Modifier Letter Small U Bar

In UPA, it marks brief or transitional vowels.

The Uralic Phonetic Alphabet (UPA) was first published by Finnish linguist E. N. Setälä in 1901 and revised during the twentieth century. A 2003 Unicode proposal describes ᶶ as a modifier for secondary or transitional vowel sounds.

Some IPA descriptions use ᶶ for a weak, fleeting vowel, one inserted between sounds, or an echo-like vowel with ʉ’s quality. Full-size ʉ is made with the tongue high near the mouth’s center and the lips rounded; an echo vowel resembles a nearby one.