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

Aims. We report the observation by Parker Solar Probe (PSP) of magnetic structures in the solar wind that present a strong peak in their magnetic field magnitude with an embedded central current sheet. Similar structures have been observed, either at the Earth’s magnetopause 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 presence of 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 magnetic field magnitude of over 30% and a central current sheet. We performed a statistical study on the 20 "magnetic increases with central current sheet" (MICCS), with 13 observed in the regular slow solar wind with a constant polarity (i.e., identical strahl direction), and 7 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 magnetic topology, as well as the characteristics of their central current sheet. We find that the latter has a preferential orientation in the TN plane of the RTN frame. We also find no significant change in the dust impact rate in the vicinity of the MICCS under study, leading us to conclude that dust probably plays no role in the MICCS formation and evolution. Our findings are overall consistent with a double flux tube-configuration that would result from initially distinct flux tubes which interact during solar wind propagation

Chromosomal Rearrangements Formed by rrn Recombination Do Not Improve Replichore Balance in Host-Specific Salmonella enterica Serovars

operons. One hypothesis explaining these rearrangements suggests that replichore imbalance introduced from horizontal transfer of pathogenicity islands and prophages drives chromosomal rearrangements in an attempt to improve balance.This hypothesis was directly tested by comparing the naturally-occurring chromosomal arrangement types to the theoretically possible arrangement types, and estimating their replichore balance using a calculator. In addition to previously characterized strains belonging to host-specific serovars, the arrangement types of 22 serovar Gallinarum strains was also determined. Only 48 out of 1,440 possible arrangement types were identified in 212 host-specific strains. While the replichores of most naturally-occurring arrangement types were well-balanced, most theoretical arrangement types had imbalanced replichores. Furthermore, the most common types of rearrangements did not change replichore balance.The results did not support the hypothesis that replichore imbalance causes these rearrangements, and suggest that the rearrangements could be explained by aspects of a host-specific lifestyle

The heliospheric current sheet and plasma sheet during Parker Solar Probe’s first orbit

We present heliospheric current sheet (HCS) and plasma sheet (HPS) observations during Parker Solar Probe's (PSP) first orbit around the Sun. We focus on the eight intervals that display a true sector boundary (TSB; based on suprathermal electron pitch angle distributions) with one or several associated current sheets. The analysis shows that (1) the main density enhancements in the vicinity of the TSB and HCS are typically associated with electron strahl dropouts, implying magnetic disconnection from the Sun, (2) the density enhancements are just about twice that in the surrounding regions, suggesting mixing of plasmas from each side of the HCS, (3) the velocity changes at the main boundaries are either correlated or anticorrelated with magnetic field changes, consistent with magnetic reconnection, (4) there often exists a layer of disconnected magnetic field just outside the high-density regions, in agreement with a reconnected topology, (5) while a few cases consist of short-lived density and velocity changes, compatible with short-duration reconnection exhausts, most events are much longer and show the presence of flux ropes interleaved with higher-β regions. These findings are consistent with the transient release of density blobs and flux ropes through sequential magnetic reconnection at the tip of the helmet streamer. The data also demonstrate that, at least during PSP's first orbit, the only structure that may be defined as the HPS is the density structure that results from magnetic reconnection, and its byproducts, likely released near the tip of the helmet streamer