We estimate the global impact of storms on the global structure and dynamics of the nightside plasma sheet (PS) from observations by the NASA mission THEMIS. We focus on an intense storm occurring in December 2015 triggered by interplanetary coronal mass ejections (ICMEs). It starts with a storm sudden commencement (SSC) phase (SYM-H~+50nT) followed by a growth phase (SYM-H~-188nT at the minimum) and then a long recovery phase. We investigate THEMIS observations when the spacecraft were located in the midnight sector of the PS at distances typically between 8 and 13RE. It is found that the PS has been globally compressed up to a value of about~>4nPa during the SSC and main phases, i.e. 8 times larger than its value during the quiet phase before the event. This compression occurs during periods of high dynamic pressure in the ICME (20nPa) about one order of magnitude larger than its value in the pristine solar wind. We infer a global increase of the lobe magnetic field from 30nT to 100nT, confirmed by THEMIS data just outside the PS. During the SSC and main phases, the PS is found thinner by a factor of 2 relative to its thickness at quiet times, while the Tsyganenko T96 magnetic field model shows very stretched magnetic field lines from inner magnetospheric regions toward the nightside. During the recovery phase, whereas the interplanetary pressure has dropped off, the PS tends to gradually recover its quiet phase characteristics (pressure, thickness, magnetic configuration, etc) during a long recovery phase.

Solar transients impinging on Earth’s magnetosphere often present a larger velocity than the surrounding solar wind, leading to a different response of the bow shock-magnetosheath system. As such, we intend to provide a systematic study of the global effects of different solar wind Mach numbers in a pure quasi-perpendicular configuration with a realistic three-dimensional terrestrial-like curved bow shock. Simulations have been performed with the hybrid code LatHyS, which is based on the widely used CAM-CL scheme. In particular, we have studied the interaction with the terrestrial magnetosphere of a solar wind at different Alfvénic Mach numbers and low-beta (less than unity, ratio between the thermal to the magnetic pressures). One of most noteworthy outcome is the generation of an intense rippling phenomenon propagating along the bow shock surface as the incoming Mach number increases. A similar rippling has been observed in-situ with satellites, as well as studied with computer simulations. However, the latter have mainly addressed by adopting ad-hoc planar-shock initial configurations, which still leaves poor knowledge of the possible effects on a global three-dimensional curved interaction. Our analysis then is expected to provide further insights into both the macroscopic and kinetic effects of different incoming solar wind conditions on the overall planetary bow-shock and magnetosheath structure.

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.

A few MHD simulations have been performed to study the interaction between a propagating interplanetary shock and Earth's standing bow shock, followed by the magnetosheath and magnetopause. They satisfactorily explain the deceleration of the interplanetary shock in the magnetosheath, which was observed a few dozen times by well-arranged satellites. In this work, we perform a hybrid particle-in-cell simulation in a similar setting with a self-consistently developed quasi-perpendicular interplanetary shock. We track the position of the interplanetary shock as it travels through the magnetosheath. We show that early in the propagation through the magnetosheath, the interplanetary shock slows down, which is in line with the conclusion of previous studies. Later in the propagation, however, we find that -- in the plane perpendicular to the interplanetary magnetic field -- the interplanetary shock travels faster inside the magnetosheath than it does in the solar wind. We also note that as the magnetic field lines are stretched along the magnetopause, the interplanetary shock becomes quasi-parallel close to the magnetopause.

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 a multi-mission magnetopause database, cumulating 17 230 crossings on 17 different spacecraft, from the dayside to lunar nightside distances. The IMF clock angle itself (all amplitudes combined) is fount not to 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. 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 study pave the way for the elaboration of a new analytical empirical expression magnetopause surface model.

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.

The shape and location of the magnetopause current sheet in the near-cusp region is still a debated question. Over time, several observations led to contradictory conclusions regarding the presence of an indentation of the magnetopause in that region. As a result several empirical models consider the surface is indented in that region, while some others do not. To tackle this issue, we fit a total of 17 230 magnetopause crossings to various indented and non-indented analytical models. The results show that while all models describe the magnetopause position and shape equivalently far from the cusp region, the non-indented version over-estimate the radial position of the near-cusp magnetopause. Among indented models, we show that the one designed from MHD simulations fits well the near-cusp magnetopause location, while the other underestimate its position probably because their design was possibly based on magnetopause crossing catalogues that contain cusp inner boundary crossings.