The Northern Hemisphere wintertime circulation response to volcanic eruptions has been explored extensively using general circulation models. In observations and some models, the response is characterized by an enhanced stratospheric polar vortex (SPV), a positive mode of the North Atlantic Oscillation (NAO), and warm surface temperatures during the winter over North America and Eurasia. A weak surface air temperature signal in previous studies has led to conflicting conclusions on the robustness of the response. Here, we use simulations with the National Center for Atmospheric Research (NCAR) Whole Atmosphere Community Climate Model (WACCM) of six nuclear war scenarios to present a new perspective on the connection between stratospheric aerosol heating, the SPV, and the surface temperature response. We show that stratospheric aerosol heating by soot is the primary contributor to the SPV response in nuclear war simulations, which is coupled to the troposphere and projects as a positive mode of the NAO at the surface. Winter warming is observed across northern Eurasia, albeit poleward of the response after volcanic eruptions. We compare the results to simulations of volcanic eruptions and find that observed Eurasian warming in the first winter after the 1963 Agung, 1982 El Chichón, and 1991 Pinatubo volcanic eruptions is simulated with the NCAR CAM5 climate model only when tropical sea surface temperatures, including the observed El Niño, are specified along with the volcanic aerosols. This suggests an undiagnosed tropospheric mechanism connecting the tropics and high latitudes, as without specifying sea surface temperatures, internal variability dominates the simulated winter warming response after historical volcanic eruptions.
The 1783–1784 CE Laki flood lava eruption began on 8 June 1783. Over the course of 8 months, the eruption released approximately 122 Tg of sulfur dioxide gas into the upper troposphere and lower stratosphere above Iceland. Previous studies that have examined the impact of the Laki eruption on sulfate aerosol and climate have either used an aerosol model coupled off‐line to a general circulation model (GCM) or used a GCM with incomplete aerosol microphysics. Here, we study the impact on stratospheric aerosol evolution and stratospheric and tropospheric circulation using a fully coupled GCM with complete aerosol microphysics, the Community Earth System Model version 1, with the Whole Atmosphere Chemistry Climate Model high‐top atmosphere component. Simulations indicate that the Laki aerosols had peak average effective radii of approximately 0.4 μm in Northern Hemisphere (NH) middle and high latitudes, with peak average effective radii of 0.25 μm in NH tropics and 0.2 μm in the Southern Hemisphere. We find that the Laki aerosols are transported globally and have significant impacts on the circulation in both hemispheres, strengthening the Southern Hemisphere polar vortex and shifting the tropospheric NH subtropical jet equatorward.
more » « less- NSF-PAR ID:
- 10460451
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 124
- Issue:
- 13
- ISSN:
- 2169-897X
- Page Range / eLocation ID:
- p. 6750-6769
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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