Es some evidence that part of the evolution of discontinuities or current sheets occurs during solar wind transport to 1 AU. There is also evidence to be found for cellularization of interplanetary turbulence in solar energetic particle (SEP) data. Prominent in this regard is the phenomenon of SEP dropouts or Sulfatinib biological activity channelling. Figure 8 shows an example from Mazur et al. [74] in which the measured count rates from energetic suprathermal particles sporadically and abruptly turn off, only to suddenly reappear a short time later. One could argue that this is evidence for a flux tube structure, which can topologically trap magnetic field lines [75] as well as particles [76]. Eventually particles can escape these temporary traps but evidently the effect can persist from the corona to 1 AU. More detailed study [77] reveals that flux tubes are likely to have `RRx-001MedChemExpress RRx-001 trapping boundaries’ contained within them that are distinct from the current sheet that may define the outer boundary of the flux tube. A complementary view relates the independence of nearby interplanetary field lines to time dependence of field-line motions at the source [78]. There of course must be a relationship between these ideas as photospheric motions probably set up the original flux tube structure, which maps outwards carried by the solar wind [78]; this connection is distorted by nonlinear effects after a few nonlinear times, but quite possibly it is not erased completely. In any case, it seems clear that flux tubes can act as conduits for transport of SEPs, and this may influence the statistical association of SEP fluxes with PVI events (coherent current structures or discontinuities). Meanwhile there may be leakage of energetic particles from flux tubes owing to particle transport effects, as well as transfer of magnetic field lines from one flux tube to a neighbouring one owing to stochastic component interchange reconnection [79]. A somewhat different but equally compelling view of the cellular structure of turbulence in the solar wind is provided by taking a closer look at the well-known phenomenon of Alfv ic fluctuations [80,81] at 1 AU. The question is whether the distribution of Alfv ic alignment angles in the solar wind is akin to that of active MHD turbulence. As usual, the latter is studied using numerical simulation. An investigation of this nature has been performed [82], using an ensemble of relatively undisturbed turbulence intervals at 1 AU. In one of these, the average normalized cross helicity is c = 2 v ?b / v 2 + b2 = 0.29. Then preparing a moderately large Reynolds number incompressible three-dimensional MHD simulation with the same c ,transport boundaries are observed: `dropouts’ of solar energetic particles (a)MeV nucleon?10?observation of H-FE ions versus arrival time for 9 Jan 1999 SEP event theoretical model-based trapped magnetic field lines Sunrsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373:…………………………………………………(b)counts bin?10?10 Bq Bj (degrees) (degrees)4 1 235612(c)(d )240 120 0 60 0 ?0 9 Jan 1999 10 Jan 1999 11 Janradius of Earth orbitFigure 8. The dropout phenomenon seen in SEP data by Mazur et al. [74] is explained by a model based on transient trapping of magnetic field lines within magnetic flux tubes. These act as conduits for transport, delaying diffusion [75]. (Online version in colour.)2.5 2.0 1.5 PDF 1.0 0.5 0 ?.0 SW MHD PDF 10 8 6 4 2 0 ?.0 SW MHD?.0 cos(q )0.1.?.0 sin(q)0.1.Figure 9. Distribut.Es some evidence that part of the evolution of discontinuities or current sheets occurs during solar wind transport to 1 AU. There is also evidence to be found for cellularization of interplanetary turbulence in solar energetic particle (SEP) data. Prominent in this regard is the phenomenon of SEP dropouts or channelling. Figure 8 shows an example from Mazur et al. [74] in which the measured count rates from energetic suprathermal particles sporadically and abruptly turn off, only to suddenly reappear a short time later. One could argue that this is evidence for a flux tube structure, which can topologically trap magnetic field lines [75] as well as particles [76]. Eventually particles can escape these temporary traps but evidently the effect can persist from the corona to 1 AU. More detailed study [77] reveals that flux tubes are likely to have `trapping boundaries’ contained within them that are distinct from the current sheet that may define the outer boundary of the flux tube. A complementary view relates the independence of nearby interplanetary field lines to time dependence of field-line motions at the source [78]. There of course must be a relationship between these ideas as photospheric motions probably set up the original flux tube structure, which maps outwards carried by the solar wind [78]; this connection is distorted by nonlinear effects after a few nonlinear times, but quite possibly it is not erased completely. In any case, it seems clear that flux tubes can act as conduits for transport of SEPs, and this may influence the statistical association of SEP fluxes with PVI events (coherent current structures or discontinuities). Meanwhile there may be leakage of energetic particles from flux tubes owing to particle transport effects, as well as transfer of magnetic field lines from one flux tube to a neighbouring one owing to stochastic component interchange reconnection [79]. A somewhat different but equally compelling view of the cellular structure of turbulence in the solar wind is provided by taking a closer look at the well-known phenomenon of Alfv ic fluctuations [80,81] at 1 AU. The question is whether the distribution of Alfv ic alignment angles in the solar wind is akin to that of active MHD turbulence. As usual, the latter is studied using numerical simulation. An investigation of this nature has been performed [82], using an ensemble of relatively undisturbed turbulence intervals at 1 AU. In one of these, the average normalized cross helicity is c = 2 v ?b / v 2 + b2 = 0.29. Then preparing a moderately large Reynolds number incompressible three-dimensional MHD simulation with the same c ,transport boundaries are observed: `dropouts’ of solar energetic particles (a)MeV nucleon?10?observation of H-FE ions versus arrival time for 9 Jan 1999 SEP event theoretical model-based trapped magnetic field lines Sunrsta.royalsocietypublishing.org Phil. Trans. R. Soc. A 373:…………………………………………………(b)counts bin?10?10 Bq Bj (degrees) (degrees)4 1 235612(c)(d )240 120 0 60 0 ?0 9 Jan 1999 10 Jan 1999 11 Janradius of Earth orbitFigure 8. The dropout phenomenon seen in SEP data by Mazur et al. [74] is explained by a model based on transient trapping of magnetic field lines within magnetic flux tubes. These act as conduits for transport, delaying diffusion [75]. (Online version in colour.)2.5 2.0 1.5 PDF 1.0 0.5 0 ?.0 SW MHD PDF 10 8 6 4 2 0 ?.0 SW MHD?.0 cos(q )0.1.?.0 sin(q)0.1.Figure 9. Distribut.