Superensemble regional climate modeling for the western US

Computing resources donated by volunteers have generated the first superensemble of regional climate model results, in which the Hadley regional model HadRM3P and atmospheric global model HadAM3P were implemented for the western US at 25km resolution. Over 136,000 valid and complete one-year runs have been generated to date: about 126,000 for 1960-2009 using observed sea surface temperatures (SSTs) and 10,000 for 2030-2049 using projected SSTs from a global model simulation. Ensemble members differ in initial conditions, model physics, and (potentially, for future runs) SSTs. This unprecedented confluence of high spatial resolution and large ensemble size allows high signal-to-noise ratio and more robust estimates of uncertainty. This paper describes the experiment, compares model output with observations, shows select results for climate change simulations, and gives examples of the strength of the large ensemble size.