Answer:
The correct answer is; adjective clause.
Explanation:
The adjective clause refers to an independent clause that modifies a noun as an adjective. This type of clause provides the necessary information about the word it modifies. Adjective clauses usually start with words like: who, where, what, why, etc.
In this example, the adjective unusual modifies the noun weather and provides additional information about the weather of 1816.
