downwardly vs downward

downwardly is not an adjective while downward is an adjective.

Word	Noun	Adjective	Verb	Adverb
downwardly	No	No	No	Yes
downward	No	Yes	No	Yes

As adverbs, downwardly and downward are synonyms defined as:

downwardly and downward: spatially or metaphorically from a higher to a lower level or position

Other synonyms of downwardly include down, downwards.

downwardly (adjective)	downward (adjective)
	extending or moving from a higher to a lower place
	on or toward a surface regarded as a base

downwardly (adverb)	downward (adverb)
spatially or metaphorically from a higher to a lower level or position	spatially or metaphorically from a higher to a lower level or position