A schwa sound [ə] may also occur as a lax realization of short vowels.
Historical short vowel *a is lengthened to /ā/ in a number of words, e.g. *katab(a) > ktāb 'he wrote', a process called by Richard Davey "iambic vowel lengthening". It does sometimes occur in other positions, perhaps as a result of stress shift.
Rarely, the historical *ā vowel has been raised and fronted to /ē/ or /ī/, or backed and rounded to /ō/. Raising and fronting of *ā is an important feature in Arabic linguistic history. Both features are unusual in the Arabian Peninsula and are today found in very few lexical items, but are documented in the primary sources of Rhodokanakis (1908,1911) and Davey (2016).
Mark Shockley (2024). "Ruʾūs al-Jibāl Arabic in Context: A Proposal for an Expanded Typology of Southeastern Arabian Dialects". Journal of Semitic Studies. 69: 1–28.