Context : The brilliant Balmer H \alpha line in the stationary emission spectrum of the Galactic microquasar SS 433 has a broad component ( \sim 1000 km s ^ { -1 } ) .
This is formed in the wind blowing from the accretion disk of the compact object , which orbits the centre of mass of the binary at \sim 175 km s ^ { -1 } with a 13-day period .
The centroid of the H \alpha emission line formed in the wind has an imperfect memory of the motion of its source .

Aims : The aim is to understand how this emission line is left with a blurred memory of the motion of the source of the wind .

Methods : We analysed stationary H \alpha spectra , taken almost nightly over two orbital periods of the binary system .

Results : The loss of memory by emission lines from the wind is easily understood quantitatively , if any parcel of wind that has been newly conditioned to radiate in H \alpha continues its emission for a period of days .
If the decay is exponential , a mean lifetime of about two days is all that is required .
This timescale is very close to what is required for the decay of H \alpha from the putative circumbinary disk to be responsible for the narrow components of the H \alpha emission line .
It is also close to the timescales observed for the individual bolides that radiate H \alpha in the relativistic jets .

Conclusions : The structure of the stationary H \alpha emission line is now well understood .
The broad component is undoubtedly formed in the wind from the accretion disk and the two narrow components carry no such signature .
Their properties are entirely consistent with an origin in a circumbinary disk .
The characteristic lifetime of H \alpha emitting material is a few days , as observed for the relativistic bolides in the jets .