Not sure why they call them 'rare'.
One of my static pictures shows two types of wave, atmospheric and sea.  (looking into wind).
Another shows shafts of sun through a cloud gap.
Time lapse illustrates clearly how cloud forms consistently in one place and similarly dissipates on the downwind side of the cloud.
Conventional wisdom is that the wind should be more-or-less perpendicular to the generating mountains.  My gliding experience and these timelapses show that the wind maybe be as much as 45 degrees away from perpendicular but the 'standing' wave clouds adopt the orientation of the generating source.  The edge of dissipating cloud [downwind edge] is often more 'cleanly' marked.
Jack