  We present an 80-d long uninterrupted high-cadence K2 light curve of the
B1Iab supergiant rho Leo (HD 91316), deduced with the method of halo
photometry. This light curve reveals a dominant frequency of
$f_{\rmrot}=0.0373$d$^{-1}$ and its harmonics. This dominant frequency
corresponds with a rotation period of 26.8d and is subject to amplitude and
phase modulation. The K2 photometry additionally reveals multiperiodic
low-frequency variability ($<1.5 $d$^{-1}$) and is in full agreement with
low-cadence high-resolution spectroscopy assembled during 1800 days. The
spectroscopy reveals rotational modulation by a dynamic aspherical wind with an
amplitude of about 20km s$^{-1}$ in the H$\alpha$ line, as well as photospheric
velocity variations of a few km s$^{-1}$ at frequencies in the range 0.2 to 0.6
d$^{-1}$ in the SiIII 4567\AA\ line. Given the large macroturbulence needed to
explain the spectral line broadening of the star, we interpret the detected
photospheric velocity as due to travelling super-inertial low-degree
large-scale gravity waves with dominant tangential amplitudes and discuss why
$\rho$~Leo is an excellent target to study how the observed photospheric
variability propagates into the wind.
