  We analyse archival ALMA (Atacama Large Millimeter/submillimeter Array)
observations of two molecular line emissions, $^{12}$CO(3-2) and
$^{29}$SiO(8-7), from oxygen-rich AGB (Asymptotic Giant Branch) star W Hya.
Together with results of earlier VLT observations at visible and infrared
wavelengths, our results suggest a two-component picture of the
morpho-kinematics of the circumstellar envelope (CSE), one stable over time, at
the scale of centuries, and the other variable, at the scale of years. The
stable component consists of an approximately spherical shell of gas and dust
expanding radially to a terminal velocity of $\sim$5 km s$^{-1}$ at a distance
of $\sim$30 au from the star. It is found to display comparable features as
seen in the CSE of R Dor, a star similar to W Hya. The variable component
projects on the plane of the sky over a region confined to the neighbourhood of
the star and elongated toward the north. Its very high density and sudden
acceleration suggest an interpretation in terms of mass ejection initiated a
few years ago. We discuss its properties in relation with earlier observations
of dust formation in the same region. Our results offer a picture of the wind
of W Hya that differs significantly from the picture that could be suggested by
earlier analyses, giving evidence for a mass ejection that had been previously
overlooked and underscoring new relations between the dust and gas emissions.
They have an impact on the evidence published earlier for the presence of CO
masers. They favour an interpretation in terms of convective cell ejections
playing the main role in the generation of the nascent wind, the stable
component of the CSE being seen as the result of many successive such events
occurring in different directions at short time intervals.
