The poetry device used here is <u><em>metaphor.</em></u>
Metaphor is a poetry device that is used in comparing two unlike things without using words like 'like' or 'as'.
The phrase 'a wave of emotion' is metaphorical because the emotion that is felt at that time is compared to that of a wave without including words such as 'like' or 'as'.
Therefore it is a metaphor.
Hope it is clear ^_^
<span>Catharsis is the effect of fear and pity created in the audience when it watches the downfall of a tragic protagonist. </span>