How Solar Orbiter will observe small-scale time variations of the solar wind and identify characteristic structures

Solar Orbiter will perform close-up studies of the Sun and the inner heliosphere. The Solar Wind Analyser (SWA) suite of in-situ plasma instruments on board Solar Orbiter will measure the three-dimensional velocity distribution functions of the plasma ions and electrons. The observations will determine the plasma bulk properties which help us to study the dynamics and identify different structures in the solar wind. In this paper, we examine the effects of short time-scale plasma variations on these measurements. We especially investigate how they will affect the estimated bulk properties of the plasma. For the purpose of this work, we simulate the expected observations of solar wind protons and electrons, in a range of plasma conditions, taking into account a realistic performance of the proton and the electron plasma sensors on board Solar Orbiter. We examine a range of the observed plasma parameters, typical for characteristic structures in the solar wind, and take into account realistic time variations. Among others, we examine the effects on the measurements of Alfvénic fluctuations typical of turbulence and sharp discontinuities associated with shocks. We then use standard analysis methods in order to derive the plasma bulk properties from the simulated observations. The comparison between the derived bulk parameters with the input bulk parameters allow us to validate which solar wind structures and dynamics we can reliably identify in the observations. Our study will significantly improve our understanding of the particle measurements with Solar Orbiter.