High-Resolution Global Climate Simulations with the ECMWF Model in Project Athena: Experimental Design, Model Climate, and Seasonal Forecast Skill

Abstract

The sensitivity to the horizontal resolution of the climate, anthropogenic climate change, and seasonal predictive skill of the ECMWF model has been studied as part of Project Athena—an international collaboration formed to test the hypothesis that substantial progress in simulating and predicting climate can be achieved if mesoscale and subsynoptic atmospheric phenomena are more realistically represented in climate models. In this study the experiments carried out with the ECMWF model (atmosphere only) are described in detail. Here, the focus is on the tropics and the Northern Hemisphere extratropics during boreal winter. The resolutions considered in Project Athena for the ECMWF model are T159 (126 km), T511 (39 km), T1279 (16 km), and T2047 (10 km). It was found that increasing horizontal resolution improves the tropical precipitation, the tropical atmospheric circulation, the frequency of occurrence of Euro-Atlantic blocking, and the representation of extratropical cyclones in large parts of the Northern Hemisphere extratropics. All of these improvements come from the increase in resolution from T159 to T511 with relatively small changes for further resolution increases to T1279 and T2047, although it should be noted that results from this very highest resolution are from a previously untested model version. Problems in simulating the Madden–Julian oscillation remain unchanged for all resolutions tested. There is some evidence that increasing horizontal resolution to T1279 leads to moderate increases in seasonal forecast skill during boreal winter in the tropics and Northern Hemisphere extratropics. Sensitivity experiments are discussed, which helps to foster a better understanding of some of the resolution dependence found for the ECMWF model in Project Athena.

The Benefits of Global High Resolution for Climate Simulation: Process Understanding and the Enabling of Stakeholder Decisions at the Regional Scale

“…Catto et al (2010) and Zappa et al (2013) show that extratropical storm structure and intensity are better represented at resolutions finer than 100 km, and hence so is the moisture transport associated with them. Jung et al (2012) demonstrate significantly improved extratropical cyclone frequency when moving from 130-to 40-km resolution, with little change at finer grid spacings.…”

“…Because of nonlinearities in the system, including a zero-mean noise into a GCM leads to systematic shifts in the climate that can reduce model biases (Jung et al 2005;Williams 2012;Berner et al 2015Berner et al , 2017 and improve variability Neelin 2000, 2003;Dawson and Palmer 2015;Christensen et al 2015Christensen et al , 2017, often analogous to refining model resolution (e.g., Berner et al 2012;Watson et al 2017). As model resolution increases, stochastic approaches will become more valuable, as representing the interaction of the resolved scales with the subgrid through purely deterministic schemes becomes harder to justify (Dorrestijn et al 2013).…”

Mean and extreme precipitation over European river basins better simulated in a 25 km AGCM

“…Multidecadal GCM simulations can now be carried out at grid spacings of about 20 km (Jung et al, 2012;Mizuta et al, 2012;Wehner et al, 2014;Mizielinski et al, 2014;van Haren et al, 2015). This offers the possibility of using a single global physically consistent model in applications that until a few years ago were in the realm of RCM simulations (van der Linden and Mitchell, 2009).…”

Atmospheric blocking in a high resolution climate model: influences of mean state, orography and eddy forcing

“…The representation of blocking frequency in numerical models depends on many factors, including the blocking index (BI) used and the horizontal resolution (Pelly and Hoskins, 2003;Jung et al ., 2012). Models often underestimate the frequency and duration of atmospheric blocks in both the Atlantic and Pacific basins (D'Andrea et al ., 1998;Matsueda et al ., 2009), and it has been argued that the horizontal resolution is the main cause for these blocking errors (Matsueda et al ., 2009).…”