"Sunlight" runs as a conceit (extended metaphor) throughout the poem.
It is emblematic of the warmth and comfort she associated with her city of birth.
Rumens employs epistrophe (a repeated word at the end of each stanza) by closing each stanza with the noun "sunlight".
This characterises "sunlight" as an irrepressible force which will break through despite anguish and tryanny.
The phrase "it tastes of sunlight" uses synaesthesia (the blending of the senses) to depict how strong her memories are, they encompass all of her senses.
Alternatively, the excessively figurative language reinforces how the city she remembers is now very much theoretical and not real.
The phrase "but I am branded by an impression of sunlight" juxtaposes the speaker's positive romanticised view with the reality of the city now as the verb "branded" has connotations of aggression and pain.
Moreover, the plosive'b' could convey the nature of the speaker's memory - it is forceful and indestructible.