Yuan et al. (2025) Weaker absorption of Asian dust than previously estimated based on observation-constrained simulation

Identification

• Journal: npj Climate and Atmospheric Science
• Year: 2025
• Date: 2025-12-18
• Authors: Y. Yuan, Hao Wang, Chenglai Wu, Tafeng Hu, Feng Wu, Daizhou Zhang, Junji Cao
• DOI: 10.1038/s41612-025-01290-8

Research Groups

• State Key Laboratory of Atmospheric Environment and Extreme Meteorology (AEEM), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
• University of Chinese Academy of Sciences, Beijing, China
• International Center for Climate and Environment Sciences, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
• State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China
• Faculty of Environmental and Symbiotic Sciences, Prefectural University of Kumamoto, Kumamoto, Japan
• Science Center for Earth System Numerical Simulation, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China

Short Summary

This study developed a revised complex refractive index for East Asian dust based on 22 soil samples, revealing significantly weaker absorption than previously estimated. Implementing these new parameters in a climate model substantially improved simulations of dust optical properties and reversed the estimated top-of-atmosphere shortwave direct radiative effect from warming to cooling.

Objective

• To formulate a region-specific dust complex refractive index scheme for East Asia using 22 surface soil samples and meticulous model validation.
• To reassess the shortwave direct radiative effect of East Asian dust aerosols using the improved optical parameters and compare it with previous assessments.

Study Configuration

• Spatial Scale: East Asian dust source regions (Gobi Desert, Taklimakan Desert, Qaidam Basin), downstream regions (North China Plain, Yellow Sea, East China Sea), and the Tibetan Plateau.
• Temporal Scale: Analysis focused on spring (March to May) for the period 2010-2015, derived from model simulations spanning January 2006 to December 2015.

Methodology and Data

• Models used: CAS-ESM2 (Chinese Academy of Sciences Earth System Model Version 2), Common Land Model (CoLM) with the Shao04 dust emission scheme, IAP AGCM5 (IAP Atmospheric General Circulation Model 5), Bulk Aerosol Module (BAM), Mie scattering theory, RRTMG radiation scheme.
• Data sources: 22 East Asian dust (EAD) surface soil samples from major source regions, laboratory measurements (Computer-controlled scanning electron microscopy - CCSEM for iron oxide mass percentages), AERONET Level 2.0 dataset (Single Scattering Albedo - SSA, Absorption Aerosol Optical Depth - AAOD, Aerosol Optical Depth - AOD, Ångström exponent at 550 nm), satellite retrievals (for total dust optical depth - DOD comparison).

Main Results

• A revised imaginary part of the complex refractive index (𝑘) for EAD was derived, ranging from 2.26 × 10⁻⁴ to 8.37 × 10⁻⁴ in the 0.3-1 µm range, which is significantly lower than values in the OPAC database and those commonly used for East Asian dust.
• Applying these improved optical parameters to CAS-ESM2 reduced the single scattering albedo (SSA) bias from 15% to 2% and corrected the absorption aerosol optical depth (AAOD) overestimation from +5.2% to -1.7% compared to AERONET observations.
• The modified scheme reduced atmospheric absorption by 79.5% (-7.61 W/m²) and reversed the top-of-atmosphere (TOA) shortwave direct radiative effect (DRE) from a warming of +0.75 W/m² to a cooling of -3.80 W/m².
• The surface (SFC) radiative cooling was diminished by 34.6%, indicating weaker dust absorption.
• Regions of intense shortwave radiative cooling at the TOA (≥-18 W/m²) were predominantly localized near dust source regions (e.g., Taklimakan and Badain Jaran Deserts), with simulated maximum SFC SW DRE reaching -27 W/m².

Contributions

• Developed a novel, region-specific complex refractive index scheme for East Asian dust based on extensive laboratory analysis of 22 soil samples, providing a more reliable data foundation than previous estimates.
• Significantly improved the accuracy of dust optical property simulations (SSA, AAOD) in a Global Climate Model (CAS-ESM2) for East Asia by constraining parameters with observations.
• Reassessed the shortwave direct radiative effect of East Asian dust, demonstrating a weaker absorption and a reversal of the TOA radiative effect from warming to cooling, thereby reducing uncertainties in dust-climate feedback.
• Highlighted the critical importance of region-specific optical properties for accurate climate modeling, especially for East Asian dust, which exhibits distinct characteristics compared to Saharan dust.

Funding

• National Natural Science Foundation of China (42030511)
• National Large Scientific and Technological Infrastructure “Earth System Numerical Simulation Facility” (https://cstr.cn/31134.02.EL)

Citation

@article{Yuan2025Weaker,
  author = {Yuan, Y. and Wang, Hao and Wu, Chenglai and Hu, Tafeng and Wu, Feng and Zhang, Daizhou and Cao, Junji},
  title = {Weaker absorption of Asian dust than previously estimated based on observation-constrained simulation},
  journal = {npj Climate and Atmospheric Science},
  year = {2025},
  doi = {10.1038/s41612-025-01290-8},
  url = {https://doi.org/10.1038/s41612-025-01290-8}
}