What part of speech is the word southwest in following sentence They are particularly numerous Southwest?

In the sentence "They are particularly numerous Southwest," the word "Southwest" is functioning as an adverb.

Here's why:

* It modifies the adjective "numerous." It tells us where they are numerous (in the Southwest).

* Adverbs often answer questions like "where," "when," or "how." In this case, "Southwest" answers the question "where?"

While "Southwest" can also be a noun (referring to a region), in this context, it modifies the adjective and therefore acts as an adverb.