Preprints
https://doi.org/10.5194/egusphere-2024-1796
https://doi.org/10.5194/egusphere-2024-1796
17 Jul 2024
 | 17 Jul 2024

The impact of uncertainty in black carbon's refractive index on simulated optical depth and radiative forcing

Ruth A. R. Digby, Knut von Salzen, Adam H. Monahan, Nathan P. Gillett, and Jiangnan Li

Abstract. The radiative forcing of black carbon (BC) is subject to many complex, interconnected sources of uncertainty. Here we isolate the role of the refractive index, which determines the extent to which BC absorbs and scatters radiation. With other parameterizations held constant, varying BC's refractive index from m550nm = 1.75–0.44i to m550nm = 1.95–0.79i increases simulated absorbing aerosol optical depth (AAOD) by 42 % and the effective radiative forcing from BC-radiation interactions (BC ERFari) by 47 %. The AAOD increase is comparable to that from recent updates to aerosol emission inventories, and in BC source regions, a third as large as the difference in AAOD retrieved from MISR and POLDER-GRASP satellites. The BC ERFari increase is comparable to the scale of the uncertainty in recent literature assessments. Although model sensitivity to the choice of BC refractive index is modulated by other parameterization choices, our results highlight the importance of considering refractive index diversity in model intercomparison projects.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Ruth A. R. Digby, Knut von Salzen, Adam H. Monahan, Nathan P. Gillett, and Jiangnan Li

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-1796', Anonymous Referee #1, 16 Aug 2024
  • RC2: 'Comment on egusphere-2024-1796', Anonymous Referee #2, 22 Sep 2024
Ruth A. R. Digby, Knut von Salzen, Adam H. Monahan, Nathan P. Gillett, and Jiangnan Li
Ruth A. R. Digby, Knut von Salzen, Adam H. Monahan, Nathan P. Gillett, and Jiangnan Li

Viewed

Total article views: 363 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
270 67 26 363 12 12
  • HTML: 270
  • PDF: 67
  • XML: 26
  • Total: 363
  • BibTeX: 12
  • EndNote: 12
Views and downloads (calculated since 17 Jul 2024)
Cumulative views and downloads (calculated since 17 Jul 2024)

Viewed (geographical distribution)

Total article views: 374 (including HTML, PDF, and XML) Thereof 374 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 06 Dec 2024
Download
Short summary
The refractive index of black carbon (BCRI), which determines how much energy black carbon absorbs and scatters, is difficult to measure and different climate models use different values. We show that varying the BCRI across commonly used values can increase absorbing aerosol optical depth by 42 % and the warming effect from interactions between black carbon and radiation by 47 %, an appreciable fraction of the overall spread between models reported in recent literature assessments.