This is the adverb: you do something in an impressionistic way. You describe, paint, or judge from a general feeling, not from a tight set of facts. “She wrote impressionistically about the city” means the piece gives atmosphere — smells, light, a mood — rather than a street-by-street guide. It is a long, bookish word. Most people never say it out loud; they say “in a loose way” or “just from a first impression”. You will meet it in reviews, art writing, and academic prose. Use it when you want to admit, honestly, that you are sketching. Though actually, saying the long adverb can itself sound a little fancy — which is fine in a careful essay, and a bit much at lunch.

印象式地、憑感覺地