Characterising Solar Wind Fluctuations at Ion-kinetic Scales

The availability of large in-situ datasets makes the solar wind an excellent astrophysical laboratory to probe kinetic processes in a collisionless plasma. As the solar wind turbulent cascade reaches ion-kinetic scales close to the proton gyro-radius, ρ_p, and inertial length, d_p, collective effects lead to interactions between electromagnetic fluctuations and particle velocity distributions. At these scales, wave-particle interactions can lead to the dissipation of turbulent fluctuations and instability growth, which in turn, moderates the macroscopic properties of the plasma. In this thesis, I use over a decade of magnetic field and ion measurements from the Wind spacecraft to investigate the physical processes ongoing at these scales. I make the first in-flight determination of the magnetometer noise-floor, enabling the most accurate interpretation of magnetic field fluctuations at these scales with Wind to date. I then conduct three detailed statistical analyses of the spectral properties of these fluctuations. I first show that the steepening of the power spectrum and a coherent signature in magnetic helicity at ion-kinetic scales are associated with the cyclotron resonance wave-number, k_c, providing evidence for ongoing wave-particle interactions at these scales. I then use magnetic helicity to characterise the polarisation properties of the fluctuations, identifying three populations at ion-kinetic scales: quasi-parallel propagating Alfvén-ion cyclotron and fast magnetosonic-whistler waves driven by proton temperature anisotropy instabilities, as well as highly-oblique kinetic Alfvén wave-like fluctuations from the turbulent cascade. Finally, I show that the KAW-like fluctuations are associated with steeper spectra and higher proton temperatures, suggesting damping of the turbulence. The results presented in this thesis indicate that wave-particle interactions play an important role in the energy transfer between the turbulent fields and ions in the solar wind, in the absence of collisions. I also show that proton heating in the solar wind depends on the polarisation properties of the fluctuations at ion-kinetic scales and the radial direction in the solar wind, in contradiction to the ergodicity hypothesis. Further investigative work is proposed to confirm these findings and identify specific dissipation mechanisms responsible for turbulent heating

Evolution of Solar Wind Turbulence from 0.1 to 1 au during the First Parker Solar Probe–Solar Orbiter Radial Alignment

International audienceThe first radial alignment between Parker Solar Probe and Solar Orbiter spacecraft is used to investigate the evolution of solar wind turbulence in the inner heliosphere. Assuming ballistic propagation, two 1.5 hr intervals are tentatively identified as providing measurements of the same plasma parcels traveling from 0.1 to 1 au. Using magnetic field measurements from both spacecraft, the properties of turbulence in the two intervals are assessed. Magnetic spectral density, flatness, and high-order moment scaling laws are calculated. The Hilbert–Huang transform is additionally used to mitigate short sample and poor stationarity effects. Results show that the plasma evolves from a highly Alfvénic, less-developed turbulence state near the Sun, to fully developed and intermittent turbulence at 1 au. These observations provide strong evidence for the radial evolution of solar wind turbulence

Thiazides in the management of hypertension in older adults - a systematic review

BACKGROUND: Thiazides are commonly prescribed to older people for the management of hypertension. The objective of this study was to identify the evidence on the risks and benefits of their use among adults aged ≥65 years and to develop recommendations to reduce potentially inappropriate use. METHODS: Systematic review (SR) of the literature covering six databases. We applied a staged search approach, where each search was undertaken only if the previous one did not yield high quality results. Searches 1 and 2 identified relevant SRs and meta-analyses published up to December 2015 from all databases. Search 3 identified additional individual interventional studies (IS) and observational studies (OS) not identified by the preceding searches. We included all studies evaluating the effect of thiazides on patient-relevant outcomes in the management of hypertension with a sufficient number of participants aged ≥65 years or a subgroup analysis based on age. Two independent reviewers extracted data and carried out quality appraisal. Recommendations were developed using the GRADE methodology. RESULTS: Searches 1 to 3 were performed. We included 34 articles reporting on 12 IS and 4 OS. Mean ages ranged from 59 to 83.8 years. Four studies had performed a subgroup analysis by age. Information on comorbidity, polypharmacy and frailty of the participants was scarce or not available. The IS compared thiazides to placebo or other antihypertensive drugs and evaluated cardiovascular endpoints or all-cause-mortality as primary outcomes. The OS investigated the association between thiazide use and the risk of gout, fractures and adverse effects. Our results suggest that thiazides are efficacious in preventing cardiovascular events for this population group. Low-dose regimens of thiazides may be safer than high-dose (low quality of evidence), and a history of gout may increase the risk of adverse events (low quality of evidence). Three recommendations were developed. CONCLUSIONS: The use of low dose treatment with thiazides for the management of hypertension in adults aged 65 and older seems justified, unless a history of gout is present. The quality of the evidence is low and studies rarely describe characteristics of the participants such as polypharmacy and frailty. Further good quality studies are needed.The PRIMA-eDS study was supported by a grant from the European Commission within the 7th Framework Programme (Grant No. 305388–2). The work of YVM was also supported by a grant from the NIHR Greater Manchester Primary Care Patient Safety Translational Research Centre. Publication of this article was funded by the UK National Institute for Health Research School for Primary Care Research, University of Manchester

Exploring the Solar Wind from Its Source on the Corona into the Inner Heliosphere during the First Solar Orbiter\u2013Parker Solar Probe Quadrature

This Letter addresses the first Solar Orbiter (SO)-Parker Solar Probe (PSP) quadrature, occurring on 2021 January 18 to investigate the evolution of solar wind from the extended corona to the inner heliosphere. Assuming ballistic propagation, the same plasma volume observed remotely in the corona at altitudes between 3.5 and 6.3 solar radii above the solar limb with the Metis coronagraph on SO can be tracked to PSP, orbiting at 0.1 au, thus allowing the local properties of the solar wind to be linked to the coronal source region from where it originated. Thanks to the close approach of PSP to the Sun and the simultaneous Metis observation of the solar corona, the flow-aligned magnetic field and the bulk kinetic energy flux density can be empirically inferred along the coronal current sheet with an unprecedented accuracy, allowing in particular estimation of the Alfven radius at 8.7 solar radii during the time of this event. This is thus the very first study of the same solar wind plasma as it expands from the sub-Alfvenic solar corona to just above the Alfven surface

Firefly: The Case for a Holistic Understanding of the Global Structure and Dynamics of the Sun and the Heliosphere

This white paper is on the HMCS Firefly mission concept study. Firefly focuses on the global structure and dynamics of the Sun's interior, the generation of solar magnetic fields, the deciphering of the solar cycle, the conditions leading to the explosive activity, and the structure and dynamics of the corona as it drives the heliosphere