When the velocity shear between the two plasmas separated by Earth’s magnetopause is locally super-Alfvénic, the Kelvin-Helmholtz (KH) instability can develop. A crucial role is played by the interplanetary magnetic field (IMF) orientation, which can stabilize the velocity shear. Although, in a linear regime, the instability threshold is equally satisfied during both northward and southward IMF orientations, in-situ measurements show that KH instability is preferentially excited during the northward IMF orientation. We investigate this different behavior by means of a mixing parameter which we apply to two KH events to identify both boundaries and the center of waves/vortices. During the northward orientation, the waves/vortex boundaries have stronger electrons than ions mixing, while the opposite is observed at their center. During the southward orientation, instead, particle mixing is observed predominantly at the boundaries. In addition, stronger local ion and electron non-thermal features are observed during the northward than the southward IMF orientation. Specifically, ion distribution functions are more distorted, due to field-aligned beams, and electrons have a larger temperature anisotropy during the northward than the southward IMF orientation. The observed kinetic features provide an insight into both local and remote processes that affect the evolution of KH structures.

We employ Magnetospheric Multiscale, Geostationary Operational Environmental and Los Alamos National Laboratory satellites, as well as the ground magnetometer networks over Greenland and North America to study a substorm on 9 August 2016 between 9 and 10 UT.We found that during the substorm two earthward flows, whose dipolarization-injection fronts exceeded 6.5 and 4 Earth’s radii (RE) in YGSM, impinged and rebounded from Earth’s dipolar field lines at L = 6–7 downtail, where L is the McIlwain number. The impingements and rebounds ended with a substorm current system of downward R1 and upward R2 currents which grew to azimuthally cover the whole North American continent. At the fronts, regions of enhanced negative j·E′ were formed and peaked toward the end of the impingements. These regions appeared to be conjugate with eastward moving aurora (along the growth phase arc and together with eastward drifting energetic electrons at geosynchronous equatorial orbit), which manifests ionospheric Ohmic losses.

Near the inner edge of the plasma sheet, where the geomagnetic field transitions from dipolar to tail-like, very low values of the northward component of the field (Bz) are known to be occasionally exhibited, particularly in the substorm growth phase. It has been suggested that this may be a signature of a localized magnetic field dip, which are notoriously difficult to observe in situ. The existence of these localized minima is significant as they would be ballooning-interchange (BI) unstable. Previous work has investigated BI instability using localized particle-in-cell simulations with an imposed Bz minimum as an initial condition. However, evidence of the existence of localized Bz minima and BI instability at their tailward edges has been very limited in self-consistent global magnetosphere simulations. In this presentation, we demonstrate that the elusive nature of the instability has been due to the insufficient resolution of previous simulations. We present a highly-resolved global magnetosphere simulation, using our newly developed code Gamera. In a synthetic substorm simulation we demonstrate the formation of a Bz minimum localized in radius, 8-10 Re from Earth. The region becomes BI unstable in the substorm growth phase, leading to the formation of earthward and azimuthally propagating bubbles, distinct from those that form further downtail and become bursty bulk flows. These bubbles generate field-aligned currents and optical auroral signatures, similar to those observed on the ground and from space. We discuss the physical mechanisms for the formation of the localized Bz minimum by magnetic flux depletion, analyze the nature of the instability, characterize both magnetospheric and ionospheric signatures of the unstable region, and compare them with those observed.

The kinetic ballooning/interchange instability (BICI) was recently found to produce azimutally narrow interchange heads extending into the dipole region from a reversed radial gradient of B$_Z$ in the near-Earth magnetotail. In their nonlinear evolution individual heads were predicted to detach from the reversed B$_Z$ gradient and grow into transient earthward moving northward magnetic field intensifications (dipolarization fronts; DFs). The distinguished signatures of such fronts would be their oblique propagation and cross-tail localization due to the finite k$_y$ structure of the BICI modes. Simultaneous conjugate observations of DFs by THEMIS probes at 11 Earth’s radii (R$_E$) downtail and of sudden brightening and growth of individual auroral beads by the all sky imagers on the ground have been suggested to be ionospheric signature of detached magnetotail interchange heads [Panov et al., 2019]. Here we compare such DFs with a simulated interchange head during later(detachment)-stage BICI head development. The comparison reveals similarly structured leading edges and trailing tails in both the observed DFs and the simulated BICI head. We further identify THEMIS trajectories through the DFs and find that the trajectories were due to oblique (earthward and dawnward) DF propagation. This analysis further supports the idea that BICI indeed releases obliquely propagating azimuthally localized dipolarization fronts in the Earth’s magnetotail.

As it was recently predicted, the kinetic ballooning/interchange instability (BICI) can provoke reconnection onsets that lead to detached azimuthally thin earthward intrusions (heads) of depleted plasma tubes when 𝛽eq ⩽ 100. Such detached BICI heads would be seen as localized earthward-propagating dipolarization fronts. Using Time History of Events and Macroscale Interactions during Substorms observations in the plasma sheet at XGSM ≈ −11 Re and conjugate All-Sky Imager and magnetometer networks observations on the ground, we show four examples when prominent dipolarization fronts with moderate earthward flows were observed amidst azimuthally drifting interchange heads and concurrently with the ionospheric current intensifications near Time History of Events and Macroscale Interactions during Substorms footprints and auroral bright spots originating from dimmer azimuthal beads/rays. These events support the idea that some of the BICI heads detach from the region with reversed radial gradient of Bz. The detached BICI heads propagate earthward-driving ionospheric pseudo-breakups.