  There is a deep astrophysical interest in the structure of $^{19}$F states
close to the alpha decay threshold. The nuclear structure of these states is
important for understanding of the development of $\alpha$ clustering in the
$^{20}$Ne region. Emergence of clustered states and generally states that favor
coupling to reaction channels near the corresponding decay thresholds is
currently of special interest in theoretical physics. Excitation function for
$^{15}$N($\alpha$,$\alpha$) elastic scattering was measured by the TTIK method.
These new data together with old, high energy resolution data, were analyzed
using the R matrix approach. $^{19}$F nuclear structure was calculated using
configuration interaction methods with the recently developed effective
interaction Hamiltonian. The parameters of broad low spin $\ell = 0$ and 1
relative partial wave resonances close to the $\alpha$ decay threshold in
$^{19}$F were identified. Detailed theoretical analysis was carried out
identifying all states coupled to the $\ell = 0$ and 1 alpha cluster channels.
Considering hierarchy of states with different harmonic oscillator shell
excitations allows to evaluate coupling to the alpha channels with different
number of nodes in the relative wave function and helps to explain the
distribution of the clustering strength and emergence of broad clustering
resonances. Comparison of clustering in $^{20}$Ne into $^{16}$O+$\alpha$ and
consideration of spin-orbit splitting of the $^{15}$N+$\alpha$ channel provides
additional evidence. Detailed analysis of new and old experimental data allows
to identify a series of $\alpha$ clustering resonances in $^{19}$F and to
assess the distribution of the clustering strength which is of importance to
questions of astrophysics and for theoretical understanding of many-body
physics and emergence of clustering in loosely bound or unstable nuclei.
