  The interaction of backstreaming ions with the incoming solar wind in the
upstream region of the bow shock gives rise to a number of plasma instabilities
from which ultra-low frequency (ULF) waves can grow. Because of their finite
growth rate, the ULF waves are spatially localized in the foreshock region.
Previous studies have reported observational evidences of the existence of a
ULF wave foreshock boundary, which geometrical characteristics are very
sensitive to the interplanetary magnetic field (IMF) cone angle. The
statistical properties of the ULF wave foreshock boundary is examined in detail
using Cluster data. A new identification of the ULF wave foreshock boundary is
presented using specific and accurate criterion for a precises determination of
boundary crossings. The criterion is based on the degree of IMF rotation as
Cluster crosses the boundary. The obtained ULF wave foreshock boundary is
compared with previous results reported in the literature as well as with
theoretical predictions. Also, we examined the possible connexion between the
foreshock boundary properties and the ion emission mechanisms at the bow shock.
