A circulation-based performance atlas of the CMIP5 and 6 models for regional climate studies in the Northern Hemisphere mid-to-high latitudes

Abstract

Abstract. Global climate models are a keystone of modern climate research. In most applications relevant for decision making, they are assumed to provide a plausible range of possible future climate states. However, these models have not been originally developed to reproduce the regional-scale climate, which is where information is needed in practice. To overcome this dilemma, two general efforts have been made since their introduction in the late 1960s. First, the models themselves have been steadily improved in terms of physical and chemical processes, parametrization schemes, resolution and implemented climate system components, giving rise to the term “Earth system model”. Second, the global models' output has been refined at the regional scale using limited area models or statistical methods in what is known as dynamical or statistical downscaling. For both approaches, however, it is difficult to correct errors resulting from a wrong representation of the large-scale circulation in the global model. Dynamical downscaling also has a high computational demand and thus cannot be applied to all available global models in practice. On this background, there is an ongoing debate in the downscaling community on whether to thrive away from the “model democracy” paradigm towards a careful selection strategy based on the global models' capacity to reproduce key aspects of the observed climate. The present study attempts to be useful for such a selection by providing a performance assessment of the historical global model experiments from CMIP5 and 6 based on recurring regional atmospheric circulation patterns, as defined by the Jenkinson–Collison approach. The latest model generation (CMIP6) is found to perform better on average, which can be partly explained by a moderately strong statistical relationship between performance and horizontal resolution in the atmosphere. A few models rank favourably over almost the entire Northern Hemisphere mid-to-high latitudes. Internal model variability only has a small influence on the model ranks. Reanalysis uncertainty is an issue in Greenland and the surrounding seas, the southwestern United States and the Gobi Desert but is otherwise generally negligible. Along the study, the prescribed and interactively simulated climate system components are identified for each applied coupled model configuration and a simple codification system is introduced to describe model complexity in this sense.

The ExtremeX global climate model experiment: investigating thermodynamic and dynamic processes contributing to weather and climate extremes

“…5). It is known that MIROC5 shows biases in the North Atlantic storm-track activity compared to ERA-Interim (e.g., Brands, 2022;Zappa et al, 2013). Correcting this circulation bias in AF_SI leads to even larger precipitation biases, which are only reduced when the soil moisture is constrained as well.…”

“…Since EC-Earth3 was used for CMIP6, it also has the most recent forcing data. Among CMIP5 and CMIP6 models, EC-Earth3 is one of the bestperforming models with regard to the representation of atmospheric circulation in the Northern Hemisphere middle to high latitudes (Brands, 2022;Fernandez-Granja et al, 2021). MIROC5 has contributed to CMIP5 as well as the 1.5 • C versus 2.0 • C global warming experiments (e.g., Hirsch et al, 2018;Mitchell et al, 2017;Shiogama et al, 2019).…”

“…EarthSyst. Dynam., 13, 1167-1196, 2022 https://doi.org/10.5194/esd-13-1167-2022 K.Wehrli et al: The ExtremeX experiment…”

Atmospheric rivers in CMIP5 climate ensembles downscaled with a high-resolution regional climate model

“…The land-surface boundary is defined according to ECO-CLIMAP (Champeaux et al, 2005) and used to calculate mass and energy fluxes between the Earth's surface and the atmosphere. Over the North Sea and Baltic Sea, RCA is interactively coupled to the 3-D ocean model NEMO (Nucleus for European Modelling of the Ocean; Madec, 2012, Fig.…”

“…First, the parent global models differ in their thermodynamic equilibrium states, such that both the air temperatures and the moisture loads at the lateral boundary of the RCA differ as well. As a result, the large-scale atmospheric circulation also differs among the global models (e.g., Brands, 2022), as the Equator-to-pole temperature gradients are likewise different (Harvey et al, 2014). This further influences the meridional position of the westerlies in the respective models.…”