Both alternating current and direct current are measured in ampere. But how is the ampere defined defined for an alternating current .

Question

$\begin{array}{1 1} \text{a.c ampere is equal to I} \\ \text{a.c ampere is proportional } \\ \text{a.c ampere is equal to }I^2 \\ \text{a.c ampere is equal to } I^2 \end{array}$