Interplanetary Path Research Articles

On determination possibility of the total electron content of the interplanetary path from distortions of an ultrashort radio pulse

The character and features of dispersion distortions of an ultrashort radio pulse in the form of a sinusoidal train propagating along the spacecraft-Earth interplanetary path are theoretically analyzed. It is established that the instantaneous field oscillation frequency in the distorted pulse is completely determined by the value of the total electron content of the path. It is shown that, theoretically, one of the main characteristics of the solar wind can be measured from the frequency of the detected signal.

The interplanetary magnetic structure that guides solar relativistic particles

Relating in situ measurements of relativistic solar particles to their parent activity in the corona requires understanding the magnetic structures that guide them from their acceleration site to the Earth. Relativistic particle events are observed at times of high solar activity, when transient magnetic structures such as Interplanetary Coronal Mass Ejections (ICMEs) often shape the interplanetary magnetic field (IMF). They may introduce interplanetary paths that are longer than nominal, and magnetic connections rooted far from the nominal Parker spiral. We present a detailed study of the IMF configurations during ten relativistic solar particle events of the 23rd activity cycle to elucidate the actual IMF configuration guiding the particles to Earth, where they are measured by neutron monitors. We use magnetic field (MAG) and plasma parameter measurements (SWEPAM) from ACE, and determine interplanetary path lengths of energetic particles through a modified version of the velocity dispersion analysis based on energetic particle measurements with SoHO/ERNE. We find that the majority (7/10) of the events is detected in the vicinity of an ICME. Their interplanetary path lengths are found to be longer (1.5-2.6 AU) than those of the two events propagating in the slow solar wind (1.3 AU). The largest apparent path length is found in an event within the fast solar wind, probably due to enhanced pitch angle scattering. The derived path lengths imply that the first energetic and relativistic protons are released at the Sun at the same time as electron beams emitting type III radio bursts. The timing of the first high-energy particle arrival at Earth is dominantly determined by the type of IMF in which the particles propagate. Initial arrival times are as expected from Parker's model in the slow solar wind, and significantly larger in or near transient structures such as ICMEs.

Solar energetic particle event onset as analyzed from simulated data

Solar energetic particle (SEP) event onset is analyzed using simulated data. A large number of simulations using different coronal and interplanetary (IP) scattering conditions are performed. Protons in the energy range of 0.13-57 MeV are considered. The simulated data are analyzed employing a velocity dispersion analysis (VDA) to the proton-flux onset times in 16 energy channels. As a result of the analysis, the apparent coronal release time, to, and the apparent IP path length, s, of the first-observed particles are obtained. It is shown that typical IP scattering conditions, i.e., 1-GV radial mean free path of A rr = 0.1-1 AU with a P 1/3 rigidity dependence, lead to apparent path lengths of s ∼ 1-2 AU, consistent with observations. Thus, SEP events with s ∼ 2 AU can simply be explained as a result of IP scattering. Models with coronal mean free paths small enough to enable proton acceleration to high energies in quasi-parallel shocks close to the Sun are shown to yield VDA results in agreement with observations, at least with A rr ? 0.3. As a result of IP scattering, the inaccuracy of the release times is tens of minutes in events with s? 2 AU, which may prevent accurate timing of particle release using the VDA method in such events. Low contrast between the time-of-maximum intensity of the studied SEP event and the pre-event background intensity and/or a large difference between the forms of the respective energy spectra may also lead to errors in derived onset times. Best timing results (with errors typically less than 10 min) are obtained for large IP mean free paths, A rr ? 0.3 AU (typically resulting in small values of s? 1.5 AU), and large intensity contrast between the SEP event and the pre-event background.