na-adjective
clearly miraculous; strikingly effective
Describes a result or effect that is so remarkable it seems almost supernatural, often used for healing, divine favor, or extraordinary efficacy.
この薬はあらたかな効き目がある。
This medicine has a strikingly effective result.
祈りのあらたかな力を感じた。
I felt the clearly miraculous power of prayer.
奇跡的 means 'miraculous' in a more literal sense of a miracle, while あらたか emphasizes the striking, almost supernatural effectiveness of something, often in a spiritual or traditional context.
The origin is uncertain. It may be related to classical Japanese words expressing clarity or striking appearance, but the exact derivation is unclear.