  Variable B supergiants (BSGs) constitute a heterogeneous group of stars with
complex photometric and spectroscopic behaviours. They exhibit mass-loss
variations and experience different types of oscillation modes, and there is
growing evidence that variable stellar winds and photospheric pulsations are
closely related. To discuss the wind properties and variability of evolved
B-type stars, we derive new stellar and wind parameters for a sample of 19
Galactic BSGs by fitting theoretical line profiles of H, He, and Si to the
observed ones and compare them with previous determinations. The mass-loss rate
of three stars has been obtained for the first time. All stars follow the known
empirical wind momentum-luminosity relationships, and the late BSGs show the
trend of the mid BSGs. We find an empirical relationship that associates the
amplitude of mass-loss variations with photometric/spectroscopic variability on
timescales of tens of days. We find that stars located on the cool side of the
bi-stability jump show a decrease in the terminal and escape velocities ratio,
while their corresponding mass-loss rates are similar to or lower than the
values found for stars on the hot side. Particularly, for those variable stars
a decrease in the terminal and escape velocities ratio is accompanied by a
decrease in the mass-loss rate. Our results also suggest that radial pulsation
modes with periods longer than 6 days might be responsible for the wind
variability in the mid/late-type BSGs. These radial modes might be identified
with strange modes, which are known to facilitate (enhanced) mass loss. On the
other hand, we propose that the wind behaviour of stars on the cool side of the
bi-stability jump could fit with predictions of the delta-slow hydrodynamics
solution for radiation-driven winds with highly variable ionization.
