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Title: Fast and slow shifts of the zonal-mean intertropical convergence zone in response to an idealized anthropogenic aerosol

Previous modeling work showed that aerosol can affect the position of the tropical rain belt, i.e., the intertropical convergence zone (ITCZ). Yet it remains unclear which aspects of the aerosol impact are robust across models, and which are not. Here we present simulations with seven comprehensive atmosphere models that study the fast and slow impacts of an idealized anthropogenic aerosol on the zonal-mean ITCZ position. The fast impact, which results from aerosol atmospheric heating and land cooling before sea-surface temperature (SST) has time to respond, causes a northward ITCZ shift. Yet the fast impact is compensated locally by decreased evaporation over the ocean, and a clear northward shift is only found for an unrealistically large aerosol forcing. The local compensation implies that while models differ in atmospheric aerosol heating, this does not contribute to model differences in the ITCZ shift. The slow impact includes the aerosol impact on the ocean surface energy balance and is mediated by SST changes. The slow impact is an order of magnitude more effective than the fast impact and causes a clear southward ITCZ shift for realistic aerosol forcing. Models agree well on the slow ITCZ shift when perturbed with the same SST pattern. However,more » an energetic analysis suggests that the slow ITCZ shifts would be substantially more model-dependent in interactive-SST setups due to model differences in clear-sky radiative transfer and clouds. In conclusion, we also discuss implications for the representation of aerosol in climate models and attributions of recent observed ITCZ shifts to aerosol.« less
ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [3] ; ORCiD logo [4] ; ORCiD logo [4] ; ORCiD logo [5] ;  [6] ; ORCiD logo [7] ; ORCiD logo [8] ; ORCiD logo [9]
  1. Karlsruhe Institute of Technology, Karlsruhe (Germany); Columbia Univ., New York, NY (United States)
  2. Univ. of Colorado, Boulder, CO (United States); NOAA/Earth System Research Lab., Boulder, CO (United States)
  3. Max Planck Institute for Meteorology, Hamburg (Germany)
  4. Univ. Pierre et Marie Curie, Paris (France)
  5. Univ. of Reading, Reading (United Kingdom)
  6. Stockholm Univ., Stockholm (Sweden)
  7. National Center for Atmospheric Research, Boulder, CO (United States)
  8. Chinese Academy of Meteorological Sciences, Beijing (China)
  9. China Meteorological Administration, Beijing (China)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Journal of Advances in Modeling Earth Systems
Additional Journal Information:
Journal Volume: 9; Journal Issue: 2; Journal ID: ISSN 1942-2466
American Geophysical Union (AGU)
Research Org:
The Regents of the Univ. of Colorado, Denver, CO (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
54 ENVIRONMENTAL SCIENCES; tropical rain belt; ITCZ; aerosol; energy transport
OSTI Identifier: