Solar Orbiter: Studies of the Solar Wind Charged Particle Populations

UCL/MSSL is the Principal Investigator (PI) Institute on an international consortium providing the Solar Wind Analyser suite (SWA) of instruments for the ESA Solar Orbiter mission. Using 3 scientific sensors, SWA is able to sample electron, proton, alpha particle and heavy ion populations at various distances down to 0.28 AU from the Sun (i.e. around a quarter the distance from the Sun to the Earth) and at high solar latitudes. In particular, UCL/MSSL has designed and built the Electron Analyser System (EAS) for the SWA suite. SWA partners in France, Italy and the USA have provided the Heavy Ion Sensor (HIS) and Proton-Alpha Sensor (PAS) for the suite. In addition, MSSL has a major role in the EUI instrument on the spacecraft, which consists of a suite of imaging telescopes to observe the solar atmosphere. EUI will allow us to determine the global structure of the solar corona and to provide a crucial understanding of fine scale processes in the dynamic solar atmosphere. Images taken by EUI offer an indispensable link between the solar surface and the outer corona, which ultimately shapes the characteristics of the interplanetary medium sampled in situ by SWA and other instruments on Solar Orbiter.

The mission was launched on 11th Feb 2020, and is now in cruise phase ahead of a nominal mission start in late 2021. Although EUI and other remote sensing data will not be regularly taken until the nominal mission starts, SWA cruise phase data is already available, and thus represents an important new data set that could immediately support analysis within this PhD program starting in September 2021. In particular, we aim to use cruise-phase measurements from the 3 SWA sensors to undertake studies of the nature of the solar wind particle populations and their variability. For example, the solar wind electron population in general consists of 3 components which together contain information about the processes occurring at the source region on the Sun, the magnetic connections of the sampled plasma back to the Sun and on the plasma processes (e.g. turbulence, wave-particle interactions and magnetic reconnection) which may be occurring within the solar wind itself. Separating the effects of these processes is a complicated task requiring high-cadence, high resolution data of the type that will be available from SWA EAS. As a kick-off project on this PhD program, we will seek to analyse 'trigger-mode' captures of high resolution data around the passage of interplanetary shocks, which are driven through the solar wind by many forms of solar activity (for example, CME eruption, co-rotating interaction regions).

Further into the project, we will seek to develop a research plan which would make use, from the start of the nominal phase, of the MSSL involvement in both SWA and EUI to support studies of the Sun-solar wind connections, which represent the headline goals of the mission. For example, the forms of activity mentioned above which drive shocks through the solar wind are prime targets for EUI. Thus linking the properties and nature of the shock to the properties of the various drivers is a good illustration of a number of potential studies that we will seek to pursue with the combined Solar Orbiter observations. In addition, the project will benefit from the availability of data from other missions, such as NASA's Parker Solar Probe, which we will use to undertake coordinated studies.

The results this project will add to the success of the overall ESA Solar Orbiter program, and the student will be an integral part of the MSSL science and science-planning teams. The student will collaborate with our partners in Europe and the USA, who have provided the HIS and PAS sensors for the SWA suite and other major subsystems for EUI. This project will place the student in a good position to collaborate more generally and to find future positions e.g. within the international Solar Orbiter community.