The effect of diamagnetic drift on motion of the dayside magnetopause reconnection line

Magnetic reconnection at the magnetopause occurs with a large density asymmetry and for a large range of magnetic shears. In these conditions, a motion of the X line has been predicted in the direction of the electron diamagnetic drift. When this motion is super Alfvenic, reconnection should be suppressed. We analysed a large data set of Double Star TC-1 dayside magnetopause crossings, which includes reconnection and nonreconnection events. Moreover, it also includes several events during which TC-1 is near the X line. With these close events, we verified the diamagnetic suppression condition with local observations near the X line. Moreover, with the same close events, we also studied the motion of the X line along the magnetopause. It is found that, when reconnection is not suppressed, the X line moves northward or southward according to the orientation of the guide field, which is related to the interplanetary magnetic field BY component, in agreement with the diamagnetic drift

Observations of IMF coherent structures and their relationship to SEP dropout events

Abstract. The solar energetic particle (SEP) events from impulsive solar flares are often characterized by short-timescale modulations affecting, at the same time, particles with different energies. Several models and simulations suggest that these modulations are observed when SEPs propagate through magnetic structures with a different connection with the flare site. However, in situ observations rarely showed clear magnetic signatures associated with these modulations. In this paper we used the Grad–Shafranov reconstruction to perform a detailed analysis of the local magnetic field topology during the SEP event of 9–10 January 1999, characterized by several SEP dropouts. An optimization procedure is used to identify, during this SEP event, the magnetic structures which better satisfy the Grad–Shafranov assumptions and to evaluate the direction of their invariant axis. We found that these two-dimensional structures, which are flux ropes or current sheets with a more complex field topology, are generally associated with the maxima in the SEP counts. This association suggests that the SEPs propagate within these structures and, since their gyration radii is much smaller than the transverse dimension of these structure, cannot escape from them

Radial Evolution of Spectral Characteristics of Magnetic Field Fluctuations at Proton Scales

This paper addresses the investigation of the character and the radial evolution of magnetic fluctuations within the dissipation range, right after the high-frequency spectral break, employing observations by Messenger and Wind of the same fast wind stream during a radial alignment. The same event has already been considered in literature to show, for the first time, that the high-frequency break separating the fluid from the kinetic regime moves to lower frequency as the wind expands. The present work aims to analyze the nature of the high-frequency magnetic fluctuations beyond the spectral break and show that their character is compatible with left-hand, outward-propagating, ion cyclotron waves and right-hand kinetic Alfv\acute{e}n waves. It is also shown that the low-frequency limit of these fluctuations follows the radial evolution of the spectral break, which also reflects in the behavior of their intermittency character. Finally, the total power and the compressive character of these two wave populations are analyzed and compared as a function of the heliocentric distance, leading us to conclude that the overall picture is in favor of a radial decrease

Automated force-free flux rope identification

We describe a method developed to automatically identify quasi force‐free magnetotail flux ropes from in situ spacecraft magnetometer data. The method locates significant (greater than 1σ) deflections of the north‐south component of the magnetic field coincident with enhancements in other field components. The magnetic field data around the deflections are then processed using Minimum Variance Analysis (MVA) to narrow the selection down to those that exhibit the characteristics of flux ropes. The subset of candidates that fulfills the requirements are then compared to a cylindrical, linear (constant‐α) force‐free model. Those that can be well approximated as force free are then accepted. The model fit also provides a measure of the physical parameters that describe the flux rope (i.e., core field and radius). This process allows for the creation of a repeatable, consistent catalog of flux ropes. Automation allows a greater volume of data to be covered, saving time and allowing the exploration of potential selection biases. The technique is applied to MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) magnetometer data in the Hermean magnetotail and successfully locates flux ropes, some of which match previously known encounters. Assumptions of the method and potential future applications are discussed

Signatures of magnetic separatrices at the borders of a crater flux transfer event connected to an active X‐line

In this paper, we present Magnetospheric Multiscale (MMS) observations of a flux transfer event (FTE) characterized by a clear signature in the magnetic field magnitude, which shows maximum at the center flanked by two depressions, detected during a period of stable southward interplanetary magnetic field. This class of FTEs are called “crater‐FTEs” and have been suggested to be connected with active reconnection X line. The MMS burst mode data allow the identification of intense fluctuations in the components of the electric field and electron velocity parallel to the magnetic field at the borders of the FTE, which are interpreted as signatures of the magnetic separatrices. In particular, the strong and persistent fluctuations of the parallel electron velocity at the borders of this crater‐FTE reported for the first time in this paper, sustain the field‐aligned current part of the Hall current system along the separatrix layer, and confirm that this FTE is connected with an active reconnection X line. Our observations suggest a stratification of particles inside the reconnection layer, where electrons are flowing toward the X line along the separatrix, are flowing away from the X line along the reconnected field lines adjacent to the separatrices, and more internally ions and electrons are flowing away from the X line with comparable velocities, forming the reconnection jets. This stratification of the reconnection layer forming the FTE, together with the reconnection jet at the trailing edge of the FTE, suggests clearly that this FTE is formed by the single X line generation mechanism

On the occurrence of magnetic reconnection equatorward of the cusps at the Earth's magnetopause during northward IMF conditions

Magnetic reconnection changes the topology of magnetic field lines. This process is most readily observable with in situ instrumentation at the Earth's magnetopause as it creates open magnetic field lines to allow energy and momentum flux to flow from the solar wind to the magnetosphere. Most models use the direction of the interplanetary magnetic field (IMF) to determine the location of these magnetopause entry points, known as reconnection lines. Dayside locations of magnetic reconnection equatorward of the cusps are generally found during sustained intervals of southward IMF, while high-latitude region regions poleward of the cusps are observed for northward IMF conditions. In this study we discuss Double Star magnetopause crossings and a conjunction with a Polar cusp crossing during northward IMF conditions with a dominant IMF BY component. During all seven dayside magnetopause crossings, Double Star detected switching ion beams, a known signature for the presence of reconnection lines. In addition, Polar observed a cusp ion-energy dispersion profile typical for a dayside equatorial reconnection line. Using the cutoff velocities for the precipitating and mirrored ion beams in the cusp, the distance to the reconnection site is calculated, and this distance is traced back to the magnetopause, to the vicinity of the Double Star satellite locations. Our analysis shows that, for this case, the predicted line of maximum magnetic shear also coincides with that dayside reconnection location

Notulae to the Italian native vascular flora: 11.

In this contribution, new data concerning the distribution of native vascular flora in Italy are presented. It includes new records, confirmations, exclusions, and status changes to the Italian administrative regions. A new combination in the genus Pilosella is proposed. Nomenclatural and distribution updates, published elsewhere, and corrigenda are provided as Suppl. material 1

Notulae to the Italian native vascular flora: 9

In this contribution, new data concerning the distribution of native vascular flora in Italy are presented. It includes new records, confirmations, exclusions, and status changes to the Italian administrative regions. Two new combinations are proposed. Nomenclatural and distribution updates, published elsewhere, and corrigenda are provided as Suppl. material 1