Global Dust Cycle and Direct Radiative Effect in E3SM Version 1: Impact of...

Feng, Y., H. Wang, P. J. Rasch, K. Zhang, W. Lin, Q. Tang, S. Xie, D. S. Hamilton, N. Mahowald, and H. Yu (2022), Global Dust Cycle and Direct Radiative Effect in E3SM Version 1: Impact of Increasing Model Resolution, J. Adv. Modeling Earth Syst..

Quantification of dust aerosols in Earth System Models (ESMs) has important implications for water cycle and biogeochemistry studies. This study examines the global life cycle and direct radiative effects (DREs) of dust in the U.S. Department of Energy's Energy Exascale Earth System Model version 1 (E3SMv1), and the impact of increasing model resolution both horizontally and vertically. The default 1° E3SMv1 captures the spatial and temporal variability in the observed dust aerosol optical depth (DAOD) reasonably well, but overpredicts dust absorption in the shortwave (SW). Simulations underestimate the dust vertical and long-range transport, compared with the satellite dust extinction profiles. After updating dust refractive indices and correcting for a bias in partitioning size-segregated emissions, both SW cooling and longwave (LW) warming of dust simulated by E3SMv1 are increased and agree better with other recent studies. The estimated net dust DRE of −0.42 Wm −2 represents a stronger cooling effect than the observationally based estimate −0.2 Wm −2 (−0.48 to +0.2), due to a smaller LW warming. Constrained by a global mean DAOD, model sensitivity studies of increasing horizontal and vertical resolution show strong influences on the simulated global dust burden and lifetime primarily through the change of dust dry deposition rate; there are also remarkable differences in simulated spatial distributions of DAOD, DRE, and deposition fluxes. Thus, constraining the global DAOD is insufficient for accurate representation of dust climate effects, especially in transitioning to higher- or variable-resolution ESMs. Better observational constraints of dust vertical profiles, dry deposition, size, and LW properties are needed. Plain Language Summary Dust aerosols affect Earth's climate through a myriad of pathways interacting with the global energy budget, atmospheric chemistry, and biogeochemical cycles. It is critical for Earth System Models to capture the global life cycle of dust aerosols for realistically quantifying the impact of climate change. As part of development of the U.S. Department of Energy's Energy Exascale Earth System Model version 1 (E3SMv1), this study examines the representation of global dust life cycle and direct radiative effects in the recently released E3SMv1, and changes resulting from both model physics improvements and increased model resolution. We find that the E3SMv1 model captures the spatial and temporal variations in the observed dust aerosols reasonably well, but underestimates the amount of dust advected from desert sources to remote regions and from the ground to the upper troposphere. Based on the model projection, dust aerosols insert a stronger cooling effect on Earth than previously estimated, after we use a better representation of dust particle size and absorption of sunlight. In addition, we show that not only dust generation but also removal and vertical transport of dust are highly sensitive to the model mesh size, thus need to be quantified in development of higher resolution models.

Research Program: 
Radiation Science Program (RSP)
Climate Variability and Change Program
Funding Sources: 
calipso/cloudsat science team