Is the word ah the same in Brazilian and European Portuguese?

Yes

The word "ah" is an interjection used in both Brazilian and Continental Portuguese to express a variety of emotions, such as surprise, realization, relief, or disappointment. There are no differences in its meaning, spelling, or grammatical function between the two dialects. The only difference lies in pronunciation, specifically in the prosody and intonation patterns (the "melody" of the sentence) which vary according to the speaker's regional accent.

Brazilian Portuguese Examples

1. Ah, agora eu entendi! (Ah, now I understand!)
2. Ah, que bom que você chegou! (Ah, how good that you arrived!)
3. Ah, que pena! (Ah, what a pity!)
4. Ah, eu lembrei! (Ah, I remembered!)
5. Ah, é você! (Ah, it's you!)

Continental Portuguese Examples

1. Ah, agora percebi! (Ah, now I realize!)
2. Ah, ainda bem que chegaste! (Ah, it's a good thing you arrived!)
3. Ah, que pena! (Ah, what a pity!)
4. Ah, lembrei-me! (Ah, I remembered!)
5. Ah, és tu! (Ah, it is you!)