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Register a new userEvolution of a Streamer-Blowout CME as Observed by Imagers on Parker Solar Probe and the Solar Terrestrial Relations Observatory
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Context: On 26-27 January 2020, the wide-field imager WISPR on Parker Solar Probe (PSP) observed a coronal mass ejection (CME) from a distance of approximately 30 solar radii as it passed through the instruments 95 degree field-of-view, providing an unprecedented view of the flux rope morphology of the CMEs internal structure. The same CME was seen by STEREO, beginning on 25 January. Aims: Our goal was to understand the origin and determine the trajectory of this CME. Methods: We analyzed data from three well-placed spacecraft: Parker Solar Probe (PSP), Solar Terrestrial Relations Observatory-Ahead (STEREO-A), and Solar Dynamics Observatory (SDO). The CME trajectory was determined using the method described in Liewer et al. (2020) and verified using simultaneous images of the CME propagation from STEREO-A. The fortuitous alignment with STEREO-A also provided views of coronal activity leading up to the eruption. Observations from SDO, in conjunction with potential magnetic field models of the corona, were used to analyze the coronal magnetic evolution for the three days leading up to the flux rope ejection from the corona on 25 January. Results: We found that the 25 January CME is likely the end result of a slow magnetic flux rope eruption that began on 23 January and was observed by STEREO-A/Extreme Ultraviolet Imager (EUVI). Analysis of these observations suggest that the flux rope was apparently constrained in the corona for more than a day before its final ejection on 25 January. STEREO-A/COR2 observations of swelling and brightening of the overlying streamer for several hours prior to eruption on January 25 led us to classify this as a streamer-blowout CME. The analysis of the SDO data suggests that restructuring of the coronal magnetic fields caused by an emerging active region led to the final ejection of the flux rope.
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A series of solar energetic particle (SEP) events were observed at Parker Solar Probe (PSP) by the Integrated Science Investigation of the Sun (ISOIS) during the period from April 18, 2019 through April 24, 2019. The PSP spacecraft was located near 0.48 au from the Sun on Parker spiral field lines that projected out to 1 au within $sim 25^circ$ of near Earth spacecraft. These SEP events, though small compared to historically large SEP events, were amongst the largest observed thus far in the PSP mission and provide critical information about the space environment inside 1 au during SEP events. During this period the Sun released multiple coronal mass ejections (CMEs). One of these CMEs observed was initiated on April 20, 2019 at 01:25 UTC, and the interplanetary CME (ICME) propagated out and passed over the PSP spacecraft. Observations by the Electromagnetic Fields Investigation (FIELDS) show that the magnetic field structure was mostly radial throughout the passage of the compression region and the plasma that followed, indicating that PSP did not directly observe a flux rope internal to the ICME, consistent with the location of PSP on the ICME flank. Analysis using relativistic electrons observed near Earth by the Electron, Proton and Alpha Monitor (EPAM) on the Advanced Composition Explorer (ACE) demonstrates the presence of electron seed populations (40--300 keV) during the events observed. The energy spectrum of the ISOIS~ observed proton seed population below 1 MeV is close to the limit of possible stationary state plasma distributions out of equilibrium. ISOIS~ observations reveal the revise{enhancement} of seed populations during the passage of the ICME, which revise{likely indicates a key part} of the pre-acceleration process that occurs close to the Sun.
The physical mechanisms that produce the slow solar wind are still highly debated. Parker Solar Probes (PSPs) 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 Solar and Heliospheric Observatory (SOHO), the Solar TErrestrial RElations Observatory (STEREO) 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 PSP that we relate to the spacecrafts magnetic connectivity (or not) to streamer flows. SWEAP measured high-density and highly variable plasma when PSP was well connected to streamers but more tenuous wind with much weaker density variations when it exited streamer flows. STEREO imaging of the release and propagation of small transients from the Sun to PSP 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 originating from the streamers are associated with larger density variations compared with reversals originating outside streamers. 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.
We make use of the Parker Solar Probe (PSP) data to explore the nature of solar wind turbulence focusing on the Alfvenic 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 solar wind streams and distance from the Sun. A more in-depth analysis from several selected periods is also presented. Our results show that as fluctuations are transported outward by the solar wind, the magnetic field spectrum steepens while the shape of the velocity spectrum remains unchanged. The steepening process is controlled by the age of the turbulence, determined by the wind speed together with the radial distance. Statistically, faster solar wind has higher Alfvenicity, with more dominant outward propagating wave component and more balanced magnetic/kinetic energies. The outward wave dominance gradually weakens with radial distance, while the excess of magnetic energy is found to be stronger as we move closer toward the Sun. We show that the turbulence properties can vary significantly stream to stream even if these streams are of similar speed, indicating very different origins of these streams. Especially, the slow wind that originates near the polar coronal holes has much lower Alfvenicity compared with the slow wind that originates from the active regions/pseudostreamers. We show that structures such as heliospheric current sheets and velocity shears can play an important role in modifying the properties of the turbulence.
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 $epsilon=langledelta nrangle/langle nrangle$ 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 $tau_{rm{d}}$ between 1 MHz 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 Alfv{e}n point, where the solar wind becomes super-Alfv{e}nic. By comparing PSP observations and Monte Carlo simulations, we predict relative density fluctuations $epsilon$ at the effective turbulence scale length at radial distances between 2.5$R_odot$ and 14$R_odot$ to range from $0.22$ and $0.09$. Finally, we calculated relative density fluctuations $epsilon$ measured in situ by PSP at a radial distance from the Sun of $35.7$~$R_odot$ during the perihelion #1, and the perihelion #2 to be $0.07$ and $0.06$, respectively. It is in a very good agreement with previous STEREO predictions ($epsilon=0.06-0.07$) obtained by remote measurements of radio sources generated at this radial distance.
Stealth coronal mass ejection (CMEs) are eruptions from the Sun that are not associated with appreciable low-coronal signatures. Because they often cannot be linked to a well-defined source region on the Sun, analysis of their initial magnetic configuration and eruption dynamics is particularly problematic. In this manuscript, we address this issue by undertaking the first attempt at predicting the magnetic fields of a stealth CME that erupted in 2020 June from the Earth-facing Sun. We estimate its source region with the aid of off-limb observations from a secondary viewpoint and photospheric magnetic field extrapolations. We then employ the Open Solar Physics Rapid Ensemble Information (OSPREI) modelling suite to evaluate its early evolution and forward-model its magnetic fields up to Parker Solar Probe, which detected the CME in situ at a heliocentric distance of 0.5 AU. We compare our hindcast prediction with in-situ measurements and a set of flux rope reconstructions, obtaining encouraging agreement on arrival time, spacecraft crossing location, and magnetic field profiles. This work represents a first step towards reliable understanding and forecasting of the magnetic configuration of stealth CMEs and slow, streamer-blowout events.
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