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Overview

Theo Murphy meeting organised by Dr Julia Stawarz, Dr Daniel Verscharen and Dr Christopher Chen.

This meeting will bring together experts on plasma turbulence in the solar wind and Earth's magnetosphere to discuss the latest cutting-edge results on the role of collision-less plasma processes in turbulent energy dissipation from the revolutionary Magnetospheric Multiscale and Parker Solar Probe spacecraft. These discussions will provide crucial input for the ongoing science operations of these and future space missions. 

The schedule of talks and speaker biographies are available below. Speaker abstracts are also available below.

Poster session

There will be a poster session on Monday 30 May. If you would like to apply to present a poster please submit your proposed title, abstract (not more than 200 words and in third person), author list, name of the proposed presenter and institution to the Scientific Programmes team no later than Tuesday 3 May 2022. Please include the text 'Poster abstract submission' in the email subject line. Please note that places are limited and posters are selected at the scientific organisers' discretion. Poster abstracts will only be considered if the presenter has requested an invitation to attend the meeting.

Attending this event

This meeting is intended for researchers in relevant fields.

  • Free to attend
  • Limited places, advance registration essential (please request an invitation).
  • This is an in-person meeting

Enquiries: contact the Scientific Programmes team.

Organisers

Schedule


Chair

09:00-09:05
Welcome by the Royal Society and the lead organiser
09:05-09:30
The discrete sources of solar wind energisation

Abstract

After eleven orbits around the Sun, measurements from the NASA Parker Solar Probe mission have begun to reveal the nature of solar wind energisation and its discrete sources. Previously termed 'microstreams', individual streams of hot, accelerated solar wind are emerging from coronal holes and are organised in Carrington longitude by the known angular scale of the photospheric network magnetic field. These discrete microstreams are highly Alfvenic, show faster, hotter solar wind, enhanced alpha particle abundance, and steep suprathermal ion tails to greater than 100 keV. The microstream structures overexpand and merge together to form a more homogeneous solar wind in the outer heliosphere. The origin of this solar wind in the network magnetic 'funnels' at the boundary of supergranulation cells provides clues as to the physical mechanisms at work to impart energy. Professor Bale will review the state of the art of the PSP measurements and their implications for the coronal heating problem.

Speakers

09:30-09:45
Discussion
09:45-10:15
Speaker tbc
10:15-10:30
Discussion
10:30-11:00
Coffee
11:00-11:30
An incomplete theory of dissipation in collisionless plasmas

Abstract

Fluid-based studies of dissipation have met with great success in collisional mediums including work in turbulence and dense plasmas. However, this success has not been fully realized in collisionless plasmas where a better understanding of dissipation has been elusive. The essence of the problem that, in a collisionless plasma, there may be no 'good' definition of fluid parameters that separates internal energy from flow energy. To avoid this issue, Professor Ergun takes an approach to dissipation that involves phase-space mixing or 'scattering domains'. He shows that, when phase-space mixing or 'scattering domains' are considered, Liouville's theorem does not necessarily apply and that Vlasov’s equation does not necessarily conserve entropy. He develops an incomplete theory based on Lyapunov-like scattering that may be able to predict dissipation rates based on electric field spectra in a simple 1D system.

Speakers

11:30-11:45
Discussion
11:45-12:15
Speaker tbc
12:15-12:30
Discussion

Chair

13:30-14:00
Kinetic physics of dissipation

Abstract

In this talk, Dr Klein will discuss recent advances in our theories for the dissipation of turbulence in weakly collisional plasmas and the role that such dissipation plays in governing the evolution of space and astrophysical systems. An overview of the various mechanisms that couple the turbulent electromagnetic fields to the particle flows and distributions is provided, as well as evidence for these different processes from numerical simulations as well as in situ measurements of the plasma from NASA and ESA missions such as Parker Solar Probe, Solar Orbiter, and MMS. Open questions regarding what work needs to be done to ascertain what dissipation mechanisms act under what conditions will be posed, as well as possible advances that will be enabled by future observations, such as multi-point, multi-scale measurements from missions such as HelioSwarm.

Speakers

14:00-14:15
Discussion
14:15-14:45
How non-equilibrium thermodynamics constrains magnetohydrodynamics, in the solar wind and beyond

Abstract

In this talk, Professor Kunz will focus on the different ways in which departures from local thermodynamic equilibrium, produced naturally in weakly collisional plasmas and biased anisotropically by magnetic fields, place constraints on plasma dynamics in the solar wind and other astrophysical environments. These constraints afflict not only simple waves and fundamental plasma processes such as magnetic reconnection, but also highly nonlinear phenomenon like plasma turbulence and particle energization. After providing some background and observational context, three demonstrations of this physics will be featured. (1) Above a beta-dependent amplitude threshold, Alfvén waves interrupt their own propagation, ion-acoustic waves stifle their own Landau damping, and other collisionless compressive fluctuations exhibit dynamics that are often more 'fluid-like' than kinetic in nature. (2) Temperature anisotropy generated adiabatically by plasma expansion (as in the solar wind) gradually reduces the effective elasticity of magnetic-field lines, causing reductions in the linear frequency and residual energy of the Alfvénic fluctuations; despite these changes, a scale-by-scale 'critical balance' persists between their characteristic linear and nonlinear frequencies. And (3), temperature anisotropy generated during current-sheet formation can drive mirror-stimulated tearing modes, which trigger reconnection on smaller scales and at earlier times than would otherwise occur. The prospects of detecting this physics in the solar wind will be briefly discussed.

Speakers

14:45-15:00
Discussion
15:00-15:30
Tea
15:30-16:00
Alfvénic and non-Alfvénic turbulence in the inner heliosphere: insights from Parker Solar Probe

Abstract

Professor Velli will discuss the turbulence embedded in the solar wind outflow observed by Parker Solar Probe over the first 10 encounters, including characteristics such as overall magnitude, Alfvénicity, relative magnitude of density fluctuations, prevalence of switchback structures. He will then describe what we have learned thanks to Parker of the relationship of the turbulence properties to the solar wind origins, before arguing how structures such as magnetic funnels, isolated coronal holes, coronal hole boundaries, pseudostreamers, helmet streamers and the nascent heliospheric current sheet contribute to the formation and evolution of turbulence in the inner heliosphere.

Speakers

16:00-16:15
Discussion
16:15-17:30
Poster session

Chair

09:00-09:30
Magnetospheric turbulence

Abstract

Turbulence is a ubiquitous process in the laboratory plasma, as well as in space and astrophysical plasmas. The analysis of turbulence in the terrestrial plasma environment is the key to understanding the impact of the energy, mass and momentum transport from the solar wind to the magnetosphere and ionosphere. The most scientifically investigated space plasma is the solar wind. However, the planetary environments represent other types of space plasma, with field and plasma parameters differing from those in the solar wind. Contrarily to the solar wind case, the terrestrial plasmas are constrained by the available volumes between large-scale boundaries, such as the bow-shock and the magnetopause or the plasma sheet boundaries in the magnetotail. As a consequence, the analysis of fluid-scale processes is often not fully accessible. Despite the large variability of solar wind driven processes, both the magnetospheric and solar wind fluctuations are associated with the formation of coherent structures, and exhibit rather similar kinetic range spectral scalings and breaks near the ion scales. In this study the emphasis is on the observations of turbulence in the terrestrial magnetosheath and magnetotail. Dr Vörös will present a review on the experimental findings on magnetospheric turbulence, with the main focus being on the observations of coherent structures and various channels of energy conversion. On this basis, they aim to outline the possible strategies for further statistical investigations of magnetospheric plasma turbulence.

Speakers

09:30-09:45
Discussion
09:45-10:15
Speaker tbc
10:15-10:30
Discussion
10:30-11:00
Coffee
11:00-11:30
Estimation of the incompressible and compressible energy cascade rates in the inner heliosphere

Abstract

Compressible turbulence has been a subject of active research within the space physics community for the last three decades and is actually believed to be essential for understanding the physics of the solar wind (for instance the heating of the fast wind), of the interstellar medium (in cold molecular clouds) and other astrophysical and space phenomena. In this talk Dr Hadid will give an overview of the different studies that the group have done regarding the compressible and incompressible cascade rates in the interplanetary space. Firstly, using the exact law of compressible isothermal magnetohydrodynamic (MHD) turbulence [Banerjee & Galtier, PRE, 2013], they give an estimation of the compressible energy cascade rate (|εC|) in the Earth’s magnetosheath using THEMIS and CLUSTER spacecraft data and show that it is at least three orders of magnitude larger than its value in the solar wind. Moreover, they show the role of the density fluctuations in increasing the spatial anisotropy in the Earth's magnetosheath [Hadid et al., PRL, 2018]. Secondly, using the exact law of compressible Hall MHD turbulence [Andrés & Sahraoui, PRE, 2017] they give a complete estimation of |εC | at the MHD and the sub-ion scales in the Earth's magnetosheath using MMS data [Andrés et al., PRL, 2019]. Finally we show the radial evolution of the turbulent cascade rate from the Sun (~0.2 A.U.) up to Mars (~1.5 A.U.), using Parker Solar Probe and Maven data [Andrés et al. in prep].

Speakers

11:30-11:45
Discussion
11:45-12:15
Observations of turbulent dissipation and particle energization in near-Earth space

Abstract

Dr Chasapis will be discussing measurements of dissipation in turbulence observed in the Earth’s magnetosheath and the near-Earth solar wind. Such turbulence is characterised by an abundance of small-scale intermittent structures, where significant dissipation and particle energisation occurs through a series of different kinetic-scale mechanisms. The Magnetospheric MultiScale mission is able to carry out very high-resolution multi-point measurements in near-Earth space, giving us a unique opportunity to study these mechanisms. The high time resolution plasma and fields measurements allow us to directly observe dissipative processes occurring at kinetic scales. In parallel, we can implement and test new methods to identify pathways of dissipation using multi-point measurements. Over the last few years, the four spacecraft have gathered a significant amount of data, both in the strong turbulence of the Earth’s magnetosheath, as well as out in the pristine solar wind, allowing us to carry out statistical studies of turbulent dissipation. Additionally, we can adequately resolve the behaviour of suprathemral particles and their statistical behaviour in different turbulence conditions, helping us understand the role of turbulence in generating such populations.

Finally, Dr Chasapis will discuss novel configurations of the MMS spacecraft constellation, and some of their scientific results so far. Ultimately, they are paving the way for a new generation of multi-spacecraft missions, that will be able to carry out simultaneous multi-scale measurements, giving us new insights into plasma turbulence and the open questions of kinetic dissipation and particle energisation. 

Speakers

12:15-12:30
Discussion

Chair

13:30-14:00
Kinetic effects and dissipation in the solar wind from the Earth back to the Sun: in-situ measurements and Vlasov simulations

Abstract

Turbulence in plasmas involves a complex cross-scale coupling of fields and distortions of particle distribution functions, with the emergence of non-thermal features. The heliosphere, strongly characterized by nonlinear processes, represents the best natural laboratory to study in-situ plasma turbulence and, thanks to new solar missions, it is finally possible to study the radial evolution of the solar wind as it expands in the inner heliosphere, from the solar corona out to 1 AU.  

Solar wind turbulence is not homogeneous but is highly space-localized and the degree of non-homogeneity increases as the spatial/time scales decrease (intermittency). Such an intermittent nature also evolves, in fast streams, during the wind expansion, possible due to the emergence of strong non-homogeneities of the magnetic field over a broad range of scales (coherent structures). Here, the nature of turbulent fluctuations close to the ion scales, is investigated by using high-time resolution magnetic field data in different regions of the heliosphere and in different solar wind conditions. The ion scales are characterized by the presence of non-compressive coherent structures, such as current sheets, vortex-like structures, and wave packets identified as ion cyclotron modes, responsible for solar wind intermittency and strongly related to the energy dissipation. Both in-situ data and numerical simulations show that particle energization is observed in and near coherent structures. Understanding the physical mechanisms that produce coherent structures and how they contribute to dissipation in collisionless plasma can provide key insights into the general problem of solar wind heating. 

 

Speakers

14:00-14:15
Discussion
14:15-14:45
Proton heating and the uncertain dimensionality of solar wind turbulence dissipation

Abstract

The solar wind has many forms of anisotropy: it has a background magnetic field; it expands roughly radially; and it is nearly collisionless, supporting non-Maxwellian particle velocity distributions. In this talk Dr Wicks will discuss how these forms of anisotropy combine together in the evolution of solar wind turbulence and hypothesise on how they may affect the dissipation of energy from fluid-like flows into kinetic particle motions. To do this, he will examine results from Parker Solar Probe and Wind, showing how turbulence interacts with fluctuations at the dissipation scale and how the thermodynamics of the solar wind and the evidence for dissipation change with radial distance from the Sun. He finds that the solar wind, overall, undertakes a close-to-3D adiabatic expansion, but locally energy flows look one dimensional. Local plasma fluctuations are dominantly perpendicular to the magnetic field and result in kinetic Alfven waves at small scales, leading to parallel proton heating, but strong perpendicular temperature anisotropies arise and drive proton cyclotron wave instabilities. These are proposed to arise from different processes, turbulence in the case of KAWs but local, cyclical instability for ICWs. The turbulence itself generates local compressions and rarefactions that drive temperature anisotropy, but only in one (roughly radial) dimension. He will therefore discuss the implications of a roughly one dimensional outcome of turbulence on the multi-dimensional and anisotropic heating / cooling of the solar wind.

Speakers

14:45-15:00
Discussion
15:00-15:30
Tea
15:30-16:00
Speaker tbc
16:00-16:15
Discussion
16:15-17:00
Panel discussion