The influence of atmospheric grid resolution in a climate model-forced ice sheet simulation

Abstract

Abstract. Coupled climate-ice sheet simulations have been growing in popularity in recent years. Experiments of this type are however challenging as ice sheets evolve over multimillennial timescales, which is beyond the practical integration limit of most Earth system models. A common method to increase model throughput is to trade resolution for computational efficiency (compromise accuracy for speed). Here we analyze how the resolution of an atmospheric general circulation model (AGCM) influences the simulation quality in a stand-alone ice sheet model. Four identical AGCM simulations of the Last Glacial Maximum (LGM) were run at different horizontal resolutions: T85 (1.4 • ), T42 (2.8 • ), T31 (3.8 • ), and T21 (5.6 • ). These simulations were subsequently used as forcing of an ice sheet model. While the T85 climate forcing reproduces the LGM ice sheets to a high accuracy, the intermediate resolution cases (T42 and T31) fail to build the Eurasian ice sheet. The T21 case fails in both Eurasia and North America. Sensitivity experiments using different surface mass balance parameterizations improve the simulations of the Eurasian ice sheet in the T42 case, but the compromise is a substantial ice buildup in Siberia. The T31 and T21 cases do not improve in the same way in Eurasia, though the latter simulates the continent-wide Laurentide ice sheet in North America. The difficulty to reproduce the LGM ice sheets in the T21 case is in broad agreement with previous studies using low-resolution atmospheric models, and is caused by a substantial deterioration of the model climate between the T31 and T21 resolutions. It is speculated that this deficiency may demonstrate a fundamental problem with using low-resolution atmospheric models in these types of experiments.

An Overview of Interactions and Feedbacks Between Ice Sheets and the Earth System

“…An important question in the context of model validation is “what level of bias is acceptable?” This is an important question particularly in light of coupled ice sheet/Earth system simulations, which are constrained by boundary conditions far from ice sheets themselves. Such models operate according to best understandings of (sometimes incomplete) physical relationships applied to coarse numerical grids and thus are prone to model‐observation bias throughout the Earth system (including, potentially, ice sheet bias; e.g., Löfverström & Liakka, ). The trade‐off between bias and resolution of ice sheet/Earth system interactions and feedbacks will be a persistent topic requiring careful consideration when designing coupled ice sheet/Earth system simulations for the purpose of future SLR projections.…”

Towards understanding potential atmospheric contributions to abrupt climate changes: characterizing changes to the North Atlantic eddy-driven jet over the last deglaciation

“…Herein we use 10 vertical levels at a spectral resolution of T42 (approximately 2.8 • × 2.8 • ), which has been previously shown to be sufficiently high to resolve phenomena of interest to the eddy-driven jet (Barnes and Hartmann, 2011;Löfverström and Liakka, 2018) while enabling fast enough model run times to make multiple deglacial experiments feasible. The dynamical atmospheric solutions are generated in spectral space, while the remaining calculations (e.g.…”

“…In the TraCE-21ka deglacial simulation (Liu et al, 2009(Liu et al, , 2012He, 2011), the NAtl jet exhibits two characteristic states: a strong, stable, zonal glacial jet and a weaker, latitudinally variable, tilted interglacial jet (Löfverström and Lora, 2017). The transition from the one jet state to the other is abrupt and coincident with the separation of the Cordilleran and Laurentide ice sheets at 13.89 kyr BP (Löfverström and Lora, 2017). A jet shift at 13.89 kyr BP lies during the middle of the B-A, which would rule out that it played an important, proximal, role in triggering abrupt climate transitions during the last deglaciation.…”

Assessment of the Greenland ice sheet–atmosphere feedbacks for the next century with a regional atmospheric model coupled to an ice sheet model

“…These changes may in turn alter both local and global climate. As an example, changes in nearsurface temperature and surface energy balance may occur in response to changes in orography (temperature-elevation feedback) or changes in ice-covered area (planetary albedo feedback; see Lunt et al, 2004and Vizcaíno et al, 2008. On the other hand, topography changes may alter the atmospheric circulation patterns (Doyle and Shapiro, 1999;Petersen et al, 2003;Moore and Renfrew, 2005) causing changes in heat and humidity transports.…”

“…Using the AGCM NCAR-CAM3 run at different spatial resolutions (T21 to T85) and coupled to the SICOPOLIS ice sheet model, Lofverstrom and Liakka (2018) investigated how the atmospheric model resolution influenced the simulated ice sheets at the Last Glacial Maximum. They found that the North American and the Eurasian ice sheets were properly reproduced with the only T85 run.…”