The pattern archives labeled a1 through a8 are temporary storage areas for your patterns.
Typically you'd copy patterns into them that you may need later.
For example:
copy p3 a2
Or you can copy patterns from the archives back into p1, p2, or p3. For example:
copy a2 p3
Or you can even run commands, such as stretch, directly on a pattern stored in an archive.
For example:
stretch a2 20