The bitter cold temperatures recorded during the Showa Era have returned. 和 The bitterly cold temperatures recorded during the Showa Era have returned. 的差別在哪裡？如果不好說明，請提供一些例句。

Actually, “An adverb is a word that modifies a verb, adjective, another adverb, determiner, noun phrase, clause, or sentence.”

In this case “cold” in “cold weather” is an adjective and can be modified by the adverb “bitterly.” I’d say that the second sentence is correct.

As for the first sentence, you could add a comma: The bitter, cold temperatures... and have “bitter” as an additional modifier of “temperature” along with “cold.”

Or drop “temperatures” in which case “cold” becomes a noun and “bitterly” wouldn’t work anymore.