Early propagation of energetic particles across the mean field in turbulent plasmas

Propagation of energetic particles across the mean field direction in turbulent magnetic fields is often described as spatial diffusion. Recently, it has been suggested that initially the particles prop- agate systematically along meandering field lines, and only later reach the time-asymptotic diffusive cross-field propagation. In this paper, we analyse cross-field propagation of 1–100 MeV protons in composite 2D-slab turbulence superposed on a constant background magnetic field, using full-orbit particle simulations, to study the non-diffusive phase of particle propagation with a wide range of turbulence parameters. We show that the early-time non-diffusive propagation of the particles is consistent with particle propagation along turbulently meandering field lines. This results in a wide cross-field extent of the particles already at the initial arrival of particles to a given distance along the mean field direction, unlike when using spatial diffusion particle transport models. The cross-field extent of the particle distribution remains constant for up to tens of hours in turbulence environ- ment consistent with the inner heliosphere during solar energetic particle events. Subsequently, the particles escape from their initial meandering field lines, and the particle propagation across the mean field reaches time-asymptotic diffusion. Our analysis shows that in order to understand so- lar energetic particle event origins, particle transport modelling must include non-diffusive particle propagation along meandering field lines. Key words: Sun: particle emission – diffusion – magnetic fields – turbulenc

The effect of turbulence strength on meandering field lines and Solar Energetic Particle event extents

Insights into the processes of Solar Energetic Particle (SEP) propagation are essential for understanding how solar eruptions affect the radiation environment of near-Earth space. SEP propagation is influenced by turbulent magnetic fields in the solar wind, resulting in stochastic transport of the particles from their acceleration site to Earth. While the conventional approach for SEP modelling focuses mainly on the transport of particles along the mean Parker spiral magnetic field, multi-spacecraft observations suggest that the cross-field propagation shapes the SEP fluxes at Earth strongly. However, adding cross-field transport of SEPs as spatial diffusion has been shown to be insufficient in modelling the SEP events without use of unrealistically large cross-field diffusion coefficients. Recently, Laitinen et al.\ (2013b, 2016) demonstrated that the early-time propagation of energetic particles across the mean field direction in turbulent fields is not diffusive, with the particles propagating along meandering field lines. This early-time transport mode results in fast access of the particles across the mean field direction, in agreement with the SEP observations. In this work, we study the propagation of SEPs within the new transport paradigm, and demonstrate the significance of turbulence strength on the evolution of the SEP radiation environment near Earth. We calculate the transport parameters consistently using a turbulence transport model, parametrised by the SEP parallel scattering mean free path at 1 AU, $\lambda*$, and show that the parallel and cross-field transport are connected, with conditions resulting in slow parallel transport corresponding to wider events. We find a scaling $\sigma\propto (1/\lambda*)^{1/4}$ for the Gaussian fitting of the longitudinal distribution of maximum intensities. The longitudes with highest intensities are shifted towards the west for strong scattering conditions. Our results emphasise the importance of understanding both the SEP transport and the interplanetary turbulence conditions for modelling and predicting the SEP radiation environment at Earth

Clinical audit of adherence to hypertension treatment guideline and control rates in hospitals of different sizes in Thailand

A clinical audit of hospitals in Thailand was conducted to assess compliance with the national hypertension treatment guidelines and determine hypertension control rates across facilities of different sizes. Stratified random sampling was used to select sixteen hospitals of different sizes from four provinces. These included community (120 beds) hospitals. Among new cases, the audit determined whether (i) the recommended baseline laboratory assessment was completed, (ii) the initial choice of medication was appropriate based on the patient's cardiovascular risk, and (iii) patients received medication adjustments when indicated. The hypertension control rates at six months and at the last visit were recorded. Among the 1406 patients, about 75% had their baseline glucose and kidney function assessed. Nearly 30% (n = 425/1406) of patients were indicated for dual therapy but only 43% of them (n = 182/425) received this. During treatment, 28% (198/1406) required adjustments in medication but this was not done. The control of hypertension at six months after treatment initiation was 53% varying between 51% in community and 56% in large hospitals (p p < .01). Failure to adjust medication when required was associated with 30% decrease in the odds of hypertension control (OR 0.69, 95% CI 0. 50 to 0.90). Failure to comply with the treatment guidelines regarding adjustment of medication and lost to follow-up are possible target areas to improve hypertension control in Thailand

Magnetic Field Line Random Walk and Solar Energetic Particle Path Lengths: Stochastic Theory and PSP/ISoIS Observation

Context:In 2020 May-June, six solar energetic ion events were observed by the Parker Solar Probe/ISoIS instrument suite at 0.35 AU from the Sun. From standard velocity-dispersion analysis, the apparent ion path length is 0.625 AU at the onset of each event. Aims:We develop a formalism for estimating the path length of random-walking magnetic field lines, to explain why the apparent ion pathlength at event onset greatly exceeds the radial distance from the Sun for these events. Methods:We developed analytical estimates of the average increase in pathlength of random-walking magnetic field lines, relative to the unperturbed mean field. Monte Carlo simulations of fieldline and particle trajectories in a model of solar wind turbulence are used to validate the formalism and study the path lengths of particle guiding-center and full-orbital trajectories. The formalism is implemented in a global solar wind model, and results are compared with ion pathlengths inferred from ISoIS observations. Results:Both a simple estimate and a rigorous theoretical formulation are obtained for fieldlines' pathlength increase as a function of pathlength along the large-scale field. From simulated fieldline and particle trajectories, we find that particle guiding centers can have pathlengths somewhat shorter than the average fieldline pathlength, while particle orbits can have substantially larger pathlengths due to their gyromotion with a nonzero effective pitch angle. Conclusions:The long apparent path length during these solar energetic ion events can be explained by 1) a magnetic field line path length increase due to the field line random walk, and 2) particle transport about the guiding center with a nonzero effective pitch angle. Our formalism for computing the magnetic field line path length, accounting for turbulent fluctuations, may be useful for application to solar particle transport in general

Spaceship Earth Observations of the Easter GLE

Abstract The ground level enhancement (GLE) of Easter (April 15) 2001 was the largest GLE of the current solar cycle, and it was also the first major event to be observed with one-minute resolution by the full eleven-station Spaceship Earth network of neutron monitors. We derive particle density and anisotropy profiles and model them with numerical solutions of the Boltzmann equation. Particle transport was rather diffusive in this event, with a radial mean free path ∼ 0.2 AU. Particle injection onto the Sun-Earth field line began at 13:42 UT ±1 minute, 14 minutes before the first arrival of particles at Earth

The 28th International Cosmic Ray Conference Spaceship Earth Observations of the Easter GLE

Abstract The ground level enhancement (GLE) of Easter (April 15) 2001 was the largest GLE of the current solar cycle, and it was also the first major event to be observed with one-minute resolution by the full eleven-station Spaceship Earth network of neutron monitors. We derive particle density and anisotropy profiles and model them with numerical solutions of the Boltzmann equation. Particle transport was rather diffusive in this event, with a radial mean free path ∼ 0.2 AU. Particle injection onto the Sun-Earth field line began at 13:42 UT ±1 minute, 14 minutes before the first arrival of particles at Earth