ALBERT

Description: Solar Orbiter was launched in February 2020, and has now completed the first 3 perihelia of its nominal mission phase. Mission science goals include establishing and understanding the links between processes occurring at the Sun and their consequences for the nature of the inner heliosphere and solar wind, as well as furthering our knowledge of the physics of the solar wind and the solar atmosphere themselves. A significant volume of science data has been accumulated by the 10 payload instruments, including novel data recorded by the 3 separate sensors which, together with a central DPU, comprise the Solar Wind Analyser (SWA) suite. Between them, these sensors, the Electron Analyser System, the Proton-Alpha Sensor and the Heavy Ion Sensor, make measurements of 3D velocity distribution functions of solar wind electron, proton and alpha particle populations, together with abundant heavy ions such as O6+ and ion charge states such as Fe9+ or Fe10+. In this presentation we summarise recent key results of studies using data from one or more of the 3 SWA sensors, and illustrate the quality of the data and their contribution to achieving the mission science goals. These include the availability of high time cadence observations which offer unique possibilities for resolving plasma kinetic processes at small scales in the solar wind. Combining with observations from other instruments on the platform, and from other missions, we also report on work to establish the origin of the solar wind stream passing the spacecraft and the physical processes driving its release.

Description: Protons are the primary carriers of Alfvén waves in the solar wind. Typically, solar wind alpha particles drift faster than the protons and do not participate in these low-frequency oscillations. In other words, alpha particles “surf” on Alfvén waves. Investigating high time-resolution observations from Solar Orbiter’s Heavy Ion Sensor, we study the interaction of heavy ions with Alfvén waves. We discuss the implications for mass-per-charge dependent nature of charged particle surfing on Alfvén waves.

Description: We investigate the turbulent energy cascade in the near-Sun solar wind by means of a high-resolution fully kinetic simulation initialised with average plasma conditions measured by Parker Solar Probe during its first solar encounter. Our simulation models the electron-scale electric field fluctuations with unprecedented accuracy. This allows us to perform the first detailed analysis of the different terms of the electric field in the generalised Ohm's law (MHD, Hall, and electron pressure terms) at ion and electron scales, both in physical space and in Fourier space. Such analysis suggests rewriting the Ohm’s law in a different form, which disentangles the contribution of different underlying plasma mechanisms in each range of scales. This provides a new insight on how energy in the turbulent electromagnetic fields is transferred through ion and electron scales and seems to favour the role of pressure-balanced structures versus waves. We finally test our assumptions and numerical results by analysing measurements of the magnetic field, electric field, and ion and electron velocity distributions and their moments performed by Solar Orbiter and Parker Solar Probe. Preliminary results show a remarkable agreement with our theoretical expectations inspired by our simulations.

Description: Interplanetary (IP) shocks can be driven in the solar wind by fast coronal mass ejections and by the interaction of fast solar wind with slow streams of plasma. These shocks can be preceded by extended foreshocks where a variety of waves and suprathermal ion populations exist. Shocks characteristics as well as the level of wave activity near them change as they propagate through the heliosphere and this can impact particle acceleration, and modify the ambient solar wind. In this work we study IP shock evolution and the wave modes upstream of them using a multispacrecaft approach with data of Solar Orbiter, STEREO, Parker Solar Probe and Wind. We find that upstream regions can be permeated by whistler waves (f ~ 1 Hz) and/or ultra low frequency (ULF) right-handed waves (f~10-2–10-1 Hz). While whistlers appear to be generated at the shock, the origin of ULF waves is associated with local kinetic ion instabilities. In contrast with planetary bow shocks, most IP shocks have a small Mach number (〈4) and most of the upstream waves studied here are mainly transverse and rarely steepening occurs.