Answer:
Alliteration: bloated clouds bulging and billowing
Personification: The storm crept in upon us; the feeble sun limped away and died; the howling of the wind
Imagery: its bloated clouds bulging and billowing to create a fortress that walled off the sky.Behind these towering, stratospheric ramparts; the official soundtrack of the apocalypse
Explanation:
Alliteration is a device in which consonant sounds are repeated at the beginning of words that are close in proximity in the structure. In the passage we are analyzing here, the /b/ sound is repeated in "bloated clouds bulging and billowing."
Personification is a literary device in which human qualities are attributed to inanimate objects. In the passage we are analyzing here, the author says the clouds crept upon them, the sun limped and died, and the wind howled. Those actions can only be performed by humans or animals, but not by inanimate objects. The purpose is to emphasize feelings and ideas.
Imagery consists of appealing to the five senses when writing, with the purpose of describing something vividly. To be fair, the whole passage consists of imagery. The description of the clouds, the sun, and the wind appeals to sight and hearing.