Mirror modes are ubiquitous in space plasma and grow from pressure anisotropy. Together with other instabilities, they play a fundamental role in constraining the free energy contained in the plasma. This study focuses on mirror modes observed in the solar wind by Solar Orbiter for heliocentric distances between 0.5 and 1 AU. Typically, mirror modes have timescales from several to tens of seconds and are considered quasi-MHD structures. In the solar wind, they also generally appear as isolated structures. However, in certain conditions, prolonged and bursty trains of higher frequency mirror modes are measured, which have been labeled previously as mirror mode storms. At present, only a handful of existing studies have focused on mirror mode storms, meaning that many open questions remain. In this study, Solar Orbiter has been used to investigate several key aspects of mirror mode storms: their dependence on heliocentric distance, association with local plasma properties, temporal/spatial scale, amplitude, and connections with larger-scale solar wind transients. The main results are that mirror mode storms often approach local ion scales and can no longer be treated as quasi-MHD, thus breaking the commonly used long-wavelength assumption. They are typically observed close to current sheets and downstream of interplanetary shocks. The events were observed during slow solar wind speeds and there was a tendency for higher occurrence closer to the Sun. The occurrence is low, so they do not play a fundamental role in regulating ambient solar wind but may play a larger role inside transients.

Solar wind electrons play an important role in the energy balance of the solar wind acceleration by carrying energy into interplanetary space in the form of electron heat flux. The heat flux is stored in the complex electron velocity distribution functions (VDFs) shaped by expansion, Coulomb collisions, and field-particle interactions. We investigate how the suprathermal electron deficit in the anti-strahl direction, which was recently discovered in the near-Sun solar wind, drives a kinetic instability and creates whistler waves with wave vectors that are quasi-parallel to the direction of the background magnetic field. We combined high-cadence measurements of electron pitch-angle distribution functions and electromagnetic waves provided by Solar Orbiter during its first orbit. Our case study is based on a burst-mode data interval from the Electrostatic Analyser System (SWA-EAS) at a distance of 112 RS (0.52 au) from the Sun, during which several whistler wave packets were detected by Solar Orbiter’s Radio and Plasma Waves (RPW) instrument. The sunward deficit creates kinetic conditions under which the quasi-parallel whistler wave becomes unstable. We directly test our predictions for the existence of these waves through solar wind observations. We find whistler waves that are quasi-parallel and almost circularly polarised, propagating away from the Sun, coinciding with a pronounced sunward deficit in the electron VDF. The cyclotron-resonance condition is fulfilled for electrons moving in the direction opposite to the direction of wave propagation, with energies corresponding to those associated with the sunward deficit. The quasilinear diffusion of the resonant electrons tends to fill the deficit, leading to a reduction in the total electron heat flux.

The Data Processing Unit (DPU) is the “heart” of the plasma suite SWA and is the only interface with the S/C. The DPU is interfaced with EAS, PAS and HIS sensors via SpW dedicated links and is in charge of supporting EAS and PAS with power, functionality control, temporary storage, communication and computational capability and, in addition, supports HIS with communication to the S/C. Its architecture derives from a trade-off analysis aiming to define a system able to perform the needed computational tasks while keeping mass, volume and power within the limits imposed by the constraints. Additionally, the DPU has been designed to be “single fault” tolerant and the “cold-spare” concept has been adopted as redundancy philosophy. It implements data and command interfaces with the S/C via the redundant SpaceWire (SpW) data links and the redundant power input HV-HPC command interface. Two independent, executable SW images represent the overall SWA DPU SW: the Boot SW (BSW) and the Flight SW (FSW). While the BSW manages the basic hardware initialization, the FSW manages TC/TM, controls all the processes related to the state of the sensors, validates and executes TC, acquires, processes, compresses and formats science data prior to downlink for EAS(1&2) and PAS sensors, while HIS autonomously processes its scientific data. In particular, FSW is in charge of data compression, moments calculation and telemetry generation restrictions to keep each sensor within its respective telemetry allocation. Remarkable level of data compression for EAS, which generates the largest data volume, is reached via customized implementation of lossless CCSDS 121.0 based on a “Complex Reordering” mechanism, which avoids periodical jumps among acquisition directions in phase space. Moments of proton and electron velocity distribution functions are computed onboard. Different Look-Up Tables (LUT) for PAS and EAS allow to perform moments calculation modulating the counts in each volume of phase space by a combination of the factors contained in these tables. Finally, since SWA data production greatly changes from normal to burst mode, a book keeping algorithm (BKA) will monitor and control, continuously along the orbit, the amount of burst mode, scheduled or triggered, used against the pro-rata expectation.

The solar wind is a continuous outflow of plasma from the Sun, which expands into the space between the planets in our solar system and forms the heliosphere. The solar wind is inherently turbulent and characterised by kinetic micro-instabilities on a range of scales. The Sun also intermittently ejects mass (coronal mass ejections; CMEs) or solar energetic particles (SEPs) which change their trajectory or energy due to their interactions with the solar wind. When these violent particle events hit the Earth’s magnetosphere, they can cause “space weather” with both long- and short-term impacts on our natural and technological environment. This presentation investigates the behaviour and the effects of kinetic instabilities in a turbulent plasma with particular emphasis on energy transfer processes. We utilise the unprecedented observations from ESA’s Solar Orbiter spacecraft, launched in February 2020, to advance our understanding of the Sun, the solar wind, and space weather. Large-scale compressions (ubiquitous in solar-wind turbulence) create conditions for proton, alpha-particle and electron microinstabilities, which then transfer energy to small-scale fluctuations. These instability-driven small-scale fluctuations, including those driven by turbulence and other sources of free energy (e.g. particle beams, differential flows, heat fluxes, temperature anisotropies), make a significant contribution to the fluctuation spectrum at kinetic scales, where energy dissipation occurs. We consider instabilities driven by turbulence in the plasma by using statistical methods to analyse the Solar Orbiter data and characterise the turbulence at the relevant scales and amplitude. Specifically, we evaluate the processes by which turbulence combined with temperature anisotropy causes instability, comparing theoretical calculations with the high resolution data available from the Solar Orbiter MAG and SWA instruments.