  Bred vectors are a type of finite perturbation used in prediction studies of
atmospheric models that exhibit spatially extended chaos. We study the
structure, spatial correlations, and the growth- rates of logarithmic bred
vectors (which are constructed by using a given norm). We find that, after a
suitable transformation, logarithmic bred vectors are roughly piecewise copies
of the leading Lyapunov vector. This fact allows us to deduce a scaling law for
the bred vector growth rate as a function of their amplitude. In addition, we
relate growth rates with the spectrum of Lyapunov exponents corresponding to
the most expanding directions. We illustrate our results with simulations of
the Lorenz '96 model.
