  Enhancements of the comic-ray intensity as observed by detectors on the
ground have been observed 71 times since 1942. They are due to solar energetic
particles accelerated in the regions of solar flares deep in the corona, or in
the shock front of coronal mass ejections (CMEs) in the solar wind. The latter
is the favoured model for the classical gradual ground-level enhancement (GLE).
In several papers since the one of McCracken et al. (2008), we pointed out,
however, that some GLEs are too impulsive to be accelerated in the CME shocks.
With this hypothesis in mind we study the time profiles of all the available
GLEs. The main results are that there is a continuous range from gradual to
impulsive, that the fastest risers are concentrated at heliolongitudes that are
magnetically well-connected to Earth, and that the shape of the pulse is a
powerful indicator of propagation conditions between Sun and Earth. This ranges
from relatively quiet to highly disturbed.
