I consider an algebraically closed field of characteristic zero $F$ as a vector space over a real closed field $R \subset F$. I would like to define a norm on $F$ in an invariant fashion, i.e. if we consider another real closed subfield $R' \subset F$ then the norm would still be equivalent to the norm defined taking $R$.

More precisely, for instance for $\mathbb{C}$ we have the norm $N(z)=a^2 +b^2$ where $z=a+ib$, $a,b \in \mathbb{R}$. If we consider $R' \subset \mathbb{C}$ then the same $z \in \mathbb{C}$ will be written as $z=a'+jb'$, $a', b' \in R'$ and $R'$ is a real closed field of index 2 in $\mathbb{C}$. Is the norm $N'(z)=a'^2+b'^2$ equivalent to $N$?