active area of research with several proposed mechanisms for their formation. Many of these theories have testable predictions, although it is not trivial to compare simulation results with in-situ data from PSP. For example, there is some debate regarding the deflection direction of switchbacks, with some theories predicting a consistent magnetic deflection in the +T direction in the RTN coordinate system. Such arguments are largely focussed on the first two PSP encounters, as these are the most studied encounters in the literature. We examine the deflection direction of switchbacks for the first eight PSP encounters, with the aim to clear up any ambiguity regarding this property of switchbacks. Much like the earlier results of Horbury et al. 2020 (during the first encounter) we find that switchbacks tend to deflect in the same direction for hours at a time. Although there is some consistency in deflection direction within an individual encounter, crucially we find that there is no preferred deflection direction across all the encounters. We speculate about the cause of these results and what implications they may have for switchback formation theories.

How to cite: Laker, R., Horbury, T., Matteini, L., Woolley, T., Stawarz, J., and Bale, S.: On the Deflections of Switchbacks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3917, https://doi.org/10.5194/egusphere-egu22-3917, 2022.

On November 27, 2021, Solar Orbiter completed its only flyby of Earth on its way to the following Sun’s encounter in March 2022. Although this fast flyby was performed primarily to decrease the spacecraft’s velocity and change orbit to get closer to the Sun, the Radio and Plasma Wave (RPW) instrument had the opportunity to perform high cadence measurements in the Earth’s magnetosphere. We review the main observation of the Time Domain Sampler (TDS) receiver, a part of the RPW instrument, made during this flyby at frequencies below 200 kHz. The TDS receiver operated in a high cadence mode providing us with the regular waveform snapshot with 62 ms length every ten seconds for two electric components. Besides the regular captures, we have got more than five hundred onboard classified snapshots and the statistical products with a sixteen-second cadence. Before entering the terrestrial magnetosphere around 02:30UT, the spacecraft wandered through the foreshock region, registering intense bursts of Langmuir waves. After the bowshock crossing, Solar Orbiter was for more than two hours in the morning sector of the magnetosphere, recording various plasma wave modes. The closest approach was reached at 04:30UT above North Africa at an altitude of 460 km. Then the spacecraft continued into the Earth’s tail and entered the magnetosheath around 13:00UT. After 15:00UT, the Solar Orbiter crossed the bowshock, and bursts of Langmuir waves were detected again pointing out to the deep downstream foreshock region. Further from the Earth, intense Auroral Kilometric Radiation (AKR) at frequencies above 100 kHz was also detected.

How to cite: Pisa, D., Soucek, J., Santolik, O., Hanzelka, M., Maksimovic, M., Vecchio, A., Khotyaintsev, Y., Chust, T., Kretzschmar, M., Matteini, L., and Horbury, T.: Observations of the Time Domain Sampler receiver from the Radio and Plasma Wave instrument during the Solar Orbiter Earth flyby, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4130, https://doi.org/10.5194/egusphere-egu22-4130, 2022.

The recently available novel Parker Solar Probe (PSP) observations allow mapping of the solar wind characteristics in the low solar corona, at only a few tens of solar radii, and study the characteristics of the solar wind and its transients close to the Sun. The first few perihelion passes of the PSP revealed the highly variable structure of the solar wind. These observations provided the unique possibility to study the solar wind originating from small coronal holes. Such studies were previously not possible as the majority of the in situ observations were taken at distances of about 1 AU, and the association of the solar wind originating from the small coronal holes and its sources on the Sun was extremely unreliable. We employ a magnetic connectivity tool (developed by ESA’s MADAWG group) to associate the solar wind parcels observed by the PSP with their source regions on the Sun.  Our study encompasses the first eight PSP perihelion passes, using a time window of about three weeks around each perihelion. The first results indicate that we can well distinguish and identify the solar wind observed by the PSP originating not only from the big, but also from the small coronal holes.

How to cite: Magdalenic, J., Valliappan, S. P., and Rodriguez, L.: Origin of the solar wind observed by PSP, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8923, https://doi.org/10.5194/egusphere-egu22-8923, 2022.

During recent decades, numerous studies were devoted to improve our understanding of the origin and the propagation of the fast solar wind, and its accurate modelling. The solar wind characteristics were poorly mapped up to now by the in situ observations, available mostly only at about 1AU. The novel Parker Solar Probe (PSP) observations, that are employed in this study, allow us to map the solar wind characteristics in the low solar corona at only few tens of solar radii, and to study the solar wind characteristics. These observations are also very important for understanding how accurately we can model the solar wind characteristics employing models such as EUHFORIA (European heliospheric forecasting information asset, Pomoell & Poedts, 2018), at distances rather close to the Sun.
In this study, we inspect the solar wind characteristics during the first eight closest PSP approaches to the Sun. The solar wind plasma characteristics observed by PSP are compared with the modelling results using the default set-up of EUHFORIA. We also calibrate the inner boundary (0.1 AU) conditions in EUHFORIA, but without changing the Wang-Sheeley-Arge formula which describes the solar wind characteristics at the inner boundary. The aim is to better model the solar wind at distances close to the Sun. We also use a magnetic connectivity tool (developed by ESA’s MADAWG group) to better associate the fast solar wind with its source region on the Sun.

How to cite: Valliappan, S. P., Magdalenic, J., Rodriguez, L., Poedts, S., and Samara, E.: Solar wind modelling with EUHFORIA and comparison with the PSP observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8932, https://doi.org/10.5194/egusphere-egu22-8932, 2022.

The solar wind is a highly variable, weakly collisional plasma originating from the Sun. The recent launches of PSP and Solar Orbiter have opened the way for the exploration of the innermost regions of our solar system and will greatly advance our understanding of several plasma phenomena occurring in the near-Sun environment, such as the heating and the acceleration of the solar wind. 

Plasma waves and wave-particle interactions play a relevant role in such phenomena, determining significant deviations of the Velocity Distribution Function (VDF) from the Local Thermodynamic Equilibrium. These deviations retain information of the interaction of particles with the turbulent electromagnetic fields and can be identified as thermal anisotropy, or non-thermal ion beams and heavy ion differential streaming in the ion component of the solar wind. This study will cover these topics with particular reference to new in-situ data from Solar Orbiter, PSP and with observations at L1  (e.g. Wind), with a focus on the central role Alfvénic fluctuations play in the evolution of the VDF features mentioned above.

How to cite: DAmicis, R., Bruno, R., De Marco, R., Velli, M., Telloni, D., Perrone, D., Sorriso-Valvo, L., and Panasenco, O.: Non-thermal features in proton and alpha velocity distribution functions in the solar wind in the inner heliosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12654, https://doi.org/10.5194/egusphere-egu22-12654, 2022.