This pattern slowly descends by half steps in a way that isn’t very obvious. A four-note quartal cell descends by a minor third, then ascends by a major 2nd. There are no half steps in the pattern itself, only perfect 4ths, minor 3rds, and major 2nds, so the eventual transposition down a half step is very subtle. Our ears can pick up half step transpositions easily, making them quite effective in small doses, and a bit too on-the-nose in larger doses. This pattern also implies a variety of keys as it goes along, as demonstrated by the analyzing brackets. As a rule of thumb, consecutive perfect fourths are harmonically ambiguous.
Since this pattern moves down the horn slowly but in constant eighth notes, we could also say it has a slow rate of registral change. Be aware of this when working it into your solos: many repetitions of the pattern can save the other registers of your instrument, but also can become monotonous. Just something to think about!