Impact of spectral nudging and domain size in studies of RCM response to parameter modification

Abstract

The paper aims at finding an RCM configuration that facilitates studies devoted to quantifying RCM response to parameter modification. When using short integration times, the response of the time-averaged variables to RCM modification tend to be blurred by the noise originating in the lack of predictability of the instantaneous atmospheric states. Two ways of enhancing the signal-tonoise ratio are studied in this work: spectral nudging and reduction of the computational domain size. The approach followed consists in the analysis of the sensitivity of RCMsimulated seasonal averages to perturbations of two parameters controlling deep convection and stratiform condensation, perturbed one at a time. Sensitivity is analyzed within different simulation configurations obtained by varying domain size and using the spectral nudging option. For each combination of these factors multiple members of identical simulations that differ exclusively in initial conditions are also generated to provide robust estimates of the sensitivities (the signal) and sample the noise. Results show that the noise magnitude is decreased both by reduction of domain size and the spectral nudging. However, the reduction of domain size alters some sensitivity signals. When spectral nudging is used significant alterations of the signal are not found.

Effects of spatial resolution in the simulation of daily and subdaily precipitation in the southwestern US

“…Separovic et al . [] showed that spectral nudging reduces significantly the internal variability and noise for RCM simulations. The nudging technique uses a correction term that depends on the difference between the model values and those of the driving model.…”

Impacts of using spectral nudging on regional climate model RCA4 simulations of the Arctic

“…Here we utilise a method called spectral nudging, which is a method of imposing the larger horizontal scales of the driving GCM data on the interior RCM domain at 850 P. Berg et al: Spectral nudging in RCA4-Arctic selected atmospheric levels (von Storch et al, 2000). The smaller scales, and especially the lower atmospheric levels of the RCM, are left untouched by the spectral nudging, allowing the RCM to develop its own internal climate under the larger-scale constraints (Alexandru et al, 2009;Separović et al, 2012). Initially, the method was a simple alternative for data assimilation, but it has been found to be efficient also in reducing systematic model biases .…”

Synchrony between reanalysis-driven RCM simulations and observations: variation with time scale

“…For reasons of availability, data coming from different simulations will be discussed: The two simulations used in the first subsection were performed on a subcontinental domain over eastern Canada on a 11-km grid mesh, while the three used in the second subsection were performed over a domain encompassing the entire North America a 22-km grid mesh. One of these three simulations uses a moderate large-scale nudging on the wind field, with a 6-h relaxation time from the top of the troposphere until 500 hPa, then diminishing linearly with height to become unforced at the surface (Separovic et al 2011). For seasonal values observations from CRU3.20 dataset are used (Harris et al 2013).…”