Does anyone know of an official pronunciation of the name "Jadis", for the White Witch, in CS Lewis's The Chronicles of Narnia?

I've heard variations on the "a" as:

1. ā: as in "jay" (seems common in the US)
2. ä: as in "yacht" (seems common outside the US)

I suppose variations on the "J" could exist as:

1. j: as in "jay" (I've only heard Jadis pronounced with this "J")
2. zh: as in "je ne sais quoi"
3. y: as in "Johannes"
4. h: as in "jalapeño"

Has Mr Lewis spoken to this, or has his estate? What about the animated film, the live-action films, and the BBC radio dramatization (and how official would these be)?

I see no offering at WikiNarnia nor Wikipedia.

I've seen suggestions that the name "Jadis" could be connected to the French jadis ("long ago") and the Persian jadu ("witch"), which could lend credence to consonant (2) and vowel (2) listed above.