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The Hot Ion Analyser (HIA), part of the Cluster Ion Spectrometry experiment, has the objective to measure the three-dimensional velocity distributions of ions. Due to a variety of factors (exposure to radiation, detector fatigue and aging, changes in the operating parameters etc.), the particles detection efficiency changes over time, prompting for continuous in-flight calibration. This is achieved by comparing the HIA data with the data provided by the WHISPER experiment on magnetosheath intervals, for the high sensitivity section of the instrument, or solar wind intervals, for the low sensitivity section. The paper presents in detail the in-flight calibration methodology, reports on the work carried out for calibrating HIA and discusses plans to extend this activity in order to ensure the instrument highest data accuracy. [ABSTRACT FROM AUTHOR]

On the basis of ARTEMIS two-probe mission magnetic reconnection (MR) outflow associated magnetic fluctuations and turbulence are analyzed on 19 February 2011. In the deep-tail, at distances between X = 45 - 51RE, evidence for reconnection associated plasma sheet thinning was found, accompanied by heating of the plasma sheet. Correlated flow and field reversals and the large-scale Hall-effect signatures indicated the presence of the reconnection X-line. Within fast reconnection plasma outflows, magnetic fluctuations exhibit the same spectral scaling features and kinked spectra as magnetic fluctuations in the solar wind or in various parts of geospace. It was shown that the proton scale magnetic fluctuations are constrained by oblique firehose, proton cyclotron and mirror instability thresholds. For parallel plasma β∥ > 1, where the thresholds converge, perpendicular magnetic fluctuations are enhanced. Magnetic compressibility decreases with the distance to the neutral sheet, however, near the instability thresholds it is comparable to the values obtained in the solar wind. [ABSTRACT FROM AUTHOR]

Abstract: In the present paper, we have studied the effect of plasma mixing on the small-scale field configurations. We have employed theoretical models and numerical simulations to describe magnetic field structures formed by the mixing motion of the interplanetary plasma. The small-scale magnetic fluctuations share properties with waves and with turbulence as well. It is shown that plasma mixing can account for both wave-like and turbulence-like behavior. Mixing can also explain the formation and the dominance of the so-called 2D fluctuations. Four-point measurements provide a new tool for the experimental investigation of the field configurations. Our effort was to identify the effect of plasma mixing. In a slow laminar mixing flow sheet-like structures are formed everywhere in the plasma. The existence of these kind of structures has been tested using the magnetometer data of the four Cluster spacecraft. Our results suggest that plasma mixing plays a significant role in the formation of the small-scale magnetic fluctuations of the solar wind. Our results support that the 2D component dominates the magnetic fluctuations. [Copyright &y& Elsevier]

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., (© The Author(s) 2022.)