Precipitation

The MMD models simulate the position of the storm tracks reasonably well but nearly all show some deficiency in the distribution and level of cyclone activity compared to reanalyses (see Section 8.3). Regional Climate Models generally capture the cyclonic events affecting the coast and the associated synoptic variability of precipitation with more fidelity (Adams, 2004; Bromwich et al., 2004a). Over the 20th century, the MMD models simulate changes in storm track position that are generally consistent with observed changes (i.e., poleward displacement of the storm tracks; see Sections 9.5 and 10.3).

The precipitation simulations by both GCMs and RCMs contain uncertainty, on all time scales (Covey et al., 2003; Bromwich et al., 2004a,b; Van de Berg et al., 2005), as a result of model physics limitations. All atmospheric models, including the models underlying the reanalyses, have incomplete parametrizations of polar cloud microphysics and ice crystal precipitation. The simulated precipitation depends, among other things, on the simulated sea ice concentrations, and is strongly affected by biases in the sea ice simulations (Weatherly, 2004). Recent RCM simulations driven by observed sea ice conditions demonstrate good precipitation skill (Van de Berg et al., 2005; Monaghan et al., 2006). However, as emphasized above, the observational uncertainty contributes to uncertainty in the differences between observations and simulations.