The Principal Investigator will develop a realistic description of the dynamics of charged energetic particles in turbulent fields typical of the solar wind between the Sun and 1AU, including all intermediate non-resonant scales. She intends to model magnetic field-line (MFL) transport and dispersion on a very broad range of size scales, as well as investigate the pitch-angle scattering and dispersal of particles in those fields. Using data from the ACE and Wind spacecraft, the PI plans a detailed analysis of solar flare particle-intensity time profiles to search for direct observational clues about solar wind field-line wandering and particle scattering, and to test innovative theoretical and numerical models. She will simulate wandering MFLs and particle trajectories in the turbulent SW in order to quantify the effects on drifts and pure particle scattering across and along MFLs, particle transport, MFL cross-field displacement, and MFL separation.
This multi-scale study of MFL and energetic particle dispersal in the turbulent solar wind is crucial to the prediction of solar energetic particle (SEP) intensities at Earth and therefore addresses the goals of the National Space Weather Program. SEPs pose major threats to satellite operations, communications, and astronauts in space. Beyond space physics and space weather forecasting, the transport of particles in turbulent magnetic fields is fundamental to research in astrophysics and plasma physics.
Charged energetic particles and magnetic fields are at the core of the disciplines of interplanetary physics and space weather prediction. The fields encountered in interplanetary space are turbulent, and therefore irregular and wildly fluctuating. The field lines, defined as the lines that have in every point the local magnetic field as a tangent, are a useful concept, even though strictly speaking, they do not have any physical existence. These field lines determine, to a first approximation, the trajectories of the energetic particles, which are of primary concern to the space weather forecaster. Being able to describe the field lines on a broad range of scales, as well as their dispersal relative to each other, would go a long way towards understanding how the particles mix and disperse, and most importantly, quantifying that particle dispersal. How much solar energetic particles (SEPs) disperse between their injection at the Sun or at the leading edge of Coronal Mass Ejections (CMEs) and 1 AU (Earth distance to the Sun) determines the impact of SEP events at Earth. The stronger the dispersal, the lower the intensity of SEPs observed, for a given injection, at Earth orbit. The stronger the fluctuations of that dispersal, the stronger the fluctuations in the observed SEP intensities, and the more Earthlings should worry about extreme SEP events. In this research project, we greatly improved the description/understanding of the field-line and SEP dispersal in interplanetary space by including in that description a very broad range of scales. In particular, magnetic flux tubes, which are bundles of magnetic field lines with a closed transversal cross section, were simulated on an unprecedented range of scales (over four decades in each direction). These simulations reveal extreme stretching / filamentation of the flux-tube cross sections, with filaments folding onto themselves many times while preserving an elongated shape at the largest scale of observation. As the filaments become thinner, SEPs escape them, but can remain trapped within the multiple folds of the filaments, where they are diluted. These findings help explain a number of intriguing observations of impulsive SEPs, some fairly recent, like the simultaneous detection of impulsive He3-rich SEPs from single solar events at points separated by up to 100° of solar longitude, some not so recent, like the observation that SEP fluxes vary wildly (over three or four orders of magnitude) in their correlation with the intensities of their related solar event.
