Internal Variability in Regional Climate Downscaling at the Seasonal Scale

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.

[1]  H. Storch.  Models of Global and Regional Climate , 2006 .

[2]  Klaus Dethloff,et al.  Internal variability in Arctic regional climate simulations: case study for the SHEBA year , 2004 .

[3]  Jan Polcher,et al.  Internal variability of regional climate models , 2001 .

[4]  H. Davies,et al.  A lateral boundary formulation for multi-level prediction models. [numerical weather forecasting , 1976 .

[5]  F. Giorgi,et al.  A study of internal variability of a regional climate model , 2000 .

[6]  R. Reynolds,et al.  The NCEP/NCAR 40-Year Reanalysis Project , 1996, Renewable Energy.

[7]  F. Chomé,et al.  One-way nested regional climate simulations and domain size , 2005 .

[8]  E. Lorenz.  Deterministic nonperiodic flow , 1963 .

[9]  Ralf Weisse,et al.  Evaluation of a method to reduce uncertainty in wind hindcasts performed with regional atmosphere models , 2003 .

[10]  Matthieu Plu,et al.  A Cyclogenesis Evolving into Two Distinct Scenarios and Its Implications for Short-Term Ensemble Forecasting , 2005 .

[11]  Daniel Caya,et al.  Internal variability of RCM simulations over an annual cycle , 2004 .

[12]  F. Giorgi,et al.  The Effects of Domain Choice on Summer Precipitation Simulation and Sensitivity in a Regional Climate Model , 1998 .

[13]  A. Lynch,et al.  Estimating the Uncertainty in a Regional Climate Model Related to Initial and Lateral Boundary Conditions , 2005 .

[14]  Richard C. J. Somerville,et al.  On the use of a coordinate transformation for the solution of the Navier-Stokes equations , 1975 .

[15]  F. Giorgi,et al.  Approaches to the simulation of regional climate change: A review , 1991 .

[16]  K. Bryan,et al.  A predictability study of simulated North Atlantic multidecadal variability , 1997 .

[17]  René Laprise,et al.  The Formulation of the Andr Robert MC (Mesoscale Compressible Community) Model , 1997 .

[18]  H. Storch,et al.  Sensitivity of a Regional Atmospheric Model to a Sea State–Dependent Roughness and the Need for Ensemble Calculations , 2000 .

[19]  Yimin Ji,et al.  Simulation of the Asian Summer Monsoons of 1987 and 1988 with a Regional Model Nested in a Global GCM , 1997 .

[20]  Georgiy L. Stenchikov,et al.  Spectral nudging to eliminate the effects of domain position and geometry in regional climate model simulations , 2004 .

[21]  Daniel Caya,et al.  RCM’s internal variability as function of domain size , 2004 .

[22]  René Laprise,et al.  A Semi-Implicit Semi-Lagrangian Regional Climate Model: The Canadian RCM , 1999 .

[23]  F. Giorgi.  Simulation of Regional Climate Using a Limited Area Model Nested in a General Circulation Model , 1990 .

[24]  J. Blanchet,et al.  The Canadian Climate Centre Second-Generation General Circulation Model and Its Equilibrium Climate , 1992 .

[25]  Klaus Dethloff,et al.  On the sensitivity of a regional Arctic climate model to initial and boundary conditions , 2000 .

[26]  R. Pielke,et al.  Dynamical downscaling: Assessment of value retained and added using the Regional Atmospheric Modeling System (RAMS) , 2005 .

[27]  R. Arritt,et al.  Observations and Regional Climate Model Simulations of Heavy Precipitation Events and Seasonal Anomalies: A Comparison , 2002 .

[28]  H. Storch,et al.  A Spectral Nudging Technique for Dynamical Downscaling Purposes , 2000 .

[29]  J. Kain,et al.  A One-Dimensional Entraining/Detraining Plume Model and Its Application in Convective Parameterization , 1990 .

[30]  E. Bazile,et al.  A mass‐flux convection scheme for regional and global models , 2001 .