Publications

Journal article

Chen CHK, Chandran BDG, Woodham LD, Jones SI, Perez JC, Bourouaine S, Bowen TA, Klein KG, Moncuquet M, Kasper JC, Bale SDet al., 2021,

The near-Sun streamer belt solar wind: turbulence and solar wind acceleration

, Astronomy & Astrophysics, Vol: 650, Pages: 1-6, ISSN: 0004-6361

The fourth orbit of Parker Solar Probe (PSP) reached heliocentric distances down to 27.9 R⊙, allowing solar wind turbulence and acceleration mechanisms to be studied in situ closer to the Sun than previously possible. The turbulence properties were found to be significantly different in the inbound and outbound portions of PSP’s fourth solar encounter, which was likely due to the proximity to the heliospheric current sheet (HCS) in the outbound period. Near the HCS, in the streamer belt wind, the turbulence was found to have lower amplitudes, higher magnetic compressibility, a steeper magnetic field spectrum (with a spectral index close to –5/3 rather than –3/2), a lower Alfvénicity, and a ‘1∕f’ break at much lower frequencies. These are also features of slow wind at 1 au, suggesting the near-Sun streamer belt wind to be the prototypical slow solar wind. The transition in properties occurs at a predicted angular distance of ≈4° from the HCS, suggesting ≈8° as the full-width of the streamer belt wind at these distances. While the majority of the Alfvénic turbulence energy fluxes measured by PSP are consistent with those required for reflection-driven turbulence models of solar wind acceleration, the fluxes in the streamer belt are significantly lower than the model predictions, suggesting that additional mechanisms are necessary to explain the acceleration of the streamer belt solar wind.

Journal article

Fargette N, Lavraud B, Rouillard A, Eastwood JP, Bale SD, Phan T, Øieroset M, Halekas JS, Kasper J, Berthomier M, Case AW, Korreck KE, Larson DE, Louarn P, Malaspina D, Pulupa M, Stevens ML, Whittlesey PLet al., 2021,

Magnetic increases with central current sheets: Observations with Parker Solar Probe

, Astronomy & Astrophysics, Vol: 650, Pages: 1-12, ISSN: 0004-6361

Aims. We report the observation by Parker Solar Probe (PSP) of magnetic structures in the solar wind that present a strong peak intheir magnetic field magnitude with an embedded central current sheet. Similar structures have been observed, either at the Earth’smagnetopause and called interlinked flux tubes, or in the solar wind and called interplanetary field enhancements.Methods. In this work, we first investigate two striking events in detail; one occurred in the regular slow solar wind on November 2,2018 and the other was observed during a heliospheric current sheet crossing on November 13, 2018. They both show the presenceof a central current sheet with a visible ion jet and general characteristics consistent with the occurrence of magnetic reconnection.We then performed a survey of PSP data from encounters 1 to 4 and find 18 additional events presenting an increase in the magneticfield magnitude of over 30% and a central current sheet. We performed a statistical study on the 20 "magnetic increases with centralcurrent sheet" (MICCS), with 13 observed in the regular slow solar wind with a constant polarity (i.e., identical strahl direction), and7 which were specifically observed near a heliospheric current sheet (HCS) crossing.Results. We analyze and discuss the general properties of the structures, including the duration, location, amplitude, and magnetictopology, as well as the characteristics of their central current sheet. We find that the latter has a preferential orientation in the TNplane of the RTN frame. We also find no significant change in the dust impact rate in the vicinity of the MICCS under study, leadingus to conclude that dust probably plays no role in the MICCS formation and evolution. Our findings are overall consistent with adouble flux tube-configuration that would result from initially distinct flux tubes which interact during solar wind propagation.

Journal article

Phan TD, Lavraud B S J, Halekas, Øieroset M, Drake JF, Eastwood JP, Shay MA, Bale SD, Larson D, Livi R, Whittlesey PL, Rahmati A, Pulupa M, McManus MD, Verniero JL, Bonnell JW, Stevens M, Case AWet al., 2021,

Prevalence of magnetic reconnection in the near-Sun heliospheric current sheet

, Astronomy & Astrophysics, Vol: 650, Pages: 1-14, ISSN: 0004-6361

During three of its first five orbits around the Sun, Parker Solar Probe (PSP) crossed the large-scale Heliospheric Current Sheet (HCS)multiple times and provided unprecedented detailed plasma and field observations of the near-Sun HCS. We report the commondetections by PSP of reconnection exhaust signatures in the HCS at heliocentric distances of 29.5-107 solar radii during Encounters1, 4 and 5. Both sunward and antisunward-directed reconnection exhausts were observed. In the sunward reconnection exhausts,PSP detected counterstreaming strahl electrons, indicating that HCS reconnection resulted in the formation of closed magnetic fieldlines with both ends connected to the Sun. In the antisunward exhausts, PSP observed dropouts of strahl electrons, consistent withthe reconnected HCS field lines being disconnected from the Sun. The common detection of reconnection in the HCS suggests thatreconnection is almost always active in the HCS near the Sun. Furthermore, the occurrence of multiple long-duration partial crossingsof the HCS suggests that HCS reconnection could produce chains of large bulges with spatial dimensions of up to several solarradii. The finding of the prevalence of reconnection in the HCS is somewhat surprising since PSP has revealed that the HCS is muchthicker than the kinetic scales required for reconnection onset. The observations are also in stark contrast with the apparent absenceof reconnection in most of the small-scale and much more intense current sheets encountered near perihelia, many of which areassociated with ‘switchbacks’. Thus, the PSP findings suggest that large-scale dynamics either locally in the solar wind or within thecoronal source of the HCS (at the tip of helmet streamers) plays a critical role in triggering reconnection onset.

Journal article

Schwadron NA, Joyce CJ, Aly A, Cohen CMS, Desai M, McComas DJ, Niehof JT, Mobius E, Lee M, Bower J, Bale S, Case A, Christian ER, Davis AJ, de Wet W, Goetz K, Giacalone J, Hill ME, Allen R, Kasper JC, Korreck K, Leske RA, Malandraki O, Matthaeus WH, McNutt RL, Mewaldt RA, Mitchell DG, Pulupa M, Rankin JS, Roelof EC, Stone EC, Szalay JR, Wiedenbeck MEet al., 2021,