  Recent studies of the diffuse parts of molecular clouds have revealed the
presence of parallel, ordered low-density filaments termed striations. Flows
along magnetic field lines, Kelvin-Helmholtz instabilities and hydromagnetic
waves are amongst the various formation mechanisms proposed. Through a synergy
of observational, numerical and theoretical analysis, previous studies singled
out the hydromagnetic waves model as the only one that can account for the
observed properties of striations. Based on the predictions of that model, we
develop here a method for measuring the temporal evolution of striations
through a combination of molecular and dust continuum observations. Our method
allows us to not only probe temporal variations in molecular clouds but also
estimate the strength of both the ordered and fluctuating components of the
magnetic field projected on the plane-of-the-sky. We benchmark our new method
against chemical and radiative transfer effects through two-dimensional
magnetohydrodynamic simulations coupled with non-equilibrium chemical modelling
and non-local thermodynamic equilibrium line radiative transfer. We find good
agreement between theoretical predictions, simulations and observations of
striations in the Taurus molecular cloud. We find a value of $\rm{27 \pm 7}
~\rm{\mu G}$ for the plane-of-sky magnetic field, in agreement with previous
estimates via the Davis-Chandrasekhar-Fermi method, and a ratio of fluctuating
to ordered component of the magnetic field of $\sim$ 10\%.
