A memorial of what? Scripture isn't really clear on what this is. The Hebrew is clear enough. The root is zayin.haf.resh (Strong's H2142). Here is the Brown-Drive-Briggs entry for that root:
1) to remember, recall, call to mind
a) (Qal) to remember, recall
b) (Niphal) to be brought to remembrance, be remembered, be thought of, be brought to mind
IMO, the purpose of Yom Teruah is to "call to mind" that Yom Kippur is at hand, and to prepare one's self accordingly.