A statistical study of the initial phases of 185 solar particle events was carried out using the data from cosmic ray experiments on IMP 4 and IMP 5. Special emphasis was placed on the identification of the associated solar flare, as the parent flare can be determined for 68% of the events. It appears probable that most of the unidentified increases occur on the non-visible disc of the sun. The existence of a 'preferred-connection' longitude between 20 W and 80 W was established by examining the heliolongitude of all the flare associated events. It is demonstrated that the energy spectra determined at the time of maximum particle in the 20 to 80 MeV or 4 to 20 Mev interval range give results identical to that obtained by the 'distance-travelled' method.

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The variation of solar proton energy spectra and size distribution with heliolongitude

The velocity dispersion for a large number of solar proton events is analyzed in the energy regime of 10–60 MeV It is found for all events that the time from the flare to particle maximum t
m is well represented by a sum of two components The first component which is energy independent describes the propagation in the solar atmosphere, the second component describes the propagation in the interplanetary medium giving a velocity dispersion v × t
m = const The additional study of time intensity profiles, onset times, and multispaceprobe observations reveals that the propagation in the solar atmosphere consists of three processes: (1) A rapid transport process in the initial (≲ 1 h) phase after the event fills up a “fast propagation region (FPR)”, which may extend up to ≈ 60° from the flare site and which is tentatively identified with a large unipolar magnetic cell as seen on Hα synoptic charts, (2) a large-scale drift process which is energy independent with drift velocities v
D in the range 1° ⩽ v
D ⩽ 4°h-1, and simultaneously (3) a diffusion process which yields the general broadening of the intensity time profiles for eastern hemisphere events, which is, however, of less importance than previously assumed

Propagation of flare protons in the solar atmosphere

The characteristics of solar energetic particles (SEP) as observed in interplanetary space provide fundamental information about the origin of these particles, and the acceleration and propagation processes at the Sun and in interplanetary space. Furthermore, energetic particles provide information on the development and structure of coronal mass ejections as they propagate from the solar corona into the interplanetary medium. In this paper we review the measurements of energetic particles in interplanetary space and discuss their implication for our understanding of the sources, and of acceleration and propagation processes.

Energetic Particle Observations

Skylab observations of the Sun in soft X-rays gave us the first possibility to study the development of a complex of activity in the solar corona during its whole lifetime of seven solar rotations. The basic components of the activity complex were permanently interconnected (including across the equator) through sets of magnetic field lines, which suggests similar connections also below the photosphere. However, the visibility of individual loops in these connections was greatly variable and typically shorter than one day. Each brightening of a coronal loop in X-rays seems to be related to a variation in the photospheric magnetic field near its footpoint. Only loops (rarely visible) connecting active regions with remnants of old fields can be seen in about the same shape for many days. The interconnecting X-ray loops do not connect sunspots.

Development of a complex of activity in the solar corona

During the February 25, 1969, solar proton event, particle measurements from the close-orbiting satellite Esro 2, and particle and magnetic field measurements outside the magnetosphere from the Heos A1 satellite are available. The Esro 2 data for proton energies from E>27 to E>90 Mev show intensity enhancements in the auroral zone region and in the central polar region relative to the rest of the polar cap. At energies of a few million electron volts such enhancements are significantly less marked. By comparison of observations inside and outside the magnetosphere and by suitable trajectory computations inside the magnetosphere, we explain the auroral zone enhancements at energies >27 Mev in terms of a form of impact zone effect allied to a particle anisotropy outside the magnetosphere. We suggest that the enhancements observed over the polar region may be due to the particle anisotropy outside the magnetosphere plus coupling between the central polar cap lines of force and the interplanetary field lines.

Penetration of solar protons over the polar cap during the February 25, 1969, event

The relationship between heliographic longitude and the delay between flare occurrence and solar proton observation is studied using results obtained aboard HEOS A1 during 1969. The result obtained differs from previous findings. We ascribe this to the formation of a long-lived magnetic field configuration close to the Sun associated with a particular group of active regions.

The solar longitude dependence of proton event delay time

During the flare sequence February 24–28, 1969, our laboratory was able to observe the time history of the particle flux close to earth in some detail. We wish to report on results obtained from the Saclay detectors aboard the HEOS Al and IRIS satellites and aboard two Centaure Rockets launched from Andenes at 1633 and 2350 UT on February 25.

M. Gros

Papers

The solar longitude dependence of proton event delay time

Observations of the spectra and time history of protons in interplanetary space, february 25--28, 1969.

Simultaneous satellite and rocket observations of the February 25th 1969 solar proton event.