  The stability of nonlinear waves on spatially extended domains is commonly
probed by computing the spectrum of the linearization of the underlying PDE
about the wave profile. It is known that convective transport, whether driven
by the nonlinear pattern itself or an underlying fluid flow, can cause
exponential growth of the resolvent of the linearization as a function of the
domain length. In particular, sparse eigenvalue algorithms may result in
inaccurate and spurious spectra in the convective regime. In this work, we
focus on spiral waves, which arise in many natural processes and which exhibit
convective transport. We prove that exponential weights can serve as effective,
inexpensive preconditioners that result in resolvents that are uniformly
bounded in the domain size and that stabilize numerical spectral computations.
We also show that the optimal exponential rates can be computed reliably from a
simpler asymptotic problem posed in one space dimension.
