Abstract
Stochastic parameterizations are used in numerical weather prediction
and climate modeling to help capture the uncertainty in the simulations
and improve their statistical properties. Convergence issues can arise
when time integration methods originally developed for deterministic
differential equations are applied naively to stochastic problems.
(Hodyss et al 2013, 2014) demonstrated that a correction term to various
deterministic numerical schemes, known in stochastic analysis as the Itô
correction, can help improve solution accuracy and ensure convergence to
the physically relevant solution without substantial computational
overhead. The usual formulation of the Itô correction is valid only when
the stochasticity is represented by white noise. In this study, a
generalized formulation of the Itô correction is derived for noises of
any color. It is applied to a test problem described by an
advection-diffusion equation forced with a spectrum of fast processes.
We present numerical results for cases with both constant and spatially
varying advection velocities to show that, for the same time step sizes,
the introduction of the generalized Itô correction helps to
substantially reduce time integration error and significantly improve
the convergence rate of the numerical solutions when the forcing term in
the governing equation is rough (fast varying); alternatively, for the
same target accuracy, the generalized Itô correction allows for the use
of significantly longer time steps and hence helps to reduce the
computational cost of the numerical simulation.