Phys 954, Solar Wind and Cosmic Rays Section VIE. MöbiusVI.Solar Energetic ParticlesVI.1 Flares, Shocks and Acceleration?We have talked about particle acceleration at shocks. This occurs in a big way, when the sun ejects material with speeds much higher than the solar wind speed (coronal mass ejections (CMEs)) which form a strong shock. Here at times very intense particle acceleration is observed, which we can describe with the tools that we studied at the Earth's bow shock. However, the situation is complicated by the origin of these shocks. This can be viewed in a similar way as the bow shock acceleration is complicated by the occasional presence of energetic particles from the Earth's magnetosphere.ViewgraphIn substantial reconfigurations of solar magnetic field in flaring regions magnetic energyis transferred into heating, acceleration and expulsion of solar material. Observed are- emission of light, x-rays and particle acceleration- emission of energetic electrons and ions- often mass ejection from the sunHowever, mass ejection may appear by the same token, when a large filament (prominence) is ejected from the sun's atmosphere, sometimes without a noticeable flare.Let us approach these phenomena from the observation of energetic particles. In fact, the first association of energetic particles with activity on the sun was found as cosmic rays on the ground with large ionization chambers, almost simultaneously with the observation on the sun. The following interpretation that has spawned a lot of detailed work is now often coined the "flare myth". Namely all following observations of energetic particles, either directly associated with observations on the sun or sometimes even without direct evidence, was put into a framework, where it came from flares on the sun, except perhaps the observation of energetic particles directly associated with a shock passing the observing satellite. ViewgraphTransportThe ions are transported outward with the solar wind and diffuse, i.e. their time structure gets smoothed. All observed temporal, spectral and directional features were subsequently put into a framework with the sun being the main source.Viewgraph1/14/19 121Phys 954, Solar Wind and Cosmic Rays Section VIE. MöbiusThe difference between scatter-free (along the B-field) and convective-diffucsive transport was invoked to explain observed differences.Solar wind1AUVsw=1.5•108km/500km/sec=3−105sec≈3daysIt takes for example 20 days to 16 AU for medium energy (MeV/Nucleon) particles, i.e.3 times faster than the solar wind, but by far not as fast as the speed of the energetic ions  diffusive transport.There are also substantial differences in the observation at different longitudes. Charged particles travel easterly along field lines, i.e. at a certain position west of the actual flare is the optimum location to get the particles.ViewgraphSunFlareHelios 1Helios 2Westmagnetic fieldWith good connection the particles are seen with a sharp rise (almost scatterfree at the beginning) and slow decay (diffusive). Smaller diffusion coefficients (lower energy and/or across B) lead to a slow rise also. What do I mean by this? If you recall the solution of Problem 2) in Homework#6, diffusive transport scales with the diffusion coefficientIf we ignore convection for a moment, we see that a larger diffusion coefficient shrinks the time scale, i.e. for  twice as large the same conditions are observed at location r already after half the time t is elapsed. A sharply peaked time profile therefore calls for a large  or long mean free path.1/14/19 122n(r' ,t) = No4πκt3e−(r'24κt)Phys 954, Solar Wind and Cosmic Rays Section VIE. MöbiusElectrons are generally less affected by scattering, because the wavelength of the magnetic fluctuations is much longer than their gyroradii.ViewgraphHowever, to see electrons there has to be a relatively good magnetic connection.Because most of the events looked so complicated, scientists started with the simple onesthat could be readily interpreted. They arrived at an explanation with diffusion in interplanetary space that seemed to call for a mean free path length of ≈ 0.1 AU at low energies. This was called the Palmer consensus after a paper in 1982. This value was alsowhat we used for the transport of pickup ions, and at first it seemed confirmed by the observations (again the easy ones!).However, it was observed that the energetic particle events came in two flavors.1/14/19 123n(r,t)0.00E+002.00E+014.00E+016.00E+018.00E+011.00E+021.20E+021.40E+020 50 100 150 200 250Time in hoursn(r,t)Phys 954, Solar Wind and Cosmic Rays Section VIE. MöbiusVI.2 Two Classes of Solar Energetic Particle EventsNot only the connection determines the temporal profile of the energetic ion fluxes.ViewgraphThese differences can only be seen for events, which are well connected magnetically. Otherwise we could blame the difference on transport effects, and this was done extensively early on. Events associated with activity on the eastern sun have good connection and seemed to show often very short rise and decay times (incompatible with diffusion theory, scatter-free along the field). They were dismissed as not diffusive.Events with ion emission of only a few hours are called- Impulsive EventsThe others were coined as- Large Flares or Long Duration Events- well connected - seen everywhere on sunViewgraph- low ion fluxes - high ion fluxes- high e/p ratioViewgraphbut they were all interpreted as solar flares and the particles were thought to come from these flares. For the differences in flux, time profile and spectra transport effects were invoked.Energy SpectraWith the temporal profiles, which are at different energies, one has to be careful in assembling the energy spectra:ViewgraphMost commonly integration over the entire event is performed. The spectra in large flares are again not pure power laws, although these flares are associated with shocks. Ifmodeled with shock acceleration, the loss of the ions out of the acceleration region has 1/14/19 124Impulsive Long DurationPhys 954, Solar Wind and Cosmic Rays Section VIE. Möbiusto be considered. However, there is also a different possibility, and we will come to this next week.Ion CompositionFinally, let's examine the composition of the energetic particles. Maybe this can tell us more about their origin, in the same way, as magnetospheric particles and bow shock particles could be distinguished. Large flares