Simulation of climate change over europe using a nested regional‐climate model. I: Assessment of control climate, including sensitivity to location of lateral boundaries

Abstract

SUMMARYPresent-day climate simulations for Europe are presented, based on a SO km regional-climate model (RCM) driven by output from a global general-circulation model (GCM) using a one-way nesting approach. Both models are components of the Meteorological Office Unified Forecast/Climate Model and use the same subgrid-scale physics. The relationship between the RCM circulation and that of the driving GCM was assessed in seasonal RCM integrations using domains of different sizes. In the larger domains, both the mean flow and the day-to-day variability in the RCM diverge from that of the GCM on the synoptic scale, rendering the RCM solution physically inconsistent with the GCM solution external to the RCM domain. At the grid-point scale the RCM freely generates its own features, even in the smaller domains-only at points adjacent to the boundary buffer zone is there evidence of significant distortion by the lateral boundary forcing from the GCM.Using one of the smaller domains, a 10-year RCM simulation was carried out, driven by a coupled atmosphere/ mixed-layer-ocean version of the GCM. Over the region of interest the general circulation and daily synoptic variability is realistically simulated by the GCM and, therefore, also by the RCM (see above). Stronger vertical motions in the RCM lead to a general increase in dynamical precipitation relative to the GCM, and thus a drier and warmer troposphere and reduced convective cloud and precipitation. Layer-cloud cover is also reduced in the RCM, due to a time-step dependence in the treatment of the dissipation of ice cloud. Significant changes occur in the surface heat balance. The spatial patterns of surface air temperature and precipitation over Europe are well simulated by both the GCM and the RCM on scales resolved by the former. At finer scales the RCM contains a strong signal which is related to orographic height. Validation against a detailed observed climatology for Great Britain demonstrates that this signal contains considerable skill.

A Possible Constraint on Regional Precipitation Intensity Changes under Global Warming

“…For most seasons and regions the models agree fairly well with observations out to about the 95th percentile, though the models' frequencies at this intensity tend to be less. The shortfall appears to be due in part to resolution, which limits the strength of upward motions that produce precipitation, either by direct uplift or by helping to trigger convection (e.g., Jones et al 1995;Gutowski et al 2003). The resolutions used also limit the models' ability to depict small-scale convective events (e.g., Gutowski et al 2003;Biasutti et al 2006).…”

A synthesis of regional climate change simulations—A Scandinavian perspective

“…In a limited area, RCMs thus respond physically consistent to external forcings whilst resolving important meso-scale atmospheric processes such as orographic enhancement/supression of precipitation, and development of frontal systems [Jones et al, 1995]. Thus, the physical mechanisms responsible for individual precipitation events and intensities are more realistically described than in a typ- …”

Multiscale Performance of the ALARO-0 Model for Simulating Extreme Summer Precipitation Climatology in Belgium

“…For this variable it has been shown that RCMs are able to add significant information to the driving global simulations, both in space and time (e.g., Jones et al 1995;Durman et al 2001;Jones et al 2004). In general terms, the RCMs produce an intensification of precipitation with respect to the driving global climate model (GCM), related to the intensification of the hydrological cycle (Jones et al 1995;Durman et al 2001;Buonomo et al 2007). Lynn et al (2010) tested a regional climate model with different physics components at two different spatial resolutions.…”