We present the results of a statistical study on the proton energy spectra in the range of 35-1600 keV during the one-hour interval centered on the time of arrival of the shock front at the spacecraft of 75 interplanetary shocks that cover the period from August 1978 until December 1980, using the low-energy proton experiment on ISEE 3. The strength of the shocks was determined by calculating the ratio of the downstream to upstream plasma density by using the ion data obtained by the Los Alamos solar wind instrument. The shock events were sub-divided into four different classes based on the behavior of their low-energy (35-238 keV) spectral index. The signatures of the shock events and their spectral index-time profiles in the different classes are (1) smooth profiles associated with oblique, strong, and fast shocks, which roughly corresponds with predictions following from diffusive shock acceleration theory; (2) irregular profiles mainly associated with quasi-perpendicular shocks and (3) spikelike profiles associated with quasi-perpendicular shock spike events, where the properties within both classes point at predominant shock drift acceleration; (4) flat profiles, mainly associated with weak shocks accompanied by little or no shock-accelerated particles. Strong and fast oblique shocks are found to be the most effective particle accelerators. The spectrum at the shock can generally be described by two power laws with a breakpoint energy near 250 keV. For only 15% of the events the spectrum followed a power law over the full energy range. We found that the low-energy spectral index, measured immediately downstream of shocks associated with clear flux enhancements, is related to the shock strength according to predictions from first-order Fermi acceleration, irrespective of the assigned diffusive or drift character of the event. 157 1843 B 1.2 .5 1.4 ß ß ß ß ß ß ee eL ß ß ee :11 .ø' ' ee •'• . ß ß ß ß ß ß ß E, ~ 3• key 0.0 1.0 . , , ß e e e ß ß ß flee ß e e e e ß ß ß ee ß ß ß ß b ß ß ß -

We present results of a detailed analysis of ISEE 3 observations of low‐energy protons (35–1600 keV) and low‐frequency waves (period greater than 6 s) associated with the passage of the large oblique interplanetary shock of April 5, 1979. We observe a foreshock region for several hours prior to the arrival of the shock. Within this region we find (1) a peak in the proton energy spectrum at about 200 keV, (2) the proton energy density (in the range 35–1600 keV) comparable with the total energy density of the magnetic field, (3) a good correlation between the amplitude of the low‐frequency waves and the 200‐keV proton intensity, and (4) a good agreement between the peak in the wave power spectrum and the resonant frequency corresponding to the peak in the proton spectrum, only if large pitch angles are considered, suggesting that the protons are responsible for the waves by virtue of a resonant interaction. Our observations suggest that the high energy density of the high‐energy solar flare protons preceding the shock could be responsible for “seed” waves which provide the scattering centers necessary for the acceleration of the lower‐energy protons via a first‐order Fermi acceleration mechanism.

We present results of a detailed analysis of three‐dimensional anisotropies of protons in the energy range 35–1000 keV observed in association with interplanetary shocks on ISEE 3. We compare observations of high time resolution anisotropies made close to the shock in seven energy channels with theoretical predictions for Fermi acceleration and shock drift acceleration, and we find good evidence for both types of acceleration. We find a small number (six) of events exhibiting the signature of Fermi acceleration, and a somewhat larger number (20) exhibiting the signature of shock drift acceleration, the “Fermi” events being associated with strong, fast quasi‐parallel shocks and the “shock drift” events being associated with weaker, slower quasi‐perpendicular events. In the solar wind frame of reference the Fermi events have moderate upstream anisotropies, with flow away from the shock persisting for periods of one to two hours, the anisotropy decreasing with increasing energy, whereas downstream these events are isotropic. These events exhibit slow quasi‐exponential intensity increases of 1–2 orders of magnitude, peaking at the shock, and slowly decaying after the shock, often rising to a secondary peak some hours later. The shock drift events have large upstream first‐order anisotropies close to the shock, with flow away from the shock, and moderate downstream first‐order anisotropies, with flow toward the shock. The most notable feature of the shock drift events is a large negative second harmonic immediately downstream of the shock, signifying protons gyrating around the magnetic field at pitch angles of around 90°. These events have shock spike intensity increases lasting for a few minutes or tens of minutes. At all energies the largest intensity increases are observed with the Fermi events. Since the Fermi events are associated with the largest fluxes of solar flare protons, this may be due to a combination of solar particle background and protons accelerated in the vicinity of the shock.

This paper assembles ISEE 1, 2, and 3 observations of the interplanetary magnetic and electric fields, plasma, magnetohydrodynamic waves, electromagnetic and electrostatic plasma waves, 1‐ to 6‐keV protons and electrons, and >30‐keV/Q ions for the interplanetary shock of November 12, 1978. The shock was high speed (640 km s−1), supercritical, quasi‐parallel, and an efficient accelerator of energetic protons. The flux of >35‐keV protons increased by a factor of 15 in the last 45 min and 270 RE before shock encounter. The >10‐keV proton energy density approached that of the magnetic field and thermal plasma upstream of the shock. The shock was inside a closed magnetic structure that was connected at both ends to the shock. The intensity of ion acoustic and low‐frequency MHD waves increased inside the closed magnetic bubble.

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