We explore the structure of the magnetopause using a crossing observed by the Magnetospheric Multiscale (MMS) spacecraft on 16 October 2015. Several methods (minimum variance analysis, BV method, and ...constant velocity analysis) are first applied to compute the normal to the magnetopause considered as a whole. The different results obtained are not identical, and we show that the whole boundary is not stationary and not planar, so that basic assumptions of these methods are not well satisfied. We then analyze more finely the internal structure for investigating the departures from planarity. Using the basic mathematical definition of what is a one‐dimensional physical problem, we introduce a new single spacecraft method, called LNA (local normal analysis) for determining the varying normal, and we compare the results so obtained with those coming from the multispacecraft minimum directional derivative (MDD) tool developed by Shi et al. (2005). This last method gives the dimensionality of the magnetic variations from multipoint measurements and also allows estimating the direction of the local normal when the variations are locally 1‐D. This study shows that the magnetopause does include approximate one‐dimensional substructures but also two‐ and three‐dimensional structures. It also shows that the dimensionality of the magnetic variations can differ from the variations of other fields so that, at some places, the magnetic field can have a 1‐D structure although all the plasma variations do not verify the properties of a global one‐dimensional problem. A generalization of the MDD tool is proposed.
Key Points
The internal structure of the magnetopause is investigated, using new analysis tools allowed by the high‐performance MMS instruments
In a case study, the observed boundary is shown to be nonplanar and nonstationary
Quasi 1‐D thin sub layers are identified separated by regions that are mainly 2‐D
The Earth magnetopause is the boundary between the magnetosphere and the shocked solar wind. Its location and shape are primarily determined by the properties of the solar wind and interplanetary ...magnetic field (IMF) but the nature of the control parameters and to what extent they impact the stand‐off distance, the flaring, and the symmetries, on the dayside and night side, is still not well known. We present a large statistical study of the magnetopause location and shape based an extensive multi‐mission magnetopause database, cumulating 17,230 crossings on 17 different spacecraft, from the dayside to lunar nightside distances. The results confirm the power‐law dependency of the stand‐off position on the solar wind pressure. The IMF clock angle itself (all amplitudes combined) does not impact the stand‐off distance, nor does the cone angle. However, the magnetopause is found to move Earthward as the IMF gets stronger and more southward. All upstream conditions combined, it is found that the function used at the root of several analytical models still holds at lunar distances. We find that the equatorial flaring is larger than the meridional one. However, the meridional flaring is found to depend on the seasonal tilt conditions, being larger in the summer hemisphere. The flaring is also found to depend on the IMF clock angle. Meridional flaring increases as the IMF turns south and is then larger than the equatorial flaring. The equatorial flaring barely changes or weakly increases as the IMF turns northward, and is larger than the meridional flaring for northward conditions. The results of the study pave the way for the elaboration of a new analytical empirical expression of the magnetopause location and shape.
Key Points
We use a multi‐mission catalog to provide a statistical analysis of the magnetopause location and shape
We confirm the expected influence of the solar wind dynamic pressure, of the interplanetary magnetic field (IMF) Bz component, of the Earth dipole tilt angle
Varying IMF clock angle is found to affects the level of flaring, resulting in an elliptic cross section in the cGSM YZ plane which major axis is oriented along the cGSM Y axis when the IMF is southward and along the cGSM X axis when the IMF is northward
This paper investigates the proton kinetic mechanisms leading to the formation of plasma jets in antiparallel magnetic reconnection. In particular, the interaction of the protons with the Hall ...electric field in the proton non‐ideal region is discussed. The study, based on a two‐dimensional hybrid simulation, details the important role of the proton pressure force in the acceleration process and its role in maintaining open and steady the proton outflow channel. When no fluid closure is assumed, it is found that this force arises from a strong anisotropy in velocity space which comes from kinetic effect. By analyzing the distribution functions and the individual particle dynamics, it is shown that the mixing of protons bouncing in a divergent electrostatic potential well associated to the Hall effect statistically couples the two in‐plane velocity components of the particles. This coupling results, from the macroscopic point of view, in off‐diagonal components of the pressure tensor.
Key Points
Fluid (proton) acceleration
Particle (proton) acceleration
Relationship between particle and fluid acceleration: pressure tensor
The Magnetospheric Multiscale (MMS) mission will provide measurement capabilities, which will exceed those of earlier and even contemporary missions by orders of magnitude. MMS will, for the first ...time, be able to measure directly and with sufficient resolution key features of the magnetic reconnection process, down to the critical electron scales, which need to be resolved to understand how reconnection works. Owing to the complexity and extremely high spatial resolution required, no prior measurements exist, which could be employed to guide the definition of measurement requirements, and consequently set essential parameters for mission planning and execution. Insight into expected details of the reconnection process could hence only been obtained from theory and modern kinetic modeling. This situation was recognized early on by MMS leadership, which supported the formation of a fully integrated Theory and Modeling Team (TMT). The TMT participated in all aspects of mission planning, from the proposal stage to individual aspects of instrument performance characteristics. It provided and continues to provide to the mission the latest insights regarding the kinetic physics of magnetic reconnection, as well as associated particle acceleration and turbulence, assuring that, to the best of modern knowledge, the mission is prepared to resolve the inner workings of the magnetic reconnection process. The present paper provides a summary of key recent results or reconnection research by TMT members.
In a companion statistical study, we showed that the expression of the magnetopause surface as a power law of an elliptic function of the zenith angle θ holds at lunar distances, that the flaring of ...the magnetopause surface is influenced by the Interplanetary Magnetic Field (IMF) By component and that the IMF Bx component had no influence on the stand‐off distance. As a follow‐up to these statistical results, this paper presents a new empirical analytical asymmetric and non‐indented model of the magnetopause location and shape. This model is obtained from fitting of 15,349 magnetopause crossings using 17 different spacecraft and is parametrized by the upstream solar wind dynamic and magnetic pressures, the IMF clock angle and the Earth dipole tilt angle. The constructed model provides a more accurate prediction of the magnetopause surface location than current Magnetopause surface models, especially on the night side of the magnetosphere.
Key Points
We use a multi‐mission crossings catalog to develop a new asymmetric, non‐indented magnetopause surface model
The model is parametrized by the solar wind dynamic and magnetic pressures, by the IMF clock angle and by the Earth dipole tilt angle
The model provides a more accurate prediction of the magnetopause location, especially on the night side of the magnetosphere
In‐situ spacecraft missions are powerful assets to study processes that occur in space plasmas. One of their main limitations, however, is extrapolating such local measurements to the global scales ...of the system. To overcome this problem at least partially, multi‐point measurements can be used. There are several multi‐spacecraft missions currently operating in the Earth's magnetosphere, and the simultaneous use of the data collected by them provides new insights into the large‐scale properties and evolution of magnetospheric plasma processes. In this work, we focus on studying the Earth's magnetopause (MP) using a conjunction between the Magnetospheric Multiscale and Cluster fleets, when both missions skimmed the MP for several hours at distant locations during radial interplanetary magnetic field (IMF) conditions. The observed MP positions as a function of the evolving solar wind conditions are compared to model predictions of the MP. We observe an inflation of the magnetosphere (∼0.7 RE), consistent with magnetosheath pressure decrease during radial IMF conditions, which is less pronounced on the flank (<0.2 RE). There is observational evidence of magnetic reconnection in the subsolar region for the whole encounter, and in the dusk flank for the last portion of the encounter, suggesting that reconnection was extending more than 15 RE. However, reconnection jets were not always observed, suggesting that reconnection was patchy, intermittent or both. Shear flows reduce the reconnection rate up to ∼30% in the dusk flank according to predictions, and the plasma β enhancement in the magnetosheath during radial IMF favors reconnection suppression by the diamagnetic drift.
Key Points
Simultaneous observations of the equatorial subsolar magnetopause and dusk flank during time‐extended radial interplanetary magnetic field
The magnetosphere enlarges ∼0.7 RE in the subsolar region but <0.2 RE in the flank due to the reduced pressure exerted by the solar wind
Simultaneous reconnection evidence in the subsolar and flank regions more than 15 RE apart is observed during part of the encounter
During periods of strong magnetic activity, cold dense plasma from the plasmasphere typically forms a plume extending toward the dayside magnetopause, eventually reaching it. In this work, we present ...a large‐scale two‐dimensional fully kinetic particle‐in‐cell simulation of a reconnecting magnetopause hit by a propagating plasmaspheric plume. The simulation is designed so that it undergoes four distinct phases: initial unsteady state, steady state prior to plume arrival at the magnetospause, plume interaction, and steady state once the plume is well engulfed in the reconnection site. We show the evolution of the magnetopause's dynamics subjected to the modification of the inflowing plasma. Our main result is that the change in the plasma temperature (cold protons in the plume) has no effects on the magnetic reconnection rate, which on average depends only on the inflowing magnetic field and total ion density, before, during, and after the impact.
Key Points
We run particle‐in‐cell simulation of asymmetric magnetic reconnection including the impact of a cold plasmaspheric plume
The impact of the plume reduces the reconnection rate following Magnetohydrodynamics scaling laws due to mass loading only
The cold temperature of the plume does not influence the reconnection rate
Magnetic field draping occurs when the magnetic field lines frozen in a plasma flow wrap around a body or plasma environment. The draping of the interplanetary magnetic field (IMF) around the Earth’s ...magnetosphere has been confirmed in the early days of space exploration. However, its global and three‐dimensional structure is known from modeling only, mostly numerical. Here, this structure in the dayside of the Earth’s magnetosheath is determined as a function of the upstream IMF orientation purely from in‐situ spacecraft observations. We show the draping structure can be organized in three regimes depending on how radial the upstream IMF is. Quantitative analysis demonstrates how the draping pattern results from the magnetic field being frozen in the magnetosheath flow, deflected around the magnetopause. The role of the flow is emphasized by a comparison of the draping structure to that predicted to a magnetostatic draping.
Key Points
Global 3D reconstruction of the magnetic field draping around the Earth magnetosphere purely from in situ observations
Draping pattern is shown as a function of the interplanetary magnetic field cone angle
The role of the magnetosheath flow to which the magnetic field is frozen is emphasized by a comparison to a vacuum magnetostatic draping
We present an automatic classification method of the three near‐Earth regions, the magnetosphere, the magnetosheath and the solar wind from their in situ data measurement by multiple spacecraft. ...Based on gradient boosting classifier, this very simple and very fast method outperforms the detection routines based on manually set thresholds. The method is used to identify 15,062 magnetopause crossings and 17,227 bow shock crossings in the data of 11 different spacecraft of the THEMIS, ARTEMIS, Cluster, MMS, and Double Star missions and for a total of 83 cumulated years. These multi‐mission catalogs are easily reproducible, can be automatically enlarged with additional data and their elaboration paves the way for future massive statistical analysis of near‐Earth boundaries.
Key Points
A gradient boosting algorithm is used to classify the magnetosphere, magnetosheath and solar wind in situ data from multiple missions
The method outperforms the detection methods based on manual threshold and is trained faster than existing machine‐learning based methods
The method is used to identify 15,062 magnetopause crossings and 17,227 bow shock crossings
PDF
