[1] Current sheets are one of the key elements of the Earth's magnetosphere, determining the magnetic energy storage and release. An analytical self-consistent model of multicomponent thin current sheets, where the plasma consists of ions of both solar wind and ionospheric origin, is presented. The influence of the electron population is taken into account assuming Boltzman-like quasi-equilibrium distribution in the electrostatic field, which can lead to a sharp peak in the electron current density in the center of the current sheet. We include the contribution of non-adiabatic O + ions in our model as one of the terms in the Grad -Shafranov-like system of equations describing the quasi-equilibrium configuration. The contribution of the oxygen ions to the total cross-tail current usually does not exceed 30% for realistic conditions, but current ''wings'' carried by O + ions produce significant broadening of the current profile.Citation: Zelenyi, L. M., H. V.

Abstract. Multiple and sporadic time-of-flight velocity dispersed ion structures (TDIS) are systematically observed above the ionosphere at • 3 R• altitude by Interball/Auroral spacecraft near the poleward edge of the auroral bulge. These events represent direct snapshots of the impulsive ion acceleration process in the equatorial plasma sheet which allow us to study the details of the connection between ionospheric and plasma sheet manifestations of the magnetospheric substorm. Two events are analyzed during which the spacecraft footpoints passed over the Scandinavian ground network. We found that the TDIS correlate with the intensifications of westward current and auroral activations at the poleward edge of the bulge, which confirms the association of these dispersed ion beams with the temporal evolution of impulsive reconnection in the tail. Furthermore, we present direct evidence of an active neutral line in the magnetotail during one of the events using plasma sheet measurements made concurrently by the Interball/Tail and Geotail spacecraft. The 2-3 rain repetition period of these •1 rain long activations indicates a fundamental time constant of the substorm instability. On the other hand, the estimated injection distances of the energy-dispersed ions were inferred to be smaller than the estimated position of the reconnection region in the tail. We also found that the TDIS ion beams are released within the closed plasma flux tubes deep inside the plasma sheet, and yet they are synchronized with auroral activations at the poleward boundary. These fkcts imply that the ion beams are formed in a spatially extended region of the plasma sheet rather than in the close vicinity of the neutral line. We argue that braking of the reconnection-induced fast flow bursts when they interact with the closed plasma flux tubes and the earthward propagating fast wave electric field generated in the braking region may be important in forming the observed multiple, sporadic, energy-dispersed ion beams.

We study the proton‐to‐electron temperature ratio (Tp/Te) in the plasma sheet (PS) of the Earth's magnetotail using 5 years of Cluster observations (2001–2005). The PS intervals are searched within a region defined with −19 < X ≤ −7 RE and |Y| < 15 RE (GSM) under the condition |BX| ≤ 10 nT. One hundred sixty PS crossings are identified. We find an average value of  ~ 6.0. However, in many PS intervals Tp/Te varies over a wide range from a few units to several tens of units. In 86 PS intervals the Tp/Te decreases below 3.5. Generally, the decreases of Tp/Te are due to some increase of Te while Tp either decreases or remains unchanged. In the majority of these intervals the Tp/Te drops are observed during magnetotail dipolarizations. A superposed epoch analysis applied to these events shows that the minimum value of Tp/Te is observed after the dipolarization onset during the “turbulent phase” of dipolarization, when a number of transient BZ pulses are reduced, but the value of BZ is still large and an intensification of wave activity is observed. The Tp/Te drops, and associated increases of Te often coincide either with bursts of broadband electrostatic emissions, which may include electron cyclotron harmonics, or with broadband electromagnetic emission in a frequency range from proton plasma frequency (fpp) up to the electron gyrofrequency (fce). These findings show that the wave activity developing in the current sheet after dipolarization onset may play a role in the additional electron heating and the associated Tp/Te decrease.

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Current sheets (CSs) are widespread objects in space plasma capable of storing and, then, explosively releasing the accumulated magnetic energy. In planetary magnetotails the cross-tail CS plays an important role in the global dynamics of the tail and in the transformation of the magnetic energy into the kinetic and thermal energies of the ambient plasma. We have analyzed 114 crossings of the cross-tail CS by the MAVEN spacecraft at X MSO ∼ [−1.0, −2.8]R M. Magnetic field observations with high time resolution allowed the observation of the inner superthin CS (STCS) with a half-thickness L STCS ∼ (1–100)ρ e (ρ e is the gyroradius of thermal electrons) in 75 intervals of the CS crossings from our database. The STCS was embedded into a thicker ion-scale CS and provides 10%–50% of the total current density in the cross-tail CS. Our analysis has shown that the observed L STCS and the embedding parameter, σ emb, characterizing the contribution of the STCS to the total current density in the CS are well described by the novel analytical kinetic model of a multilayered CS with an inner embedded electron-scale layer: L STCS∼ (0.9–1.2)λ and σ emb ∼ (0.9–1.2) σ model, where the universal spatial scaling λ ∼ δ i 2/ρ P and the embedding parameter σ model ∼ δ i /ρ P are determined by the local ion inertial length (δ i ) and gyroradius of thermal protons (ρ P ) in the STCS.