Parametric dependencies of spontaneous hot flow anomalies at the quasi-parallel bow shock are investigated using global hybrid (kinetic ions and fluid electron) simulations with a variety of solar wind Mach numbers and directions of the interplanetary magnetic field (IMF). Simulations with solar wind Alfvénic Mach number of 3 and small IMF cone angles (with the flow velocity) show sporadic formation of spontaneous hot flow anomalies (SHFAs). Increasing the Mach number shows the formation of copious number of SHFAs whose properties are examined in this study. It is shown that the duration of SHFAs does not show much variation with Mach number indicating that their size generally increases with Mach number. Additionally, the level of solar wind deceleration associated with SHFAs increases with Mach number as does the core ion temperature. It is also found that the edges of SHFAs are associated with jumps in magnetic field that increase with shock Mach number. The results also show that the rate of SHFA formation increases with increasing Mach number. Simulations with IMF cone angle of 90°show that SHFAs form at the quasi-parallel bow shock provided the shock Alfvén Mach number is~>3. This shows that SHFAs may form at all cone angles.

Abstract. Hot flow anomalies (HFAs) at Earth's bow shock were identified in Time History of Events and Macroscale Interactions During Substorms (THEMIS) satellite data from 2007 to 2009. The events were classified as young or mature and also as regular or spontaneous hot flow anomalies (SHFAs). The dataset has 17 young SHFAs, 49 mature SHFAs, 15 young HFAs, and 55 mature HFAs. They span a wide range of magnetic local times (MLTs) from approximately 7 to 16.5 MLT. The largest ratio of solar wind to HFA core density occurred near dusk and at larger distances from the bow shock. In this study, HFAs and SHFAs were observed up to 6.3 R E and 6.1 R E (Earth radii), respectively, upstream from the model bow shock. HFA-SHFA occurrence decreases with distance upstream from the bow shock. HFAs of the highest event core ion temperatures were not seen at the flanks. The ratio of HFA ion temperature increase to HFA electron temperature increase is highest around 12 MLT and slightly duskward. For SHFAs, (T ihfa /T isw )/(T ehfa /T esw ) generally increased with distance from the bow shock. Both mature and young HFAs are more prevalent when there is an approximately radial interplanetary magnetic field. HFAs occur most preferentially for solar wind speeds from 550 to 600 km s −1 . The correlation coefficient between the HFA increase in thermal energy density from solar wind values and the decrease in kinetic energy density from solar wind values is 0.62. SHFAs and HFAs do not show major differences in this study.

We present a case study of the Magnetospheric Multiscale (MMS) observations of the Southern Hemispheric dayside magnetospheric boundaries under southward interplanetary magnetic field direction with strong By component. During this event MMS encountered several magnetic field depressions characterized by enhanced plasma beta and high fluxes of high‐energy electrons and ions at the dusk sector of the southern cusp region that resemble previous Cluster and Polar observations of cusp diamagnetic cavities. Based on the expected maximum magnetic shear model and magnetohydrodynamic simulations, we show that for the present event the diamagnetic cavity‐like structures were formed in an unusual location. Analysis of the composition measurements of ion velocity distribution functions and magnetohydrodynamics simulations show clear evidence of the creation of a new kind of magnetic bottle structures by component reconnection occurring at lower latitudes. We propose that the high‐energy particles trapped in these cavities can sometimes end up in the loss cone and leak out, providing a likely explanation for recent high‐energy particle leakage events observed in the magnetosheath.

The solar wind plasma is a major plasma source for the Earth's magnetosphere, which has a strong influence on the magnetotail plasma and field properties. The relative importance of different plasma entry mechanisms and pathways is largely determined by the solar wind conditions. Therefore, the spatial and temporal dependence of magnetotail plasma and field properties under different kinds of solar wind conditions is critically important for understanding the Earth's magnetosphere. This study presents a statistical study of fundamental magnetotail plasma properties in a normalized reference frame by utilizing 12+ years of data from NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission. These statistical maps are mostly in agreement with the magnetosheath of MHD runs from the CCMC BATS-R-US model, but some features in the maps can be explained by kinetic particle physics, not present in the MHD. The results are also used to investigate the presence of any magnetotail plasma parameter asymmetries and their possible causes. Plain Language Summary Earth's intrinsic magnetic field, generated by the currents in the Earth's interior, protects our planet from solar radiation and plasma called the solar wind. However, physical processes such as magnetic reconnection occurring at the boundary of this magnetic barrier, the magnetosphere, can break this shield, enabling access of solar wind plasma into the Earth's magnetosphere. Earth's ionosphere provides another source for magnetospheric plasma. This plasma can be further accelerated to huge energies, which provides a threat for astronauts and satellites. The effectiveness of physical mechanisms that control the entry and acceleration of this plasma strongly depends on the local magnetic field geometry and plasma properties, which in turn are affected by the solar wind. However, the solar wind properties are not constant but vary as it can originate from different regions of the sun. While the magnetic field of the Sun, the interplanetary magnetic field (IMF), on average forms an "Archimedean Spiral," flapping of the heliospheric current sheet and fluctuations along field lines will make the IMF "hit" the Earth at different orientations, thus impacting the shock geometry in front of the planet, which in turn affects the downstream plasma and field properties in the turbulent boundary layer called the magnetosheath. In this paper, we have characterized the dependence of the large-scale plasma properties in the Earth's magnetosphere and magnetosheath on the solar wind and IMF conditions by using over 12 years (thus covering over one solar cycle) of data from NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission.