Average plasma sheet polytropic index as observed by THEMIS

Multi-spacecraft data from the years 2008 to 2015 of the THEMIS mission particularly in the near-Earth plasma sheet are used in order to empirically determine the polytropic index in the quiet and active time magnetotail. The results of a number of previous studies in the 1990s can be confirmed. An analysis of the total database, although showing poor correlation, results in an average polytropic index of γ = 1. 72. The active time plasma sheet is well correlated with an average γ = 1. 49. However, the data scattering suggests that the analysis of the data in total is not adequate. In order to reduce the timescales, individual spacecraft orbits are analyzed, giving a broad distribution of polytropic indices throughout the plasma sheet. The major part of the distribution falls in a range between γ = 0. 67 and γ = 2. Our results indicate a variety of thermodynamic processes in the magnetotail and an all-time presence of heat exchange of the plasma. A description of the plasma sheet using an equation of state with a single γ is probably inadequate. This necessitates the application of more sophisticated approaches, such as a parametrization of the heat flux vector in magnetohydrodynamic equations or a superposition of polytropic indices

Geodesy, Geophysics and Fundamental Physics Investigations of the BepiColombo Mission

In preparation for the ESA/JAXA BepiColombo mission to Mercury, thematic working groups had been established for coordinating the activities within the BepiColombo Science Working Team in specific fields. Here we describe the scientific goals of the Geodesy and Geophysics Working Group (GGWG) that aims at addressing fundamental questions regarding Mercury’s internal structure and evolution. This multidisciplinary investigation will also test the gravity laws by using the planet Mercury as a proof mass. The instruments on the Mercury Planetary Orbiter (MPO), which are devoted to accomplishing the GGWG science objectives, include the BepiColombo Laser Altimeter (BELA), the Mercury orbiter radio science experiment (MORE), and the MPO magnetometer (MPO-MAG). The onboard Italian spring accelerometer (ISA) will greatly aid the orbit reconstruction needed by the gravity investigation and laser altimetry. We report the current knowledge on the geophysics, geodesy, and evolution of Mercury after the successful NASA mission MESSENGER and set the prospects for the BepiColombo science investigations based on the latest findings on Mercury’s interior. The MPO spacecraft of the BepiColombo mission will provide extremely accurate measurements of Mercury’s topography, gravity, and magnetic field, extending and improving MESSENGER data coverage, in particular in the southern hemisphere. Furthermore, the dual-spacecraft configuration of the BepiColombo mission with the Mio spacecraft at higher altitudes than the MPO spacecraft will be fundamental for decoupling the internal and external contributions of Mercury’s magnetic field. Thanks to the synergy between the geophysical instrument suite and to the complementary instruments dedicated to the investigations on Mercury’s surface, composition, and environment, the BepiColombo mission is poised to advance our understanding of the interior and evolution of the innermost planet of the solar system

Study of Extreme Magnetopause Distortions Under Varying Solar Wind Conditions

AbstractTo first order, the magnetopause (MP) is defined by a pressure balance between the solar wind and the magnetosphere. The boundary moves under the influence of varying solar wind conditions and transient foreshock phenomena, reaching unusually large and small distances from the Earth. We investigate under which solar wind conditions such extreme MP distortions occur. Therefore, we construct a database of magnetopause crossings (MPCs) observed by the THEMIS spacecraft in the years 2007 to mid‐2022 using a simple Random Forest Classifier. Roughly 7% of the found crossing events deviate beyond reported errors in the stand‐off distance from the Shue et al. (1998, https://doi.org/10.1029/98JA01103) MP model and thus are termed extreme distortions. We find the occurrence of these extreme events in terms of expansion or compression of the MP to be linked to different solar wind parameters, most notably to the IMF magnitude, cone angle, velocity, Alfvén Mach number and temperature. Foreshock transients like hot‐flow anomalies and foreshock bubbles could be responsible for extreme magnetospheric expansions. The results should be incorporated into future magnetopause models and may be helpful for the reconstruction of the MP locations out of soft x‐ray images, relevant for the upcoming SMILE mission.Key Points: More than 160.000 magnetopause crossings (MPCs) identified in THEMIS data between 2007 and 2022 using a Random Forest Classifier Magnetopause crossings that extremely deviate in location from the Shue et al. (1998, https://doi.org/10.1029/98JA01103) model are quite common Important solar wind parameters associated with deviations include the interplanetary magnetic field cone angle, solar wind velocity and Alfvén Mach number German Ministerium für Wirtschaft und Klimaschutz and Deutsches Zentrum für Luft‐und Raumfahrt http://dx.doi.org/10.13039/501100002946UKRI Stephen Hawking FellowshipGerman Ministry for Economy and Technology andGerman Center for Aviation and Spacehttps://osf.io/b6kux/https://github.com/spedas/pyspedashttp://themis.ssl.berkeley.edu/data/themis/https://omniweb.gsfc.nasa.gov/https://scikit-learn.org/stable/supervised_learning.html#supervised-learnin

Dayside magnetopause reconnection and flux transfer events under radial interplanetary magnetic field (IMF): BepiColombo Earth-flyby observations

International audienceThis study analyzes the flux transfer event (FTE)-type flux ropes and magnetic reconnection around the dayside magnetopause during BepiColombo's Earth flyby. The magnetosheath has a high plasma β (∼ 8), and the interplanetary magnetic field (IMF) has a significant radial component. Six flux ropes are identified around the magnetopause. The motion of flux ropes together with the maximum magnetic shear model suggests that the reconnection X-line possibly swipes BepiColombo near the magnetic equator due to an increase in the radial component of the IMF. The flux rope with the highest flux content contains a clear coalescence signature, i.e., two smaller flux ropes merge, supporting theoretical predictions that the flux contents of flux ropes can grow through coalescence. The coalescence of the two FTE-type flux ropes takes place through secondary reconnection at the point of contact between the two flux ropes. The BepiColombo measurements indicate a large normalized guide field and a reconnection rate comparable to that measured at the magnetopause (∼ 0.1)

Natural variation of histone modification and its impact on gene expression in the rat genome

10.1101/gr.169029.113Genome Research246942-953GERE

Natural variation of histone modification and its impact on gene expression in the rat genome

Histone modifications are epigenetic marks that play fundamental roles in many biological processes including the control of chromatin-mediated regulation of gene expression. Little is known about interindividual variability of histone modification levels across the genome and to what extent they are influenced by genetic variation. We annotated the rat genome with histone modification maps, identified differences in histone trimethyl-lysine levels among strains, and described their underlying genetic basis at the genome-wide scale using ChIP-seq in heart and liver tissues in a panel of rat recombinant inbred and their progenitor strains. We identified extensive variation of histone methylation levels among individuals and mapped hundreds of underlying cis- and trans-acting loci throughout the genome that regulate histone methylation levels in an allele-specific manner. Interestingly, most histone methylation level variation was trans-linked and the most prominent QTL identified influenced H3K4me3 levels at 899 putative promoters throughout the genome in the heart. Cis- acting variation was enriched in binding sites of distinct transcription factors in heart and liver. The integrated analysis of DNA variation together with histone methylation and gene expression levels showed that histoneQTLs are an important predictor of gene expression and that a joint analysis significantly enhanced the prediction of gene expression traits (eQTLs). Our data suggest that genetic variation has a widespread impact on histone trimethylation marks that may help to uncover novel genotype-phenotype relationships