The interjection 'Ah!' expresses his surprise.

I was surprised by his sudden visit.

He has difficulty expressing his emotions in words.

He showed his gratitude on his face.

I always admire his talent.

His admiration for his art work could be read from his face.

Ah, he solved the problem in that other way.

Ah, that's right!

Eh, that's a surprise!

Alas, it's raining again.