somberness vs soberness

somberness and soberness both are nouns.

Word	Noun	Adjective	Verb	Adverb
somberness	Yes	No	No	No
soberness	Yes	No	No	No

As nouns, somberness and soberness are synonyms defined as:

Other synonyms of somberness include graveness, gravity, sobriety, sombreness.

somberness (noun)	soberness (noun)
a manner that is serious and solemn	a manner that is serious and solemn
a feeling of melancholy apprehension	the state of being sober and not intoxicated by alcohol
a state of partial or total darkness