Internal Variability in Regional Climate Downscaling at the Seasonal Scale

Abstract

To study the internal variability of the model and its consequences on seasonal statistics, large ensembles of twenty 3-month simulations of the Canadian Regional Climate Model (CRCM), differing only in their initial conditions, were generated over different domain sizes in eastern North America for a summer season. The degree of internal variability was measured as the spread between the individual members of the ensemble during the integration period. Results show that the CRCM internal variability depends strongly on synoptic events, as is seen by the pulsating behavior of the time evolution of variance during the period of integration. The existence of bimodal solutions for the circulation is also noted. The geographical distribution of variance depends on the variables; precipitation shows maximum variance in the southern United States, while 850-hPa geopotential height exhibits maximum variance in the northeast part of the domain. Results suggest that strong precipitation events in the southern United States may act as a triggering mechanism for the 850-hPa geopotential height spread along the storm track, which reaches its maximum toward the northeast of the domain. This study reveals that successive reductions of the domain size induce a general decrease in the internal variability of the model, but an important variation in its geographical distribution and amplitude was detected. The influence of the internal variability at the seasonal scale was evaluated by computing the variance between the individual member seasonal averages of the ensemble. Large values of internal variability for precipitation suggest possible repercussions of internal variability on seasonal statistics.

Investigation of indiscriminate nudging and predictability in a nested quasi‐geostrophic model

“…Conversely, Vannitsem and Chomé (2005) show that for a large domain a small error in initial condition leads to different simulations. The study of Alexandru et al(2007) suggests that a reduction of the domain size generally results in a significant reduction of LAM internal variability. Finally, Lucas-Picher et al(2008) have computed the time spent by air parcels in the domain of an RCM.…”

A review on regional dynamical downscaling in intraseasonal to seasonal simulation/prediction and major factors that affect downscaling ability

“…Domain size and domain position significantly affect dynamic downscaling ability for precipitation and atmospheric variables (e.g., Jacob and Podzun, 1997;Vannitsem and Chomé, 2005;Alexandru et al, 2007). When the domain size becomes big, the internal variability of the model also becomes large, such that there is more possibility for an RCM to drift away from the LBCs' climatology.…”

Energy cycle associated with inter-member variability in a large ensemble of simulations with the Canadian RCM (CRCM5)

“…Previous studies, such as those of Giorgi and Bi (2000) and Alexandru et al (2007), have shown that the IV is not associated with magnitude or nature of the IC differences. These studies converge to the same conclusion that the IV magnitude strongly fluctuates according to synoptic events in RCM simulations.…”

“…With global models the IV asymptotes to the transient-eddy variability in the limit of large ensembles. In the case of regional models, however, the LBC exert a constraint that limits the inter-member spread (at least at the large scales), which contributes to generally maintaining the magnitude of IV below the transient-eddy variability (e.g., Weisse et al 2000;Giorgi and Bi 2000;Rinke and Dethloff 2000;Christensen et al 2001;Caya and Biner 2004;Rinke et al 2004;Lucas-Picher et al 2004 and2008a, b;Alexandru et al 2007;Nikiéma and Laprise 2011a, b).…”