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We present a nonlocal gyrokinetic theory for the drift‐mirror mode in high‐β$\\beta $anisotropic plasmas. Here, β$\\beta $represents the ratio of plasma pressure to magnetic pressure. The equilibrium distribution is established self‐consistently via guiding‐center Hamiltonian theory. To keep the nonuniformity and finite Larmor radius (FLR) effects on an equal footing, we derive the three‐field nonlocal eigenmode equations in Fourier space under the assumption of weak nonuniformity. It is found that the drift‐mirror mode is essentially a dissipative instability confined within the potential well due to the FLR effect. Numerical analyses demonstrate that the drift‐mirror mode originates from the coupling between shear Alfvén and mirror branch, where the ion‐sound wave component is negligible. Furthermore, the β$\\beta $threshold of this nonlocal drift‐mirror mode is significantly lower than that of the conventional drift‐mirror mode. Plain Language Summary The drift‐mirror instability has been intensively investigated in space physics. It can be destabilized by pressure anisotropy in magnetized plasmas and result in the formation of the cavity across the field lines where the mode is confined. In this study, we investigate the linear properties of the nonlocal drift‐mirror mode by employing the electromagnetic gyrokinetic theory. The nonuniform equilibrium is self‐consistently established, with both magnetic and plasma inhomogeneities taken into account on the equal footing. An eigenmode system describing the nonlocal drift‐mirror mode is then derived in Fourier space. It is found that the drift‐mirror mode arises from the coupling between the shear Alfvén branch and the mirror branch. The ion‐sound wave branch, however, is negligible. Additionally, further numerical analyses demonstrate that the kinetic drift‐mirror mode is more easily excited than the mirror mode in uniform and fluid limits. These results provide a deeper understanding of the drift‐mirror mode. Key Points By employing the nonlocal electromagnetic gyrokinetic theory, we present a self‐consistent description of the drift‐mirror mode It is showed that the drift‐mirror mode is a dissipative instability confined within the potential well arising from the FLR effect The drift‐mirror mode originates from the coupling between shear Alfvén and mirror branch, where the ion‐sound wave component is subdominant

In the solar wind, STEREO occasionally observes mirror‐mode storms, periods in which small amplitude waves suddenly appear and persist for hours. Two triggers of these storms are high‐plasma beta and weak shocks, both consistent with conditions for the growth of mirror‐mode waves. The appearance of these waves is quite distinct from the isolated mirror‐mode structure that is frequently seen in the solar wind. They have not been reported previously. Here we show three examples of their occurrence.

Dayside transients, such as hot flow anomalies, foreshock bubbles, magnetosheath jets, flux transfer events, and surface waves, are frequently observed upstream from the bow shock, in the magnetosheath, and at the magnetopause. They play a significant role in the solar wind-magnetosphere-ionosphere coupling. Foreshock transient phenomena, associated with variations in the solar wind dynamic pressure, deform the magnetopause, and in turn generates field-aligned currents (FACs) connected to the auroral ionosphere. Solar wind dynamic pressure variations and transient phenomena at the dayside magnetopause drive magnetospheric ultra low frequency (ULF) waves, which can play an important role in the dynamics of Earth’s radiation belts. These transient phenomena and their geoeffects have been investigated using coordinated in-situ spacecraft observations, spacecraft-borne imagers, ground-based observations, and numerical simulations. Cluster, THEMIS, Geotail, and MMS multi-mission observations allow us to track the motion and time evolution of transient phenomena at different spatial and temporal scales in detail, whereas ground-based experiments can observe the ionospheric projections of transient magnetopause phenomena such as waves on the magnetopause driven by hot flow anomalies or flux transfer events produced by bursty reconnection across their full longitudinal and latitudinal extent. Magnetohydrodynamics (MHD), hybrid, and particle-in-cell (PIC) simulations are powerful tools to simulate the dayside transient phenomena. This paper provides a comprehensive review of the present understanding of dayside transient phenomena at Earth and other planets, their geoeffects, and outstanding questions.

Electromagnetic ion cyclotron (EMIC) waves and mirror modes (MMs), both driven by ion temperature anisotropy, are commonly observed in planetary magnetosheaths. Conventional explanations for their co‐occurrence are largely based on linear instability theory in proton–electron plasmas, which requires comparable growth rates for the EMIC and MM instabilities. Magnetosheath plasmas, however, contain a fraction of heavy ions, and how such composition affects the coexistence of EMIC waves and MMs has been less explored. Using kinetic hybrid simulations with typical magnetosheath parameters, we show that although the presence of heavy ions suppresses the initial linear EMIC instability, EMIC waves arise as MMs develop. The evolving MMs generate flat‐top proton velocity distributions with enhanced resonant populations, which in turn excite EMIC waves. These results extend the conventional coexistence scenario of MMs and EMIC waves and reveal a new pathway for energy transfer among MMs, EMIC waves, and particles in magnetosheath plasmas.

There has been considerable confusion in the literature about what mirror mode (MM), magnetic decrease (MD), and linear magnetic decrease (LMD) structures are and are not. We will reexamine past spacecraft observations to demonstrate the observational similarities and differences between these magnetic and plasma structures. MM structures in planetary magnetosheaths, cometary sheaths, and the heliosheath have the following characteristics: (1) the structures have little or no changes in the magnetic field direction across the magnetic dips; (2) the structures have quasiperiodic spacings, varying from ∼20 proton gyroradii (rp) in the Earth's magnetosheath to ∼57 rp in the heliosheath; and (3) the magnetic dips have smooth edges. Magnetosheath MM structures are generated by the mirror instability where β⊥/β∥ > 1 + 1/β⊥ (β is the plasma thermal pressure divided by the magnetic pressure). In general, the sources of free energy for the mirror instability are reasonably well understood: shock compression, field line draping, and, in the cases of comets and the heliosheath, also ion pickup. The observational properties of interplanetary MDs are as follows: (1) there is a broad range of magnetic field angular changes across them; (2) their thicknesses can range from as little as 2–3 rp to thousands of rp, with no “characteristic” size; and (3) they typically are bounded by discontinuities. The mechanism(s) for interplanetary MD generation is (are) currently unresolved, although at least five different mechanisms have been proposed in the literature. Tsurutani et al. (2009a) have argued against mirror instability for those MDs generated within interplanetary corotating interaction regions. Interplanetary LMDs are by definition a subset of MDs with small angular changes across them (θ < 10°). Are LMDs generated by the mirror instability or by another mechanism? Is it possible that there are several different types of LMDs involving different generation mechanisms? At the present time, no one knows the answers to these latter questions.

Magnetic holes at the ion-to-electron kinetic scale (KSMHs) are one of the extremely small intermittent structures generated in turbulent magnetized plasmas. In recent years, the explorations of KSMHs have made substantial strides, driven by the ultra-high-precision observational data gathered from the Magnetospheric Multiscale (MMS) mission. This review paper summarizes the up-to-date characteristics of the KSMHs observed in Earth’s turbulent magnetosheath, as well as their potential impacts on space plasma. This review starts by introducing the fundamental properties of the KSMHs, including observational features, particle behaviors, scales, geometries, and distributions in terrestrial space. Researchers have discovered that KSMHs display a quasi-circular electron vortex-like structure attributed to electron diamagnetic drift. These electrons exhibit noticeable non-gyrotropy and undergo acceleration. The occurrence rate of KSMH in the Earth’s magnetosheath is significantly greater than in the solar wind and magnetotail, suggesting the turbulent magnetosheath is a primary source region. Additionally, KSMHs have also been generated in turbulence simulations and successfully reproduced by the kinetic equilibrium models. Furthermore, KSMHs have demonstrated their ability to accelerate electrons by a novel non-adiabatic electron acceleration mechanism, serve as an additional avenue for energy dissipation during magnetic reconnection, and generate diverse wave phenomena, including whistler waves, electrostatic solitary waves, and electron cyclotron waves in space plasma. These results highlight the magnetic hole’s impact such as wave-particle interaction, energy cascade/dissipation, and particle acceleration/heating in space plasma. We end this paper by summarizing these discoveries, discussing the generation mechanism, similar structures, and observations in the Earth’s magnetotail and solar wind, and presenting a future extension perspective in this active field.

AbstractThe paper is devoted to propagation of time-harmonic mirror wave modes in hemitropic micropolar media. Dynamics equations of a hemitropic micropolar elastic solid are formulated in terms of pseudotensors formalism. Transformation formulae for translational and spinor displacements, differential pseudovector operators and constitutive pseudoscalars for the cases of space inversion and mirror reflection relative to a given plane are obtained. Simultaneous existence of the direct, inverse and mirror reflected wave modes of propagating plane waves is predicted. Plane wave propagating in hemitropic micropolar elastic media comprises the three types of wave modes: direct, inverse and mirror. Algorithm for transformation direct wave modes into inverse and mirror modes of spinor and translational displacements is proposed.

Magnetic holes in the solar wind with little or no directional change across the magnetic depression are related to mirror mode structures. Recently, Zhang et al. (2008) determined the characteristic size and shape of such mirror mode structures in the solar wind at 0.72 AU. They found that the mirror mode structure in the solar wind is quite elongated along the field direction. In this report, we examine the size and shape of isolated magnetic holes and train of holes, separately. We find that the isolated holes are slightly smaller in width and more elongated than the multiple holes. This observation suggests a particular evolutionary history of mirror mode structures in the solar wind in which multiple holes coalesce with time into isolated structures more elongated parallel to the magnetic field.

Nonpropagating mirror‐mode structures are commonly observed in many regions of natural plasma such as solar wind, planetary magnetosheaths, in cometary plasma, Io wake, terrestrial ring current and even on the outskirts of solar system. Mirror structures are typically observed in the shape of magnetic holes or peaks. Fast survey mode plasma data from the THEMIS satellites are used to solve the puzzle of how mirror structures in the form of dips can be observed in the regions of mirror stable plasma. THEMIS data also show that for mirror structures with spatial scales that considerably exceed ion Larmor radius the perpendicular temperature anticorrelates with the strength of the magnetic field. This contradiction with the conservation of adiabatic invariants is explained by the role of trapped particles.

We present a high-power, wavelength-tunable picosecond Yb3+: CaGdAlO4 (Yb:CALGO) laser based on MgO-doped lithium niobate (MgO:LN) nonlinear mirror mode locking. The output wavelength in the continuous wave (CW) regime is tunable over a 45 nm broad range. Mode locking with a MgO:LN nonlinear mirror, the picosecond laser is tunable over 23 nm from 1039 to 1062 nm. The maximum output power of the mode-locked laser reaches 1.46 W, and the slope efficiency is 18.6%. The output pulse duration at 1049 nm is 8 ps. The laser repetition rate and bandwidth are 115.5 MHz and 1.7 nm, respectively.