  The physics goal of the strong interaction program of the NA61/SHINE
experiment at the CERN Super Proton Synchrotron (SPS) is to study the phase
diagram of hadronic matter by a scan of particle production in collisions of
nuclei with various sizes at a set of energies covering the SPS energy range.
This paper presents differential inclusive spectra of transverse momentum,
transverse mass and rapidity of $\pi^{-}$ mesons produced in $central$
${}^{40}$Ar+${}^{45}$Sc collisions at beam momenta of 13$A$, 19$A$, 30$A$,
40$A$, 75$A$ and 150$A$ GeV/$c$. Energy and system size dependence of
parameters of these distributions -- mean transverse mass, the inverse slope
parameter of transverse mass spectra, width of the rapidity distribution and
mean multiplicity -- are presented and discussed. Furthermore, the dependence
of the ratio of the mean number of produced pions to the mean number of wounded
nucleons on the collision energy was derived. The results are compared to
predictions of several models.
